Stock-based Compensation - Summary of Information Related to Stock Options (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options Outstanding, Beginning Balance	1,474,346
Number of Options Outstanding, Granted	80,930
Number of Options Outstanding, Exercised	(50,833)
Number of Options Outstanding, Forfeited	(31,758)
Number of Options Outstanding, Ending Balance	1,472,685
Number of Options Outstanding, Vested	583,150
Number of Options Outstanding, Exercisable	589,797
Weighted Average Exercise Price, Beginning Balance	$ 23.50
Weighted Average Exercise Price, Ending Balance	$ 24.69
Weighted Average Exercise Price Vested, Ending Balance	$ 11.81
Weighted Average Exercise Price Exercisable, Ending Balance	$ 11.71
Weighted Average Remaining Contractual Term (years), Ending Balance	7 years 10 months 17 days
Weighted Average Remaining Contractual Term (years), Vested, Ending Balance	6 years 4 months 2 days
Weighted Average Remaining Contractual Term (years), Exercisable, Ending Balance	6 years 4 months 2 days
Aggregate Intrinsic Value, Ending Balance	$ 12,476,513
Aggregate Intrinsic Value Vested, Ending Balance	10,133,063
Aggregate Intrinsic Value Exercisable, Ending Balance	$ 8,707,609