Performance Based Awards - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Performance period			3 years
Compensation expense	$ 0.1
Unearned compensation expense	2.2		$ 2.2
Performance Awards
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Compensation expense	0.2	$ 0.2	0.4	$ 0.5
Unearned compensation expense	$ 1.2	$ 1.5	$ 1.2	$ 1.5