Real Estate and Other Investments - Schedule of Investment in and Equity in Earnings of Unconsolidated Affiliates (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated affiliates	$ 705,721				$ 571,897				$ 705,721	$ 571,897
Income from operations									7,407	7,595	$ 16,663
Net gain on sales									96,094	13,686	70,011
Equity in earnings of unconsolidated affiliates	1,176	$ 45,075	$ 16,790	$ 40,460	2,376	$ 13,029	$ 6,421	$ (545)	103,501	21,281	$ 86,674
Real Estate
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated affiliates	402,780				386,981				402,780	386,981
Equity and Fixed Income
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated affiliates	278,611				156,121				278,611	156,121
Other
Schedule of Equity Method Investments [Line Items]
Total investments in unconsolidated affiliates	$ 24,330				$ 28,795				$ 24,330	$ 28,795