Amortized Cost or Cost, Gross Unrealized Gains, Gross Unrealized Losses, and Fair Values of Available-For-Sale Securities (Detail) - USD ($)
$ in Thousands |
Dec. 31, 2017 |
Dec. 31, 2016 |
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total fixed-maturity securities, available-for-sale |
$ 966,168
|
$ 734,957
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized gains |
30,637
|
24,161
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized losses |
5,582
|
7,587
|
| Total fixed-maturity securities, available-for-sale, Fair value |
991,223
|
751,531
|
| U.S. government |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total fixed-maturity securities, available-for-sale |
77,857
|
48,676
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized gains |
253
|
644
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized losses |
450
|
103
|
| Total fixed-maturity securities, available-for-sale, Fair value |
77,660
|
49,217
|
| States and political subdivisions |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total fixed-maturity securities, available-for-sale |
10,502
|
10,546
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized gains |
503
|
285
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized losses |
|
187
|
| Total fixed-maturity securities, available-for-sale, Fair value |
11,005
|
10,644
|
| Corporate Securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total fixed-maturity securities, available-for-sale |
615,077
|
491,518
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized gains |
28,056
|
21,500
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized losses |
2,258
|
3,739
|
| Total fixed-maturity securities, available-for-sale, Fair value |
640,875
|
509,279
|
| Mortgage-backed securities |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total fixed-maturity securities, available-for-sale |
259,748
|
184,217
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized gains |
1,825
|
1,732
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized losses |
2,823
|
3,558
|
| Total fixed-maturity securities, available-for-sale, Fair value |
258,750
|
$ 182,391
|
| Foreign Government |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Total fixed-maturity securities, available-for-sale |
2,984
|
|
| Total fixed-maturity securities, available-for-sale, Gross unrealized losses |
51
|
|
| Total fixed-maturity securities, available-for-sale, Fair value |
$ 2,933
|
|