Retirement Benefits - Additional Information (Detail) (USD $)	12 Months Ended				12 Months Ended						12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Postretirement Health Care Plans	Dec. 31, 2012 Supplemental Employee Retirement Plan Agreements Benefits Installment	Dec. 31, 2011 Supplemental Employee Retirement Plan Agreements Benefits	Dec. 31, 2006 Supplemental Employee Retirement Plan Agreements Benefits	Dec. 31, 2012 Other Liabilities	Dec. 31, 2011 Other Liabilities	Dec. 31, 2012 Estimated For 2013	Dec. 31, 2012 Employee Stock Ownership Plan E S O P Plan	Dec. 31, 2011 Employee Stock Ownership Plan E S O P Plan	Dec. 31, 2012 Plan 401 k	Dec. 31, 2011 Plan 401 k	Dec. 31, 2010 Plan 401 k	Dec. 31, 2012 Plan 401 k Minimum	Dec. 31, 2012 Plan 401 k Maximum	Dec. 31, 2012 Plan 401 k Subsequent	Dec. 31, 2012 Plan 401 k Subsequent Minimum	Dec. 31, 2012 Plan 401 k Subsequent Maximum
Defined Benefit Plan Disclosure [Line Items]
Percentage Of Investments By Employees From Base Compensation																2.00%	15.00%
Percentage of Employers Contribution Based on Participants Compensation													25.00%
Percentage of Contribution from Employees of the First Base Compensation													6.00%					6.00%
Company Matching Contributions Percentage																			25.00%	50.00%
Percentage of Contribution from Employees of the First Base Compensation Vesting Period													5 years
Company's Contribution to Its Plan													$ 226,000	$ 218,000	$ 166,000
Contribution The Profit Sharing Plan													0	0	0
Employee stock ownership plan authorized to purchase	2,463,884
Initial public offering price	$ 7.13
ESOP loan payment due date	Dec. 31, 2007
Outstanding loan balance											14,500,000	15,000,000
Shares released to participants											84,887	86,701
ESOP compensation expense	856,000	790,000	774,000
Company contribution to SESOP plan	25,000	25,000	33,000
Net loss	(376,000)	(288,000)								36,207
Transition obligation	(50,000)	(67,000)								16,711
Prior service cost	90,000	106,000								15,575
Medical cost trend rate	8.75%
Medical cost trend rate decreasing	0.50%
Medical cost trend rate ultimate rate	4.75%
Benefit payments	107,000	104,000	108,000
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months				113,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Two				119,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Three				123,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Four				126,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Five				127,000
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter				619,000
Benefit plan obligations								4,677,000	4,145,000
Benefit plan expenses	384,000	151,000	597,000
Agreement execution date					Jul. 18, 2006
Number of monthly payments					120
Agreement monthly payment					17,450
Present value of agreement obligation					$ 712,000	$ 880,000	$ 1,625,000