Basis of Presentation - Schedule of Vesting Information Stock Options Outstanding (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Intrinsic Value [Roll Forward]
Unvested at beginning of period, Weighted-Average Exercise Price	$ 43.92	$ 38.53	$ 38.57	$ 36.08
Granted, Weighted-Average Exercise Price	$ 49.52	$ 38.93	$ 49.09	$ 39.66
Vested, Weighted-Average Exercise Price	$ 38.72	$ 35.12	$ 35.43	$ 32.94
Forfeited, Weighted-Average Exercise Price	$ 47.50		$ 47.50
Unvested at end of period, Weighted-Average Exercise Price	$ 47.63	$ 38.68	$ 47.63	$ 38.68
Unvested at beginning of period, Shares	237,861	110,137	157,298	112,258
Granted, Shares	400,000	55,477	522,357	88,307
Vested, Shares	(14,351)	(800)	(56,145)	(35,751)
Forfeited	(13,081)		(13,081)
Unvested at end of period, Shares	610,429	164,814	610,429	164,814