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The Company and Summary of Significant Accounting Policies (Details Textual)
 1 Months Ended 12 Months Ended
Oct. 09, 2018
$ / shares
Apr. 11, 2018
$ / shares
Feb. 22, 2019
USD ($)
Dec. 31, 2018
USD ($)
Patients
Segment
Dec. 31, 2017
USD ($)
Company And Summary Of Significant Accounting Policies Table [Line Items]          
Revenues       $ 0  
Concentrations of credit risk       $ 0  
Number of segments | Segment       1  
Nasdaq Capital Market          
Company And Summary Of Significant Accounting Policies Table [Line Items]          
Common stock not met minimum closing bid price, preceding days   30 days      
Minimum consecutive business days 10 days        
Additional granted days for common stock to meet minimum bid price 180 days        
Common stock bid price, description       On April 11, 2018, the Company received notification from Nasdaq of potential delisting of its shares from the Nasdaq Capital Market because the closing bid price of its common stock had not met the minimum closing bid price of $1.00 per share during the preceding 30 days. On October 9, 2018, ARCA received a written notification from NASDAQ granting an additional 180 calendar day period, until April 8, 2019, to regain compliance with the minimum bid price requirement. The minimum bid price requirement will be met if the Common Stock has a closing bid of at least $1.00 per share for a minimum of 10 consecutive business days during the 180 day period.  
Nasdaq Capital Market | Minimum          
Company And Summary Of Significant Accounting Policies Table [Line Items]          
Minimum closing bid price | $ / shares $ 1.00 $ 1.00      
Sales Agreement          
Company And Summary Of Significant Accounting Policies Table [Line Items]          
Net proceeds from issuance of common stock       $ 3,400,000 $ 6,100,000
Subsequent Event | Sales Agreement          
Company And Summary Of Significant Accounting Policies Table [Line Items]          
Net proceeds from issuance of common stock     $ 2,400,000    
Phase 2B | GENETIC-AF Trial          
Company And Summary Of Significant Accounting Policies Table [Line Items]          
Number of patients enrolled | Patients       267