Supplemental Balance Sheet Information - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 19,139	$ 20,655
Less accumulated depreciation and amortization	(9,124)	(7,066)
Property and equipment, net	$ 10,015	13,589
Office and Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	3 years
Property and equipment, gross	$ 409	409
Software [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	3 years
Property and equipment, gross	$ 743	708
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Property and equipment, gross	$ 4,224	4,516
Furniture [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 200	200
Furniture [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Furniture [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	7 years
Manufacturing Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Property and equipment, gross	$ 910	897
Manufacturing Tooling and Molds [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	6 months
Property and equipment, gross	$ 255	154
T2-Owned Instruments and Components [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Property and equipment, gross	$ 7,370	9,119
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,437	3,353
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,591	$ 1,299