Commitments and Contingencies - Additional Information (Detail) - USD ($)		12 Months Ended
	May 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Commitments [Line Items]
Deferred lease obligation		$ 1,718,000	$ 1,570,000
Stamford Operating Lease [Member]
Other Commitments [Line Items]
Operating Lease, description		The Stamford Lease requires monthly lease payments, including rent escalations and rent holidays, during the initial lease term. The Company began to make rental payments from the Commencement Date. The Company records monthly rent expense on a straight-line basis from March 2016, upon taking possession of the Premises, through November 2023. As of December 31, 2017 and 2016, the balance of deferred lease obligation, representing the difference between cash rent paid and straight-line rent expense, was $876 and $583, respectively. The Stamford Lease is renewable for one five-year term.
Operating Lease, renewable term		5 years
Operating lease, expiration date		Nov. 30, 2023
Deferred lease obligation		$ 876,000	583,000
Tenant improvement expenses	$ 1,094,000
Lease, rent expense		935,000	797,000
Stamford Operating Lease [Member] | Standby Letter of Credit [Member]
Other Commitments [Line Items]
Letter of credit, amount		$ 769,000
Operating lease, renewable term description		Automatically renewed annually through November 2023.
Stamford Operating Lease [Member] | Standby Letter of Credit [Member] | Maximum [Member]
Other Commitments [Line Items]
Letter of credit, renewal date		Nov. 30, 2023
Stamford Operating Lease [Member] | Leasehold Improvements [Member]
Other Commitments [Line Items]
Deferred lease obligation		$ 842,000	987,000
Shelton Operating Lease [Member]
Other Commitments [Line Items]
Operating lease, expiration date		Nov. 30, 2017
Lease, rent expense			1,127,000	$ 665,000
Accrued cease use date liability	$ 1,312,000
Additional amortization expense			$ 899,000	$ 67,000
Additional loss per share			$ 0.03
Shelton Operating Lease [Member] | Standby Letter of Credit [Member]
Other Commitments [Line Items]
Letter of credit, remaining amount			$ 700,000
Letter of credit, expiration date		Dec. 13, 2017