Liquidity (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net proceeds from sales of common stock		$ 97,392	$ 100,060	$ 63,425
January 2020 Sales Agreement [Member]
Net proceeds from sales of common stock	$ 156,000

The cash inflow from the additional capital contribution to the entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3255-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration