Derivative Contracts - Derivative Gains (Losses) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gain (loss)	$ 1,396	$ 4,037
Common Stock options/warrants
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gain (loss)	1,671	(955)
Notes
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gain (loss)	0	4,945
Forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gain (loss)	$ (275)	$ 47