Goodwill, In-Process Research and Development and Intellectual Property - Additional Information (Detail) - USD ($)			3 Months Ended		12 Months Ended
	Oct. 31, 2018	Sep. 21, 2015	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Goodwill And Intangible Assets [Line Items]
Goodwill			$ 79,509,000	$ 80,131,000	$ 80,131,000
Accumulated impairment of goodwill			61,800,000	61,800,000	61,800,000
Goodwill impairment			$ 0	$ 0	$ 0
In-Process Research and Development [Member]
Goodwill And Intangible Assets [Line Items]
Discount rate	15.00%	45.00%
Intellectual Property [Member]
Goodwill And Intangible Assets [Line Items]
Discount rate		45.00%
Technology and Patents Purchased [Member]
Goodwill And Intangible Assets [Line Items]
Weighted average remaining useful life			8 years 1 month 6 days		8 years 3 months 18 days
Developed Technology [Member]
Goodwill And Intangible Assets [Line Items]
Weighted average remaining useful life			3 years 6 months		3 years 9 months 18 days
Safe Stitch Medical Inc [Member]
Goodwill And Intangible Assets [Line Items]
Goodwill			$ 93,800,000
Senhance Surgical Robotic System Acquisition [Member]
Goodwill And Intangible Assets [Line Items]
Goodwill			38,300,000
Intellectual property		$ 48,500,000
Senhance Surgical Robotic System Acquisition [Member] | In-Process Research and Development [Member]
Goodwill And Intangible Assets [Line Items]
In-process research and development		$ 17,100,000
Senhance Surgical Robotic System Acquisition [Member] | Technology and Patents Purchased [Member]
Goodwill And Intangible Assets [Line Items]
Acquisition price						$ 400,000
Medical Surgery Technologies Ltd. [Member]
Goodwill And Intangible Assets [Line Items]
Goodwill	$ 9,638,000		$ 9,600,000
Acquisition price	20,314,000
Medical Surgery Technologies Ltd. [Member] | In-Process Research and Development [Member]
Goodwill And Intangible Assets [Line Items]
In-process research and development	$ 10,600