Commitments and Contingencies - Additional Information (Detail)				3 Months Ended
	Apr. 25, 2018 USD ($)	Apr. 25, 2018 USD ($)	Jan. 25, 2018	Mar. 31, 2018 USD ($) Installment	Dec. 31, 2017 USD ($)
Commitments And Contingencies [Line Items]
Prepayment amount received				$ 2,500,000
Discount on prepayment liability				548,000
Deferred revenue				488,000
Short term deferred revenue				1,019,000	$ 1,304,000
Line of credit facility amount withdrawn				$ 3,750,000	3,750,000
Revolving Credit Facility [Member]
Commitments And Contingencies [Line Items]
Extended maturity date				Apr. 28, 2019
Line of credit facility amount withdrawn				$ 3,800,000
Silicon Valley Bank Credit Facility [Member] | Loan Agreement [Member]
Commitments And Contingencies [Line Items]
Interest rate description				The interest rate applicable to borrowings may be based on the prime rate or LIBOR. Prime rate-based rates vary from prime rate plus 0.75% per annum to prime rate plus 2.00% per annum, while LIBOR-based rates vary from LIBOR plus 3.75% per annum to LIBOR plus 4.25% per annum.
Silicon Valley Bank Credit Facility [Member] | Loan Agreement [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Maximum increased borrowing amount	$ 20,000,000	$ 20,000,000
Percentage of unused portion of facility, monthly fee		0.50%
Silicon Valley Bank Credit Facility [Member] | Loan Agreement [Member] | Revolving Credit Facility [Member]
Commitments And Contingencies [Line Items]
Extended maturity date			Apr. 28, 2018
Line of credit facility amount withdrawn				$ 3,800,000	3,800,000
Letters of credit outstanding				2,100,000	$ 2,300,000
Available borrowing capacity				6,700,000
Silicon Valley Bank Credit Facility [Member] | Loan Agreement [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Extended maturity date	Apr. 28, 2019	Apr. 28, 2019
Maximum [Member]
Commitments And Contingencies [Line Items]
Short term deferred revenue				$ 100,000
Maximum [Member] | Prime Rate [Member] | Silicon Valley Bank Credit Facility [Member] | Loan Agreement [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Additional interest rate per annum		2.00%
Maximum [Member] | LIBOR Rate [Member] | Silicon Valley Bank Credit Facility [Member] | Loan Agreement [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Additional interest rate per annum		4.25%
Minimum [Member] | Prime Rate [Member] | Silicon Valley Bank Credit Facility [Member] | Loan Agreement [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Additional interest rate per annum		0.75%
Minimum [Member] | LIBOR Rate [Member] | Silicon Valley Bank Credit Facility [Member] | Loan Agreement [Member] | Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Additional interest rate per annum		3.75%
Supply and Joint Development Agreement Amended [Member] | BASF [Member]
Commitments And Contingencies [Line Items]
Supply agreement termination date				Dec. 31, 2027
Non-interest bearing prepayment, aggregate amount agreed to remit				$ 5,000,000
Number of equal installments during 2018 | Installment				2
Prepayment amount received				$ 2,500,000
Discount on prepayment liability				500,000
Supply and Joint Development Agreement Amended [Member] | BASF [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Non-interest bearing prepayments, aggregate amount				$ 22,000,000
Credit limit percentage on prepayment balance				25.30%