Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Energy Assets and Asset Retirement Obligations (Details)

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Summary of Significant Accounting Policies - Energy Assets and Asset Retirement Obligations (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Accounting Policies [Abstract]          
Interest costs capitalized $ 925,000 $ 289,000 $ 3,452,000 $ 616,000  
Property, Plant and Equipment [Line Items]          
Capital lease assets, net 4,830,000   $ 4,830,000   $ 5,018,000
Minimum qualifying operating period for prorated repayments of grants     5 years    
Deferred grant income 7,326,000   $ 7,326,000   7,739,000
Asset retirement obligation         0
Assets Held under Capital Leases          
Property, Plant and Equipment [Line Items]          
Capital lease assets 30,430,000   30,430,000   15,640,000
Less - accumulated depreciation and amortization $ (1,630,000)   $ (1,630,000)   $ (744,000)