Fair Value Measurements - Quantitative Inputs and Assumptions Used to Determine Fair Value for Private Label CMOs and Asset-backed Securities Available-for-sale (Details) - Level 3 - Fair Value, Measurements, Recurring	9 Months Ended
	Sep. 30, 2020
Measurement Input, Prepayment Rate | Minimum | Private label collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.053
Measurement Input, Prepayment Rate | Minimum | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.100
Measurement Input, Prepayment Rate | Maximum | Private label collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.161
Measurement Input, Prepayment Rate | Maximum | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.150
Measurement Input, Prepayment Rate | Weighted Average | Covered Private Label Collateralized Mortgage Obligations Member [Domain]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.107	[1]
Measurement Input, Prepayment Rate | Weighted Average | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.121	[2]
Measurement Input, Default Rate | Minimum | Private label collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.007	[3]
Measurement Input, Default Rate | Minimum | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.020
Measurement Input, Default Rate | Maximum | Private label collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.298	[3]
Measurement Input, Default Rate | Maximum | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.020
Measurement Input, Default Rate | Weighted Average | Covered Private Label Collateralized Mortgage Obligations Member [Domain]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.031	[1],[3]
Measurement Input, Default Rate | Weighted Average | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.020	[2],[3]
Measurement Input, Loss Severity | Minimum | Private label collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.019	[3]
Measurement Input, Loss Severity | Minimum | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.600
Measurement Input, Loss Severity | Maximum | Private label collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	1.652	[3]
Measurement Input, Loss Severity | Maximum | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.600
Measurement Input, Loss Severity | Weighted Average | Covered Private Label Collateralized Mortgage Obligations Member [Domain]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.530	[1],[3]
Measurement Input, Loss Severity | Weighted Average | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.600	[2],[3]
Measurement Input, Discount Rate | Minimum | Private label collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.021
Measurement Input, Discount Rate | Minimum | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.030
Measurement Input, Discount Rate | Maximum | Private label collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.079
Measurement Input, Discount Rate | Maximum | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.052
Measurement Input, Discount Rate | Weighted Average | Covered Private Label Collateralized Mortgage Obligations Member [Domain]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private Label Collateralized Mortgage Obligations, Measurement Input	0.060	[1]
Measurement Input, Discount Rate | Weighted Average | Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Asset-Backed Securities, Measurement Input	0.038	[2]

[1] Unobservable inputs for private label residential CMOs were weighted by the relative fair values of the instruments.

[2] Voluntary annual prepayment speeds and discount rates for asset-backed securities were weighted by the relative fair values of the instruments.

[3] Annual default rates and loss severity rates were the same for all of the asset-backed securities.