Quarterly report pursuant to Section 13 or 15(d)

Debt and Credit Arrangements (Details)

v3.7.0.1
Debt and Credit Arrangements (Details)
6 Months Ended
Jun. 30, 2017
USD ($)
Dec. 31, 2016
USD ($)
Line of Credit Facility [Line Items]    
Revolving credit facility $ 109,498,000 $ 140,000,000
Revolving Credit Facility [Member] | Line of Credit [Member]    
Line of Credit Facility [Line Items]    
Revolving credit facility 110,000,000 $ 140,000,000
Credit Agreement [Member] | Citibank, National Association [Member]    
Line of Credit Facility [Line Items]    
Aggregate secured revolving credit facility $ 150,000,000.0  
Leverage Ratio 1.52  
Interest Coverage Ratio 20.91  
All-in rate 3.72%  
Credit Agreement [Member] | Citibank, National Association [Member] | Federal Funds Rate    
Line of Credit Facility [Line Items]    
Interest rate 0.50%  
Credit Agreement [Member] | Citibank, National Association [Member] | LIBOR rate    
Line of Credit Facility [Line Items]    
Interest rate 1.00%  
Credit Agreement [Member] | Citibank, National Association [Member] | Maximum [Member]    
Line of Credit Facility [Line Items]    
Leverage Ratio 2.75  
Credit Agreement [Member] | Citibank, National Association [Member] | Maximum [Member] | LIBOR rate    
Line of Credit Facility [Line Items]    
Interest rate 275.00%  
Credit Agreement [Member] | Citibank, National Association [Member] | Minimum [Member]    
Line of Credit Facility [Line Items]    
Interest Coverage Ratio 1.75  
Credit Agreement [Member] | Citibank, National Association [Member] | Minimum [Member] | LIBOR rate    
Line of Credit Facility [Line Items]    
Interest rate 175.00%