Annual report pursuant to Section 13 and 15(d)

Derivative Contracts - Losses and Gains on Derivative Instruments (Details)

v3.8.0.1
Derivative Contracts - Losses and Gains on Derivative Instruments (Details) - Not Designated as Hedging Instrument - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (loss) on derivative instruments $ 52 $ 2,778 $ (39,083)
Common stock options/warrants      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (loss) on derivative instruments (2,533) (4,262) (2,854)
2033 Senior Notes      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (loss) on derivative instruments 3,185 7,001 (36,588)
Forward contracts      
Derivative Instruments, Gain (Loss) [Line Items]      
Gain (loss) on derivative instruments $ (600) $ 39 $ 359