Fair Value Disclosures of Financial Assets and Liabilities - Schedule of Financial Instruments Carried at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	$ 1,944,914	$ 1,205,079
Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets	4,884	2,098
Total assets measured at fair value	1,949,798	1,207,177
Other liabilities	3,918	3,493
Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value	198,803	112,313
Other real estate owned	2,605	2,668
Impaired loans, net	42,280	47,094
Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets	0	0
Total assets measured at fair value	0	0
Other liabilities	0	0
Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value	0	0
Other real estate owned	0	0
Impaired loans, net	0	0
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets	4,884	2,098
Total assets measured at fair value	1,949,798	1,207,177
Other liabilities	3,918	3,493
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value	83,872	25,318
Other real estate owned	0	0
Impaired loans, net	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets	0	0
Total assets measured at fair value	0	0
Other liabilities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total assets measured at fair value	114,931	86,995
Other real estate owned	2,605	2,668
Impaired loans, net	42,280	47,094
CMO
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	340,230	371,750
CMO | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	340,230	371,750
CMO | Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	0	0
CMO | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	340,230	371,750
CMO | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	0	0
FNMA MBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	1,242,453	644,073
FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	1,242,453	644,073
FNMA MBS | Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	0	0
FNMA MBS | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	1,242,453	644,073
FNMA MBS | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	0	0
FHLMC MBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	328,946	153,922
FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	328,946	153,922
FHLMC MBS | Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	0	0
FHLMC MBS | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	328,946	153,922
FHLMC MBS | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	0	0
GNMA MBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	33,285	35,334
GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	33,285	35,334
GNMA MBS | Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	0	0
GNMA MBS | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	33,285	35,334
GNMA MBS | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	0	0
Other equity investments | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	70,046	37,233
Other equity investments | Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	0	0
Other equity investments | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	0	0
Other equity investments | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	70,046	37,233
Loans held for sale | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans, held for sale	83,872	25,318
Loans held for sale | Quoted Prices in Active Markets for Identical Asset (Level 1) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans, held for sale	0	0
Loans held for sale | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans, held for sale	83,872	25,318
Loans held for sale | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans, held for sale	$ 0	$ 0