Share Repurchases - Additional Information (Detail) (USD $)	1 Months Ended	20 Months Ended	3 Months Ended	6 Months Ended
	May 31, 2011	Jun. 30, 2011	Jun. 30, 2011 Repurchase Of Equity	Jun. 30, 2011 Repurchase Of Equity
Equity, Class of Treasury Stock [Line Items]
Share repurchase program, authorized amount	$ 50,000,000	$ 150,000,000
Number of shares repurchased		2,258,980	597,026	853,120
Aggregate purchase price		100,500,000	28,400,000	41,400,000
Weighted average price Per Share		$ 44.43	$ 47.55	$ 48.58
Amount available for future repurchases				$ 49,500,000