Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities Credit Risk - Counterparty Exposure (Details)

v3.8.0.1
Derivative Instruments and Hedging Activities Credit Risk - Counterparty Exposure (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Offsetting Assets and Liabilities [Line Items]    
Derivative assets, at fair value $ 309,918 $ 324,182
Derivative liabilities, at fair value $ 31,903 $ 12,501