Description of Business and Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue Recognition
Revenue from rental of electronic point-of-sale equipment	$ 10,800	$ 9,900	$ 32,100	$ 29,400
Summary of revenue
Processing and other revenue	488,564	455,851	1,409,569	1,283,223
Interchange and card network fees	(282,823)	(264,095)	(820,328)	(746,778)
Subtotal	205,741	191,756	589,241	536,445
Commissions	(43,345)	(40,273)	(123,985)	(119,083)
Card network processing costs and other	(17,638)	(18,837)	(51,325)	(51,197)
Revenue	$ 144,758	$ 132,646	$ 413,931	$ 366,165