Quarterly report pursuant to Section 13 or 15(d)

Debt and Interest Rate Swap (Details)

v3.10.0.1
Debt and Interest Rate Swap (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended 17 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Dec. 31, 2017
Nov. 03, 2017
May 12, 2017
Dec. 31, 2016
Debt Instrument [Line Items]                  
Debt Instrument, Unamortized Discount $ (2,100)   $ (2,100)   $ (2,100)        
Long-term debt 270,470   270,470   270,470 $ 347,609      
Line of Credit Facility, Incremental Borrowing Capacity $ 160,000   $ 160,000   $ 160,000        
Debt Instrument, Frequency of Periodic Payment     quarterly installments            
Debt Instrument, Quarterly Amortization Rate 0.25%   0.25%   0.25%        
Debt Instrument, Term     7 years            
Debt Instrument, Call Feature     1.0% soft call premium            
Debt Instrument, Soft Call Premium Rate     1.00%            
Repayments of Debt         $ 148,000        
Debt Instrument, Interest Rate, Effective Percentage 4.60%   4.60%   4.60% 4.10%      
Long-term Debt, Fair Value $ 265,800   $ 265,800   $ 265,800 $ 360,000   $ 398,500  
Debt Instrument, Interest Rate, Basis for Effective Rate     4.60%            
Debt Issuance Costs, Gross 6,000   $ 6,000   6,000        
Amortization of debt issuance costs and discount 300 $ 300 861 $ 476          
Debt Instrument, Annual Principal Payment $ 277,000   $ 277,000   $ 277,000 355,000      
Derivative, Fixed Interest Rate 4.25%   4.25%   4.25%   1.74685%    
Derivative Asset $ 2,452 $ 0 $ 2,452 0 $ 2,452 734     $ 0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Other Comprehensive Income (Loss) 0   $ 1,718 $ 0          
Base Rate [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate Terms     a base rate            
Debt Instrument, Basis Spread on Variable Rate     1.50%            
Federal Funds Effective Swap Rate [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate Terms     the federal funds rate, plus 0.50%            
Debt Instrument, Basis Spread on Variable Rate     0.50%            
Prime Rate [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate Terms     prime rate            
One, Two, Or Three Month London Interbank Offered Rate (LIBOR) [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate Terms     an adjusted LIBOR rate determined on the basis of a one- three- or six-month interest period, plus 1.0%            
Debt Instrument, Basis Spread on Variable Rate     1.00%            
London Interbank Offered Rate (LIBOR) Subject to Floor [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Interest Rate Terms     adjusted LIBOR rate, subject to a floor of 0.75%            
Debt Instrument, Basis Spread on Variable Rate     2.50%            
Debt Instrument, Variable Rate Basis Floor     0.75%            
London Interbank Offered Rate (LIBOR) [Member]                  
Debt Instrument [Line Items]                  
Debt Instrument, Basis Spread on Variable Rate     2.50%            
Medium-term Notes [Member]                  
Debt Instrument [Line Items]                  
Long-term Debt, Gross 277,000   $ 277,000   277,000 355,000   $ 425,000  
Debt Instrument, Unamortized Discount (1,705)   (1,705)   (1,705) (1,930)      
Debt Issuance Costs, Net (4,825)   (4,825)   (4,825) (5,461)      
Long-term Debt 270,470   270,470   270,470 347,609      
Long-term Debt, Current Maturities 0   0   0 0      
Long-term debt 270,470   270,470   270,470 347,609      
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Derivative Financial Instruments, Assets [Member]                  
Debt Instrument [Line Items]                  
Derivative Asset $ 2,452   $ 2,452   $ 2,452 $ 734