Fair Value Measurements (Narrative) (Detail) $ in Thousands	Mar. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash	$ 4,800	$ 27,300
Available for sale debt securities, at fair value	2,072,337	2,057,851
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, at fair value	260,165	196,329
Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,812,172	1,861,522
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	2,072,337	2,057,851
Measured on a Recurring Basis | 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, at fair value	260,165	196,329
Measured on a Recurring Basis | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,812,172	1,861,522
Measured on a Recurring Basis | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis | U.S. Treasury obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	260,165	196,329
Measured on a Recurring Basis | U.S. Treasury 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, at fair value	260,165	196,329
Measured on a Recurring Basis | U.S. Treasury obligations | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis | U.S. Treasury obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	$ 0	$ 0
Minimum | Measurement Input, Cost to Sell | Valuation, Market Approach
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired loans, measurement input | security	0.05
Foreclosed assets, measurement input | security	0.05
Maximum | Measurement Input, Cost to Sell | Valuation, Market Approach
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired loans, measurement input | security	0.10
Foreclosed assets, measurement input | security	0.10