Notes Payable - Additional Information (Detail) - USD ($)					1 Months Ended	12 Months Ended
	May 10, 2017	Sep. 18, 2015	Aug. 14, 2015	Sep. 26, 2014	May 31, 2017	Dec. 31, 2017	Apr. 28, 2017	Dec. 31, 2016	Jan. 17, 2012
Debt Instrument [Line Items]
Warrant expiration period				7 years
Issue of warrants to purchase shares of company's common stock							24,900,000
Loss on Extinguishment of notes payable						$ (308,000)
Notes Payable [Member]
Debt Instrument [Line Items]
Debt issuance costs paid to prior lenders and third parties						371,000
Debt issuance cost						$ 280,000
Debt unamortized balance								$ 107,000
Notes Payable [Member] | Loss on Extinguishment of Notes Payable [Member]
Debt Instrument [Line Items]
Debt unamortized balance					$ 63,000
First Amended SVB Loan Agreement [Member]
Debt Instrument [Line Items]
Warrant expiration period				7 years
Warrants, exercise price				$ 4.015
Interest only payment percentage			7.50%
Maturity date of the term loans						Oct. 01, 2018
First Amended SVB Loan Agreement [Member] | Maximum [Member] | First Tranche [Member]
Debt Instrument [Line Items]
Amount of borrowing under agreement			$ 20,000,000
First Amended SVB Loan Agreement [Member] | Minimum [Member] | First Tranche [Member]
Debt Instrument [Line Items]
Amount of borrowing under agreement			$ 10,000,000
Second Amended SVB Loan Agreement [Member]
Debt Instrument [Line Items]
Warrant expiration period			7 years
Warrants, exercise price			$ 3.10
Interest only payment percentage		7.50%
Maturity date of the term loans						Jul. 01, 2018
Loan and Security Agreement [Member]
Debt Instrument [Line Items]
Note issuance date						Jan. 17, 2012
Debt discount liability, facility fee				$ 75,000	255,000
Issue of warrants to purchase shares of company's common stock									430,815
Unamortized debt discount						$ 210,000
Debt Instrument, redemption price amount					$ 1,300,000
Approximated Amount of debt discount				129,000
Fair value of warrants on the issue date				54,000
Debt discount liability, legal fees				$ 30,000
Debt extinguishment date						2017-05
Loan and Security Agreement [Member] | Notes Payable [Member] | Interest Expense [Member]
Debt Instrument [Line Items]
Loss on Extinguishment of notes payable						$ (308,000)
Loan and Security Agreement [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Debt issuance costs recorded as debt discount	$ 1,200,000
Warrant expiration period	5 years
Loan and Security Agreement [Member] | Term Loan [Member] | First Tranche [Member]
Debt Instrument [Line Items]
Debt discount liability, facility fee	$ 170,000
Warrants, exercise price	$ 1.00
Estimated fair value of warrants	$ 300,000
Unamortized debt discount						$ 209,000
Loan and Security Agreement [Member] | Term Loan [Member] | First Tranche [Member] | Maximum [Member]
Debt Instrument [Line Items]
Issue of warrants to purchase shares of company's common stock	1,244,746
Loan and Security Agreement [Member] | Innovatus Life Sciences Lending Fund I, LP [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Note issuance date						May 10, 2017
Term loans aggregate principal amount	$ 17,000,000
Interest only payment period	24 months
Term loans maturity period	4 years
Repayment of term loans period	2 years
Debt instrument amortization schedule	24 months
Debt instrument repayment term						The interest-only period will end if the Company fails to meet any Interest-Only Milestone. Commencing on the first day of the month following such failure to achieve an Interest-Only Milestone, the Company will be required to repay the term loans over a two year period, based on a twenty-four (24) month amortization schedule.
