Summary of Range of Exercise Prices of Options Outstanding (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding	600,000		800,000		612,500
Exercise Price Range One
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Ranges of Exercise Prices, minimum	$ 17.87		$ 17.87		$ 17.87
Ranges of Exercise Prices, maximum	$ 19.99		$ 19.99		$ 19.99
Options outstanding	300,000		300,000		300,000
Weighted Average Per Share Exercise Price	$ 17.87		$ 17.87		$ 17.87
Weighted Average Remaining Life	4 years 8 months 12 days		5 years 8 months 12 days		6 years 8 months 12 days
Exercise Price Range Two
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Ranges of Exercise Prices, minimum	$ 20.00		$ 20.00		$ 20.00
Ranges of Exercise Prices, maximum	29.99		$ 29.99		29.99
Options outstanding			200,000
Weighted Average Per Share Exercise Price			$ 28.37
Weighted Average Remaining Life			9 years
Exercise Price Range Three
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Ranges of Exercise Prices, minimum	30.00		$ 30.00		30.00
Ranges of Exercise Prices, maximum	$ 37.70		$ 37.70		$ 37.70
Options outstanding	300,000	[1]	300,000	[1]	312,500	[2]
Weighted Average Per Share Exercise Price	$ 32.38		$ 32.38		$ 32.59
Weighted Average Remaining Life	7 years 1 month 6 days		8 years 1 month 6 days		8 years 9 months 18 days

[1] the weighted average per share exercise price on these shares outstanding is variable. See note below under Chief Executive Officer for additional information.

[2] the weighted average per share exercise price on 300,000 of these shares outstanding is variable. See note below under Chief Executive Officer for additional information.