Fair Value Measurements - Reconciliation of Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Details) - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Contingent purchase consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 76,900	$ 52,800
Changes in fair value	1,300	24,100
Ending Balance	78,200	76,900
Common stock warrant liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	512	809
Changes in fair value	(169)	(297)
Ending Balance	$ 343	$ 512