Derivatives - Derivatives Associated With Interest Rate Risk Management Activities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,390,963	$ 2,271,448
Assets	63,951	18,744
Liabilities	3,084	27,768
Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,390,963	2,271,448
Assets	2,666	4,014
Liabilities	5,638	9,041
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,355,604	2,029,162
Assets	78,051	20,262
Liabilities	3,851	25,880
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,355,604	2,029,162
Assets	1,927	8,154
Liabilities	10,762	9,153
Debt Hedging | Hedging Instruments And Hedged Items | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional	900,000	900,000
Assets	118	127
Liabilities	71	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	(4,223)	(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	(1,487)	(2,295)
Debt Hedging | Hedging Instruments And Hedged Items | Term Borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	$ 894,290	$ 882,611