Investment in Sunrise Energy (Condensed Balance Sheet - Sunrise) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets	$ 64,867	$ 66,615
Total assets	544,021	540,378
Total liabilities	325,690	333,558
Total liabilities and stockholders' equity	544,021	$ 540,378
Sunrise Energy [Member]
Current assets	2,156
Oil and gas properties, net	7,706
Total assets	9,862
Total liabilities	697
Members' capital	9,165
Total liabilities and stockholders' equity	$ 9,862