Derivative Financial Instruments - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional amount		$ 11,346,407,000	$ 13,589,356,000
Stockholders' equity attributable to parent		1,110,899,000	1,827,231,000	$ 1,348,794,000	$ 1,212,287,000
Interest Expense [Member]
Derivative [Line Items]
Expected amortization of realized losses related to terminated cash flow hedges		4,000,000
Net Unrealized Losses on Interest Rate Agreements Accounted for as Cash Flow Hedges
Derivative [Line Items]
Stockholders' equity attributable to parent		(80,557,000)	(50,939,000)	(34,045,000)
Mortgage Banking Activities, Net
Derivative [Line Items]
Changes in fair value of assets		66,482,000	69,326,000	57,000,000
LPCs, IRLCs, and FSCs | Mortgage Banking Activities, Net
Derivative [Line Items]
Changes in fair value of assets		57,000,000	62,000,000	(1,000,000)
Interest Rate Contract
Derivative [Line Items]
Notional amount		1,630,000,000	4,780,000,000
TBAs
Derivative [Line Items]
Notional amount		6,630,000,000	6,610,000,000
Futures
Derivative [Line Items]
Notional amount			226,000,000
Residential and Commercial Loans
Derivative [Line Items]
Valuation adjustments on derivatives		(93,000,000)	(134,000,000)	40,000,000
Interest rate agreements | Cash Flow Hedging
Derivative [Line Items]
Valuation adjustments on derivatives		$ (33,000,000)	$ (17,000,000)	$ 9,000,000
Derivative payment	$ 84,000,000