Variable Interest Entities - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Investment securities available-for-sale	$ 4,709,815	$ 3,931,115
Accrued Liabilities and Other Liabilities	216,688	243,207
Other assets	260,505	292,861
Total assets	21,005,211	19,736,544
Liabilities	18,167,095	16,989,895
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum Loss	212,082	223,509
Total assets	180,585	190,686
Liabilities	19,852	18,526
Variable Interest Entity, Not Primary Beneficiary | Multifamily Loan Securitization
Variable Interest Entity [Line Items]
Investment securities available-for-sale	90,575	100,927
Accrued Liabilities and Other Liabilities	448	448
Variable Interest Entity, Not Primary Beneficiary | Multifamily Loan Securitization, Asset
Variable Interest Entity [Line Items]
Maximum Loss	90,575	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 Liabilities and Other Liabilities	19,404	18,078
Other assets	90,010	89,759
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership, Asset
Variable Interest Entity [Line Items]
Maximum Loss	70,606	71,681
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership, Liability
Variable Interest Entity [Line Items]
Maximum Loss	$ 0	$ 0