Investment in Sunrise Energy (Condensed Balance Sheet - Sunrise) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets	$ 63,479	$ 66,615
Total assets	540,083	540,378
Total liabilities	317,860	333,558
Total liabilities and stockholders' equity	540,083	$ 540,378
Sunrise Energy [Member]
Current assets	2,080
Oil and gas properties, net	7,646
Total assets	9,726
Total liabilities	773
Members' capital	8,953
Total liabilities and stockholders' equity	$ 9,726