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Segments (Details) $ in Thousands	3 Months Ended		6 Months Ended
Segments (Details) $ in Thousands	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) item	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments \| item			2
Revenue, net	$ 3,676		$ 4,794
Cost of revenue	1,181		2,148
Research and development	13,984	$ 7,965	27,590	$ 15,737
Sales and marketing	12,368	2,188	23,601	3,626
General and administrative	8,121	5,142	14,381	8,862
Loss from operations	(31,978)	(15,295)	(62,926)	(28,225)
UNITED KINGDOM
Segment Reporting Information [Line Items]
Net assets	77		77		$ 175
Dermatology Therapeutics Segment [Member]
Segment Reporting Information [Line Items]
Revenue, net	2,533		2,533
Cost of revenue	152		152
Research and development	13,984	7,965	27,590	15,737
Sales and marketing	12,360	2,188	23,581	3,626
General and administrative		58		151
Loss from operations	(23,963)	(10,211)	(48,790)	(19,514)
Contract Research Segment [Member]
Segment Reporting Information [Line Items]
Revenue, net	3,053		5,554
Cost of revenue	2,621		4,740
Sales and marketing	8		20
General and administrative	521		992
Loss from operations	(97)		(198)
Corporate and Other
Segment Reporting Information [Line Items]
Revenue, net	(1,910)		(3,293)
Cost of revenue	(1,592)		(2,744)
General and administrative	7,600	5,084	13,389	8,711
Loss from operations	(7,918)	$ (5,084)	(13,938)	$ (8,711)
Intersegment Eliminations [Member] \| Contract Research Segment [Member]
Segment Reporting Information [Line Items]
Revenue, net	$ (1,910)		$ 3,293