Annual report pursuant to Section 13 and 15(d)

Debt (Conv) (Details)

v3.10.0.1
Debt (Conv) (Details)
 1 Months Ended 12 Months Ended
May 25, 2018
USD ($)
days
$ / shares
Dec. 15, 2014
USD ($)
days
$ / shares
May 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
$ / shares
Dec. 31, 2017
USD ($)
$ / shares
Dec. 31, 2016
USD ($)
Sep. 30, 2018
Dec. 31, 2014
USD ($)
Debt Instrument [Line Items]                
Face amount   $ 172,500,000            
Net proceeds from offering   $ 166,967,000            
Interest rate (as a percent)   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            
Threshold trading days (in days) | days   20            
Consecutive trading days | days   30            
Threshold percentage of stock price trigger (as a percent)   130.00%            
Threshold business days   5 days            
Threshold consecutive trading-day period 5 days 5 days            
Threshold percentage of trading price trigger (as a percent) 98.00% 98.00%            
Allocated to equity components $ 46,611,000 $ 26,618,000            
Offering costs 1,389,000 882,000            
Discount 48,000,000 $ 27,500,000            
Effective interest rate (as a percent)       6.00% 6.00% 6.00%    
Other non-current assets                
Debt Instrument [Line Items]                
Issuance costs               $ 4,651,000
Convertible Notes                
Debt Instrument [Line Items]                
Face amount       $ 172,500,000 $ 172,500,000      
Interest rate (as a percent)   1.75%            
Conversion price (in dollars per share) | $ / shares       $ 68.31 $ 62.88      
Discount       $ 5,890,000 $ 11,677,000      
Accretion of debt discount       5,690,000 5,472,000 $ 5,237,000    
Convertible Notes Due 2023                
Debt Instrument [Line Items]                
Face amount $ 345,000,000     345,000,000 0      
Net proceeds from offering     $ 335,018,000          
Interest rate (as a percent) 1.75%              
Issuance costs       8,593,000        
Repurchase percentage of principal (as a percent) 100.00%              
Conversion rate 0.0146381              
Principal amount | $ / shares $ 1,000              
Conversion price (in dollars per share) | $ / shares $ 68.31              
Threshold trading days (in days) | days 20              
Consecutive trading days | days 30              
Threshold percentage of stock price trigger (as a percent) 130.00%              
Discount       42,641,000 $ 0      
Accretion of debt discount       $ 5,444,000        
Effective interest rate (as a percent)             6.00%