Business and Significant Accounting Policies - Additional Information (Details) enterprise in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) segment country enterprise	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business and Significant Accounting Policies [Line Items]
Amortization of deferred sales commissions, amortization period	1 year
Number of enterprises served | enterprise	15
Number of countries in which entity operates | country	100
Number of reportable segments | segment	3
Acquisition and integration charges	$ 107,197	$ 158,450	$ 42,598
Stock-based compensation expense	66,172	78,943	46,661
Rent expense	93,500	87,900	38,000
Depreciation expense	68,592	63,897	37,172
Net capitalized development costs for internal use software	37,400	26,900
Amortization of capitalized internal software development costs	13,200	9,900	8,800
Amortization of intangibles	187,009	176,274	24,797
Pension expense	3,900	3,600	3,500
Long-term debt, gross	2,312,092	3,323,062
Foreign currency transaction gain (loss)	9,200	(5,500)	(400)
Derivative instruments, gain (loss) recognized in income, net	8,500	7,100	7,900
Payments for purchases of treasury stock	260,832	41,272	58,961
Foreign currency exchange contracts
Business and Significant Accounting Policies [Line Items]
Derivative instruments, gain (loss) recognized in income, net	$ (10,400)	$ 800	(300)
Customer Relationships | Minimum
Business and Significant Accounting Policies [Line Items]
Remaining amortization period	4 years
Customer Relationships | Maximum
Business and Significant Accounting Policies [Line Items]
Remaining amortization period	13 years
Software | Minimum
Business and Significant Accounting Policies [Line Items]
Remaining amortization period	3 years
Software | Maximum
Business and Significant Accounting Policies [Line Items]
Remaining amortization period	7 years
Content | Minimum
Business and Significant Accounting Policies [Line Items]
Remaining amortization period	1 year 6 months
Content | Maximum
Business and Significant Accounting Policies [Line Items]
Remaining amortization period	5 years
Non-Compete | Minimum
Business and Significant Accounting Policies [Line Items]
Remaining amortization period	2 years
Non-Compete | Maximum
Business and Significant Accounting Policies [Line Items]
Remaining amortization period	5 years
ASU 2016-09
Business and Significant Accounting Policies [Line Items]
Adoption of ASU				$ (261)
ASU 2016-09 | Accumulated Earnings
Business and Significant Accounting Policies [Line Items]
Adoption of ASU				$ (261)
ASU 2016-09 | Pro Forma | Accumulated Earnings
Business and Significant Accounting Policies [Line Items]
Adoption of ASU			$ (300)