Fair Value Measurements - Contingent Consideration Liabilities (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Contingent consideration liabilities measured at fair value
Balance at beginning of period	$ 13,779
Balance at end of period	14,281
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	502
Balance at end of period	$ 14,281