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Long-Term Debt - Schedule of Future Principal Payments and the Final Payments Due (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Maturities [Line Items]
2019	$ 4,259
2020	8,767
2021	6,520
Long-term debt	19,546	$ 10,000
Hercules Loan Agreement [Member]
Debt Maturities [Line Items]
2019	1,345
2020	4,305
2021	4,350
Long-term debt	10,000
FFG Loan Agreement [Member]
Debt Maturities [Line Items]
2019	2,914
2020	4,462
2021	2,170
Long-term debt	$ 9,546

X

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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-Publisher FASB
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X

- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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-Publisher FASB
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-SubTopic 10
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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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