Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) $ / shares shares
Options Outstanding
Outstanding, beginning balance | shares	1,178,585
Granted | shares	169,740
Forfeited | shares	(178,089)
Exercised | shares	(104,957)
Unearned performance-based options | shares	(23,328)
Outstanding, ending balance | shares	1,041,951
Options exercisable at end of period | shares	558,556
Weighted-Average Exercise Price
Outstanding, beginning balance | $ / shares	$ 48.14
Granted | $ / shares	33.04
Forfeited | $ / shares	44.65
Exercised | $ / shares	17.65
Unearned performance-based options | $ / shares	59.97
Outstanding, ending balance | $ / shares	49.08
Options exercisable at end of period | $ / shares	$ 50.64
Weighted-Average Remaining Contractual Term
Outstanding at end of period	4 years 8 months 12 days
Options exercisable at end of period	3 years 7 months 6 days
Aggregate Intrinsic Value
Outstanding at end of period | $	$ 553,354
Options exercisable at end of period | $	$ 211,118