Option Intrinsic Values (Detail) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding		800,000		412,500	612,500	464,743
Exercisable		360,000
Exercised		0	[1]	14,292
Outstanding		$ 25.94		$ 18.62	$ 25.38	$ 19.87
Exercisable	[2]	20.29
Exercised		$ 0	[1]	$ 20.00
Outstanding		$ 3.5
Exercisable		$ 3.3

[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.

[2] Includes the weighted average strike price on 60,000 of options which are excluded from the intrinsic value calculation of $3.3 million due to the strike price of the options exceeding the fair value of $29.02 at December 31, 2015.