Finite-Lived Intangible Assets and Liabilities and Goodwill - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Mar. 07, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 57,736		$ 57,736		$ 60,300		$ 0
Power Purchase Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	2,500	$ 700	3,900	$ 1,500
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	100	100	200	200
Industrial revenue bond tax savings [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 100	$ 200	$ 300	$ 200
Tsugaru Holdings [Member]
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets						$ 103,170
Finite lived intangible liability						9,252
Goodwill						$ 60,302