Fair Value Measurements - Level 3 Contingent Purchase Price (Details) - Contingent Purchase Price Liability - Fair Value, Measurements, Recurring - Significant Unobservable Inputs (Level 3) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 18,825	$ 20,300	$ 19,650	$ 31,832
Payments	(3)	0	(570)	0
Fair value adjustments to contingent purchase prices included in net loss	0	(1,600)	(258)	(13,132)
Balance at end of period	$ 18,822	$ 18,700	$ 18,822	$ 18,700