Fair Value Measurements - Reconciliation of Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Details) - Level 3 - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Contingent consideration liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 74,400	$ 53,900	$ 76,900	$ 52,800
Changes in fair value	5,700	10,500	3,200	11,600
Ending Balance	80,100	64,400	80,100	64,400
Common stock warrant liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	543	69	512	809
Changes in fair value	64	380	95	(360)
Ending Balance	$ 607	$ 449	$ 607	$ 449