Summary of Significant Accounting Policies - Summary of Property and Equipment and Related Accumulated Depreciation (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 5,505	$ 4,676
Less accumulated depreciation	(1,697)	(1,059)
Net property and equipment	$ 3,808	3,617
Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Gross property, plant and equipment	$ 914	630
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	5 years
Gross property, plant and equipment	$ 845	800
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Gross property, plant and equipment	$ 1,011	628
Leasehold improvements
Property, Plant and Equipment [Line Items]
Leasehold improvements, Useful Life	Shorter of the useful life or remaining lease term (10 years)
Gross property, plant and equipment	$ 2,621	2,582
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	10 years
Office equipment under capital lease
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Gross property, plant and equipment	$ 114	$ 36