Derivative Financial Instruments - Free-Standing (Details) - USD ($) $ in Thousands	12 Months Ended			96 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2015
Visa | Class B shares
Derivative financial instruments
Number of shares sold		274,000		0
Derivatives Not Designated as Hedging Instruments | Interest rate swaps
Derivative financial instruments
Notional Amount	$ 1,820,442	$ 1,297,101
Net interest expense on derivative	$ 900	$ 1,100	$ 1,200
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Minimum
Derivative financial instruments
Fixed interest rate (as a percent)	1.36%	0.77%
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Maximum
Derivative financial instruments
Fixed interest rate (as a percent)	5.33%	4.90%
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Customer swap program
Derivative financial instruments
Notional Amount	$ 1,700,000	$ 1,200,000
Derivative asset value	14,700	16,000
Derivative liability value	11,700	16,000
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Customer swap program | Other noninterest income
Derivative financial instruments
Upfront fees on the dealer swap	6,700	7,300	$ 3,500
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Other assets
Derivative financial instruments
Positive fair value, derivative asset	14,658	15,982
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Other liabilities
Derivative financial instruments
Fair value loss (derivative liability)	13,017	18,299
Derivatives Not Designated as Hedging Instruments | Funding Swap (Visa Derivative)
Derivative financial instruments
Notional Amount	43,113	37,143
Derivatives Not Designated as Hedging Instruments | Funding Swap (Visa Derivative) | Other liabilities
Derivative financial instruments
Fair value loss (derivative liability)	$ 5,439	$ 7,460