Commitments and Contingencies - Additional Information (Detail)			9 Months Ended
	Mar. 31, 2020 Officer	Oct. 17, 2019 Officer	Sep. 30, 2020 USD ($)	Oct. 08, 2020 USD ($)	Dec. 31, 2019 USD ($)
Contingencies And Commitments [Line Items]
Commitments related to performance bonds			$ 12,000,000.0		$ 9,300,000
Commitments related to performance bonds expiration month and year			2024-08
Letter of credit secured by pledge of a portion of fixed income securities			$ 5,900,000
Commitments towards private equity funds			4,900,000
Investment Commitments [Member]
Contingencies And Commitments [Line Items]
Aggregate investment committed in private equity funds			5,000,000.0
Restricted Cash [Member]
Contingencies And Commitments [Line Items]
Letter of credit secured by pledge of a portion of fixed income securities			300,000
Long-term Investments [Member]
Contingencies And Commitments [Line Items]
Letter of credit secured by pledge of a portion of fixed income securities			5,600,000
Minimum [Member]
Contingencies And Commitments [Line Items]
Collateral value required to be maintained			4,500,000
Letter of credit secured by pledge of collateral value fluctuation between restricted cash and long term investment			13,000,000.0
Minimum [Member] | Subsequent Event [Member]
Contingencies And Commitments [Line Items]
Collateral value required to be maintained				$ 9,000,000.0
Maximum [Member]
Contingencies And Commitments [Line Items]
Letter of credit secured by pledge of collateral value fluctuation between restricted cash and long term investment			$ 15,000,000.0
Current Executive Officers [Member]
Contingencies And Commitments [Line Items]
Number of officers | Officer	2	2
Former Executive Officers [Member]
Contingencies And Commitments [Line Items]
Number of officers | Officer	1	1