Fair Values of Assets and Liabilities (Narrative) (Detail)	3 Months Ended
	Mar. 31, 2023 USD ($) $ / shares	Dec. 31, 2022 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 3,259,845,000	$ 3,243,017,000	$ 2,998,898,000
Loans held-for-investment	207,532,000		57,984,000
MSRs	224,470,000	230,225,000	199,146,000	$ 147,571,000
Individually assessed loans - foreclosure probable and collateral-dependent	71,622,000		72,846,000
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3,259,845,000	3,243,017,000	2,998,898,000
Remaining contractual principal balance outstanding, mortgage loans held-for-sale	307,300,000	308,900,000	606,700,000
Remaining contractual principal balance outstanding, mortgage loans held-for-investment	204,500,000	184,000,000	58,700,000
Non-performing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held-for-sale classified as nonaccrual	3,300,000	5,800,000	0
Mortgage loans held-for-sale classified greater than 90 days past due and still accruing	$ 41,400,000	44,000,000	113,000,000
Weighted Average | Loans held-for-investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life of loans	5 years 4 months 24 days
Appraisal adjustment - cost of sale | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other real estate owned, measurement input	0.10
Measured at fair value on a recurring basis:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held-for-sale	$ 302,493,000	299,935,000	606,545,000
Loans held-for-investment	202,143,000	179,932,000	57,984,000
MSRs	224,470,000	230,225,000	199,146,000
Derivative assets	274,004,000	296,848,000	153,534,000
Measured at fair value on a non-recurring basis:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	71,622,000
Other real estate owned	9,361,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	71,600,000
Level 3 | Portion at Other than Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	0
Level 3 | Measured at fair value on a recurring basis:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held-for-sale	44,250,000	48,655,000	0
Loans held-for-investment	69,493,000	84,165,000	44,464,000
MSRs	224,470,000	230,225,000	199,146,000
Derivative assets	$ 5,356,000	1,711,000	3,447,000
Level 3 | Measured at fair value on a recurring basis: | Discount rate | Weighted Average | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input	0.1033
Level 3 | Measured at fair value on a recurring basis: | Discount rate | Weighted Average | Mortgage loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.0596
Level 3 | Measured at fair value on a recurring basis: | Discount rate | Weighted Average | Loans held-for-investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.0598
Level 3 | Measured at fair value on a recurring basis: | Discount rate | Weighted Average | Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.1033
Level 3 | Measured at fair value on a recurring basis: | Discount rate | Minimum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input	0.03
Level 3 | Measured at fair value on a recurring basis: | Discount rate | Minimum | Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.03
Level 3 | Measured at fair value on a recurring basis: | Discount rate | Maximum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input	0.33
Level 3 | Measured at fair value on a recurring basis: | Discount rate | Maximum | Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.33
Level 3 | Measured at fair value on a recurring basis: | Constant prepayment rate (CPR) | Weighted Average | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input	0.0692
Level 3 | Measured at fair value on a recurring basis: | Constant prepayment rate (CPR) | Weighted Average | Loans held-for-investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.0692
Level 3 | Measured at fair value on a recurring basis: | Constant prepayment rate (CPR) | Weighted Average | Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.0692
Level 3 | Measured at fair value on a recurring basis: | Constant prepayment rate (CPR) | Minimum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input	0
Level 3 | Measured at fair value on a recurring basis: | Constant prepayment rate (CPR) | Minimum | Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0
Level 3 | Measured at fair value on a recurring basis: | Constant prepayment rate (CPR) | Maximum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input	1
Level 3 | Measured at fair value on a recurring basis: | Constant prepayment rate (CPR) | Maximum | Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	1
Level 3 | Measured at fair value on a recurring basis: | Credit discount | Weighted Average | Mortgage loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.0022
Level 3 | Measured at fair value on a recurring basis: | Credit discount | Weighted Average | Loans held-for-investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.0086
Level 3 | Measured at fair value on a recurring basis: | Credit discount | Minimum | Mortgage loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0
Level 3 | Measured at fair value on a recurring basis: | Credit discount | Minimum | Loans held-for-investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0
Level 3 | Measured at fair value on a recurring basis: | Credit discount | Maximum | Mortgage loans held-for-sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.10
Level 3 | Measured at fair value on a recurring basis: | Credit discount | Maximum | Loans held-for-investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	0.13
Level 3 | Measured at fair value on a recurring basis: | Cost of servicing | Weighted Average | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input	76
Level 3 | Measured at fair value on a recurring basis: | Cost of servicing | Minimum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input | $ / shares	70
Level 3 | Measured at fair value on a recurring basis: | Cost of servicing | Maximum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input | $ / shares	200
Level 3 | Measured at fair value on a recurring basis: | Cost of servicing - delinquent | Weighted Average | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input	403
Level 3 | Measured at fair value on a recurring basis: | Cost of servicing - delinquent | Minimum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input | $ / shares	200
Level 3 | Measured at fair value on a recurring basis: | Cost of servicing - delinquent | Maximum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
MSRs, measurement input | $ / shares	1,000
Level 3 | Measured at fair value on a recurring basis: | Pull-through rate | Weighted Average | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, measurement input	0.8206
Level 3 | Measured at fair value on a recurring basis: | Pull-through rate | Minimum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, measurement input	0.31
Level 3 | Measured at fair value on a recurring basis: | Pull-through rate | Maximum | Discounted cash flows
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, measurement input	1
Level 3 | Measured at fair value on a non-recurring basis:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	$ 71,622,000
Other real estate owned	9,361,000
Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	160,386,000	168,655,000	155,489,000
Municipal securities | Measured at fair value on a recurring basis:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	160,386,000	168,655,000	155,489,000
Municipal securities | Level 3 | Measured at fair value on a recurring basis:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 112,257,000	$ 117,537,000	$ 100,401,000