Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Total revenue	$ 3,069	$ 1,677	$ 1,804	$ 1,785	$ 1,792	$ 2,466	$ 3,931	$ 2,311	$ 8,335	$ 10,500	$ 4,666
Costs and expenses:
Research and development	4,279	4,098	4,048	3,901	3,297	2,725	3,749	4,718	16,326	14,489	23,733
Selling, general and administrative	7,546	5,981	6,722	7,055	6,458	5,873	7,611	5,755	27,304	25,697	22,757
Total costs and expenses	15,436	14,023	15,590	15,344	15,386	11,640	14,818	13,746	60,393	55,590	58,518
Loss from operations	(12,367)	(12,346)	(13,786)	(13,559)	(13,594)	(9,174)	(10,887)	(11,435)	(52,058)	(45,090)	(53,852)
Net loss	$ (14,041)	$ (14,171)	$ (15,647)	$ (15,147)	$ (15,149)	$ (10,767)	$ (12,324)	$ (12,913)	$ (59,006)	$ (51,153)	$ (62,428)
Per share data:
Net loss per common share - basic and diluted (in dollars per share)	$ (0.29)	$ (0.31)	$ (0.35)	$ (0.34)	$ (0.34)	$ (0.25)	$ (0.32)	$ (0.36)	$ (1.30)	$ (1.26)	$ (1.94)
Product [Member]
Revenue:
Total revenue	$ 1,562	$ 1,177	$ 1,274	$ 1,314	$ 1,319	$ 1,218	$ 1,220	$ 1,048	$ 5,327	$ 4,805	$ 3,440
Costs and expenses:
Cost of product revenue	3,611	3,944	4,820	4,388	5,631	3,042	3,458	3,273	16,763	15,404	12,028
Research [Member]
Revenue:
Total revenue	294	56	71	142	$ 473	$ 1,248	$ 2,711	$ 1,263	563	$ 5,695	$ 1,226
Contribution [Member]
Revenue:
Total revenue	$ 1,213	$ 444	$ 459	$ 329					$ 2,445

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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