Borrowings - Narrative (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Repurchase agreements	$ 75,000,000	$ 0
FHLB advances	1,430,000,000
Unencumbered securities	284,800,000
Multifamily loans held as collateral	$ 1,100,000,000
Repurchase agreements | Mortgage-backed securities
Debt Instrument [Line Items]
Mortgage-backed securities amortized cost		78,900,000
Mortgage-backed securities held for sale fair value		$ 78,300,000