Benefit Plans - Additional Information (Detail)			12 Months Ended
	Dec. 31, 2006	Dec. 31, 2002	Dec. 31, 2019 USD ($) retirement_payment $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 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			3.10%
Decrease (increase) in other comprehensive income from retirement plans			$ 730	$ 3,000	$ 1,000
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			$ 31,100,000
Number of shares released under ESOP | shares			280,522	243,527
Unallocated ESOP shares held in suspense | shares			1,456,487
Fair market value of ESOP shares			$ 35,900,000
ESOP compensation expenses			4,500,000	$ 4,500,000	4,600,000
Estimated expense under the supplemental ESOP provision			$ 140,000	121,000	105,000
Number of shares authorized for issuance under stock award plan | shares			1,350,000
Unrecognized compensation cost relating go unvested restricted stock			$ 6,400,000
Weighted average period in which unrecognized compensation cost recognized years			1 year 8 months 12 days
Fair value of options vesting			$ 193,000	$ 189,000	$ 168,000
Projected share based compensation expense, 2019			135,000
Projected share based compensation expense, 2020			74,000
Projected share based compensation expense, 2021			11,000
Aggregate intrinsic value of stock options outstanding			3,000,000.0
Aggregate intrinsic value of stock options exercisable			$ 2,800,000
Weighted average fair value of options granted (in dollars per share) | $ / shares			$ 4.57	$ 4.29	$ 4.20
Restricted Stock
Defined Benefit Plan Disclosure [Line Items]
Share based payment award vesting period in years			3 years
Outstanding Stock Awards
Defined Benefit Plan Disclosure [Line Items]
Share based payment award compensation expense			$ 6,700,000	$ 6,000,000.0	$ 5,000,000.0
Outstanding Stock Awards | Share-based Compensation Award, Tranche Two
Defined Benefit Plan Disclosure [Line Items]
Share based payment award vesting period in years			3 years
Stock Options
Defined Benefit Plan Disclosure [Line Items]
Share based payment award vesting period in years			5 years
Share based payment award compensation expense			$ 181,000	190,000	203,000
Share based payment award expiration period in years			10 years
Performance Shares
Defined Benefit Plan Disclosure [Line Items]
Share based payment award vesting period in years			3 years
Board of Directors
Defined Benefit Plan Disclosure [Line Items]
Benefit plans compensation expense			$ 15,000	10,000	12,500
Other Liabilities
Defined Benefit Plan Disclosure [Line Items]
Retirement plan liabilities			1,900,000	2,000,000.0
Other Liabilities | Board of Directors
Defined Benefit Plan Disclosure [Line Items]
Retirement plan liabilities			130,000	139,000
Supplemental Executive Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Aggregate contributions to the benefit plan			85,000	82,000	91,000
Decrease (increase) in other comprehensive income from retirement plans			$ (187,000)	$ 119,000	$ 120,000
401(k) Plan
Defined Benefit Plan Disclosure [Line Items]
Percentage of matching contribution			25.00%	25.00%	25.00%
Percentage of contribution made by the participants in benefit plans			6.00%	6.00%	6.00%
Contribution to the Plan			$ 981,000	$ 973,000	$ 890,000
Estimated expense of supplemental ESOP provision			22,000	18,000	17,500
Pension
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			$ 16,874,000	$ 14,571,000	$ 14,900,000
Discount rate			3.10%	4.25%	3.50%
Contribution to the Plan			$ 0	$ 0	$ 0
Post-retirement
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			$ (23,323,000)	$ (20,028,000)	$ (22,757,000)
Discount rate			3.10%	4.25%	3.50%
Contribution to the Plan			$ 600,000	$ 590,000	$ 560,000