Investments - Unrealized Losses (Details)
$ in Thousands |
Jun. 30, 2017
USD ($)
security
|
Dec. 31, 2016
USD ($)
security
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of securities, less than 12 months | security |
109
|
154
|
| Fair value, less than 12 months |
$ 205,396
|
$ 253,569
|
| Unrealized losses, less than 12 months |
$ (2,172)
|
$ (4,044)
|
| Number of securities,12 months or greater | security |
13
|
15
|
| Fair value, 12 months or greater |
$ 18,781
|
$ 18,049
|
| Unrealized losses, 12 months or greater |
$ (352)
|
$ (497)
|
| Number of securities, total | security |
122
|
169
|
| Fair value |
$ 224,177
|
$ 271,618
|
| Unrealized Losses |
$ (2,524)
|
$ (4,541)
|
| U.S. Treasury securities and obligations of U.S. government agencies |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of securities, less than 12 months | security |
34
|
33
|
| Fair value, less than 12 months |
$ 53,299
|
$ 51,093
|
| Unrealized losses, less than 12 months |
$ (645)
|
$ (962)
|
| Number of securities,12 months or greater | security |
3
|
0
|
| Fair value, 12 months or greater |
$ 4,738
|
$ 0
|
| Unrealized losses, 12 months or greater |
$ (12)
|
$ 0
|
| Number of securities, total | security |
37
|
33
|
| Fair value |
$ 58,037
|
$ 51,093
|
| Unrealized Losses |
$ (657)
|
$ (962)
|
| Municipal debt securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of securities, less than 12 months | security |
14
|
14
|
| Fair value, less than 12 months |
$ 26,390
|
$ 28,659
|
| Unrealized losses, less than 12 months |
$ (353)
|
$ (617)
|
| Number of securities,12 months or greater | security |
1
|
1
|
| Fair value, 12 months or greater |
$ 1,732
|
$ 1,704
|
| Unrealized losses, 12 months or greater |
$ (18)
|
$ (46)
|
| Number of securities, total | security |
15
|
15
|
| Fair value |
$ 28,122
|
$ 30,363
|
| Unrealized Losses |
$ (371)
|
$ (663)
|
| Corporate debt securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of securities, less than 12 months | security |
49
|
77
|
| Fair value, less than 12 months |
$ 105,388
|
$ 135,115
|
| Unrealized losses, less than 12 months |
$ (1,066)
|
$ (1,955)
|
| Number of securities,12 months or greater | security |
5
|
8
|
| Fair value, 12 months or greater |
$ 7,916
|
$ 13,873
|
| Unrealized losses, 12 months or greater |
$ (289)
|
$ (401)
|
| Number of securities, total | security |
54
|
85
|
| Fair value |
$ 113,304
|
$ 148,988
|
| Unrealized Losses |
$ (1,355)
|
$ (2,356)
|
| Asset-backed securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Number of securities, less than 12 months | security |
12
|
30
|
| Fair value, less than 12 months |
$ 20,319
|
$ 38,702
|
| Unrealized losses, less than 12 months |
$ (108)
|
$ (510)
|
| Number of securities,12 months or greater | security |
4
|
6
|
| Fair value, 12 months or greater |
$ 4,395
|
$ 2,472
|
| Unrealized losses, 12 months or greater |
$ (33)
|
$ (50)
|
| Number of securities, total | security |
16
|
36
|
| Fair value |
$ 24,714
|
$ 41,174
|
| Unrealized Losses |
$ (141)
|
$ (560)
|