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DEBT - CREDIT AGREEMENT (Details)
1 Months Ended 3 Months Ended
Dec. 31, 2017
USD ($)
Apr. 30, 2016
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Mar. 31, 2018
USD ($)
Credit Agreement          
Credit Agreement          
Maximum borrowing capacity     $ 100,000,000    
Amount of additional borrowings by which maximum borrowing capacity may be increased $ 100,000,000        
Outstanding borrowings     0   $ 0
Credit Agreement Availability          
Minimum liquidity level allowing unrestricted access to the Credit Agreement $ 300,000,000        
Available borrowings     98,334,000   98,355,000
Outstanding letters of credit     1,664,000   $ 1,664,000
Interest expense and fees     $ 110,000 $ 110,000  
Trailing period for measurement of interest coverage ratio   12 months      
Maximum liquidity level triggering the requirement to maintain an interest coverage ratio of one to one   $ 30,000,000      
Credit Agreement | Minimum          
Credit Agreement          
Monthly fee on unused available balance (as a percent) 0.25%        
Credit Agreement Availability          
Interest coverage ratio   1      
Credit Agreement | Maximum          
Credit Agreement          
Monthly fee on unused available balance (as a percent) 0.375%        
Credit Agreement | Base rate          
Credit Agreement          
Interest rate, variable rate basis base rate        
Interest rate at end of period     5.00%    
Credit Agreement | Base rate | Minimum          
Credit Agreement          
Interest rate added to base rate 0.25%        
Credit Agreement | Base rate | Maximum          
Credit Agreement          
Interest rate added to base rate 0.75%        
Credit Agreement | LIBOR          
Credit Agreement          
Interest rate, variable rate basis LIBOR        
Interest rate at end of period     2.09%    
Credit Agreement | LIBOR | Minimum          
Credit Agreement          
Interest rate added to base rate 1.25%        
Credit Agreement | LIBOR | Maximum          
Credit Agreement          
Interest rate added to base rate 1.75%        
Letter of Credit          
Credit Agreement          
Maximum borrowing capacity     $ 5,000,000