Basis of Presentation - Schedule of Unvested Stock Option Outstanding (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Stock Options:
Unvested at beginning of period, Shares	576,381	609,029
Granted, Shares	24,576	43,686
Vested, Shares	(216,687)	(53,822)
Unvested at end of period, Shares	384,270	598,893
Unvested at beginning of period, Weighted-Average Exercise Price	$ 50.01	$ 47.66
Granted, Weighted-Average Exercise Price	$ 78.71	$ 71.47
Vested, Weighted-Average Exercise Price	$ 49.79	$ 44.11
Unvested at end of period, Weighted-Average Exercise Price	$ 51.97	$ 49.72