Fair Values of Assets and Liabilities (Schedule of Valuation Techniques and Significant Unobservable Inputs Used to Measure Both Recurring and Non-Recurring) (Detail)	Mar. 31, 2022 USD ($) $ / shares	Dec. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities, at fair value	$ 2,998,898,000	$ 2,327,793,000	$ 2,430,749,000
Loans held-for-investment	57,984,000		51,916,000
MSRs	199,146,000	147,571,000	124,316,000	$ 92,081,000
Individually assessed loans - foreclosure probable and collateral-dependent	72,846,000		124,404,000
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	72,800,000
Measured at fair value on a recurring basis:
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment	57,984,000	38,598,000	51,916,000
MSRs	199,146,000	147,571,000	124,316,000
Derivative assets	153,534,000	165,008,000	253,509,000
Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment	44,464,000	15,891,000	6,408,000
MSRs	199,146,000	147,571,000	124,316,000
Derivative assets	3,447,000	10,560,000	25,634,000
Measured at fair value on a non-recurring basis:
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	44,844,000
Other real estate owned	6,203,000
Measured at fair value on a non-recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	44,844,000
Other real estate owned	6,203,000
Municipal Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities, at fair value	155,489,000	165,594,000	148,300,000
Municipal Securities | Measured at fair value on a recurring basis:
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities, at fair value	155,489,000	165,594,000	148,300,000
Municipal Securities | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities, at fair value	$ 100,401,000	$ 105,687,000	$ 101,748,000
Discount rate | Discounted cash flows | Minimum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0400
MSRs, measurement input	0.06
Discount rate | Discounted cash flows | Maximum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0425
MSRs, measurement input	0.19
Discount rate | Discounted cash flows | Weighted Average | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0425
MSRs, measurement input	0.0979
Credit discount | Discounted cash flows | Minimum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0
Credit discount | Discounted cash flows | Maximum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.03
Credit discount | Discounted cash flows | Weighted Average | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0036
Constant prepayment rate (CPR) | Discounted cash flows | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0711
Constant prepayment rate (CPR) | Discounted cash flows | Minimum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs, measurement input	0
Constant prepayment rate (CPR) | Discounted cash flows | Maximum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs, measurement input	1
Constant prepayment rate (CPR) | Discounted cash flows | Weighted Average | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-investment, measurement input	0.0711
MSRs, measurement input	0.0711
Cost of servicing | Discounted cash flows | Minimum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs, measurement input | $ / shares	70
Cost of servicing | Discounted cash flows | Maximum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs, measurement input | $ / shares	200
Cost of servicing | Discounted cash flows | Weighted Average | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs, measurement input	75
Cost of servicing - delinquent | Discounted cash flows | Minimum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs, measurement input | $ / shares	200
Cost of servicing - delinquent | Discounted cash flows | Maximum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs, measurement input | $ / shares	1,000
Cost of servicing - delinquent | Discounted cash flows | Weighted Average | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
MSRs, measurement input	305
Pull-through rate | Discounted cash flows | Minimum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives, measurement input	0
Pull-through rate | Discounted cash flows | Maximum | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives, measurement input	1
Pull-through rate | Discounted cash flows | Weighted Average | Measured at fair value on a recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivatives, measurement input	0.871
Appraisal adjustment - cost of sale | Appraisal value | Measured at fair value on a non-recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Individually assessed loans— foreclosure probable and collateral-dependent, measurement input	0.10
Other real estate owned, measurement input	0.10
Appraisal adjustment - cost of sale | Appraisal value | Weighted Average | Measured at fair value on a non-recurring basis: | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Individually assessed loans— foreclosure probable and collateral-dependent, measurement input	0.1000
Other real estate owned, measurement input	0.1000