Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 35
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6394232&loc=d3e17558-110866

Long-Term Debt - 2019 Amended and Restated Loan Agreement (Details)	1 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 27, 2019 USD ($)	Mar. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)
Line of Credit Facility [Line Items]
Debt covenant, cash requirement percentage		125.00%
Debt covenant, minimum consolidated cash amount		$ 2,500,000
Unamortized discount		317,000	$ 226,000
Hercules Amended and Restated Loan Agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 35,000,000.0
Credit outstanding	$ 10,000,000.0
Current borrowing capacity				$ 20,000,000.0
Variable interest rate	8.75%
Increase in interest rate	4.00%
Periodic payment	$ 800,000
Principal percentage	0.040
Debt covenant, cash requirement percentage	125.00%
Debt covenants, liquidity percentage	100.00%
Debt covenant, minimum consolidated cash amount	$ 2,500,000
Upfront payments	180,000
Debt discount amortization	$ 180,000
Hercules Amended and Restated Loan Agreement \| Prime Rate
Line of Credit Facility [Line Items]
Interest rate	6.00%
Hercules Amended and Restated Loan Agreement \| Minimum
Line of Credit Facility [Line Items]
Variable interest rate	8.75%
Payment premium percentage	0.020
Hercules Amended and Restated Loan Agreement \| New Borrowings
Line of Credit Facility [Line Items]
Current borrowing capacity				10,000,000.0
Hercules Amended and Restated Loan Agreement \| Previous Borrowings
Line of Credit Facility [Line Items]
Current borrowing capacity				$ 10,000,000.0
Hercules Amended and Restated Loan Agreement \| Additional Term Loan One
Line of Credit Facility [Line Items]
Additional borrowing capacity	$ 5,000,000.0
Hercules Amended and Restated Loan Agreement \| Additional Term Loan Two
Line of Credit Facility [Line Items]
Additional borrowing capacity	$ 10,000,000.0
Hercules Loan Agreements
Line of Credit Facility [Line Items]
Maximum borrowing capacity						$ 13,000,000.0
Interest expense		1,800,000	236,000
Accretion expense		61,000	$ 355,000
Unamortized discount		$ 317,000
Effective interest rate		10.90%
Principal payments		$ 0
Hercules Loan Agreements \| Additional Term Loan One
Line of Credit Facility [Line Items]
Maximum borrowing capacity					$ 3,000,000.0	$ 2,000,000.0