Changes in Accumulated Postretirement Benefits Obligations (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	$ 27	$ 32	$ 34
Postretirement Benefit Costs [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	35	28
Interest Cost	24	25
Net Postretirement Benefit Expense	59	53
Net Gain During Period Recognized in Other Comprehensive Income	0	0
Total Recognized in Net Postretirement Benefit Expense and Other Comprehensive Income	$ 59	$ 53