Annual report pursuant to Section 13 and 15(d)

Debt (Conv) (Details)

v3.8.0.1
Debt (Conv) (Details) - Convertible Notes
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 15, 2014
USD ($)
item
$ / shares
Dec. 31, 2017
USD ($)
$ / shares
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Debt          
Face amount $ 172,500 $ 172,500 $ 172,500    
Net proceeds from offering $ 166,967        
Interest rate (as a percent) 1.75% 1.75%      
Repurchase percentage of principal (as a percent) 100.00%        
Conversion rate 0.0159022        
Principal amount | $ / shares $ 1,000        
Conversion price (in dollars per share) | $ / shares $ 62.88 $ 62.88      
Threshold trading days (in days) | item 20        
Consecutive trading days | item 30        
Threshold percentage of stock price trigger (as a percent) 130.00%        
Threshold business days 5 days        
Threshold consecutive trading-day period 5 days        
Threshold percentage of trading price trigger (as a percent) 98.00%        
Allocated to equity components $ 26,618        
Offering costs 882        
Discount $ 27,500 $ 11,677 17,149    
Accretion of debt discount   $ 5,472 $ 5,237 $ 4,932  
Effective interest rate (as a percent)   6.00% 6.00% 6.00%  
Other non-current assets          
Debt          
Issuance costs         $ 4,651