Quarterly report pursuant to Section 13 or 15(d)

Assets and Liabilities Measured at Fair Value (Details)

v3.10.0.1
Assets and Liabilities Measured at Fair Value (Details)
$ in Thousands
 1 Months Ended
Aug. 31, 2018
USD ($)
shares
Jun. 30, 2018
USD ($)
shares
Apr. 30, 2018
USD ($)
shares
Sep. 30, 2018
USD ($)
item
shares
Dec. 31, 2017
USD ($)
Recurring          
Assets and Liabilities Measured at Fair Value          
Cash equivalents | $       $ 28,335 $ 76,304
Derivative Asset | $       50,000  
Zero-strike call option          
Assets and Liabilities Measured at Fair Value          
Derivative settlement proceeds | $   $ 46,500      
Level 1 | Recurring          
Assets and Liabilities Measured at Fair Value          
Cash equivalents | $       28,335 $ 76,304
Level 2 | Recurring          
Assets and Liabilities Measured at Fair Value          
Derivative Asset | $       $ 50,000  
Minimum | Volatility          
Level 2 input          
Derivative Measurement Input | item       0.202  
Minimum | Interest Rate          
Level 2 input          
Derivative Measurement Input | item       0.010  
Minimum | Dividend Yield          
Level 2 input          
Derivative Measurement Input | item       0  
Maximum | Volatility          
Level 2 input          
Derivative Measurement Input | item       0.380  
Maximum | Interest Rate          
Level 2 input          
Derivative Measurement Input | item       0.023  
Maximum | Dividend Yield          
Level 2 input          
Derivative Measurement Input | item       0  
Series C common stock | Zero-strike call option | Call Option          
Assets and Liabilities Measured at Fair Value          
Derivative underlying share amount | shares 621,920 632,911 610,325 621,920  
Derivative premium paid | $ $ 48,600   $ 47,800