Business and Significant Accounting Policies - Intangible Assets Subject to Amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite-lived Intangible Assets [Roll Forward]
Gross cost	$ 1,482,982	$ 116,767
Divestitures	(46,129)
Additions due to acquisitions		1,600,190
Write-off of fully amortized intangible assets	(15,998)	(4,227)
Reclassified as held-for-sale		(250,472)
Foreign currency translation impact	(27,994)	20,724
Gross cost	1,392,861	1,482,982
Accumulated amortization	(350,296)	(190,960)
Finite-lived intangible assets, net	1,042,565	1,292,022
Customer Relationships
Finite-lived Intangible Assets [Roll Forward]
Gross cost	1,200,316	63,369
Divestitures	(45,175)
Additions due to acquisitions		1,253,312
Write-off of fully amortized intangible assets	(303)	0
Reclassified as held-for-sale		(140,156)
Foreign currency translation impact	(23,182)	23,791
Gross cost	1,131,656	1,200,316
Accumulated amortization	(184,918)	(92,983)
Finite-lived intangible assets, net	946,738	1,107,333
Software
Finite-lived Intangible Assets [Roll Forward]
Gross cost	123,424	16,025
Divestitures	(321)
Additions due to acquisitions		180,787
Write-off of fully amortized intangible assets	(11,715)	0
Reclassified as held-for-sale		(69,012)
Foreign currency translation impact	(687)	(4,376)
Gross cost	110,701	123,424
Accumulated amortization	(38,901)	(26,344)
Finite-lived intangible assets, net	71,800	97,080
Content
Finite-lived Intangible Assets [Roll Forward]
Gross cost	104,313	3,728
Divestitures	(473)
Additions due to acquisitions		141,707
Write-off of fully amortized intangible assets	(669)	(4,227)
Reclassified as held-for-sale		(38,593)
Foreign currency translation impact	(4,329)	1,698
Gross cost	98,842	104,313
Accumulated amortization	(92,717)	(47,475)
Finite-lived intangible assets, net	6,125	56,838
Other
Finite-lived Intangible Assets [Roll Forward]
Gross cost	54,929	33,645
Divestitures	(160)
Additions due to acquisitions		24,384
Write-off of fully amortized intangible assets	(3,311)	0
Reclassified as held-for-sale		(2,711)
Foreign currency translation impact	204	(389)
Gross cost	51,662	54,929
Accumulated amortization	(33,760)	(24,158)
Finite-lived intangible assets, net	$ 17,902	$ 30,771