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Benefit Plans - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2016
USD ($)
Dec. 31, 2006
Dec. 31, 2002
Dec. 31, 2017
USD ($)
retirement_payment
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Dec. 31, 2015
USD ($)
$ / shares
Defined Benefit Plan Disclosure [Line Items]            
Defined benefit plan age attained for coverage       21 years    
Service period for employees of coverage age, years       1 year    
Vesting percentage of participants in pension plan       100.00%    
Expected future employer contributions next year       $ 0    
Requisite service period for deferred compensation arrangement 10 years 10 years 10 years      
Discount rate       3.50%    
Percentage of matching contribution         25.00% 25.00%
Percentage of contribution made by the participants in benefit plans         6.00% 6.00%
Retirement plan for the board of directors to get maximum payments minimum age       72 years    
Number of quarterly payments made to Board of Directors from Retirement Plan | retirement_payment       40    
Benefit plans compensation expense       $ 1,250    
Period in which undistributed balance of accrued benefit will be distributed       60 days    
Shares purchased under ESOP | shares       4,769,464    
Average price per share purchased under ESOP (in dollars per share) | $ / shares       $ 17.09    
Outstanding loan principal       $ 41,400,000    
Number of shares released under ESOP | shares       242,254 219,623  
Unallocated ESOP shares held in suspense | shares       1,980,536    
Fair market value of ESOP shares       $ 53,400,000    
ESOP compensation expenses       4,600,000 $ 3,700,000 $ 3,000,000
Estimated expense under the supplemental ESOP provision       $ 105,000 93,000 54,000
Number of shares authorized for issuance under stock award plan | shares       3,686,510    
Limited number of shares authorized for issuance | shares       2,100,000    
Unrecognized compensation cost relating go unvested restricted stock       $ 5,700,000    
Weighted average period in which unrecognized compensation cost recognized years       1 year 11 months 6 days    
Fair value of options vesting       $ 168,000 $ 247,000 $ 274,000
Projected share based compensation expense, 2018       138,000    
Projected share based compensation expense, 2019       70,582    
Projected share based compensation expense, 2020       10,000    
Aggregate intrinsic value of stock options outstanding       5,249,000    
Aggregate intrinsic value of stock options exercisable       $ 4,380,000    
Weighted average fair value of options granted (in dollars per share) | $ / shares       $ 4.20 $ 2.26 $ 2.52
Retirement Plan for the Board of Directors [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Increase (decrease) in other comprehensive income from retirement plans       $ (1,000) $ (3,000) $ 1,800
Restricted Stock [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Share based payment award vesting period in years       3 years    
Outstanding Stock Awards [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Share based payment award compensation expense       $ 5,000,000 3,800,000 4,600,000
Stock Options [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Share based payment award vesting period in years       5 years    
Share based payment award compensation expense       $ 203,000 172,000 272,000
Share based payment award expiration period in years       10 years    
Performance Shares [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Share based payment award vesting period in years       3 years    
401(k) Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Percentage of matching contribution       25.00%    
Percentage of contribution made by the participants in benefit plans       6.00%    
Contribution to the Plan       $ 890,000 850,000 770,000
Estimated expense of supplemental ESOP provision $ 14,500     17,500 14,500 11,500
Supplemental Executive Retirement Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Aggregate contributions to the benefit plan       91,000 96,000 93,000
Increase (decrease) in other comprehensive income from retirement plans       (120,000) (30,000) (82,000)
Other Liabilities [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Retirement plan liabilities 2,100,000     2,000,000 2,100,000  
Other Liabilities [Member] | Retirement Plan for the Board of Directors [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Retirement plan liabilities 148,000     142,000 148,000  
Board of Directors [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Benefit plans compensation expense       13,000 17,500 20,000
Pension [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Actuarial gain (loss) during the period       0 (70,000) (78,000)
Defined benefit plan, funded (unfunded) status of plan $ 13,620,000     $ 14,900,000 $ 13,620,000 $ 13,174,000
Discount rate 4.25%     3.50% 4.25% 4.50%
Contribution to the Plan       $ 0 $ 0 $ 0
Post-retirement [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Actuarial gain (loss) during the period       0 0 (122,000)
Defined benefit plan, funded (unfunded) status of plan $ (20,805,000)     $ (22,757,000) $ (20,805,000) $ (25,694,000)
Discount rate 4.25%     3.50% 4.25% 4.50%
Contribution to the Plan       $ 560,000 $ 682,000 $ 644,000
Share-based Compensation Award, Tranche Two [Member] | Outstanding Stock Awards [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Share based payment award vesting period in years       3 years