Variable Interest Entities - Summary of Variable Interest Entities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Investment securities available-for-sale	$ 2,336,066	$ 1,368,384
Accrued expenses and other liabilities	343,353	131,367
Other assets	344,786	154,992
Total assets	20,517,074	11,776,012
Liabilities	17,862,427	9,763,418
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Maximum loss	246,905	32,466
Total assets	215,494	53,880
Liabilities	19,953	21,414
Variable Interest Entity, Not Primary Beneficiary | Multifamily Loan Securitization
Variable Interest Entity [Line Items]
Investment securities available-for-sale	119,932	0
Accrued expenses and other liabilities	463	0
Variable Interest Entity, Not Primary Beneficiary | Multifamily Loan Securitization, Asset
Variable Interest Entity [Line Items]
Maximum loss	119,932	0
Variable Interest Entity, Not Primary Beneficiary | Multifamily Loan Securitization, Liability
Variable Interest Entity [Line Items]
Maximum loss	50,901	0
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership
Variable Interest Entity [Line Items]
Accrued expenses and other liabilities	19,490	21,414
Other assets	95,562	53,880
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership, Asset
Variable Interest Entity [Line Items]
Maximum loss	76,072	32,466
Variable Interest Entity, Not Primary Beneficiary | Affordable Housing Partnership, Liability
Variable Interest Entity [Line Items]
Maximum loss	$ 0	$ 0