Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected quarterly financial data and earnings per share [Abstract]
Revenues	$ 298,969	$ 256,877	$ 293,163	$ 250,531	$ 348,255	$ 439,893	$ 600,558	$ 555,573	$ 1,099,540	$ 1,944,279	$ 4,132,826
Earnings (Loss) from Continuing Operations	$ (168)	$ (983)	$ 3,540	$ 1,554	$ (8,404)	$ (308)	$ 4,340	$ 3,097	$ 3,943	$ (1,275)	$ 6,219
Earnings (Loss) from Continuing Operations, Per Share (in dollars per share)	$ (0.04)	$ (0.23)	$ 0.84	$ 0.37	$ (1.99)	$ (0.07)	$ 1.03	$ 0.73	$ 0.94	$ (0.30)	$ 1.48
Net Earnings (Loss), Amount	$ (168)	$ (2,153)	$ 3,404	$ 1,430	$ (8,404)	$ (308)	$ 4,340	$ 3,097	$ 2,513	$ (1,275)	$ 6,523
Net Earnings (Loss), Per Share (in dollars per share)	$ (0.04)	$ (0.51)	$ 0.81	$ 0.34	$ (1.99)	$ (0.07)	$ 1.03	$ 0.73	$ 0.60	$ (0.30)	$ 1.55
Dividends	$ 927	$ 928	$ 928	$ 928	$ 928	$ 928	$ 928	$ 928	$ 3,711	$ 3,712	$ 3,711
Dividends, Per share (in dollars per share)	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.88	$ 0.88