Derivatives - Derivatives Associated With Interest Rate Risk Management Activities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	$ 2,279,361	$ 2,271,448
Assets	30,632	18,744
Liabilities	14,245	27,768
Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,279,361	2,271,448
Assets	5,056	4,014
Liabilities	4,834	9,041
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,122,743	2,029,162
Assets	37,754	20,262
Liabilities	14,260	25,880
Customer Interest Rate Contracts Hedging | Hedging Instruments And Hedged Items | Offsetting upstream interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional	2,122,743	2,029,162
Assets	7,232	8,154
Liabilities	6,731	9,153
Debt Hedging | Hedging Instruments And Hedged Items | Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Notional	900,000	900,000
Assets		127
Liabilities	448	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	(10,828)	(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	(1,891)	(2,295)
Debt Hedging | Hedging Instruments And Hedged Items | Term Borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	$ 887,281	$ 882,611