Share-based Compensation - Summary of SARs Activity (Detail)	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Stock-Settled SARs Activity [Member]
Shares
Outstanding, beginning balance (in shares) | shares	810,759
Exercised (in shares) | shares	(97,644)
Expired or forfeited (in shares) | shares	(7,167)
Outstanding, ending balance (in shares) | shares	705,948
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 33.89
Exercised (in dollars per share) | $ / shares	36.70
Expired or forfeited (in dollars per share) | $ / shares	37.85
Outstanding, ending balance (in dollars per share) | $ / shares	$ 33.46
Cash Settled S A Rs Activity [Member]
Shares
Outstanding, beginning balance (in shares) | shares	58,428
Exercised (in shares) | shares	(37,330)
Expired or forfeited (in shares) | shares	(1,193)
Outstanding, ending balance (in shares) | shares	19,905
Weighted-Average Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 30.71
Exercised (in dollars per share) | $ / shares	29.53
Expired or forfeited (in dollars per share) | $ / shares	19.37
Outstanding, ending balance (in dollars per share) | $ / shares	$ 33.59