Fair Value of Financial Instruments - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Liabilities:
Accruals and other current liabilities	$ 6,900	$ 2,884
Fair Value, Recurring
Assets:
Total assets	9,566	35,043
Liabilities:
Acquisition contingent consideration	9,033	4,299
Deferred compensation plan liabilities	96,480	2,591
Cash-settled equity awards	247	195
Total liabilities	105,760	7,085
Accruals and other current liabilities	6,900	2,884
Deferred compensation plan, current	7,306	169
Fair Value, Recurring | Money Market Funds
Assets:
Money market funds	21	34,696
Fair Value, Recurring | Interest Rate Swap
Assets:
Interest rate swap	9,545	347
Level 1 | Fair Value, Recurring
Assets:
Total assets	21	34,696
Liabilities:
Acquisition contingent consideration	0	0
Deferred compensation plan liabilities	96,480	2,591
Cash-settled equity awards	247	195
Total liabilities	96,727	2,786
Level 1 | Fair Value, Recurring | Money Market Funds
Assets:
Money market funds	21	34,696
Level 1 | Fair Value, Recurring | Interest Rate Swap
Assets:
Interest rate swap	0	0
Level 2 | Fair Value, Recurring
Assets:
Total assets	9,545	347
Liabilities:
Acquisition contingent consideration	0	0
Deferred compensation plan liabilities	0	0
Cash-settled equity awards	0	0
Total liabilities	0	0
Level 2 | Fair Value, Recurring | Money Market Funds
Assets:
Money market funds	0	0
Level 2 | Fair Value, Recurring | Interest Rate Swap
Assets:
Interest rate swap	9,545	347
Level 3 | Fair Value, Recurring
Assets:
Total assets	0	0
Liabilities:
Acquisition contingent consideration	9,033	4,299
Deferred compensation plan liabilities	0	0
Cash-settled equity awards	0	0
Total liabilities	9,033	4,299
Level 3 | Fair Value, Recurring | Money Market Funds
Assets:
Money market funds	0	0
Level 3 | Fair Value, Recurring | Interest Rate Swap
Assets:
Interest rate swap	$ 0	$ 0