Repurchase of Shares of Common Stock (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Equity [Abstract]
Number of Shares Repurchased and Canceled	421,060	540,390	74,820	43,500	0	38,552	1,036,270	82,052
Amount Paid for Repurchases (000’s)	$ 48,356	$ 59,015	$ 7,160	$ 3,913	$ 0	$ 2,945	$ 114,531	$ 6,858	$ 48,028
Average Price Paid per Share	$ 114.84	$ 109.21	$ 95.70	$ 89.97	$ 0.00	$ 76.38	$ 110.52	$ 83.58