Investments - Continuous loss position investments (Details)
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3 Months Ended |
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|
Mar. 31, 2018
USD ($)
security
|
Dec. 31, 2017
USD ($)
security
|
| Schedule of Available-for-sale Securities [Line Items] |
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|
| Number of Securities with Unrealized Losses (positions) | security |
996
|
722
|
| Maximum |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Percentage of book value (percent) |
95.00%
|
|
| Minimum |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Unrealized loss amount |
$ 100,000
|
|
| Less than 12 Months |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
680
|
398
|
| Less than 12 Months, Fair Value |
$ 849,333,000
|
$ 489,771,000
|
| Less than 12 Months, Gross Unrealized Losses |
$ (11,252,000)
|
$ (3,233,000)
|
| Unrealized Losses as Percentage of Cost |
1.30%
|
0.70%
|
| Less than 12 Months | Fixed Maturities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
680
|
398
|
| Less than 12 Months, Fair Value |
$ 849,333,000
|
$ 489,771,000
|
| Less than 12 Months, Gross Unrealized Losses |
$ (11,252,000)
|
$ (3,233,000)
|
| Unrealized Losses as Percentage of Cost |
1.30%
|
0.70%
|
| Less than 12 Months | U.S. government |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
28
|
25
|
| Less than 12 Months, Fair Value |
$ 48,202,000
|
$ 46,160,000
|
| Less than 12 Months, Gross Unrealized Losses |
$ (881,000)
|
$ (422,000)
|
| Unrealized Losses as Percentage of Cost |
1.80%
|
0.90%
|
| Less than 12 Months | State and Municipal |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
99
|
82
|
| Less than 12 Months, Fair Value |
$ 184,046,000
|
$ 163,997,000
|
| Less than 12 Months, Gross Unrealized Losses |
$ (2,147,000)
|
$ (939,000)
|
| Unrealized Losses as Percentage of Cost |
1.20%
|
0.60%
|
| Less than 12 Months | Mortgage- Backed Securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
278
|
156
|
| Less than 12 Months, Fair Value |
$ 174,756,000
|
$ 85,419,000
|
| Less than 12 Months, Gross Unrealized Losses |
$ (2,427,000)
|
$ (483,000)
|
| Unrealized Losses as Percentage of Cost |
1.40%
|
0.60%
|
| Less than 12 Months | Residential |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
263
|
154
|
| Less than 12 Months, Fair Value |
$ 144,098,000
|
$ 81,841,000
|
| Less than 12 Months, Gross Unrealized Losses |
$ (2,250,000)
|
$ (453,000)
|
| Unrealized Losses as Percentage of Cost |
1.50%
|
0.60%
|
| Less than 12 Months | Commercial |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
15
|
2
|
| Less than 12 Months, Fair Value |
$ 30,658,000
|
$ 3,578,000
|
| Less than 12 Months, Gross Unrealized Losses |
$ (177,000)
|
$ (30,000)
|
| Unrealized Losses as Percentage of Cost |
0.60%
|
0.80%
|
| Less than 12 Months | Asset-backed securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
43
|
31
|
| Less than 12 Months, Fair Value |
$ 74,670,000
|
$ 35,407,000
|
| Less than 12 Months, Gross Unrealized Losses |
$ (628,000)
|
$ (193,000)
|
| Unrealized Losses as Percentage of Cost |
0.80%
|
0.50%
|
| Less than 12 Months | Corporates |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
232
|
104
|
| Less than 12 Months, Fair Value |
$ 367,660,000
|
$ 158,788,000
|
| Less than 12 Months, Gross Unrealized Losses |
$ (5,168,000)
|
$ (1,197,000)
|
| Unrealized Losses as Percentage of Cost |
1.40%
|
0.70%
|
| Less than 12 Months | Equity securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
|
0
|
| Less than 12 Months, Fair Value |
|
$ 0
|
| Less than 12 Months, Gross Unrealized Losses |
