Annual report pursuant to Section 13 and 15(d)

Borrowings (Credit Facility) (Narrative) (Details)

v3.6.0.2
Borrowings (Credit Facility) (Narrative) (Details) - USD ($)
$ in Thousands
12 Months Ended
Jul. 13, 2016
Dec. 31, 2016
Nov. 21, 2016
Dec. 31, 2015
Mar. 11, 2014
Line of Credit Facility [Line Items]          
Debt instrument outstanding   $ 400,000   $ 340,000  
Senior Secured Revolving Credit Facility [Member]          
Line of Credit Facility [Line Items]          
Maximum borrowing capacity     $ 500,000   $ 500,000
Current borrowing capacity $ 385,000 $ 385,000      
Increase in interest rate on credit facility   0.25%      
Interest rate at period end (as a percent)   2.60%      
Debt instrument outstanding       $ 40,000  
Outstanding balance on credit facility   $ 0      
Unused capacity, commitment fee (as a percent)   0.50%      
Credit facility 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 2.00% 2.00%      
Senior Secured Revolving Credit Facility [Member] | Maximum [Member] | LIBOR [Member]          
Line of Credit Facility [Line Items]          
Debt instrument interest rate 3.00% 3.00%