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, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	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, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Equity Method Investments [Line Items]
Total income	$ 119,943	$ 126,654	$ 125,926	$ 127,040	$ 112,320	$ 99,217	$ 101,504	$ 94,874	$ 70,313	$ 104,027	$ 80,717	$ 55,380	$ 499,563	$ 407,915	$ 310,437
Net income (loss)	2,651	$ (51,503)	$ (8,542)	$ 2,791	1,435	$ (4,868)	$ 3,830	$ 6,845	$ 2,707	$ 15,390	$ 8,936	$ 547	(54,603)	7,242	27,580
Balance sheet:
Total assets	1,803,328				1,176,857								1,803,328	1,176,857
Total liabilities	1,548,521				762,399								1,548,521	762,399
Limited Partnership [Member]
Schedule Of Equity Method Investments [Line Items]
Total income													1,252,264	705,610	(1,432,907)
Total expenses													(139,174)	(131,463)	(133,281)
Net income (loss)													1,113,090	574,147	$ (1,566,188)
Balance sheet:
Total assets	5,119,695				5,855,616								5,119,695	5,855,616
Total liabilities	$ 430,354				$ 564,732								$ 430,354	$ 564,732