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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 |  |

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