Annual report pursuant to Section 13 and 15(d)

Debt (Details)

v3.8.0.1
Debt (Details)
 1 Months Ended 12 Months Ended
Feb. 28, 2018
Jan. 31, 2018
USD ($)
bank
Dec. 31, 2017
USD ($)
bank
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Debt Instrument [Line Items]          
Deferred financing costs     $ 1,100,000 $ 1,700,000  
Long-term Debt, Fiscal Year Maturity [Abstract]          
Number of banks | bank     6    
Amended and Restated          
Debt Instrument [Line Items]          
Revolving loans, potential increment in maximum borrowing capacity     $ 75,000,000    
Duration of interest rate cash flow hedge     3 years    
Derivative, notional amount     $ 85,000,000    
Effective interest rate     3.66%    
Interest expense, net     $ 7,200,000 7,800,000 $ 7,300,000
Long-term Debt, Fiscal Year Maturity [Abstract]          
Debt outstanding     $ 173,700,000 216,300,000  
Amended and Restated | LIBOR          
Debt Instrument [Line Items]          
Base margin     2.00%    
Amended and Restated | Base Rate          
Debt Instrument [Line Items]          
Base margin     0.75%    
Revolving Loans          
Debt Instrument [Line Items]          
Revolving loans maximum borrowing capacity     $ 150,000,000    
Revolving loans amount outstanding     79,300,000 100,000,000  
Letters of credit outstanding     $ 0 $ 0  
Minimum | Amended and Restated          
Debt Instrument [Line Items]          
Stated interest rate     3.25%    
Maximum | Amended and Restated          
Debt Instrument [Line Items]          
Stated interest rate     5.25%    
Subsequent Event          
Long-term Debt, Fiscal Year Maturity [Abstract]          
Number of banks | bank   9      
Ratio of indebtedness to net capital   3.0      
Subsequent Event | Amended and Restated          
Debt Instrument [Line Items]          
Revolving loans, potential increment in maximum borrowing capacity   $ 100,000,000      
Duration of interest rate cash flow hedge   3 years      
Long-term Debt, Fiscal Year Maturity [Abstract]          
Extension on duration of interest rate cash flow hedge 3 years        
Subsequent Event | Amended and Restated | LIBOR          
Debt Instrument [Line Items]          
Base margin   1.75%      
Subsequent Event | Amended and Restated | Base Rate          
Debt Instrument [Line Items]          
Base margin   0.50%      
Subsequent Event | Term Loan          
Long-term Debt, Fiscal Year Maturity [Abstract]          
2018   $ 7,500,000      
2019   10,000,000      
2020   11,900,000      
2021   14,400,000      
2022   15,000,000      
2023   41,200,000      
Debt outstanding   100,000,000      
Subsequent Event | Revolving Loans          
Debt Instrument [Line Items]          
Revolving loans maximum borrowing capacity   $ 300,000,000