Investments - Summary of Unaudited Financial Information and Unaudited Financial Position of Limited Partnerships (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Schedule Of Equity Method Investments [Line Items]
Total income	$ 80,717	$ 58,630	$ 136,097	$ 119,264
Limited Partnership [Member]
Schedule Of Equity Method Investments [Line Items]
Total income	(1,230,124)	338,414	(1,681,016)	247,901
Total expenses	(25,708)	(32,140)	(80,520)	(81,173)
Net (loss) income	(1,255,832)	$ 306,274	(1,761,536)	$ 166,728
Balance Sheet:
Total assets	5,101,450		5,101,450		$ 6,850,913
Total liabilities	$ 641,725		$ 641,725		$ 549,562