Variable Interest Entities - Summary of Variable Interest Entities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Investment securities available-for-sale	$ 3,857,337	$ 3,931,115
Accrued expenses and other liabilities	218,582	243,207
Other assets	240,730	292,861
Total assets	20,173,298	19,736,544
Liabilities	17,470,200	16,989,895
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum loss	221,401	223,509
Total assets	185,311	190,686
Liabilities	15,259	18,526
Variable Interest Entity, Not Primary Beneficiary | Multifamily Loan Securitization
Variable Interest Entity [Line Items]
Investment securities available-for-sale	98,863	100,927
Accrued expenses and other liabilities	448	448
Variable Interest Entity, Not Primary Beneficiary | Multifamily Loan Securitization, Asset
Variable Interest Entity [Line Items]
Maximum loss	98,863	100,927
Variable Interest Entity, Not Primary Beneficiary | Multifamily Loan Securitization, Liability
Variable Interest Entity [Line Items]
Maximum loss	50,901	50,901
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership
Variable Interest Entity [Line Items]
Accrued expenses and other liabilities	14,811	18,078
Other assets	86,448	89,759
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership, Asset
Variable Interest Entity [Line Items]
Maximum loss	71,637	71,681
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership, Liability
Variable Interest Entity [Line Items]
Maximum loss	$ 0	$ 0