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Debt - Conversion and Earnings Per Share Impact (Details)
1 Months Ended 3 Months Ended 12 Months Ended
Nov. 27, 2017
USD ($)
Mar. 31, 2017
USD ($)
Dec. 31, 2013
d
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2012
USD ($)
Debt Instrument [Line Items]              
Convertible notes settled by cash payment       $ 125,407,000 $ 0 $ 0  
Convertible senior notes sold       483,500,000 448,500,000    
Total consideration allocated to re-acquisition of equity component       1,532,000 $ 1,280,000    
2017 Convertible Senior Notes              
Debt Instrument [Line Items]              
Convertible debt, threshold percentage of stock price trigger (exceeded)     130.00%        
Convertible debt, threshold trading days (more than) | d     20        
Convertible debt, threshold consecutive trading days | d     30        
2017 Convertible Senior Notes | Secured Debt              
Debt Instrument [Line Items]              
Gain (loss) on debt conversion       $ 0      
Convertible Notes | 2017 Convertible Senior Notes              
Debt Instrument [Line Items]              
Convertible notes settled by cash payment $ 65,000,000 $ 60,400,000          
Convertible senior notes sold   50,000,000.0         $ 115,000,000.0
Extinguishment of liability component   49,700,000          
Total consideration allocated to re-acquisition of equity component   10,700,000          
Carrying value of repurchased notes   48,900,000.0          
Loss recognized on repurchase transaction   $ (800,000)