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Investment in Dalea Investment Group, LLC (Details) - Dalea Investment Group, LLC - USD ($)
1 Months Ended 12 Months Ended
Jun. 30, 2012
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Investment in Dalea Investment Group, LLC        
Note receivable cancelled $ 11,000,000      
Non-controlling membership interest (as a percent) 7.66%      
Recorded investment $ 11,000,000   $ 8,400,000  
Cost-method Investments, Other than Temporary Impairment   $ 8,400,000 $ 2,600,000 $ 0