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Organization and Description of Business (Details) - USD ($)
$ / shares in Units, $ in Thousands
6 Months Ended
Jul. 26, 2018
May 08, 2018
Jun. 30, 2018
Jun. 30, 2019
Dec. 31, 2018
Convertible Senior Notes          
Net proceeds from offering     $ 279,126    
2025 Notes          
Convertible Senior Notes          
Face amount   $ 287,500   $ 287,500 $ 287,500
Interest rate (as a percent)   1.375%      
Net proceeds from offering   $ 279,100      
Offering costs   $ 8,400      
Follow-On Offering          
Follow-On Offering          
Issuance of stock (in shares) 5,000,000        
Price of stock issued (in dollars per share) $ 66.28        
Proceeds received, net of issuance costs $ 330,900        
Offering expenses $ 500