Goodwill and Intangible Assets - Carrying Amounts of Amortizable Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Finite-lived Intangible Assets [Roll Forward]
Gross cost, beginning balance			$ 1,279,386
Additions due to an acquisition			19,500
Intangible assets fully amortized			(89,519)
Foreign currency translation impact			1,401
Gross cost, ending balance	$ 1,210,768		1,210,768
Accumulated amortization	(466,818)		(466,818)		$ (472,388)
Finite-lived intangible assets, net	743,950		743,950		806,998
Amortization of intangibles	27,109	$ 31,228	83,777	$ 94,615
Customer Relationships
Finite-lived Intangible Assets [Roll Forward]
Gross cost, beginning balance			1,154,210
Additions due to an acquisition			7,980
Intangible assets fully amortized			(24,603)
Foreign currency translation impact			1,271
Gross cost, ending balance	1,138,858		1,138,858
Accumulated amortization	(429,234)		(429,234)		(381,776)
Finite-lived intangible assets, net	709,624		$ 709,624		772,434
Customer Relationships | Minimum
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets useful life			6 years
Customer Relationships | Maximum
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets useful life			13 years
Software
Finite-lived Intangible Assets [Roll Forward]
Gross cost, beginning balance			$ 110,597
Additions due to an acquisition			11,200
Intangible assets fully amortized			(60,631)
Foreign currency translation impact			130
Gross cost, ending balance	61,296		61,296
Accumulated amortization	(33,058)		(33,058)		(83,320)
Finite-lived intangible assets, net	28,238		$ 28,238		27,277
Software | Minimum
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets useful life			3 years
Software | Maximum
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets useful life			7 years
Content
Finite-lived Intangible Assets [Roll Forward]
Gross cost, beginning balance			$ 3,965
Additions due to an acquisition			0
Intangible assets fully amortized			(3,965)
Foreign currency translation impact			0
Gross cost, ending balance	0		0
Accumulated amortization	0		0		(3,595)
Finite-lived intangible assets, net	0		$ 0		370
Content | Minimum
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets useful life			2 years
Content | Maximum
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets useful life			3 years
Other
Finite-lived Intangible Assets [Roll Forward]
Gross cost, beginning balance			$ 10,614
Additions due to an acquisition			320
Intangible assets fully amortized			(320)
Foreign currency translation impact			0
Gross cost, ending balance	10,614		10,614
Accumulated amortization	(4,526)		(4,526)		(3,697)
Finite-lived intangible assets, net	$ 6,088		$ 6,088		$ 6,917
Other | Minimum
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets useful life			2 years
Other | Maximum
Finite-lived Intangible Assets [Roll Forward]
Finite-lived intangible assets useful life			11 years