Repurchase of Shares of Common Stock (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2012
Equity [Abstract]
Number of Shares Repurchased and Canceled	540,390	74,820	0	38,552	615,210	38,552
Amount Paid for Repurchases (000’s)	$ 59,015	$ 7,160	$ 0	$ 2,945	$ 66,175	$ 2,945
Average Price Paid per Share	$ 109.21	$ 95.70	$ 0.00	$ 76.38	$ 107.57	$ 76.38