Derivatives - Derivatives Associated With Interest Rate Risk Management Activities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,679,166	$ 2,271,448
Assets	93,314	18,744
Liabilities	1,285	27,768
Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,679,166	2,271,448
Assets	541	4,014
Liabilities	5,509	9,041
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,681,149	2,029,162
Assets	120,031	20,262
Liabilities	1,456	25,880
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,681,149	2,029,162
Assets	1,094	8,154
Liabilities	13,072	9,153
Debt Hedging | Hedging Instruments And Hedged Items | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional	900,000	900,000
Assets	42	127
Liabilities	14	6
Debt Hedging | Hedging Instruments And Hedged Items | Term Borrowings, Par
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	900,000	900,000
Debt Hedging | Hedging Instruments And Hedged Items | Term Borrowings, Cumulative Fair Value Hedging Adjustments
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	(2,218)	(15,094)
Debt Hedging | Hedging Instruments And Hedged Items | Term Borrowings, Unamortized Premium (Discount) and Issuance Costs
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	(1,084)	(2,295)
Debt Hedging | Hedging Instruments And Hedged Items | Term Borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	$ 896,698	$ 882,611