Earnings Per Share - Summary of Earnings Per Share, Basic and Diluted (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Earnings Per Share [Abstract]
Net income	$ 302,000	$ 157,694	$ 176,852	$ 174,937	$ 282,696	$ 202,823	$ 130,987	$ 123,693	$ 811,483	[1],[2]	$ 740,200	[2]	$ 452,385	[2]
Denominator for basic earnings per share (in shares)	87,636	88,456	89,169	89,765	89,676	90,751	92,013	92,108	88,750	[1]	91,129		92,597
Dilutive securities (in shares)									3,401		2,465		2,616
Denominator for diluted earnings per share (in shares)	90,703	92,081	92,702	93,250	92,623	93,001	94,223	94,560	92,151	[1]	93,594		95,213
Basic earnings per share (in usd per share)	$ 3.45	$ 1.78	$ 1.98	$ 1.95	$ 3.15	$ 2.23	$ 1.42	$ 1.34	$ 9.14	[1]	$ 8.12		$ 4.89
Diluted earnings per share (in usd per share)	$ 3.33	$ 1.71	$ 1.91	$ 1.88	$ 3.05	$ 2.18	$ 1.39	$ 1.31	$ 8.81	[1]	$ 7.91		$ 4.75

[1] Reflects the impact of the Company's adoption of Accounting Standards Update 2014-09, Revenue from Contracts with Customers (Topic 606) ("ASC 606") and related cost capitalization guidance, which was adopted by the Company on January 1, 2018 using the modified retrospective transition method. The adoption of ASC 606 resulted in an adjustment to retained earnings in our consolidated balance sheet for the cumulative effect of applying the standard, which included costs incurred to obtain a contract, as well as presentation changes in our statements of income, including the classification of certain amounts previously classified as merchant commissions and processing expense net with revenues. As a result of the application of the modified retrospective transition method, the Company's prior period results within its Form 10-K and quarterly reports on Form 10-Q will not be restated to reflect ASC 606.

[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 statement of cash flows.