Related Party Transactions - Additional Information (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) RenewalOption Agreement Building	Jun. 30, 2020 USD ($)	Dec. 31, 2018 RenewalOption Agreement	Dec. 31, 2020 USD ($)
Related Party Transaction [Line Items]
Advanced billings	$ 5,900,000		$ 5,900,000			$ 6,500,000
Accounts receivable and unbilled, net	6,100,000		6,100,000			2,600,000
Operating lease cost recognized	5,817,000	$ 4,871,000	11,547,000	$ 8,639,000
Operating lease right-of-use assets	110,730,000		110,730,000			113,809,000
Current portion of lease liability	15,179,000		15,179,000			15,890,000
Long-term portion of lease liabilities	112,850,000		112,850,000			115,143,000
Accounts payable	700,000		700,000			200,000
Employee Loans | Prepaid Expenses and Other Current Assets and Other Assets
Related Party Transaction [Line Items]
Employee advances receivables	200,000		200,000			200,000
Service Agreement | LIB
Related Party Transaction [Line Items]
Advanced billings	700,000		700,000			700,000
Accounts receivable and unbilled, net	2,300,000		2,300,000			300,000
Service Agreement | LIB | Revenue Net
Related Party Transaction [Line Items]
Revenue with related parties	2,800,000	400,000	3,300,000	1,400,000
Service Agreement | CinRx Pharma and Subsidiaries
Related Party Transaction [Line Items]
Advanced billings	5,100,000		5,100,000			5,800,000
Accounts receivable and unbilled, net	3,800,000		3,800,000			2,200,000
Service Agreement | CinRx Pharma and Subsidiaries | Revenue Net
Related Party Transaction [Line Items]
Revenue with related parties	7,100,000	2,400,000	11,900,000	6,800,000
Service Agreement | The Summit
Related Party Transaction [Line Items]
Expenses incurred			$ 100,000	200,000
Service Agreement | The Summit | Maximum
Related Party Transaction [Line Items]
Expenses incurred	$ 100,000	100,000
Leased Real Estate | Chief Executive Officer
Related Party Transaction [Line Items]
Term of lease	12 years		12 years
Lease expiration period			2022-11
Number of lease renewal, 10-year option | RenewalOption			1
Lease term upon renewal	10 years		10 years
Leased Real Estate | Chief Executive Officer | Direct Costs and Selling, General And Administrative
Related Party Transaction [Line Items]
Operating lease cost recognized	$ 500,000	500,000	$ 1,000,000.0	1,000,000.0
Leased Real Estate | Chief Executive Officer And Immediate Family | Office Space
Related Party Transaction [Line Items]
Number of lease renewal, 10-year option | RenewalOption					2
Lease term upon renewal					10 years
Lease expiration year					2040
Number of lease agreements | Agreement					1
Leased Real Estate | Chief Executive Officer And Immediate Family | Building
Related Party Transaction [Line Items]
Number of lease renewal, 10-year option | RenewalOption			1
Lease term upon renewal	10 years		10 years
Lease expiration year			2027
Number of lease agreements | Agreement			2
Number of buildings | Building			2
Lease occupancy year			2012
Leased Real Estate | Chief Executive Officer And Immediate Family | Direct Costs and Selling, General And Administrative | Office Space
Related Party Transaction [Line Items]
Operating lease cost recognized	$ 1,400,000	900,000	$ 2,800,000	900,000
Leased Real Estate | Chief Executive Officer And Immediate Family | Direct Costs and Selling, General And Administrative | Building
Related Party Transaction [Line Items]
Operating lease cost recognized	900,000	900,000	1,800,000	1,800,000
Leased Real Estate | Operating Lease Right-of-Use Assets | Chief Executive Officer
Related Party Transaction [Line Items]
Operating lease right-of-use assets	2,600,000		2,600,000			3,500,000
Leased Real Estate | Operating Lease Right-of-Use Assets | Chief Executive Officer And Immediate Family | Office Space
Related Party Transaction [Line Items]
Operating lease right-of-use assets	55,800,000		55,800,000			56,600,000
Leased Real Estate | Operating Lease Right-of-Use Assets | Chief Executive Officer And Immediate Family | Building
Related Party Transaction [Line Items]
Operating lease right-of-use assets	18,500,000		18,500,000			19,700,000
Leased Real Estate | Other Current Liabilities | Chief Executive Officer
Related Party Transaction [Line Items]
Current portion of lease liability	1,900,000		1,900,000			1,900,000
Leased Real Estate | Other Current Liabilities | Chief Executive Officer And Immediate Family | Office Space
Related Party Transaction [Line Items]
Current portion of lease liability	800,000		800,000			700,000
Leased Real Estate | Other Current Liabilities | Chief Executive Officer And Immediate Family | Building
Related Party Transaction [Line Items]
Current portion of lease liability	2,500,000		2,500,000			2,400,000
Leased Real Estate | Operating Lease Liabilities | Chief Executive Officer
Related Party Transaction [Line Items]
Long-term portion of lease liabilities	700,000		700,000			1,600,000
Leased Real Estate | Operating Lease Liabilities | Chief Executive Officer And Immediate Family | Office Space
Related Party Transaction [Line Items]
Long-term portion of lease liabilities	66,400,000		66,400,000			66,800,000
Leased Real Estate | Operating Lease Liabilities | Chief Executive Officer And Immediate Family | Building
Related Party Transaction [Line Items]
Long-term portion of lease liabilities	15,900,000		15,900,000			17,200,000
Travel Services
Related Party Transaction [Line Items]
Accounts payable	500,000		500,000
Travel Services | Maximum
Related Party Transaction [Line Items]
Accounts payable						$ 100,000
Travel Services | Chief Executive Officer
Related Party Transaction [Line Items]
Travel expenses with related party	$ 400,000	$ 200,000	$ 500,000	$ 400,000