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