Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) $ / shares shares
Options Outstanding
Outstanding, beginning balance | shares	1,178,585
Granted | shares	168,740
Forfeited | shares	(142,694)
Exercised | shares	(103,073)
Unearned performance-based options | shares	(23,328)
Outstanding, ending balance | shares	1,078,230
Options exercisable at end of period | shares	567,175
Weighted-Average Exercise Price
Outstanding, beginning balance | $ / shares	$ 48.14
Granted | $ / shares	33.04
Forfeited | $ / shares	43.17
Exercised | $ / shares	17.38
Unearned performance-based options | $ / shares	59.97
Outstanding, ending balance | $ / shares	49.09
Options exercisable at end of period | $ / shares	$ 50.55
Weighted-Average Remaining Contractual Term
Outstanding at end of period	5 years 3 months 18 days
Options exercisable at end of period	3 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding at end of period | $	$ 315,056
Options exercisable at end of period | $	$ 181,256