Regulatory Information - Schedule of Statutory Surplus, Contingency Reserve and RTC Ratio (Details) - Combined $ in Thousands |
Jun. 30, 2018
USD ($)
|
Dec. 31, 2017
USD ($)
|
|---|---|---|
| Statutory Accounting Practices [Line Items] | ||
| Statutory surplus | $ 439,754 | $ 371,084 |
| Contingency reserve | $ 253,817 | $ 186,641 |
| RTC Ratio | 13.7 | 13.2 |