Derivative Financial Instruments Fair Value Gains and Losses on Derivative Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
Net fair value gains (losses) on derivative financial instruments	$ 30,841	$ (1,947)	$ 48,136	$ (10,325)
Interest rate lock with customers [Member]
Derivative [Line Items]
Net fair value gains (losses) on derivative financial instruments	355	231	961	360
Forward Commitments [Member]
Derivative [Line Items]
Net fair value gains (losses) on derivative financial instruments	(403)	(541)	(347)	(315)
Interest Rate Swap with Customer [Member]
Derivative [Line Items]
Net fair value gains (losses) on derivative financial instruments	81,576	(12,375)	132,093	(55,017)
Interest Rate Swap with Counterparty [Member]
Derivative [Line Items]
Net fair value gains (losses) on derivative financial instruments	(50,673)	10,811	(84,605)	44,625
Foreign Exchange Contracts With Customer [Member]
Derivative [Line Items]
Net fair value gains (losses) on derivative financial instruments	(154)	(23)	65	(16)
Foreign Exchange Contracts With Correspondent Banks [Member]
Derivative [Line Items]
Net fair value gains (losses) on derivative financial instruments	140	(50)	(31)	38
Centrally Cleared Interest Rate Swap with Counterparty [Member]
Derivative [Line Items]
Net fair value gains (losses) on derivative financial instruments	$ (31,200)	$ 1,600	$ (47,500)	$ 10,400