Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Guarantor Obligations [Line Items]
Amortization Method Qualified Affordable Housing Project Investments	$ 128,000	$ 109,800
FDIC loss share receivable	2,223	4,172	$ 4,054	$ 28,701
FDIC shared-loss payable	101,342	97,008
Federal Home Loan Bank, Advances, Maturities Summary, Fixed Rate	200,000
Gain On Termination of Forward Starting Advance	12,500
Commitments to Extend Credit
Guarantor Obligations [Line Items]
Unused Commitments to Extend Credit	9,629,365	8,808,218
Affordable Housing Program Obligation	61,819	57,079
Standby Letters of Credit
Guarantor Obligations [Line Items]
Guarantor obligations amount	$ 81,530	83,750
Recourse Obligation on Mortgage Loans Sold
Guarantor Obligations [Line Items]
Recourse Period, Maximum1	180 days
Obligation to Repurchase Receivables Sold
Guarantor Obligations [Line Items]
Reserve for estimated losses arising from repurchase of loans	$ 882	$ 3,000
Each Individual Advance
Guarantor Obligations [Line Items]
Federal Home Loan Bank, Advances, Maturities Summary, Fixed Rate	$ 100,000