Inventories - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventory [Line Items]
Write down of inventory	$ 2,565,000		$ 2,565,000
SurgiBot System [Member]
Inventory [Line Items]
Write down of inventory		$ 0	$ 2,600,000	$ 0