Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Level 1
Assets:
Short-term investments	$ 10,998	$ 10,997
Total	10,998	10,997
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	1,019	412
Total	$ 1,019	$ 412