Income Taxes - Components of Net Accumulated Deferred Income Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets (liabilities):
Stock-based compensation	$ 587	$ 264
Depreciation and amortization	(318)
Depreciation and amortization		43
Section 181 qualified production expense	(1,933)	(2,550)
Net operating loss carryforward	6,012
Charitable carryforward	278
Other	342	737
Tax credits	276	953
Valuation allowance	(5,907)
Total deferred tax liabilities, net of valuation allowance	$ (663)	$ (553)