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Organization (Details)
3 Months Ended 12 Months Ended
Mar. 31, 2019
USD ($)
segment
$ / shares
Mar. 31, 2018
USD ($)
Dec. 31, 2018
USD ($)
$ / shares
shares
Nov. 13, 2018
USD ($)
Jan. 16, 2018
USD ($)
Restructuring Cost and Reserve [Line Items]          
Number of operating segments | segment 1        
Proceeds from borrowings on senior secured convertible notes (related party) $ 0 $ 85,000,000      
Common stock, par value (in dollars per share) | $ / shares $ 0.001   $ 0.001    
Convertible senior notes          
Restructuring Cost and Reserve [Line Items]          
Face value of senior secured convertible notes $ 204,000,000   $ 204,000,000    
Convertible senior notes | Initial Notes | Starboard Value LP          
Restructuring Cost and Reserve [Line Items]          
Face value of senior secured convertible notes     204,000,000.0    
Proceeds from borrowings on senior secured convertible notes (related party)     $ 100,000,000    
Converted shares issued (in shares) | shares     4,000,000    
Debt instrument, debt covenant, minimum cash balance       $ 20,000,000.0  
Convertible senior notes | Right Offering Notes | Starboard Value LP          
Restructuring Cost and Reserve [Line Items]          
Backstop reduced by the amount of option notes purchased         $ 50,000,000.0
Convertible senior notes | Right Offering Notes | Minimum | Starboard Value LP          
Restructuring Cost and Reserve [Line Items]          
Right to increase borrowing         35,000,000.0
Increase borrowing limit in cash if conversion is fully subscribed         105,000,000.0
Convertible senior notes | Right Offering Notes | Maximum | Starboard Value LP          
Restructuring Cost and Reserve [Line Items]          
Additional borrowing option         $ 150,000,000.0
Debt convenant, period one | Convertible senior notes | Initial Notes | Starboard Value LP          
Restructuring Cost and Reserve [Line Items]          
Debt instrument, debt covenant, minimum cash balance 20,000,000   $ 20,000,000.0    
Debt convenant, period two | Convertible senior notes | Initial Notes | Starboard Value LP          
Restructuring Cost and Reserve [Line Items]          
Debt instrument, debt covenant, minimum cash balance $ 40,000,000.0   $ 40,000,000.0