Supplementary Balance Sheet Information - Contract Acquisition Costs, Net - Significant Components (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Identifiable intangible assets acquired
Contract acquisition costs, net of accumulated amortization	$ 147,512		$ 147,512		$ 258,665
Contract cost assets
Identifiable intangible assets acquired
Accumulated amortization	173,400		173,400		176,400
Amortization expense	8,511	$ 7,157	19,238	$ 15,330
Contract acquisition costs, net of accumulated amortization	$ 147,512		$ 147,512		139,249
Payments for processing rights
Identifiable intangible assets acquired
Amortization expense		$ 5,110		$ 10,329
Contract acquisition costs, net of accumulated amortization					119,416
Contract acquisition costs, accumulated amortization					$ 166,300