Derivative Financial Instruments - Aggregate Fair Value and Notional Amount of Derivative Financial Instruments (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Fair Value	$ 37,166,000	$ (127,723,000)
Notional Amount	11,346,407,000	13,589,356,000
Derivative Liabilities
Derivative [Line Items]
Fair Value	(16,072,000)	(163,424,000)
Notional Amount	3,582,153,000	6,929,494,000
Derivative Assets
Derivative [Line Items]
Fair Value	53,238,000	35,701,000
Notional Amount	7,764,254,000	6,659,862,000
Interest rate agreements | Derivative Liabilities
Derivative [Line Items]
Fair Value	0	(97,235,000)
Notional Amount	0	2,314,300,000
Interest rate agreements | Derivative Liabilities | Cash Flow Hedging
Derivative [Line Items]
Fair Value	0	(51,530,000)
Notional Amount	0	139,500,000
Interest rate agreements | Derivative Assets
Derivative [Line Items]
Fair Value	224,000	17,095,000
Notional Amount	42,000,000	1,399,000,000
TBAs
Derivative [Line Items]
Notional Amount	6,630,000,000	6,610,000,000
TBAs | Derivative Liabilities
Derivative [Line Items]
Fair Value	(15,495,000)	(13,359,000)
Notional Amount	3,105,000,000	4,160,000,000
TBAs | Derivative Assets
Derivative [Line Items]
Fair Value	18,260,000	5,755,000
Notional Amount	3,520,000,000	2,445,000,000
Futures
Derivative [Line Items]
Notional Amount		226,000,000
Futures | Derivative Liabilities
Derivative [Line Items]
Fair Value	0	(10,000)
Notional Amount	0	12,300,000
Futures | Derivative Assets
Derivative [Line Items]
Fair Value	0	777,000
Notional Amount	0	213,700,000
Swaptions | Derivative Assets
Derivative [Line Items]
Fair Value	19,727,000	1,925,000
Notional Amount	1,585,000,000	1,065,000,000
Loan purchase and interest rate lock commitments | Derivative Liabilities
Derivative [Line Items]
Fair Value	(577,000)	(1,290,000)
Notional Amount	477,153,000	303,394,000
Loan purchase and interest rate lock commitments | Derivative Assets
Derivative [Line Items]
Fair Value	15,027,000	10,149,000
Notional Amount	$ 2,617,254,000	$ 1,537,162,000