Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) Segment shares	Dec. 31, 2018 USD ($) shares	Dec. 11, 2019 shares	Dec. 10, 2019 shares	Jan. 01, 2019
Accounting Policies [Line Items]
Common stock, shares outstanding (in shares) | shares					20,691,301	16,641,999	20,200,000	261,900,000
Cumulative effect on retained earnings, net of tax					$ 0	$ 11,000
Accumulated deficit					(663,600,000)	(509,406,000)
Right-of-use asset					2,300,000
Stock-based compensation					11,508,000	9,039,000
Inventory write-down related to restructuring					7,400,000
Restricted cash						590,000
Short-term investments					0	51,790,000
Bad debt expense					$ 1,634,000	0
Number of business segments | Segment					1
Intangible assets impairment	$ 7,900,000				$ 7,912,000	$ 0
Period of service sale arrangement						5 years
Product warranty						1 year
Period of service sale arrangement at stated service price						4 years
Revenue, remaining performance obligation					3,700,000
Contract assets included in accounts receivable					200,000	$ 200,000
Revenue recognized, included in deferred revenue			$ 1,300,000		1,000,000.0	400,000
Reversal of transfer fee accrual					0	2,994,000
Decrease in valuation allowance due to newly enacted tax rate						36,100,000
Assets					74,779,000	239,307,000
Cash and cash equivalents used in operating activities					73,484,000	48,493,000
Cash and cash equivalents provided by investing activities					67,645,000	(53,481,000)
Goodwill and in-process research and development impairment					86,881,000	0
Goodwill impairment	$ 79,000,000.0			$ 79,000,000.0	78,969,000	0
Present value of future minimum lease payments					2,512,000
Lease Liability					1,112,000	0
Operating lease, liability, noncurrent					$ 1,400,000
Operating leases, rent expense						1,200,000
Operating lease, weighted average remaining lease term					2 years 7 months 6 days
Operating lease, payments					$ 1,700,000
Operating lease, weighted average discount rate, percent					7.80%
Working capital					$ 14,900,000
Inventory write-down					$ 1,523,000	$ 0
U.S
Accounting Policies [Line Items]
Percentage of total consolidated assets					19.00%	54.00%
International
Accounting Policies [Line Items]
Percentage of total consolidated assets, excluding goodwill					81.00%	34.00%
Stock Options
Accounting Policies [Line Items]
Share based compensation, expense recognized					$ 9,039,000
Senhance Surgical Robotic System Acquisition
Accounting Policies [Line Items]
Reversal of transfer fee accrual		$ 3,000,000.0
Transfer fee accrual term		3 years
Senhance Surgical Robotic System Acquisition | Europe
Accounting Policies [Line Items]
Assets					$ 60,500,000	$ 111,000,000.0
Patents
Accounting Policies [Line Items]
Amortization period					10 years
Intangible assets impairment				$ 0	$ 0
Minimum
Accounting Policies [Line Items]
Incremental borrowing rate									6.10%
Amortization period					5 years
Minimum | Developed Technology
Accounting Policies [Line Items]
Amortization period					5 years
Maximum
Accounting Policies [Line Items]
Incremental borrowing rate									8.50%
Amortization period					10 years
Maximum | Developed Technology
Accounting Policies [Line Items]
Amortization period					7 years
Customer Concentration Risk | Accounts Receivable | Eight Customer
Accounting Policies [Line Items]
Concentration risk					85.00%
Customer Concentration Risk | Accounts Receivable | Five Customer
Accounting Policies [Line Items]
Concentration risk						89.00%
Customer Concentration Risk | Sales | Six Customer
Accounting Policies [Line Items]
Concentration risk					82.00%
Customer Concentration Risk | Sales | Twelve Customer
Accounting Policies [Line Items]
Concentration risk						89.00%
Geographic Concentration Risk | Sales | U.S
Accounting Policies [Line Items]
Concentration risk					6.00%	16.00%
Geographic Concentration Risk | Sales | Europe
Accounting Policies [Line Items]
Concentration risk					39.00%	78.00%
Geographic Concentration Risk | Sales | Asia
Accounting Policies [Line Items]
Concentration risk					55.00%	6.00%
U.S. Government Securities
Accounting Policies [Line Items]
Short-term investments						$ 51,800,000
Short-term investments, other-than-temporary impairment					$ 0	0
Held In Cash Collateral Accounts
Accounting Policies [Line Items]
Restricted cash					969,000	600,000
Operating Expense
Accounting Policies [Line Items]
Operating lease, cost					1,400,000
SurgiBot System
Accounting Policies [Line Items]
Inventory write-down					$ 1,500,000	$ 0