Quarterly report pursuant to Section 13 or 15(d)

Investing Receivables (Details)

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Investing Receivables (Details) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Investing receivables $ 53,570 $ 52,279
Notes Receivable from City of Huntsville    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Investing receivables $ 50,570 49,258
Notes Receivable from City of Huntsville | LW Redstone Company, LLC    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Stated interest rate (as a percent) 9.95%  
Other investing loans receivable    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Investing receivables $ 3,000 $ 3,021