Summary Of Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Options Outstanding
Outstanding, beginning balance	865,445
Granted	240,866
Forfeited	(17,557)
Exercised	(231,109)
Outstanding, ending balance	857,645
Options exercisable at end of period	389,619
Weighted-Average Exercise Price
Outstanding, beginning balance	$ 26.72
Granted	$ 57.00
Forfeited	$ 30.01
Exercised	$ 24.23
Outstanding, ending balance	$ 35.84
Options exercisable at end of period	$ 24.54
Weighted-Average Remaining Contractual Term
Outstanding at end of period	5 years
Options exercisable at end of period	3 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding at end of period	$ 8,944
Options exercisable at end of period	$ 6,834