CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) Non-Cash Activities - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Other Significant Noncash Transactions [Line Items]
Unrealized gain on available-for-sale securities	$ 192	$ 219
Net change in accounts payable and accrued expenses related to purchases of property and equipment	667	3,100
Common Stock Issued to Board of Directors and Scientific Advisory Board that was Earned and Accrued for in Previous Period [Member]
Other Significant Noncash Transactions [Line Items]
Other significant noncash transaction, value of consideration received	$ 300	$ 300

The value of the noncash (or part noncash) consideration received in a transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of a transaction not resulting in cash receipts or cash payments in the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

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Period Type:	duration