Balance Sheet Offsetting Balance Sheet Offsetting - Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase [Line Items]
Remaining contractual maturity of the agreements overnight and continuous	$ 875,920	$ 782,589
Remaining contractual maturity of the agreements up to 30 Days	0	0
Remaining contractual maturity of the agreements 30 to 90 Days	8,027	8,530
Remaining contractual maturity of the agreements greater than 90 Days	0	0
Remaining contractual maturity of the agreements total	883,947	791,119
Securities Sold under Agreements to Repurchase, Gross	883,947	791,119
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	0	0
US Treasury [Member]
Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase [Line Items]
Remaining contractual maturity of the agreements overnight and continuous	664,419	427,402
Remaining contractual maturity of the agreements up to 30 Days	0	0
Remaining contractual maturity of the agreements 30 to 90 Days	0	0
Remaining contractual maturity of the agreements greater than 90 Days	0	0
Remaining contractual maturity of the agreements total	664,419	427,402
Residential Mortgage Backed Securities [Member]
Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase [Line Items]
Remaining contractual maturity of the agreements overnight and continuous	211,501	355,187
Remaining contractual maturity of the agreements up to 30 Days	0	0
Remaining contractual maturity of the agreements 30 to 90 Days	8,027	8,530
Remaining contractual maturity of the agreements greater than 90 Days	0	0
Remaining contractual maturity of the agreements total	$ 219,528	$ 363,717