Summary of Significant Accounting Policies - Effect of Topic 606 on Financial Statements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018		Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Consolidated Revenues, net	$ 585,500	[1]	$ 520,433
Expenses:
Merchant commissions	0	[1]	24,384
Processing	116,485	[1]	101,824
Selling	47,111	[1]	38,837
General and administrative	90,315	[1]	95,454
Depreciation and amortization	71,502	[1]	64,866
Operating income	260,087	[1]	195,068
Total other expense	30,768	[1]	27,700
Income before income taxes	229,319	[1]	167,368
Provision for income taxes	54,382	[1]	43,675
Net income	$ 174,937	[1],[2]	$ 123,693
Basic earnings per share (in dollars per share)	$ 1.95	[1]	$ 1.34
Diluted earnings per share (in dollars per share)	$ 1.88	[1]	$ 1.31
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Consolidated Revenues, net	$ 24,218
Expenses:
Merchant commissions	26,903
Processing	(2,071)
Selling	2,120
General and administrative	0
Depreciation and amortization	0
Operating income	(2,734)
Total other expense	0
Income before income taxes	(2,734)
Provision for income taxes	(757)
Net income	$ (1,977)
Basic earnings per share (in dollars per share)	$ (0.02)
Diluted earnings per share (in dollars per share)	$ (0.02)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Consolidated Revenues, net	$ 609,718
Expenses:
Merchant commissions	26,903
Processing	114,414
Selling	49,231
General and administrative	90,315
Depreciation and amortization	71,502
Operating income	257,353
Total other expense	30,768
Income before income taxes	226,585
Provision for income taxes	53,625
Net income	$ 172,960
Basic earnings per share (in dollars per share)	$ 1.93
Diluted earnings per share (in dollars per share)	$ 1.86

[1] Reflects the January 1, 2018 adoption of Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" using the modified retrospective transition method. As a result of the application of the modified retrospective transition method, the Company's prior period results within its annual report on Form 10-K and quarterly reports on Form 10-Q will not be restated to reflect the impact of Topic 606. See footnote 1.

[2] Reflects the impact of the Company's adoption of Accounting Standards Update 2016-18, Statement of Cash Flows (Topic 230), which was adopted by the Company on January 1, 2018 and applied retrospectively to results for 2017. The adoption of Topic 230 resulted in the statement of cash flows presenting the changes in the total of cash, cash equivalents and restricted cash. As a result, the Company will no longer present transfers between cash and cash equivalents and restricted cash in the consolidated statement of cash flows.