Property and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Property and equipment held under capital lease	$ 100,000	$ 200,000	$ 200,000
Accumulated depreciation	97,000	$ 58,000	$ 80,000
Loss on disposal of assets	$ (600,000)