Stock-Based Compensation - Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Beginning balance | shares	1,097,331
Options, Granted | shares	130,371
Options, Exercised | shares	(15,500)
Options, Forfeited | shares	(28,149)
Options Outstanding, Ending balance | shares	1,184,053
Weighted Average Exercise Price, Outstanding, Beginning Balance | $ / shares	$ 47.60
Weighted Average Exercise Price, Granted | $ / shares	54.68
Weighted Average Exercise Price, Exercised | $ / shares	46.13
Weighted Average Exercise Price, Forfeited | $ / shares	57.56
Weighted Average Exercise Price, Outstanding, Ending Balance | $ / shares	$ 48.16