Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Options Outstanding
Outstanding at December 31, 2012	732,839
Granted	58,196
Exercised	(63,004)
Canceled	(1)
Outstanding at March 31, 2013	728,030	732,839
Exercisable at March 31, 2013	509,685
Weighted-Average Exercise Price per Share
Outstanding at December 31, 2012	$ 40.48
Granted	$ 96.58
Exercised	$ 25.21
Canceled	$ 10.77
Outstanding at March 31, 2013	$ 46.28	$ 40.48
Exercisable at March 31, 2013	$ 36.45
Aggregate Intrinsic Value
Outstanding at December 31, 2012	$ 34,487
Granted	322
Exercised	(4,845)
Outstanding at March 31, 2013	40,641	34,487
Exercisable at March 31, 2013	$ 33,465
Weighted- Average Remaining Contractual Life
Weighted- Average Remaining Contractual Life, outstanding	6 years 7 months 6 days	6 years 3 months 18 days
Exercisable at March 31, 2013	5 years 10 months 24 days