Debt - Additional Information (Detail)		1 Months Ended				12 Months Ended
	Jun. 26, 2015 USD ($)	Dec. 31, 2018 USD ($) Installment	Oct. 31, 2017 USD ($)	Apr. 30, 2017 USD ($)	May 31, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 25, 2016	Mar. 31, 2016 USD ($)
Debt Instrument [Line Items]
Debt extinguishment loss						$ (2,416,000)	$ 0	$ 0
CRG Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 50,000,000
Current borrowing capacity	30,000,000
Remaining borrowing capacity				$ 5,000,000					$ 20,000,000		$ 20,000,000
Debt drawn	$ 30,000,000		$ 0		$ 15,000,000
Debt maturity date						Jun. 30, 2020
Interest payment end date				Mar. 31, 2020
Frequency of periodic payment						quarterly
Debt Instrument Interest Payment Period						3 years
Debt instrument interest rate percentage	12.50%
Debt instrument cash interest rate percentage										8.00%
Deferred payment in-kind interest rate										4.50%
Facility fee	7.00%
Term loan first amendment description						In March 2016, the Company amended the agreement with regard to the conditions for borrowing the remaining $20.0 million under the CRG Term Loan if certain product and service revenue amounts were achieved.
Term loan second, third and fourth amendment description						In April and October 2017, and in February 2018, the Company executed three amendments, which allowed the Company to borrow the remaining $5.0 million through June 30, 2017, included an additional $15.0 million borrowing capacity available through December 31, 2017, extended the interest only and payment in-kind period, decreased the combined 2016 and 2017 revenue covenant, and increased the facility fee by 1.75%.
Additional borrowing capacity				$ 15,000,000
Existing capacity extended expiration date				Jun. 30, 2017
Additional capacity extended expiration date			Dec. 31, 2017
Increase in facility fee				1.75%
Debt extinguishment loss						$ 2,400,000
Write-off of unamortized debt discount and debt issuance costs						$ 300,000
CRG Term Loan | First 12 Months
Debt Instrument [Line Items]
Prepayment penalty	3.00%
CRG Term Loan | After Year 1 but on or Before Year 2
Debt Instrument [Line Items]
Prepayment penalty	2.00%
CRG Term Loan | After Year 2 but on or Before Year 3
Debt Instrument [Line Items]
Prepayment penalty	1.00%
CRG Term Loan | After Year 3 Thereafter Until Maturity
Debt Instrument [Line Items]
Prepayment penalty	0.00%
SVB Term Loan
Debt Instrument [Line Items]
Debt maturity date		Dec. 01, 2023
Frequency of periodic payment		monthly
Debt instrument interest rate percentage		6.30%				6.30%
Total principal amout		$ 56,000,000				$ 56,000,000
Number of installments | Installment		36
Number of installments if achieving trailing revenue target | Installment		30
Debt instrument description						Beginning on December 1, 2020 (or June 1, 2021, if the Company achieves a trailing twelve-month revenue of at least a specified amount and elects to apply such later date), the Company will make thirty-six equal monthly payments of principal (or thirty equal payments, if the Company so elects).
Percentage of payments equal principal amount		3.15%				3.15%
Proceeds from term loan						$ 55,400,000
Legal and consulting fees						$ 600,000