Loans Receivable, Net - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average risk rating on loan exposure	2.8	2.8
Increase (decrease) in CECL reserve	$ (2,500,000)		$ (1,400,000)
CECL reserve	122,221,000	$ 124,679,000	172,100,000	$ 173,549,000
Reversal of remaining CECL reserve	2,537,000		1,293,000
Loans held	25,627,588,000	23,669,111,000
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held	6,584,594,000	5,771,517,000
Multifamily | Joint Venture
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held	833,200,000	746,900,000
Multifamily Properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount of loans	37,500,000	37,500,000
Multifamily Asset in New York City
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in CECL reserve		14,800,000
CECL reserve	0
Principal charge-offs		14,400,000
Reversal of remaining CECL reserve		$ 360,000
Income recorded on loan			0
Hospitality Asset in New York City
Accounts, Notes, Loans and Financing Receivable [Line Items]
CECL reserve	54,900,000
Carrying amount of loans	286,300,000
Income recorded on loan	$ 0		$ 0