Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Liabilities:
Payment for contingent consideration	$ 900	$ 500
Undiscounted maximum payment, based on certain milestone	6,000
Level 1 | Fair Value, Measurements, Recurring
Liabilities:
Contingent consideration	0	0
Total	0	0
Level 2 | Fair Value, Measurements, Recurring
Liabilities:
Contingent consideration	0	0
Total	0	0
Level 3 | Fair Value, Measurements, Recurring
Liabilities:
Contingent consideration	5,531	412
Total	$ 5,531	$ 412