Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 22, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2013	Dec. 31, 2017
Loss Contingencies [Line Items]
Incentive awarded to the company by the State of Connecticut, total				$ 11,500
Incentive awarded to the company by the State of Connecticut, non-interest bearing loans				8,000
Incentive awarded to the company by the State of Connecticut, grants				$ 3,500
Non-interest bearing incentive loan term			10 years
Forgiveness awarded to the company by the state of Connecticut			$ 7,000
Incentive awarded to the company by the State of Connecticut, other revenue recognized		$ 300	1,000
Incentive awarded to the company by the State of Connecticut, deferred revenue included in other liabilities		$ 5,000	$ 5,000		$ 4,400
The Hartford
Loss Contingencies [Line Items]
Merger Termination Fee	$ 68,250
Merger Transaction-Related Expenses	$ 7,000