Annual report pursuant to Section 13 and 15(d)

Debt - 2014 Credit Facility (Details)

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Debt - 2014 Credit Facility (Details)
9 Months Ended 12 Months Ended
Sep. 30, 2014
USD ($)
Dec. 31, 2016
USD ($)
Feb. 28, 2017
USD ($)
Sep. 30, 2016
USD ($)
Feb. 29, 2016
USD ($)
Dec. 31, 2015
USD ($)
Line of Credit Facility [Line Items]            
Interest coverage ratio 3.00          
Revolving facility   $ 0       $ 40,000,000
Consolidated net coverage ratio following permitted acquisition 3.50          
Revolving line of credit facility borrowed   $ 40,000,000        
Weighted-average interest rate   1.75%       1.58%
Revolving line of credit facility, available borrowing capacity   $ 200,000,000        
Issuance of letters of credit outstanding, amount   10,000,000        
Unamortized debt issuance costs   1,300,000       $ 1,000,000
Permitted Acquisition            
Line of Credit Facility [Line Items]            
Consolidated net coverage ratio following permitted acquisition 3.75          
Revolving Credit Facility            
Line of Credit Facility [Line Items]            
Aggregate principal amount $ 200,000,000          
Additional borrowing capacity $ 150,000,000          
Revolving facility   $ 0        
Consolidated net coverage ratio following permitted acquisition 3.25          
Revolving Credit Facility | LIBOR | Minimum            
Line of Credit Facility [Line Items]            
Basis spread on variable rate 1.25% 1.25%        
Revolving Credit Facility | LIBOR | Maximum            
Line of Credit Facility [Line Items]            
Basis spread on variable rate 2.00% 1.75%        
Revolving Credit Facility | Base Rate | Minimum            
Line of Credit Facility [Line Items]            
Basis spread on variable rate 0.25% 0.25%        
Revolving Credit Facility | Base Rate | Maximum            
Line of Credit Facility [Line Items]            
Basis spread on variable rate 1.00% 0.75%        
Revolving Credit Facility | Federal Funds Rate            
Line of Credit Facility [Line Items]            
Basis spread on variable rate 0.50%          
Revolving Credit Facility | One-Month LIBOR            
Line of Credit Facility [Line Items]            
Basis spread on variable rate 1.00%          
Standby Letters of Credit            
Line of Credit Facility [Line Items]            
Sub limit for issuance of letters of credit $ 10,000,000          
Swingline Loan            
Line of Credit Facility [Line Items]            
Sub limit for issuance of letters of credit $ 20,000,000          
Revolving line of credit facility, available borrowing capacity   $ 20,000,000        
Term Loan, Amendment            
Line of Credit Facility [Line Items]            
Additional borrowing capacity       $ 25,000,000    
Line of Credit | Term Loan, Amendment            
Line of Credit Facility [Line Items]            
Aggregate principal amount         $ 125,000,000  
Gross debt issuance costs         $ 700,000  
Line of Credit | Term Loan, Amendment | Base Rate            
Line of Credit Facility [Line Items]            
Consolidated net coverage ratio following permitted acquisition         4.00  
Convertible Debt | Term Loan, Amendment            
Line of Credit Facility [Line Items]            
Debt instrument, face amount         $ 150,000,000.0  
Term Loan            
Line of Credit Facility [Line Items]            
Revolving facility   122,600,000        
Long-term Debt, Fiscal Year Maturity [Abstract]            
2017   5,469,000        
2018   6,250,000        
2019   110,918,000        
Total Long-term Debt   122,637,000        
Term Loan | Term Loan, Amendment            
Line of Credit Facility [Line Items]            
Unamortized debt issuance costs   $ 500,000        
Subsequent Event | Revolving Credit Facility            
Line of Credit Facility [Line Items]            
Aggregate principal amount     $ 522,646,000      
Subsequent Event | Term Loan, Amendment            
Line of Credit Facility [Line Items]            
Additional borrowing capacity     $ 200,000,000