Derivative Financial Instruments Fair Value Gains and Losses on Derivative Financial Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income
Derivatives, Fair Value [Line Items]
Net fair value gains on derivative financial instruments	$ 2,787	$ 1,157	$ 1,507
Centrally Cleared Interest Rate Swap With Counterparty
Derivatives, Fair Value [Line Items]
Derivatives variation margin	4,600
Interest rate locks with customers | Mortgage Banking Income
Derivatives, Fair Value [Line Items]
Gain (loss) on interest rate derivative instruments	364	(639)	(110)
Forward Commitments | Mortgage Banking Income
Derivatives, Fair Value [Line Items]
Gain (loss) on interest rate derivative instruments	(2,290)	1,930	1,345
Interest Rate Swaps with Customers | Other Income
Derivatives, Fair Value [Line Items]
Gain (loss) on interest rate derivative instruments	(1,872)	(25,461)	13,342
Interest Rate Swaps with Dealer Counterparties | Other Income
Derivatives, Fair Value [Line Items]
Gain (loss) on interest rate derivative instruments	6,576	25,461	(13,342)
Foreign Exchange Contracts with Correspondent Banks | Other Income
Derivatives, Fair Value [Line Items]
Gain (loss) on foreign currency derivatives	135	(487)	711
Foreign exchange contracts with customers | Other Income
Derivatives, Fair Value [Line Items]
Gain (loss) on foreign currency derivatives	$ (126)	$ 353	$ (439)