Income Taxes - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Estimated annual effective tax rate	4.10%
Deferred tax benefit	$ 2,300,000	$ 4,700,000
Effective tax rate	3.30%	4.30%
Unrecognized tax benefits	$ 0