Derivative Instruments - Fair value of Derivative Instruments (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Derivative [Line Items]
Fair value of derivative assets	$ 5,833	$ 46,207
Fair value of derivative liabilities	52,197	15,901
Unrealized loss on interest rate swaps, net	98,907	(585)	$ (8,310)
Interest rate swaps
Derivative [Line Items]
Fair value of derivative assets	5,302	40,192
Fair value of derivative liabilities	$ 52,197	15,901
Interest rate swap agreements
Derivative [Line Items]
Derivative contract, weighted average maturity (in months)	48 months
Number of matured or terminated interest rate swap agreements | item	36
Notional amount of swap agreements matured or terminated during period	$ 1,840,000
Number of new swap agreements | item	26
Notional amount of swap agreements added during period	$ 1,035,000
Amount in AOCI relating to interest rate swaps	7,600
Interest rate cash flow hedge gain (loss) to be reclassified during next 12 months	$ 3,300
Swap agreements, maximum maturity term	10 years
TBA Agency MBS
Derivative [Line Items]
Fair value of derivative assets	$ 531	$ 6,015
Minimum | Interest rate swap agreements
Derivative [Line Items]
Fixed interest rate	1.411%
Minimum | TBA Agency MBS
Derivative [Line Items]
Fixed interest rate	3.00%
Maximum | Interest rate swap agreements
Derivative [Line Items]
Fixed interest rate	3.2205%
Maximum | TBA Agency MBS
Derivative [Line Items]
Fixed interest rate	4.50%