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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	$ 2,065	$ (2,341)	$ 3,592	$ (2,220)
Energy derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Electricity sales	1,482	404	(4,071)	4,061
Foreign currency forward contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives	$ 6,736	$ (2,410)	$ 10,869	$ (3,179)