Debt - Mortgages Segment, Master Repurchase Agreements Narrative (Detail) - USD ($)	Dec. 31, 2021	Sep. 17, 2021	Sep. 16, 2021	Jun. 11, 2021	Mar. 19, 2021	Dec. 31, 2020
Line of Credit | Mortgages
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 460,000,000
Line of Credit | Mortgages | Citibank, N.A.
Debt Instrument [Line Items]
Committed amount under repurchase agreement				$ 25,000,000
Credit Suisse AG, Cayman Islands
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 1,500,000,000	$ 500,000,000
Credit Suisse AG, Cayman Islands | Mortgages
Debt Instrument [Line Items]
Short-term debt	76,392,000					$ 149,913,000
Credit Suisse AG, Cayman Islands | Line of Credit | Mortgages
Debt Instrument [Line Items]
Maximum borrowing capacity	300,000,000				$ 300,000,000
Credit Suisse and Citibank, N.A | Mortgages
Debt Instrument [Line Items]
Short-term debt	$ 87,000,000					$ 240,100,000