Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016	Aug. 30, 2018	Jan. 01, 2018
Significant Accounting Policies [Line Items]
Maximum allocation period (in year)		1 year
Capitalized computer software costs		$ 37,300,000		$ 37,400,000	$ 33,100,000
Capitalized computer software amortization expense		$ 24,200,000		21,800,000	17,700,000
Minimum percentage of likelihood required to recognize uncertain income tax position		50.00%
Provisional income tax benefit due to corporate rate reduction	$ 202,900,000	$ 202,500,000		210,000,000
Provisional income tax expense (benefit)		$ (103,700,000)		(128,200,000)
Maturity of cash equivalent, max (in months)		3 months
Foreign exchange gain (loss) recognized		$ (100,000)		(200,000)	(2,800,000)
Foreign currency losses on long-term intra-entity transactions		79,600,000
Advertising expense		26,300,000		26,100,000	$ 22,200,000
Retained earnings		3,817,656,000	[1]	2,958,921,000
Prepaid expenses and other current assets		199,278,000	[1]	187,820,000
Other assets		147,632,000	[1]	114,962,000
Deferred income taxes		491,946,000	[1]	518,912,000
Deferred tax assets, net		91,868,000		81,839,000
Term Loan
Significant Accounting Policies [Line Items]
Deferred financing costs		10,900,000		11,800,000
Revolving Credit Facility and Securitization Facility
Significant Accounting Policies [Line Items]
Deferred financing costs		10,400,000		16,300,000
Securitization Facility
Significant Accounting Policies [Line Items]
Securitized accounts receivable facility						$ 1,200,000,000
Securitization Facility | Second Amendment
Significant Accounting Policies [Line Items]
Securitized accounts receivable facility		1,200,000,000
New Credit Facility
Significant Accounting Policies [Line Items]
Payments of debt issuance costs		$ 4,900,000		$ 12,900,000
Minimum | Stock options
Significant Accounting Policies [Line Items]
Period of vesting provisions (in years)		1 year
Minimum | Restricted Stock And Restricted Stock Units
Significant Accounting Policies [Line Items]
Period of vesting provisions (in years)		1 year
Maximum
Significant Accounting Policies [Line Items]
Customer payment terms (in days)		14 days
Term of derivative contract		1 year
Maximum | Stock options
Significant Accounting Policies [Line Items]
Period of vesting provisions (in years)		5 years
Maximum | Restricted Stock And Restricted Stock Units
Significant Accounting Policies [Line Items]
Period of vesting provisions (in years)		3 years
Customer Concentration Risk
Significant Accounting Policies [Line Items]
Period past due for accounts receivable deemed as uncollectible		90 days
Period past due for allowance of trade accounts receivable maximum		90 days
Customer Concentration Risk | Accounts Receivable
Significant Accounting Policies [Line Items]
Concentration risk, percentage		99.00%		96.00%
Accounting Standards Update 2016-15
Significant Accounting Policies [Line Items]
Retained earnings							$ 17,100,000
Deferred tax assets, net							25,900,000
Prepaid taxes							8,800,000
Impact of ASC 606 | Accounting Standards Update 2014-09
Significant Accounting Policies [Line Items]
Retained earnings							30,200,000
Prepaid expenses and other current assets							10,200,000
Other assets							30,300,000
Deferred income taxes							$ 10,300,000

[1] Reflects the impact of the Company's adoption of 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.