XML 17 R1.htm IDEA: XBRL DOCUMENT v3.8.0.1
Document and Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2017
Feb. 28, 2018
Jun. 30, 2017
Document And Entity Information [Abstract]      
Entity Registrant Name MIDDLESEX WATER CO    
Entity Central Index Key 0000066004    
Document Type 10-K    
Document Period End Date Dec. 31, 2017    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Entity a Well-known Seasoned Issuer No    
Entity a Voluntary Filer No    
Entity Reporting Status Current Yes    
Entity Filer Category Accelerated Filer    
Entity Public Float     $ 624,441,708
Entity Common Stock, Shares Outstanding   16,351,940  
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2017