The Company and Basis of Presentation - Additional Information (Details)		1 Months Ended	6 Months Ended
	Mar. 08, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2018 USD ($) segment	May 17, 2018 shares	Mar. 09, 2018 shares	Dec. 31, 2017 USD ($)
Company And Basis Of Presentation [Line Items]
Number of reportable segments | segment			1
Proceeds raised from financing transactions		$ 50,000,000
Working capital			$ 51,500,000
Cash			44,912,000			$ 22,466,000
Net proceeds from equity offering			51,500,000
Series B Convertible Preferred Stock | Common Stock
Company And Basis Of Presentation [Line Items]
Preferred stock convertible to common stock | shares				14,349,236,000
Private Placement
Company And Basis Of Presentation [Line Items]
Proceeds from private placement		45,200,000
2018 Private Placement
Company And Basis Of Presentation [Line Items]
Proceeds from private placement	$ 45,200
Aggregate consideration received from warrant exercise agreement		4,800,000
SafeOp Surgical, Inc.
Company And Basis Of Presentation [Line Items]
Portion of net proceeds from 2018 private placement and warrant exercise used to fund cash portion of purchase price			14,100,000
Preferred stock convertible to common stock | shares					987,578
SafeOp Surgical, Inc. | 2018 Private Placement
Company And Basis Of Presentation [Line Items]
Portion of net proceeds from 2018 private placement and warrant exercise used to fund cash portion of purchase price		$ 15,100,000	$ 14,300,000