Fair Value Measurements - Financial Assets And Liabilities Measured At Fair Value On Recurring Basis (Details) - Fair value, measurements, recurring - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Acquisition-related contingent consideration—current
Liabilities:
Fair value of financial liabilities measured on recurring basis	$ 6,534	$ 36,514
Acquisition-related contingent consideration—noncurrent
Liabilities:
Fair value of financial liabilities measured on recurring basis	23,123	80,189
Money market funds
Assets:
Fair value of financial assets measured on recurring basis	427,033	137,215
Level 1 Inputs | Acquisition-related contingent consideration—current
Liabilities:
Fair value of financial liabilities measured on recurring basis	0	0
Level 1 Inputs | Acquisition-related contingent consideration—noncurrent
Liabilities:
Fair value of financial liabilities measured on recurring basis	0	0
Level 1 Inputs | Money market funds
Assets:
Fair value of financial assets measured on recurring basis	427,033	137,215
Level 2 Inputs | Acquisition-related contingent consideration—current
Liabilities:
Fair value of financial liabilities measured on recurring basis	0	0
Level 2 Inputs | Acquisition-related contingent consideration—noncurrent
Liabilities:
Fair value of financial liabilities measured on recurring basis	0	0
Level 2 Inputs | Money market funds
Assets:
Fair value of financial assets measured on recurring basis	0	0
Level 3 Inputs | Acquisition-related contingent consideration—current
Liabilities:
Fair value of financial liabilities measured on recurring basis	6,534	36,514
Level 3 Inputs | Acquisition-related contingent consideration—noncurrent
Liabilities:
Fair value of financial liabilities measured on recurring basis	23,123	80,189
Level 3 Inputs | Money market funds
Assets:
Fair value of financial assets measured on recurring basis	$ 0	$ 0