Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Commitments to purchase inventory	$ 1,300,000
Purchase commitments inventory expire year	2019
Assets Held under Capital Leases [Member]
Loss Contingencies [Line Items]
Assets held under capital leases	$ 0	$ 0