Option Intrinsic Values (Detail) - USD ($)		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Mar. 06, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding		800,000	800,000	200,000	600,000	600,000
Exercisable		600,000
Exercised	[1]	0
Outstanding		$ 35.06	$ 35.06		$ 25.13	$ 25.13
Exercisable		32.01
Exercised	[1]	$ 0
Outstanding		$ 3,500,000
Exercisable		3,500,000
Exercised	[1]	$ 0

[1] The intrinsic value of the exercised options is the difference between the fair market value at time of exercise and the strike price of the option.