Employee Benefits Plans (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Contribution Plan, Cost Recognized	$ 317,000	$ 84,000	$ 89,000
Life Insurance Benefits, Age of Eligible Retired Employees	55
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	3,000
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components	100
Deferred Compensation Liability, Current	1,300,000	1,300,000
Cash Surrender Value of Life Insurance	19,500,000	19,200,000
Interest Expense	2,402,000	2,355,000	3,537,000
Defined Benefit Postretirement Life Insurance [Member]
Interest Expense	2,400,000	2,200,000	2,000,000
Minimum [Member]
Health Care Benefits, Age of Eligible Retired Employees	55
Maximum [Member]
Health Care Benefits, Age of Eligible Retired Employees	65
Supplemental Employee Retirement Plans, Defined Benefit [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	162,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	159,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	157,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	154,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	151,000
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	707,000
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	184,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	151,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	131,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	122,000
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	112,000
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	$ 429,000