Supplementary Balance Sheet Information - Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Supplementary Balance Sheet Information
Accrued card brand fees	$ 47,443	$ 43,814
Accrued third-party commissions	43,221	34,276
Accrued expenses	30,688	34,260
Dividends payable	24,565	24,886
Accrued interest	24,749	19,330
Other	88,171	69,356
Total	$ 258,837	$ 225,922