Long Term Stock Incentive Plan - Additional Information (Detail) (Employee Stock Plan, 2006 Plan, Restricted Stock Units (RSUs), USD $)	1 Months Ended
	May 31, 2011 Certain Officers and Managers	May 31, 2011 Certain Officers and Managers Third Anniversary Of Grant Date	May 31, 2011 Certain Officers and Managers Fifth Anniversary Of Grant Date	Jul. 31, 2011 Certain Non-Employee Directors	Jul. 31, 2011 Certain Non-Employee Directors One year anniversary after grant date
Share awarded and issued	50,798			10,560
Vesting percentage of stock options issued		50.00%	50.00%		100.00%
Weighted average grant date fair value	$ 30.60			$ 28.41