Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 30, 2018	Nov. 30, 2015	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 25, 2018	Dec. 31, 2017
Nature Of Business And Basis Of Presentation [Line Items]
Net loss			$ 17,980	$ 11,311	$ 33,857	$ 25,186
Accumulated deficit			158,115		158,115			$ 124,258
Cash, cash equivalents and available-for-sale securities			162,759		162,759
Net loss attributable to non-controlling interest						(1,060)
Corporate Conversion [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock, conversion ratio							84.85%
Solid GT, LLC [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Voting ownership percentage before transactions		100.00%
Voting ownership percentage after transactions		77.00%
Net loss attributable to non-controlling interest			$ 0	$ 0	$ 0	$ 1,060
IPO [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Number of shares sold	8,984,375
Public offering price per share	$ 16.00
Net proceeds from issuance	$ 129,096