Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Liabilities:
Operating cash balances not included in fair value table	$ 38,624	$ 18,987
Recurring Basis
Assets:
Money market funds	27,125	28,672
Total assets	27,125	28,672
Liabilities:
Contingent consideration on acquisition liability	0	1,500
Total liabilities	0	1,500
Recurring Basis | Level 1
Assets:
Money market funds	27,125	28,672
Total assets	27,125	28,672
Liabilities:
Contingent consideration on acquisition liability	0	0
Total liabilities	0	0
Recurring Basis | Level 2
Assets:
Money market funds	0	0
Total assets	0	0
Liabilities:
Contingent consideration on acquisition liability	0	0
Total liabilities	0	0
Recurring Basis | Level 3
Assets:
Money market funds	0	0
Total assets	0	0
Liabilities:
Contingent consideration on acquisition liability	0	1,500
Total liabilities	$ 0	$ 1,500