Changes in Accumulated Other Comprehensive Income Balances (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 5,820	$ 4,746
Other comprehensive income before reclassifications, net of tax	(1,097)	2,009
Amounts reclassified from accumulated other comprehensive income, net of tax	(723)	(935)	(1,398)
Other comprehensive (loss) income	(1,820)	1,074	2,277
Ending balance	4,000	5,820	4,746
Unrealized Gains on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	2,925	1,618
Other comprehensive income before reclassifications, net of tax	(1,097)	2,009
Amounts reclassified from accumulated other comprehensive income, net of tax	(447)	(702)
Other comprehensive (loss) income	(1,544)	1,307
Ending balance	1,381	2,925
Retirement Plans Prior Service Benefit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	2,895	3,128
Amounts reclassified from accumulated other comprehensive income, net of tax	(276)	(233)
Other comprehensive (loss) income	(276)	(233)
Ending balance	$ 2,619	$ 2,895