Derivative Financial Instruments - Aggregate Fair Value and Notional Amount of Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Fair Value	$ (127,723)	$ (49,066)
Notional Amount	13,589,356	5,911,385
Derivative Liabilities
Derivative [Line Items]
Fair Value	(163,424)	(84,855)
Notional Amount	6,929,494	2,953,724
Derivative Assets
Derivative [Line Items]
Fair Value	35,701	35,789
Notional Amount	6,659,862	2,957,661
Interest rate agreements | Derivative Liabilities
Derivative [Line Items]
Fair Value	(97,235)	(36,416)
Notional Amount	2,314,300	1,742,000
Interest rate agreements | Derivative Liabilities | Cash Flow Hedging
Derivative [Line Items]
Fair Value	(51,530)	(34,492)
Notional Amount	139,500	139,500
Interest rate agreements | Derivative Assets
Derivative [Line Items]
Fair Value	17,095	28,211
Notional Amount	1,399,000	2,106,500
TBAs
Derivative [Line Items]
Notional Amount	6,610,000	1,460,000
TBAs | Derivative Liabilities
Derivative [Line Items]
Fair Value	(13,359)	(13,215)
Notional Amount	4,160,000	935,000
TBAs | Derivative Assets
Derivative [Line Items]
Fair Value	5,755	4,665
Notional Amount	2,445,000	520,000
Interest rate futures
Derivative [Line Items]
Notional Amount	226,000
Interest rate futures | Derivative Liabilities
Derivative [Line Items]
Fair Value	(10)	0
Notional Amount	12,300	0
Interest rate futures | Derivative Assets
Derivative [Line Items]
Fair Value	777	0
Notional Amount	213,700	0
Swaptions | Derivative Assets
Derivative [Line Items]
Fair Value	1,925	0
Notional Amount	1,065,000	0
Loan purchase and interest rate lock commitments | Derivative Liabilities
Derivative [Line Items]
Fair Value	(1,290)	(732)
Notional Amount	303,394	137,224
Loan purchase and interest rate lock commitments | Derivative Assets
Derivative [Line Items]
Fair Value	10,149	2,913
Notional Amount	$ 1,537,162	$ 331,161