Annual report pursuant to Section 13 and 15(d)

Debt - Convertible Debt Narrative (Details)

v3.8.0.1
Debt - Convertible Debt Narrative (Details)
$ / shares in Units, $ in Thousands
12 Months Ended
May 23, 2017
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
day
tradingdays
shares
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
May 31, 2017
USD ($)
Debt Instrument [Line Items]          
Proceeds from borrowings on convertible senior notes   $ 345,000 $ 0 $ 0  
Convertible notes, net   281,199 0    
Proceeds from issuance of warrants $ 31,500 31,499 $ 0 $ 0  
Number of securities called by warrants (in shares) | shares 8,200,000        
Purchases of convertible note hedges $ 62,500 $ 62,549      
Exercise price of warrants (in dollars per share) | $ / shares $ 57.58        
Warrants exercised (in shares) | shares   0      
Maximum          
Debt Instrument [Line Items]          
Number of securities called by warrants (in shares) | shares 8,200,000        
Convertible Notes          
Debt Instrument [Line Items]          
Proceeds from borrowings on convertible senior notes $ 304,200        
Convertible Notes | Convertible Senior Notes Due November 2022          
Debt Instrument [Line Items]          
Principal amount   $ 345,000     $ 345,000
Interest rate stated percentage 1.50%        
Conversion ratio (in shares)   0.02384      
Conversion price (in dollars per share) | $ / shares $ 41.95        
Threshold trading days | day   20      
Threshold consecutive trading days | day   30      
Measurement period threshold trading days | tradingdays   5      
Measurement period threshold consecutive trading days | day   5      
Redemption price   100.00%      
Convertible notes, net   $ 281,199     282,500
Equity component, net of issuance costs and deferred tax:   $ 61,390     62,500
Gross debt issuance costs         9,800
Convertible Notes | Convertible Senior Notes Due November 2022 | Minimum          
Debt Instrument [Line Items]          
Threshold percentage of stock price trigger   130.00%      
Ratio of trading price per $1000 principle amount   98.00%      
Percentage of debt held by individual owner   25.00%      
Convertible Notes | Over-Allotment Option          
Debt Instrument [Line Items]          
Principal amount         $ 45,000