Share-Based Compensation - Summary of SAR's Outstanding (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for SARs (years)	1 year 6 months
SARs
SARs, Shares Outstanding
Shares, Outstanding at beginning of year	1,817,991	1,740,786	1,397,611
Shares Granted	88,042	402,029	627,971
Shares, Exercised	(598,249)	(250,326)	(160,946)
Shares, Forfeited	(46,161)	(66,550)	(115,215)
Shares, Expired	(438)	(7,948)	(8,635)
Shares, Outstanding at end of year	1,261,185	1,817,991	1,740,786
Shares, Exercisable at end of year	595,086	874,942	828,754
Weighted- Average Exercise Price
Outstanding at beginning of year (in USD per share)	$ 65.73	$ 56.15	$ 56.78
Granted (in USD per share)	149.75	98.87	52.13
Exercised (in USD per share)	55.93	48.66	35.37
Forfeited (in USD per share)	80.41	75.38	65.74
Expired (in USD per share)	108.20	108.20	88.65
Outstanding at end of year (in USD per share)	75.71	65.73	56.15
Exercisable at end of year (in USD per share)	$ 60.85	$ 50.86	$ 45.14
SARs | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for SARs (years)	4 years