Derivative Instruments - Summary of Effects of Undesignated Derivatives on Consolidated Statements of Operations (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Interest Rate Contract [Member] | Change in Fair Value, Net of Settlement [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss on undesignated derivatives, net	$ (1,477)	$ (3,937)	$ (387)	$ (12,818)
Interest Rate Contract [Member] | Derivative Settlement [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss on undesignated derivatives, net	(864)	(1,280)	(1,833)	(2,606)
Energy derivative [Member] | Change in Fair Value, Net of Settlement [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Electricity sales	(4,663)	(9,327)	(7,021)	(14,152)
Energy derivative [Member] | Derivative Settlement [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Electricity sales	5,067	6,752	11,082	13,485
Foreign currency forward contracts [Member] | Change in Fair Value, Net of Settlement [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss on undesignated derivatives, net	(1,752)	(654)	(2,845)	(4,615)
Foreign currency forward contracts [Member] | Derivative Settlement [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss on undesignated derivatives, net	$ (658)	$ (8)	$ (334)	$ 529