Commitments (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Contractual Obligation [Line Items]
Capital lease obligation amount		$ 3,733,000	$ 2,557,000
Laboratory And Computer Equipment
Contractual Obligation [Line Items]
Capital lease obligation amount	$ 300,000	$ 3,700,000
Lease term		36 months
Capital leases buy out amount	$ 1	$ 1
Minimum | Laboratory And Computer Equipment
Contractual Obligation [Line Items]
Capital lease interest rate	4.60%	4.60%
Maximum | Laboratory And Computer Equipment
Contractual Obligation [Line Items]
Capital lease interest rate	5.80%	5.80%