Fair Value Measurements - Contingent Consideration Liabilities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Contingent consideration liabilities measured at fair value
Balance at beginning of period	$ 13,779
Balance at end of period	12,167
Fair value | Level 3
Contingent consideration liabilities measured at fair value
Balance at beginning of period	13,779
Fair value adjustments included in operating expenses	(1,612)
Balance at end of period	$ 12,167