Investments - Textual (Details) - USD ($) |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
Dec. 31, 2015 |
|
| Investments, Debt and Equity Securities [Abstract] | |||||
| Proceeds from sale of available-for-sale securities | $ 68,000,000 | $ 75,900,000 | $ 276,800,000 | $ 232,600,000 | |
| Receivable for securities sold | 1,714,000 | 2,700,000 | 1,714,000 | 2,700,000 | $ 0 |
| Gross realized gains | 1,300,000 | 1,600,000 | 3,500,000 | 4,300,000 | |
| Gross realized losses | $ 42,000 | $ 1,900,000 | $ 1,900,000 | $ 2,600,000 | |