Segment Reporting - Financial Information with Respect to Company's Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenue	$ 4,865	$ 2,541	$ 15,716	$ 5,943
Total allocation of centralized research and development operational cash expenditures	19,791	9,737	62,512	28,723
Loss from operations	(21,978)	(10,447)	(65,343)	(31,807)
Adjustments to reconcile segment operating loss to consolidated loss from operations:
Interest income received	(1,236)	(691)	(3,322)	(1,213)
Depreciation and amortization			(3,508)	(1,555)
Share-based compensation			(6,319)	(697)
Loss on disposal of assets			(22)	(8)
Changes in prepaid expenses, accounts payable and accrued expenses	5,179	7,866	15,988	10,772
Operating Segments
Segment Reporting Information [Line Items]
Revenue	4,865	2,541	15,716	5,943
Total segment operational cash expenditures	16,232	12,584	48,198	28,493
Total allocation of centralized research and development operational cash expenditures	4,081	2,984	10,952	8,159
Loss from operations	(15,448)	(13,027)	(43,434)	(30,709)
Operating Segments \| Therapeutics
Segment Reporting Information [Line Items]
Revenue	4,719	2,115	14,357	5,009
Total segment operational cash expenditures	14,290	11,727	42,072	25,903
Total allocation of centralized research and development operational cash expenditures	4,081	2,387	10,952	6,329
Loss from operations	(13,652)	(11,999)	(38,667)	(27,223)
Operating Segments \| Food
Segment Reporting Information [Line Items]
Revenue	146	426	1,359	934
Total segment operational cash expenditures	1,942	857	6,126	2,590
Total allocation of centralized research and development operational cash expenditures		597		1,830
Loss from operations	(1,796)	(1,028)	(4,767)	(3,486)
Segment Reconciling Items
Adjustments to reconcile segment operating loss to consolidated loss from operations:
Corporate general and administrative cash expenditures	(6,581)	(3,719)	(24,726)	(8,397)
Interest income received	(1,236)	(691)	(3,322)	(1,213)
Depreciation and amortization	(1,401)	(584)	(3,508)	(1,555)
Share-based compensation	$ (2,491)	$ (292)	(6,319)	(697)
Loss on disposal of assets			$ (22)	$ (8)

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