Share-Based Compensation - Stock Options Activity (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Shares
Beginning balance (in shares)	2,516,618
Granted (in shares)	486,505
Exercised (in shares)	(180,617)
Forfeited/Expired (in shares)	(50,949)
Ending balance (in shares)	2,771,557	2,516,618
Vested and expected to vest (in shares)	2,603,891
Exercisable (in shares)	1,428,590
Weighted Average Price
Beginning Balance, Weighted Average Price (in dollars per share)	$ 39.60
Granted, Weighted Average Price (in dollars per share)	$ 72.74
Exercised, Weighted Average Price (in dollars per share)	$ 34.08
Forfeited/Expired, Weighted Average Price (in dollars per share)	$ 45.93
Ending Balance, Weighted Average Price (in dollars per share)	$ 45.66	$ 39.60
Vested and expected to vest , Weighted Average Price (in dollars per share)	$ 44.74
Exercisable at March 31, 2013, Weighted Average Price (in dollars per share)	$ 35.99
Weighted-Average Remaining Contractual Term
Weighted-Average Remaining Contractual Term, Ending	7 years 3 months 4 days	6 years 10 months 13 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	7 years 1 month 17 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 9 months 11 days
Aggregate Intrinsic Value
Stock options outstanding, Beginning aggregate intrinsic value	$ 86,200,655
Stock options outstanding, Ending aggregate intrinsic value	75,477,956	86,200,655
Stock options, vested and expected to vest aggregate intrinsic value	73,299,119
Stock options, exercisable aggregate intrinsic value	$ 52,718,583