Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2013	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Incentive awarded to the company by the State of Connecticut, total		$ 11.5	$ 11.5
Incentive awarded to the company by the State of Connecticut, non-interest bearing loans		8.0	8.0
Incentive awarded to the company by the State of Connecticut, grants		$ 3.5	$ 3.5
Non-interest bearing incentive loan term		10 years
Forgiveness awarded to the company by the state of Connecticut		$ 7.0
Incentive awarded to the company by the State of Connecticut, revenue recognized	$ 0.7	0.4
Incentive awarded to the company by the State of Connecticut, deferred revenue	$ 5.3	$ 5.3		$ 4.4