Derivative Financial Instruments - Free-Standing (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended	96 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Visa | Class B shares
Derivative financial instruments
Number of shares sold	0	0	274,000	0
Derivatives Not Designated as Hedging Instruments | Interest rate swaps
Derivative financial instruments
Notional Amount	$ 1,988,253				$ 1,820,442
Net interest expense on derivative	$ 200	$ 300
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Minimum
Derivative financial instruments
Fixed interest rate (as a percent)	1.89%				1.36%
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Maximum
Derivative financial instruments
Fixed interest rate (as a percent)	5.47%				5.33%
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Customer swap program
Derivative financial instruments
Notional Amount	$ 1,900,000				$ 1,700,000
Upfront fees on the dealer swap	3,200	$ 3,000
Derivative asset value	3,900				14,700
Derivative liability value	15,800				11,700
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Included in other assets
Derivative financial instruments
Positive fair value, derivative asset	3,936				14,658
Derivatives Not Designated as Hedging Instruments | Interest rate swaps | Included in other liabilities
Derivative financial instruments
Negative fair value, derivative liability	16,737				13,017
Derivatives Not Designated as Hedging Instruments | Funding Swap (Visa Derivative)
Derivative financial instruments
Notional Amount	56,107				43,113
Derivatives Not Designated as Hedging Instruments | Funding Swap (Visa Derivative) | Included in other liabilities
Derivative financial instruments
Negative fair value, derivative liability	$ 4,845				$ 5,439