Fair Value Measurements - Schedule of Changes to Deferred Acquisition Consideration (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	$ 82,598,000	$ 119,086,000	$ 82,598,000	$ 119,086,000	$ 224,754,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments			122,426,000
Other			374,000	4,819,000	$ (8,227,000)
Ending balance of contingent payments	83,695,000	122,426,000	83,695,000	122,426,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			(54,947,000)	(110,234,000)
Additions - acquisition and step-up transactions			14,943,000	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings			3,512,000	3,273,000
Foreign translation adjustment			4,000	1,293,000
Fixed payments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments			3,340,000
Ending balance of contingent payments	1,097,000	3,340,000	1,097,000	3,340,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			6,000
Contingent Payment [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Other	$ (8,979,000)	$ (18,173,000)	$ 3,679,000	$ 6,021,000