Investments - Summary of Unaudited Financial Information and Unaudited Financial Position of Limited Partnerships (Detail) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Equity Method Investments [Line Items]
Total income	$ 112,320	$ 99,217	$ 101,504	$ 94,874	$ 70,313	$ 104,027	$ 80,717	$ 55,380	$ 63,231	$ 59,979	$ 58,630	$ 60,634	$ 407,915	$ 310,437	$ 242,474
Net income	1,435	$ (4,868)	$ 3,830	$ 6,845	2,707	$ 15,390	$ 8,936	$ 547	$ 6,432	$ 5,853	$ 7,553	$ 6,738	7,242	27,580	26,576
Balance sheet:
Total assets	1,176,857				941,313								1,176,857	941,313
Total liabilities	762,399				740,177								762,399	740,177
Limited Partnership [Member]
Schedule Of Equity Method Investments [Line Items]
Total income													705,610	(1,432,907)	27,171
Total expenses													(131,463)	(133,281)	(139,252)
Net income													574,147	(1,566,188)	$ (112,081)
Balance sheet:
Total assets	5,855,616				5,529,199								5,855,616	5,529,199
Total liabilities	$ 564,732				$ 612,048								$ 564,732	$ 612,048