Fair Value Disclosures - Schedule of Financial Instruments Carried at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	$ 838,122	$ 794,543
Total assets measured at fair value on a recurring basis	838,869	796,051
Other liabilities	3,225	3,380
Loans held for sale	31,055	54,782
Impaired loans	57,089	46,499
Total assets measured at fair value on a nonrecurring basis	90,647	104,872
GSE | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	35,010
Other assets | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	747	1,508
Other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other real estate owned	2,503	3,591
CMO
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	246,539	261,216
CMO | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	246,539	261,215
FNMA MBS
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	473,987	405,764
FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	473,987	405,764
FHLMC MBS
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	87,875	63,514
FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	87,875	63,515
GNMA MBS
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	29,098	28,416
GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	29,098	28,416
Other investments | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	623	623
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total assets measured at fair value on a recurring basis	623	623
Other liabilities	0	0
Loans held for sale	0	0
Impaired loans	0	0
Total assets measured at fair value on a nonrecurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | GSE | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other assets | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other real estate owned	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | CMO | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other investments | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	623	623
Significant Other Observable Inputs (Level 2)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total assets measured at fair value on a recurring basis	838,246	795,428
Other liabilities	3,225	3,380
Loans held for sale	31,055	54,782
Impaired loans	0	0
Total assets measured at fair value on a nonrecurring basis	31,055	54,782
Significant Other Observable Inputs (Level 2) | GSE | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	35,010
Significant Other Observable Inputs (Level 2) | Other assets | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	747	1,508
Significant Other Observable Inputs (Level 2) | Other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other real estate owned	0	0
Significant Other Observable Inputs (Level 2) | CMO | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	246,539	261,215
Significant Other Observable Inputs (Level 2) | FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	473,987	405,764
Significant Other Observable Inputs (Level 2) | FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	87,875	63,515
Significant Other Observable Inputs (Level 2) | GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	29,098	28,416
Significant Other Observable Inputs (Level 2) | Other investments | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Significant Unobservable Inputs (Level 3)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total assets measured at fair value on a recurring basis	0	0
Other liabilities	0	0
Loans held for sale	0	0
Impaired loans	57,089	46,499
Total assets measured at fair value on a nonrecurring basis	59,592	50,090
Significant Unobservable Inputs (Level 3) | GSE | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Significant Unobservable Inputs (Level 3) | Other assets | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Significant Unobservable Inputs (Level 3) | Other real estate owned
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Other real estate owned	2,503	3,591
Significant Unobservable Inputs (Level 3) | CMO | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Significant Unobservable Inputs (Level 3) | FNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Significant Unobservable Inputs (Level 3) | FHLMC MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Significant Unobservable Inputs (Level 3) | GNMA MBS | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	0	0
Significant Unobservable Inputs (Level 3) | Other investments | Fair Value, Measurements, Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value	$ 0	$ 0