Share-based Compensation - Summary of Cash-Settled SARs Activity (Detail) - Cash-Settled SARs Activity [Member]	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at January 1, 2017 | shares	500,486
Exercised, Shares | shares	(185,359)
Expired or forfeited, Shares | shares	(14,503)
Shares, Outstanding at June 30, 2017 | shares	300,624
Weighted-Average Exercise Price, Outstanding at January 1, 2017 | $ / shares	$ 32.08
Exercised, Weighted-Average Exercise Price | $ / shares	32.90
Expired or forfeited, Weighted-Average Exercise Price | $ / shares	23.69
Weighted-Average Exercise Price, Outstanding at June 30, 2017 | $ / shares	$ 31.98