Annual report pursuant to Section 13 and 15(d)

Borrowings (Senior secured revolving credit facility ) (Narrative) (Details)

v3.3.1.900
Borrowings (Senior secured revolving credit facility ) (Narrative) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Mar. 11, 2014
Line of Credit Facility [Line Items]      
Senior secured revolving credit facility $ 40,000 $ 35,000  
Senior Secured Revolving Credit Facility [Member]      
Line of Credit Facility [Line Items]      
Maximum borrowing capacity     $ 500,000
Current borrowing capacity 300,000    
Senior secured revolving credit facility $ 40,000    
Interest rate at period end (as a percent) 2.07%    
Unused capacity, commitment fee (as a percent) 0.50%    
Remaining borrowing capacity $ 260,000    
Debt instrument maturity date Mar. 11, 2019    
Senior Secured Revolving Credit Facility [Member] | Minimum [Member] | LIBOR [Member]      
Line of Credit Facility [Line Items]      
Debt instrument interest rate 1.75%    
Senior Secured Revolving Credit Facility [Member] | Maximum [Member] | LIBOR [Member]      
Line of Credit Facility [Line Items]      
Debt instrument interest rate 2.75%