Investments - Narrative (Details) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2014 |
Dec. 31, 2015 |
|
| Schedule of Available-for-sale Securities [Line Items] | ||
| Other investments, at cost | $ 17,037 | $ 17,455 |
| Maximum percentage of shareholders' equity security holdings held of one issuer | 10.00% | 10.00% |
| Available-for-sale securities pledged as collateral, fair value | $ 315,800 | $ 334,400 |
| Available for sale securities transferred to held to maturity | 46,600 | |
| Mortgage-backed securities, weighted average life | 4 years | |
| Des Moines | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Other investments, at cost | $ 8,300 |