Variable Interest Entities - Summary of Variable Interest Entities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Investment securities available-for-sale	$ 3,931,115	$ 1,368,384
Accrued expenses and other liabilities	243,207	131,367
Other assets	292,861	154,992
Assets	19,736,544	11,776,012
Liabilities	16,989,895	9,763,418
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum loss	223,509	32,466
Assets	190,686	53,880
Liabilities	18,526	21,414
Multifamily Loan Securitization | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Investment securities available-for-sale	100,927	0
Accrued expenses and other liabilities	448	0
Multifamily Loan Securitization, Asset | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum loss	100,927	0
Multifamily Loan Securitization, Liability | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum loss	50,901	0
Affordable Housing Partnership | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Accrued expenses and other liabilities	18,078	21,414
Other assets	89,759	53,880
Affordable Housing Partnership, Asset | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum loss	71,681	32,466
Affordable Housing Partnership, Liability | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum loss	$ 0	$ 0