XML 55 R41.htm IDEA: XBRL DOCUMENT v3.3.1.900
Common Stock and Preferred Stock - Additional Information (Detail) - USD ($)
 3 Months Ended 12 Months Ended
Jan. 26, 2016
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Class of Stock [Line Items]        
Common stock, shares outstanding   14,043,280 13,966,150 13,991,430
Common stock, shares issued   8,630 10,114  
Proceeds from Issuance of Common Stock   $ 300,000 $ 300,000  
Share based compensation expense   $ 1,600,000 1,300,000  
Percentage of fully-vested restricted stock units that directors will receive in common shares when settled   70.00%    
Percentage of fully-vested restricted stock units that directors will receive in cash when settled   30.00%    
Fair value of liabilities associated with fully vested RSUs that will be settled in cash   $ 600,000 400,000 $ 500,000
Preferred Stock   200,000 200,000 $ 200,000
Maximum        
Class of Stock [Line Items]        
Dividend declared   100,000 $ 100,000  
Dividend and Distribution Reinvestment and Share Purchase Plan        
Class of Stock [Line Items]        
Proceeds from Issuance of Common Stock   $ 338,000    
Dividend and Distribution Reinvestment and Share Purchase Plan | Average        
Class of Stock [Line Items]        
Common stock price per share   $ 39.19    
Dividend and Distribution Reinvestment and Share Purchase Plan | Common Stock        
Class of Stock [Line Items]        
Common stock, shares issued   8,630    
Unitil Energy Systems Inc | Series 6        
Class of Stock [Line Items]        
Preferred stock, outstanding   1,898 2,250 1,898
Preferred Stock   $ 200,000 $ 200,000 $ 200,000
Dividend rate   6.00% 6.00% 6.00%
Restricted Stock        
Class of Stock [Line Items]        
Restricted stock vesting period   4 years    
Restricted stock non-vested   94,706 81,251  
Restricted stock weighted average grant date fair value   $ 35.24 $ 33.15  
Unrecognized share based compensation   $ 1,700,000    
Share compensation recognition period   2 years 10 months 24 days    
Forfeitures or cancellations under the stock plan   0    
Restricted Shares issued 43,220      
Aggregate Market Value $ 1,600,000      
Restricted Stock | Maximum        
Class of Stock [Line Items]        
Restricted stock available for awards   677,500    
Restricted stock that may be awarded in any one calendar year to any one participant   20,000    
Restricted Stock | Vesting Annually        
Class of Stock [Line Items]        
Restricted stock vesting percentage annually   25.00%    
Restricted Stock Units (RSUs)        
Class of Stock [Line Items]        
Restricted Shares issued   0    
Restricted stock units outstanding     23,819  
Weighted-Average Stock Price     $ 29.94