Quarterly report pursuant to Section 13 or 15(d)

Debt Instruments - Convertible Debt Offering (Details)

v3.8.0.1
Debt Instruments - Convertible Debt Offering (Details)
Dec. 09, 2015
USD ($)
$ / shares
Mar. 31, 2018
USD ($)
$ / shares
Debt Instruments    
Share price (in dollars per share) | $ / shares   $ 5.03
Convertible debt | Notes    
Debt Instruments    
Aggregate principal amount $ 345,000,000.0  
Interest rate 1.75% 1.75%
Net proceeds from sale of debt $ 336,500,000  
Payments for capped call transactions $ 43,200,000  
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 $ 316,600,000
Carrying amount of equity component reported in additional paid-in-capital 103,000,000.0  
Debt fees and expenses $ 2,600,000