Repurchase of Shares of Common Stock (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Class of Stock [Line Items]
Number of Shares Repurchased and Cancelled	38,552	0
Amount Paid for Repurchases	$ 2,945	$ 0	$ 124,056
Average Price Paid per Share	$ 76.38	$ 0.00