Summary of Offsetting Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivative instruments (assets)
Gross fair value of recognized assets	$ 52,738	$ 119,862
Financial instruments	(47,827)	(26,254)
Cash collateral pledged	(4,911)	(92,756)
Net fair value	0	852
Securities purchased under agreements to resell, gross	23,200
Securities purchased under agreements to resell, not offset	(23,200)
Securities purchased under agreements to resell, collateral, obligation to return cash	0
Securities purchased under agreements to resell, offset against collateral, net of not subject to master netting arrangement, policy election	0
Derivative asset, securities purchased under agreements to resell, securities borrowed	75,938
Derivative asset, securities purchased under agreements to resell, securities borrowed, not offset	(71,027)
Derivative asset, securities purchased under agreements to resell, securities borrowed, collateral, obligation to return cash	(4,911)
Derivative asset, securities purchased under agreements to resell, securities borrowed, amount offset against collateral	0
Derivatives instrument (liabilities)
Gross fair value of recognized liabilities	93,761	26,254
Financial Instruments	(47,827)	(26,254)
Cash collateral pledged	(42,750)
Net fair value	$ 3,184	$ 0