Interest-only milestone terms						The Interest-Only Milestones require the Company to (i) achieve certain twelve month revenue targets, measured quarterly, commencing with the quarter ending March 31, 2018, (ii) meet a minimum capital raising threshold through the sale and issuance of equity securities during the period from April 10, 2017 through May 31, 2018 and (iii) obtain clearance for commercialization of the Senhance System by the FDA (“Senhance Clearance”) by May 30, 2018 (each such milestone, an “Interest-Only Milestone”).
Term loans fixed interest rate	11.00%
Term loans fixed interest rate, paid in-kind percentage	2.50%
Term loans payment terms						The Company will be required to repay the term loans if they are accelerated following an event of default. In addition, the Company is permitted to prepay the term loans in full at any time upon five (5) business days’ written notice to the Lender. Upon the earliest to occur of the maturity date, acceleration of the term loan, or prepayment of the term loan, the Company is required to make a final payment equal to the total term loan commitment multiplied by four percent (4%) (the “Final Fee”); provided, however, that in the event the Company refinances its obligations with the Lender after Senhance Clearance, no Final Fee or Prepayment Fee (as defined below) will be due thereunder; and provided, further, that if the Company elects to refinance its obligations prior to the funding of the Second Tranche, the Final Fee with respect to the Second Tranche shall be paid in full on the date of such refinancing. Any prepayment of the term loans in full, whether mandatory or voluntary, must include (i) the Final Fee, (ii) interest at the default rate (which is the rate otherwise applicable plus five percent (5%)) with respect to any amounts past due, (iii) the Lender’s expenses and all other obligations that are due and payable to the Lender and (iv) a prepayment fee of three percent (3%) if the term loan is paid in full on or before the first anniversary of the effective date, two percent (2%) if paid off after the first anniversary but on or before the second anniversary of the effective date and one percent (1%) if paid off after the second anniversary but on or before the third anniversary of the effective date (the “Prepayment Fee”).
Term loans prepayment written notice period	5 days
Multiplier percentage of term loan commitment final fee payment	4.00%
Percentage of additional interest rate added to default rate	5.00%
Debt instrument covenant terms						Under the terms of the Innovatus Loan Agreement, the Company is required to maintain minimum unrestricted cash in an amount equal to (x) six million dollars ($6,000,000), at all times prior to Senhance Clearance; and (y) at all times thereafter, the least of (i) $6,000,000, (ii) the Company’s trailing three (3) months’ cash used to fund operating activities, as determined as of the most recent month end and (iii) the then outstanding principal amount of the term loans, together with accrued but unpaid interest.
Minimum unrestricted cash requirement prior to clearance	$ 6,000,000
Covenants unrestricted cash requirement amount	$ 6,000,000
Covenant measurement trailing period for cash operating activities	3 months
Loan and Security Agreement [Member] | Innovatus Life Sciences Lending Fund I, LP [Member] | Term Loan [Member] | On or Before First Anniversary of Effective Date [Member]
Debt Instrument [Line Items]
Prepayment fee percentage	3.00%
Loan and Security Agreement [Member] | Innovatus Life Sciences Lending Fund I, LP [Member] | Term Loan [Member] | After First Anniversary but on or Before Second Anniversary of the Effective Date [Member]
Debt Instrument [Line Items]
Prepayment fee percentage	2.00%
Loan and Security Agreement [Member] | Innovatus Life Sciences Lending Fund I, LP [Member] | Term Loan [Member] | After Second Anniversary but on or Before Third Anniversary of the Effective Date [Member]
Debt Instrument [Line Items]
Prepayment fee percentage	1.00%
Loan and Security Agreement [Member] | Innovatus Life Sciences Lending Fund I, LP [Member] | Term Loan [Member] | First Tranche [Member]
Debt Instrument [Line Items]
Term loans aggregate principal amount	$ 14,000,000
Loan and Security Agreement [Member] | Innovatus Life Sciences Lending Fund I, LP [Member] | Term Loan [Member] | Second Tranche [Member]
Debt Instrument [Line Items]
Term loans aggregate principal amount	$ 3,000,000