Stock Repurchase Plan - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended	61 Months Ended
	Feb. 29, 2012	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012
Maximum stock authorized to purchase under stock repurchase program	$ 262,100,000		$ 210,000,000
Increase in maximum stock authorized to purchase under stock repurchase program	52,100,000
Repurchase of common stock, shares		164,100		8,246,280
Repurchase of common stock, value		6,241,000		193,300,000
Maximum remaining dollar value of shares authorized for purchase under the stock repurchase program		$ 68,800,000