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Borrowings (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Line of Credit Facility [Line Items]      
Interest income $ 521 $ 482 $ 1,285
Interest expense 2,011 1,227 $ 3,425
Capitalized leases $ 8,187    
Revolving Credit Facility [Member]      
Line of Credit Facility [Line Items]      
Credit Agreement initiation date Oct. 10, 2014    
Credit Agreement aggregate principal amount $ 150,000    
Credit Agreement term 5 years    
Credit Agreement optional increase in aggregate principal amount $ 75,000    
Credit Agreement maturity date Oct. 10, 2019    
Credit Agreement maximum consolidated total leverage ratio 3.00    
Credit Agreement minimum interest coverage ratio 3.50    
Credit Agreement availability $ 150,000    
Credit Agreement maximum cash dividends in a fiscal year 30,000    
Credit Agreement outstanding balance $ 0 $ 0  
Revolving Credit Facility [Member] | Federal Funds Open Rate [Member]      
Line of Credit Facility [Line Items]      
Credit Agreement applicable margin 0.50%    
Revolving Credit Facility [Member] | LIBOR Rate [Member]      
Line of Credit Facility [Line Items]      
Credit Agreement applicable margin 1.00%    
Senior Convertible Notes [Member]      
Line of Credit Facility [Line Items]      
Interest rate   5.50% 5.50%
Minimum [Member] | Revolving Credit Facility [Member]      
Line of Credit Facility [Line Items]      
Credit Agreement quarterly commitment fee percentage 0.20%    
Minimum [Member] | Revolving Credit Facility [Member] | Leverage Ratio [Member]      
Line of Credit Facility [Line Items]      
Credit Agreement applicable margin 0.25%    
Minimum [Member] | Revolving Credit Facility [Member] | LIBOR Rate Plus Levarage Ratio [Member]      
Line of Credit Facility [Line Items]      
Credit Agreement applicable margin 1.25%    
Maximum [Member] | Revolving Credit Facility [Member]      
Line of Credit Facility [Line Items]      
Credit Agreement quarterly commitment fee percentage 0.25%    
Maximum [Member] | Revolving Credit Facility [Member] | Leverage Ratio [Member]      
Line of Credit Facility [Line Items]      
Credit Agreement applicable margin 0.50%    
Maximum [Member] | Revolving Credit Facility [Member] | LIBOR Rate Plus Levarage Ratio [Member]      
Line of Credit Facility [Line Items]      
Credit Agreement applicable margin 1.50%