Credit Facility - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Line of Credit Facility [Line Items]
Revolving credit facility, maximum borrowing capacity	$ 2.5
Credit facility expiration date	Jan. 15, 2019
Credit facility limit restricted to support letter of credit	$ 0.2
Line of credit facility, remaining borrowing capacity	$ 2.3
Prime Rate
Line of Credit Facility [Line Items]
Interest rate over prime rate	0.50%