Investments - Narrative (Details) - USD ($) $ in Thousands |
Jun. 30, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Schedule of Available-for-sale Securities [Line Items] | ||
| Unrealized loss position, accumulated loss | $ 2,524 | $ 4,541 |
| Unrealized loss position, 12 months or greater | 352 | 497 |
| U.S. Treasury securities and obligations of U.S. government agencies | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Cash and investments held with various state insurance departments | 7,000 | 7,000 |
| Unrealized loss position, accumulated loss | 657 | 962 |
| Unrealized loss position, 12 months or greater | $ 12 | $ 0 |