Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Level 1
Assets:
Short-term investments	$ 10,970	$ 42,942
Total	10,970	42,942
Liabilities:
Contingent consideration	0	0
Total	0	0
Level 2
Assets:
Short-term investments	0	0
Total	0	0
Liabilities:
Contingent consideration	0	0
Total	0	0
Level 3
Assets:
Short-term investments	0	0
Total	0	0
Liabilities:
Contingent consideration	1,742	2,100
Total	$ 1,742	$ 2,100