Derivative Financial Instruments - Additional Information (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional amount	$ 2,575,858,000			$ 2,575,858,000			$ 13,589,356,000
Accumulated other comprehensive income (loss)	1,053,464,000		$ 1,785,059,000	1,053,464,000	$ 1,785,059,000	$ 936,576,000	1,827,231,000	$ 1,564,032,000	$ 1,348,794,000
Interest Rate Agreements Accounted for as Cash Flow Hedges
Derivative [Line Items]
Accumulated other comprehensive income (loss)	(81,597,000)		(61,175,000)	(81,597,000)	(61,175,000)	$ (82,637,000)	(50,939,000)	$ (49,384,000)	$ (34,045,000)
Interest Expense
Derivative [Line Items]
Cash flow hedge gain (loss) to be reclassified over the next 12 months				(4,000,000)
Mortgage Banking Activities, Net
Derivative [Line Items]
Market valuations gains (losses), net	56,619,000		6,205,000	18,173,000	33,625,000
Loan purchase commitments and forward sales commitments | Mortgage Banking Activities, Net
Derivative [Line Items]
Market valuations gains (losses), net	14,000,000		14,000,000	35,000,000	42,000,000
Interest rate contract
Derivative [Line Items]
Notional amount	335,000,000			335,000,000			4,780,000,000
TBAs
Derivative [Line Items]
Notional amount	245,000,000			245,000,000			6,610,000,000
Interest rate futures
Derivative [Line Items]
Notional amount	40,000,000			40,000,000			$ 226,000,000
Unsecuritized Residential and Commercial Loans
Derivative [Line Items]
Derivative gain (loss)	0		(36,000,000)	(98,000,000)	(147,000,000)
Interest rate swaps | Cash Flow Hedging
Derivative [Line Items]
Derivative gain (loss)	$ 0		$ (12,000,000)	$ (33,000,000)	$ (27,000,000)
Derivative, cost of hedge		$ 84,000,000