Fair Value Measurements - Schedule of Activity of Major Classes of Assets Measured at Fair Value Using Level 3 Inputs (Details) - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (8,631)	$ (7,100)
Fair value adjustment to contingent consideration included in general and administrative expense	(1,835)	(2,781)
Cash paid upon achievement of milestone	4,166	1,250
Ending balance	$ (6,300)	$ (8,631)