|
$ 0
|
| Unrealized Losses as Percentage of Cost |
|
0.00%
|
| Less than 12 Months | Short-term investments |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
0
|
0
|
| Less than 12 Months, Fair Value |
$ 0
|
$ 0
|
| Less than 12 Months, Gross Unrealized Losses |
$ 0
|
$ 0
|
| Unrealized Losses as Percentage of Cost |
0.00%
|
0.00%
|
| 12 Months or More |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
316
|
324
|
| Unrealized Losses as Percentage of Cost |
3.90%
|
2.40%
|
| 12 Months or More, Fair Value |
$ 179,380,000
|
$ 193,309,000
|
| 12 Months of More, Gross Unrealized Losses |
$ (7,369,000)
|
$ (4,809,000)
|
| 12 Months or More | Fixed Maturities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
316
|
324
|
| Unrealized Losses as Percentage of Cost |
3.90%
|
2.40%
|
| 12 Months or More, Fair Value |
$ 179,380,000
|
$ 193,309,000
|
| 12 Months of More, Gross Unrealized Losses |
$ (7,369,000)
|
$ (4,809,000)
|
| 12 Months or More | U.S. government |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
16
|
16
|
| Unrealized Losses as Percentage of Cost |
2.40%
|
1.70%
|
| 12 Months or More, Fair Value |
$ 12,743,000
|
$ 14,368,000
|
| 12 Months of More, Gross Unrealized Losses |
$ (307,000)
|
$ (246,000)
|
| 12 Months or More | State and Municipal |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
4
|
5
|
| Unrealized Losses as Percentage of Cost |
1.40%
|
0.60%
|
| 12 Months or More, Fair Value |
$ 4,573,000
|
$ 10,529,000
|
| 12 Months of More, Gross Unrealized Losses |
$ (64,000)
|
$ (60,000)
|
| 12 Months or More | Mortgage- Backed Securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
280
|
288
|
| Unrealized Losses as Percentage of Cost |
4.40%
|
2.80%
|
| 12 Months or More, Fair Value |
$ 142,480,000
|
$ 150,383,000
|
| 12 Months of More, Gross Unrealized Losses |
$ (6,569,000)
|
$ (4,267,000)
|
| 12 Months or More | Residential |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
272
|
279
|
| Unrealized Losses as Percentage of Cost |
4.60%
|
2.80%
|
| 12 Months or More, Fair Value |
$ 119,273,000
|
$ 127,317,000
|
| 12 Months of More, Gross Unrealized Losses |
$ (5,730,000)
|
$ (3,644,000)
|
| 12 Months or More | Commercial |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
8
|
9
|
| Unrealized Losses as Percentage of Cost |
3.50%
|
2.60%
|
| 12 Months or More, Fair Value |
$ 23,206,000
|
$ 23,066,000
|
| 12 Months of More, Gross Unrealized Losses |
$ (839,000)
|
$ (623,000)
|
| 12 Months or More | Asset-backed securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
1
|
2
|
| Unrealized Losses as Percentage of Cost |
0.10%
|
0.20%
|
| 12 Months or More, Fair Value |
$ 1,458,000
|
$ 1,561,000
|
| 12 Months of More, Gross Unrealized Losses |
$ (2,000)
|
$ (3,000)
|
| 12 Months or More | Corporates |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
15
|
13
|
| Unrealized Losses as Percentage of Cost |
2.30%
|
1.40%
|
| 12 Months or More, Fair Value |
$ 18,126,000
|
$ 16,468,000
|
| 12 Months of More, Gross Unrealized Losses |
$ (427,000)
|
$ (232,000)
|
| 12 Months or More | Equity securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
|
0
|
| Unrealized Losses as Percentage of Cost |
|
0.00%
|
| 12 Months or More, Fair Value |
|
$ 0
|
| 12 Months of More, Gross Unrealized Losses |
|
$ 0
|
| 12 Months or More | Short-term investments |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of Securities with Unrealized Losses (positions) | security |
0
|
0
|
| Unrealized Losses as Percentage of Cost |
0.00%
|
0.00%
|
| 12 Months or More, Fair Value |
$ 0
|
$ 0
|
| 12 Months of More, Gross Unrealized Losses |
$ 0
|
$ 0
|