Executive Compensation Plan - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended		9 Months Ended
	Mar. 31, 2012	Apr. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Executive Compensation Plan Expense [Line Items]
Deferred executive compensation plan, grant date value of awards	$ 1,100,000	$ 1,600,000
Deferred executive compensation plan, net expense			$ 781,000	$ 160,000	$ 2,264,000	$ 1,194,000