Supplementary Balance Sheet Information - Contract Acquisition Costs, Net - Significant Components (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Identifiable intangible assets acquired
Contract acquisition costs, net of accumulated amortization	$ 147,732		$ 147,732		$ 258,665
Contract cost assets
Identifiable intangible assets acquired
Amortization expense	8,592	$ 7,266	27,830	$ 22,596
Contract acquisition costs, net of accumulated amortization	$ 147,732		$ 147,732		139,249
Payments for processing rights
Identifiable intangible assets acquired
Amortization expense		$ 5,076		$ 15,405
Contract acquisition costs, net of accumulated amortization					$ 119,416