Derivative Contracts - Derivative Gains (Losses) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gain (loss)	$ (155)	$ (7,550)	$ 3,489	$ 1,969
Common Stock options/warrants
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gain (loss)	(288)	(342)	3,299	(854)
Notes
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gain (loss)	0	(6,829)	0	3,185
Forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative gain (loss)	$ 133	$ (379)	$ 190	$ (362)