Income Taxes - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Deferred income tax assets	$ 71,973,000	$ 73,068,000
Valuation allowance	$ 0	0
Federal income tax at statutory rate	35.00%
Tax Credit Carryforward [Line Items]
Approximate Federal net operating losses (NOLs) available to offset future taxable income		$ 126,000,000
Research Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax credit carryforward	$ 1,300,000
Research Tax Credit Carryforward [Member] | Tax Year 2015 [Member]
Tax Credit Carryforward [Line Items]
Tax credit carryforward	100,000
Research Tax Credit Carryforward [Member] | Tax Year 2016 [Member]
Tax Credit Carryforward [Line Items]
Tax credit carryforward	$ 300,000