Fair Value Measurements (Narrative) (Detail) $ in Thousands	Mar. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash	$ 42,600	$ 114,300
Available for sale debt securities:	1,216,936	1,105,489
Subordinated debentures	25,173	25,135
Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,216,936	1,105,489
Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0	1,009
Subordinated debentures	0	0
Quoted Prices in Active  Markets for Identical Assets (Level 1) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0	1,009
Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,216,936	1,104,480
Subordinated debentures	30,325	24,375
Significant Other Observable  Inputs (Level 2) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,216,936	1,104,480
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0	0
Subordinated debentures	0	0
Significant Unobservable Inputs (Level 3) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0	0
Agency Obligations | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:		1,009
Agency Obligations | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:		1,009
Agency Obligations | Quoted Prices in Active  Markets for Identical Assets (Level 1) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:		1,009
Agency Obligations | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:		0
Agency Obligations | Significant Other Observable  Inputs (Level 2) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:		0
Agency Obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:		0
Agency Obligations | Significant Unobservable Inputs (Level 3) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:		0
Mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,060,152	938,413
Mortgage-backed securities | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,060,152	938,413
Mortgage-backed securities | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0	0
Mortgage-backed securities | Quoted Prices in Active  Markets for Identical Assets (Level 1) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0	0
Mortgage-backed securities | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,060,152	938,413
Mortgage-backed securities | Significant Other Observable  Inputs (Level 2) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,060,152	938,413
Mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0	0
Mortgage-backed securities | Significant Unobservable Inputs (Level 3) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0	0
Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	49,205	53,830
Asset-backed securities | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	49,205	53,830
Asset-backed securities | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:
Asset-backed securities | Quoted Prices in Active  Markets for Identical Assets (Level 1) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0
Asset-backed securities | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	49,205	53,830
Asset-backed securities | Significant Other Observable  Inputs (Level 2) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	49,205	53,830
Asset-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:
Asset-backed securities | Significant Unobservable Inputs (Level 3) | Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	0
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,216,936	1,105,489
Subordinated debentures	25,173	25,135
Carrying Value | Agency Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:		1,009
Carrying Value | Mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,060,152	938,413
Carrying Value | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	49,205	53,830
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,216,936	1,105,489
Subordinated debentures	30,325	24,375
Fair Value | Agency Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:		1,009
Fair Value | Mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	1,060,152	938,413
Fair Value | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities:	$ 49,205	$ 53,830
Valuation, Market Approach | Measurement Input, Cost to Sell | Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired loans, measurement input | security	0.05
Foreclosed assets, measurement input | security	0.05
Valuation, Market Approach | Measurement Input, Cost to Sell | Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired loans, measurement input | security	0.10
Foreclosed assets, measurement input | security	0.10