Financial Derivatives Narrative (Details) - USD ($) $ in Thousands |
Dec. 31, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Derivative [Line Items] | ||
| U.S. Treasury securities sold short, at fair value | $ 78,447 | $ 13,959 |
| US Treasury Securities [Member] | ||
| Derivative [Line Items] | ||
| U.S. Treasury securities sold short, at fair value | 78,447 | 13,959 |
| Investment Sold, Not yet Purchased, Balance, Principal Amount | $ 79,600 | $ 13,900 |