Offsetting Assets and Liabilities - Additional Information (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Assets	$ 26,385	$ 6,896
Derivative liabilities, at fair value	20,354	32,765
Central Clearing Counterparty
Derivative [Line Items]
Derivative liabilities, at fair value	$ 12,200	$ 10,300