Fair Value Measurement - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets:
Money market funds	$ 0	$ 667
Liabilities:
Contingent consideration	19,283	22,162
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Money market funds	0	667
Liabilities:
Contingent consideration	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Money market funds	0	0
Liabilities:
Contingent consideration	0	0
Significant Unobservable Inputs (Level 3)
Assets:
Money market funds	0	0
Liabilities:
Contingent consideration	$ 19,283	$ 22,162	$ 32,582