Variable Interest Entities - Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Investment securities available-for-sale	$ 4,487,447	$ 3,931,115
Accrued expenses and other liabilities	224,348	243,207
Other assets	257,823	292,861
Total assets	20,529,486	19,736,544
Liabilities	17,716,067	16,989,895
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum Loss	217,194	223,509
Total assets	189,082	190,686
Liabilities	23,237	18,526
Variable Interest Entity, Not Primary Beneficiary | Multifamily Loan Securitization
Variable Interest Entity [Line Items]
Investment securities available-for-sale	95,857	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	95,857	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	22,789	18,078
Other assets	93,225	89,759
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership, Asset
Variable Interest Entity [Line Items]
Maximum Loss	70,436	71,681
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership, Liability
Variable Interest Entity [Line Items]
Maximum Loss	$ 0	$ 0