Fair Value Measurements (Assets and Liabilities) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	$ 1,083,601	$ 1,063,079
Equity securities	724	635
Derivative liabilities	11,800
Measured on a non-recurring basis:
Foreclosed assets	1,264	1,565
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	724	635
Derivative assets	0	0
Derivative liabilities	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,083,601	1,063,079
Equity securities	0	0
Derivative assets	17,718	15,634
Derivative liabilities	17,959	14,766
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	0	0
Derivative assets	0	0
Derivative liabilities	0	0
Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,054,482	1,034,969
Mortgage-Backed Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Mortgage-Backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,054,482	1,034,969
Mortgage-Backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
State And Municipal Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	4,088	2,912
State And Municipal Obligations [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
State And Municipal Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	4,088	2,912
State And Municipal Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Corporate Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	25,031	25,198
Corporate Obligations [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Corporate Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	25,031	25,198
Corporate Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
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 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,083,601	1,063,079
Equity securities	724	635
Derivative assets	17,718	15,634
Total assets at fair value	1,102,043	1,079,348
Derivative liabilities	17,959	14,766
Measured on a Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	724	635
Derivative assets	0	0
Total assets at fair value	724	635
Derivative liabilities	0	0
Measured on a Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,083,601	1,063,079
Equity securities	0	0
Derivative assets	17,718	15,634
Total assets at fair value	1,101,319	1,078,713
Derivative liabilities	17,959	14,766
Measured on a Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	0	0
Derivative assets	0	0
Total assets at fair value	0	0
Derivative liabilities	0	0
Measured on a Recurring Basis [Member] | Mortgage-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,054,482	1,034,969
Measured on a Recurring Basis [Member] | Mortgage-Backed Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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 [Member] | Mortgage-Backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,054,482	1,034,969
Measured on a Recurring Basis [Member] | Mortgage-Backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
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 [Member] | State And Municipal Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	4,088	2,912
Measured on a Recurring Basis [Member] | State And Municipal Obligations [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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 [Member] | State And Municipal Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	4,088	2,912
Measured on a Recurring Basis [Member] | State And Municipal Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
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 [Member] | Corporate Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	25,031	25,198
Measured on a Recurring Basis [Member] | Corporate Obligations [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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 [Member] | Corporate Obligations [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	25,031	25,198
Measured on a Recurring Basis [Member] | Corporate Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Non-Recurring Basis [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	11,132	5,850
Measured on a non-recurring basis:
Loans measured for impairment based on the fair value of the underlying collateral	9,868	4,285
Foreclosed assets	1,264	1,565
Measured on a Non-Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	0	0
Measured on a non-recurring basis:
Loans measured for impairment based on the fair value of the underlying collateral	0	0
Foreclosed assets	0	0
Measured on a Non-Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	0	0
Measured on a non-recurring basis:
Loans measured for impairment based on the fair value of the underlying collateral	0	0
Foreclosed assets	0	0
Measured on a Non-Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	11,132	5,850
Measured on a non-recurring basis:
Loans measured for impairment based on the fair value of the underlying collateral	9,868	4,285
Foreclosed assets	$ 1,264	$ 1,565