Derivative Financial Instruments - Free-Standing (Details) $ in Thousands	12 Months Ended			96 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 shares	Jul. 31, 2018 USD ($)	Jun. 28, 2018
Visa | Class B restricted shares
Derivative financial instruments
Number of shares sold | shares			274,000	0
Funding Swap (Visa Derivative) | Class B restricted shares
Derivative financial instruments
Conversion rate		1.6483				1.6298
Funding Swap (Visa Derivative) | Visa
Derivative financial instruments
Estimated liability that was subsequently paid to the buyer					$ 700
Derivatives Not Designated as Hedging Instruments | Interest rate swaps
Derivative financial instruments
Notional Amount	$ 2,269,247	$ 1,820,442
Net interest expense on derivative	$ 500	$ 900	$ 1,100
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Minimum
Derivative financial instruments
Fixed interest rate (as a percent)	2.02%	1.36%
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Maximum
Derivative financial instruments
Fixed interest rate (as a percent)	5.78%	5.33%
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Customer swap program
Derivative financial instruments
Notional Amount	$ 2,200,000	$ 1,700,000
Derivative asset value	12,300	14,700
Derivative liability value	11,200	11,700
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Customer swap program | Other noninterest income
Derivative financial instruments
Upfront fees on the dealer swap	7,300	6,700	$ 7,300
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Included in other assets
Derivative financial instruments
Positive fair value, derivative asset	12,305	14,658
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Included in other liabilities
Derivative financial instruments
Negative fair value, derivative liability	12,007	13,017
Derivatives Not Designated as Hedging Instruments | Funding Swap (Visa Derivative)
Derivative financial instruments
Notional Amount	62,039	43,113
Derivatives Not Designated as Hedging Instruments | Funding Swap (Visa Derivative) | Included in other liabilities
Derivative financial instruments
Negative fair value, derivative liability	$ 2,607	$ 5,439