Debt - Additional Information (Details)						3 Months Ended		9 Months Ended
	Sep. 24, 2019 $ / shares	Sep. 23, 2019 USD ($) $ / shares	Aug. 29, 2019 USD ($) shares	Jun. 10, 2019 USD ($)	Nov. 30, 2018 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Gross proceeds from issuance of equity securities									$ 19,803,000
Proceeds from issuance of convertible note									2,600,000
Convertible debt converted into shares of common stock | shares			2,267,042
Gain on debt extinguishment			$ 900,000				$ 928,000		928,000
2018 Convertible Bridge Notes
Debt Instrument [Line Items]
Convertible note, principal amount					$ 6,800,000
Proceeds from issuance of convertible note					$ 6,600,000
Debt instrument, interest rate					10.00%
Debt maturity date					Mar. 31, 2019
Increase in interest rate if bridge notes not paid or converted								15.00%
Percentage of multiplier on price per share of new stock paid in qualified financing by investors								70.00%
Denominator for calculating capitalization value for price per share						$ 45,000,000		$ 45,000,000
Debt discount						2,500,000		$ 2,500,000
Maturity date, description								As part of the amendment, the maturity dates of the notes were extended to the earliest of (i) September 24, 2019; (ii) the occurrence of an Event of Default (as defined in the 2018 Bridge Notes); (iii) the consummation of a liquidation or dissolution of DermTech Operations; (iv) a Liquidation Transaction (as defined in the 2018 Bridge Notes); or (v) the consummation of a merger with or into the Company or any of its subsidiaries.
Convertible notes conversion ratio		0.70
Description of merger consideration								“Merger Consideration” means (i) the lesser of $6.46 and (ii) the offering price per share of the private investment in public equity transaction to be consummated concurrently with the consummation of the Qualifying Merger (the “2019 PIPE Financing”) multiplied by the Conversion Ratio.
Merger consideration maximum price per share | $ / shares		$ 6.46
Debt Conversion Ratio Number Used As Numerator to Derive Quotient		$ 8,000,000
Liability balance						0		$ 0		$ 0
2018 Convertible Bridge Notes | Other Expense
Debt Instrument [Line Items]
Loss on change in fair value of derivative liability						0	100,000	0	400,000
2018 Convertible Bridge Notes | Minimum
Debt Instrument [Line Items]
Gross proceeds from issuance of equity securities								20,000,000
2019 Convertible Bridge Notes
Debt Instrument [Line Items]
Debt instrument, interest rate				10.00%
Debt discount						300,000		$ 300,000
Maturity date, description								These convertible bridge notes carried an interest rate of 10% and matured after the earliest to occur of: (i) September 25, 2019; (ii) the occurrence of an Event of Default (as defined in the 2019 Bridge Notes); (iii) the consummation of a liquidation or dissolution of DermTech Operations; (iv) a Liquidation Transaction (as defined in the 2019 Bridge Notes); or (v) the consummation of a merger of DermTech Operations with DT Merger Sub, Inc., a previous subsidiary of the Company, in accordance with the Merger Agreement.
Debt Conversion Ratio Number Used As Numerator to Derive Quotient		$ 8,000,000
Proceeds from issuance of convertible note				$ 2,600,000
Debt conversion feature								Upon the conversion of these notes, the note holders were entitled to receive a number of shares of DermTech Operations’ common stock equal to the quotient obtained by dividing (i) the unpaid principal amount of these notes plus interest accrued but unpaid thereon, by (1) if the Qualifying Merger consummates prior to the maturity date, the lesser of (x) $5.80 and (y) 90% of the Merger Consideration (as defined below), or (2) if the Qualifying Merger consummates on or after the maturity date, the lesser of (x) $4.51 and (y) 70% of the Merger Consideration.
Liability balance						0		$ 0		$ 0
2019 Convertible Bridge Notes | Other Expense
Debt Instrument [Line Items]
Loss on change in fair value of derivative liability						$ 0	$ 11,000	$ 0	$ 14,000
2019 Convertible Bridge Notes | Maximum
Debt Instrument [Line Items]
Convertible notes conversion ratio	0.70	0.90
Convertible notes conversion price | $ / shares	$ 4.51	$ 5.80