Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Reserves and accrued expenses	$ 1,969	$ 2,497
Share based compensation	2,381	2,636
Intangible assets	1,564	3,679
Credit carryforwards	2,486	2,148
Net operating loss and capital loss carryforwards	16,701	21,117
Total deferred tax assets	25,101	32,077
Valuation allowance	(23,714)	(30,746)
Net deferred tax assets	1,387	1,331
Deferred tax liabilities:
Prepaid expenses	(444)	(2,017)
Property, plant, and equipment	(950)	(1,219)
Total deferred tax liabilities	(1,394)	(3,236)
Net deferred tax liabilities	$ (7)	$ (1,905)