Accounting Policies and Basis of Presentation Accounting Policies and Basis of Presentation (Recently Adopted Accounting Standards) (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) basis_points	Sep. 30, 2017 USD ($)	Oct. 23, 2018 shares
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income taxes		$ 16,198	$ 36,585	$ 76,844	$ 151,242
Effective income tax rate reconciliation, percent		12.10%	35.30%	19.80%	36.00%
Tax cuts and jobs act of 2017, measurement period adjustment, income tax expense (benefit)		$ (15,700)
Merchant processing			$ 20,400		$ 60,400
Cardholder processing			7,700		20,300
Cardholder reward programs			$ 1,300		$ 6,800
Cumulative effect adjustments				$ (50,052)
Income tax ASU cumulative effect adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		31,300		31,300
Financial Instruments ASU cumulative effect adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ 18,700		18,700
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments				65,000
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustments				$ 85,000
Capital basis points | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Capital Quantification | basis_points				4
Capital basis points | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Capital Quantification | basis_points				6
Class A Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock repurchased during period (in shares) | shares		125,000
Stock repurchased during period		$ 58,100		$ 58,086
Stock repurchased during period (in USD per share) | $ / shares		$ 464.68
Class A Common Stock | Subsequent Event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock repurchased during period (in shares) | shares	75,000
Stock repurchased during period	$ 32,900
Stock repurchased during period (in USD per share) | $ / shares	$ 438.26
Number of shares authorized to be repurchased (in shares) | shares						800,000
Affiliated Entity | Class A Common Stock
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock repurchased during period (in shares) | shares		100,000