Accounting Policies and Basis of Presentation Accounting Policies and Basis of Presentation (Recently Adopted Accounting Standards) (Details) $ in Thousands		6 Months Ended		12 Months Ended
	Dec. 22, 2017 Rate	Jun. 30, 2018 USD ($) basis_points	Jun. 30, 2017 USD ($)	Dec. 31, 2017 Rate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Federal Statutory Income Tax Rate, Percent | Rate	21.00%			35.00%
Cumulative effect adjustments		$ (50,052)
Merchant processing			$ 20,800
Cardholder processing			6,800
Cardholder reward programs			$ 3,000
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
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
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