Quarterly report pursuant to Section 13 or 15(d)

Debt Instruments - Convertible Debt Offering Due 2023 (Details)

v3.10.0.1
Debt Instruments - Convertible Debt Offering Due 2023 (Details)
$ / shares in Units, shares in Millions
May 24, 2018
USD ($)
day
$ / shares
shares
Dec. 09, 2015
USD ($)
$ / shares
Sep. 30, 2018
USD ($)
$ / shares
Dec. 31, 2017
USD ($)
Debt Instrument [Line Items]        
Carrying value     $ 255,272,000 $ 273,014,000
Convertible senior notes due 2023        
Debt Instrument [Line Items]        
Debt fees and expenses $ 1,700,000      
Convertible debt | Convertible senior notes due 2020        
Debt Instrument [Line Items]        
Carrying value 192,900,000   $ 127,647,000 273,014,000
Aggregate principal amount 157,400,000 $ 345,000,000.0    
Interest rate   1.75% 1.75%  
Debt instrument, conversion ratio   0.060905    
Debt instrument, conversion price (in dollars per share) | $ / shares   $ 16.42 $ 16.42  
Value of debt   $ 233,500,000 $ 148,700,000  
Debt fees and expenses   2,600,000    
Carrying amount of equity component reported in additional paid-in-capital   $ 103,000,000.0    
Convertible debt | Convertible senior notes due 2023        
Debt Instrument [Line Items]        
Carrying value     $ 127,625,000 $ 0
Aggregate principal amount $ 192,900,000      
Interest rate 1.75%   1.75%  
Debt instrument, conversion ratio 104.4778      
Debt instrument, conversion price (in dollars per share) | $ / shares $ 9.57   $ 9.57  
Debt instrument, redemption price, percentage of principal 100.00%      
Debt conversion, maximum number of shares of common stock convertible by notes (shares) | shares 27.2      
Value of debt $ 124,300,000   $ 222,700,000  
Debt fees and expenses 3,200,000      
Carrying amount of equity component reported in additional paid-in-capital $ 67,300,000      
Convertible debt | Convertible senior notes due 2023 | Redemption period 1        
Debt Instrument [Line Items]        
Debt instrument, threshold percentage of stock price trigger 130.00%      
Debt instrument, threshold trading days | day 20      
Debt instrument, threshold consecutive trading days | day 30      
Convertible debt | Convertible senior notes due 2023 | Redemption period 2        
Debt Instrument [Line Items]        
Debt instrument, threshold percentage of stock price trigger 130.00%      
Debt instrument, threshold trading days | day 20      
Debt instrument, threshold consecutive trading days | day 30      
Convertible debt | Convertible senior notes due 2023 | Redemption period 3        
Debt Instrument [Line Items]        
Debt instrument, threshold note trading days | day 5      
Debt instrument, threshold consecutive note trading days 10 days      
Debt instrument, threshold principle amount of note trigger $ 1,000      
Debt instrument, threshold percentage of note price trigger 98.00%