Related Party Transactions - Providence (Details Textual) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Related Party Transaction [Line Items]
Total collaboration revenue	$ 3,318	$ 3,423	$ 17,821	$ 8,176
Providence Therapeutics, Inc [Member] \| Research Collaboration and License Agreement [Member]
Related Party Transaction [Line Items]
Total collaboration revenue	100	$ 400	400	$ 500
Accounts receivable, balance amount	$ 400		$ 400

For an unclassified balance sheet, amount of receivables arising from transactions with related parties.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant