Annual report pursuant to Section 13 and 15(d)

Investing Receivables (Details)

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Investing Receivables (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Investing receivables $ 52,279 $ 47,875
Notes receivable from City of Huntsville [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Investing receivables $ 49,258 44,875
Notes receivable from City of Huntsville [Member] | LW Redstone Company, LLC [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Stated interest rate (as a percent) 9.95%  
Debt instrument, term 30 years  
Other investing loans receivable [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Investing receivables $ 3,021 $ 3,000