Accounting for Uncertainty in Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Liability for unrecognized tax	$ 5.3	$ 4.6
Unrecognized tax favorable impact on effective tax rate	4.6
Accrued interest and penalties applied to uncertain tax positions	$ 2.1	$ 1.9