Fair Value Measurements, Reconciliation of Assets Measured at Fair Value Using Significant Unobservable Inputs (Level 3) (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | |||
| Level 1 to level 2 transfers | $ 0 | $ 0 | |
| Level 2 to level 1 transfers | 0 | 0 | |
| Fair Value, Measurements, Recurring [Member] | |||
| Reconciliation of assets measured at fair value on a recurring basis using significant unobservable inputs [Roll Forward] | |||
| Beginning balance | 7,958 | 13,349 | $ 17,910 |
| Realized gains | 324 | 1,538 | 2,552 |
| Unrealized in other accumulated comprehensive income | (1,458) | (4,207) | (2,937) |
| Purchases | 23,991 | 1,207 | 501 |
| Sales | 0 | 0 | 0 |
| Capital distributions | (3,283) | (3,929) | (4,677) |
| Ending balance | $ 27,532 | $ 7,958 | $ 13,349 |