Share-Based Compensation - Schedule of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Options
Stock options outstanding beginning of period (in shares) | shares	2,418
Stock options granted (in shares) | shares	131
Stock options exercised (in shares) | shares	(123)
Stock options forfeited (in shares) | shares	(168)
Stock options outstanding end of period (in shares) | shares	2,258
Stock options exercisable at end of period (in shares) | shares	1,683
Weighted Average Exercise Price
Stock options outstanding, Weighted Average Exercise Price, beginning of period (in dollars per share) | $ / shares	$ 40.79
Stock options granted, Weighted Average Exercise Price (in dollars per share) | $ / shares	40.36
Stock options exercised, Weighted Average Exercise Price (in dollars per share) | $ / shares	33.69
Stock options forfeited, Weighted Average Exercise Price (in dollars per share) | $ / shares	47.76
Stock options outstanding, Weighted Average Exercise Price, end of period (in dollars per share) | $ / shares	40.63
Stock options exercisable, end of period, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 42.32
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Stock options outstanding, Weighted Average Remaining Contractual Term (in Years)	4 years 4 months 24 days
Stock options exercisable, Weighted Average Remaining Contractual Term (in Years)	3 years 6 months
Stock options outstanding, Aggregate Intrinsic Value | $	$ 11,724
Stock options exercisable, Aggregate Intrinsic Value | $	$ 7,531