Fair Value Measurements - Fair Value of Contingent Consideration Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at December 31, 2020			$ 189,600
Decrease in fair value of contingent payments	$ 1,200	$ 1,800	(1,100)	$ 12,600
Balance at September 30, 2021	$ 188,500		$ 188,500