Fair Value Measurement - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets:
Money market funds	$ 667	$ 667
Liabilities:
Contingent consideration	(22,162)	(32,582)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Money market funds	667	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	$ (22,162)	$ (32,582)	$ (87,333)