Commitments (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Contractual Obligation [Line Items]
Capital lease obligation amount	$ 3,355,000	$ 1,898,000
Laboratory And Computer Equipment
Contractual Obligation [Line Items]
Capital lease obligation amount	$ 3,400,000
Lease term	36 months
Capital leases buy out amount	$ 1
Minimum | Laboratory And Computer Equipment
Contractual Obligation [Line Items]
Capital lease interest rate	4.60%
Maximum | Laboratory And Computer Equipment
Contractual Obligation [Line Items]
Capital lease interest rate	5.60%