Annual report pursuant to Section 13 and 15(d)

DEBT (Details)

v3.8.0.1
DEBT (Details)
12 Months Ended
Dec. 31, 2017
USD ($)
extension
Oct. 31, 2012
USD ($)
Revolving Credit Agreement    
Short-term Debt [Line Items]    
Maximum borrowing capacity   $ 175,000,000.0
Number of anniversaries for optional annual extensions of the credit agreement | extension 3  
Period of extension 1 year  
Amount outstanding $ 0  
Number of options available for calculating variable interest rate | extension 2  
Letter of credit subfacility    
Short-term Debt [Line Items]    
Maximum borrowing capacity   75,000,000.0
Letter of credit amount maintained $ 29,400,000  
Swingline subfacility    
Short-term Debt [Line Items]    
Maximum borrowing capacity   $ 25,000,000.0
Amount outstanding $ 0  
Federal Funds rate    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 0.50%  
Adjusted LIBOR rate    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 1.00%  
Eurodollar borrowings, Adjusted LIBOR    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 0.75%  
Minimum | Eurodollar borrowings, Adjusted LIBOR    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 0.75%  
Maximum | Eurodollar borrowings, Adjusted LIBOR    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 1.00%