Changes in Accumulated Other Comprehensive Income Balances (Parenthetical) (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]
Other comprehensive income before reclassifications, tax	$ 216	$ 370	$ 1,247
Amounts reclassified from accumulated other comprehensive income, tax	(257)	(201)	(581)
Amounts reclassified from accumulated other comprehensive income, tax	(159)	(134)	9
Unrealized gains on marketable securities, tax	794	835	666
Retirement plans prior service benefit, tax	(284)	(125)	9
Unrealized Gains on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications, tax	216	370
Amounts reclassified from accumulated other comprehensive income, tax	(257)	(201)
Other comprehensive income (loss), tax	(41)	169
Retirement Plans Prior Service Benefit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income, tax	(159)	(134)
Other comprehensive income (loss), tax	$ (159)	$ (134)