Derivatives and Hedging Activities - Outstanding Interest Rate Swaptions and Derivative Instrument Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2020	$ 8,033,084
Additions	5,215,279
Settlement, Termination, Expiration or Exercise	(3,584,767)
Notional Amount as of December 31, 2021	9,663,596
Transitioned From LIBOR to SOFR
Changes in notional amount of derivative instruments [Roll Forward]
Additions	7,300,000
Settlement, Termination, Expiration or Exercise	(7,300,000)
Interest Rate Swaps
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2020	6,300,000
Additions	4,250,000
Settlement, Termination, Expiration or Exercise	(2,500,000)
Notional Amount as of December 31, 2021	8,050,000
Interest Rate Swaptions
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2020	0
Additions	1,000,000
Settlement, Termination, Expiration or Exercise	(1,000,000)
Notional Amount as of December 31, 2021	0
Currency Forward Contracts
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2020	33,084
Additions	65,279
Settlement, Termination, Expiration or Exercise	(84,767)
Notional Amount as of December 31, 2021	13,596
TBA Purchase Contracts
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2020	1,700,000
Additions	23,125,000
Settlement, Termination, Expiration or Exercise	(23,225,000)
Notional Amount as of December 31, 2021	1,600,000
TBA Sale Contracts
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2020	0
Additions	(23,225,000)
Settlement, Termination, Expiration or Exercise	23,225,000
Notional Amount as of December 31, 2021	0
Interest Rate Swap, Forward Start Dates | 1-Month LIBOR
Changes in notional amount of derivative instruments [Roll Forward]
Notional Amount as of December 31, 2021	$ 1,300,000