Company's Contributions to Employee Retirement Savings Plans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Postretirement benefit obligation [Member] Split Dollar Life Insurance Arrangement [Member]		Dec. 31, 2011 Postretirement benefit obligation [Member] Split Dollar Life Insurance Arrangement [Member]
Defined Contribution Plan Disclosure [Line Items]
401(k) plan contributions	$ 245	$ 208	$ 977	$ 770
Postretirement benefit obligation					77		114
Unrealized gains (losses) in AOCI					$ 503	[1]	$ 459	[1]

[1] Unrealized gains (losses) are due to changes in discount rates related to the postretirement obligation.