Annual report pursuant to Section 13 and 15(d)

Debt (CredAg) (Details)

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Debt (CredAg) (Details) - USD ($)
$ in Thousands
12 Months Ended
Nov. 19, 2015
Dec. 31, 2017
Jul. 18, 2017
Dec. 31, 2016
Jun. 19, 2014
Debt          
Amount outstanding   $ 81,168      
Credit Agreement          
Debt          
Credit facility amount         $ 70,000
Voting equity of foreign subsidiary pledged (as a percent) 66.00%        
Non-voting equity of foreign subsidiary pledged (as a percent) 100.00%        
Commitment fee   0.25%      
Amount outstanding   $ 81,168      
Credit Agreement | Other non-current assets          
Debt          
Debt issuance cost, outstanding   3,106      
Term Notes          
Debt          
Face amount       $ 142,000  
Second Amended and Restated Credit Agreement          
Debt          
Credit facility amount     $ 350,000    
Right to increase credit facility, amount     50,000    
Second Amended and Restated Credit Agreement | Prepaid expense and other current assets          
Debt          
Debt issuance cost, outstanding   $ 855      
Letters of credit          
Debt          
Credit facility amount     $ 5,000   $ 5,000
Minimum | Credit Agreement | LIBOR          
Debt          
Spread on variable rate basis (as a percent) 1.50%        
Maximum | Credit Agreement | LIBOR          
Debt          
Spread on variable rate basis (as a percent) 3.25%