Organization, Basis of Presentation and Recent Accounting Pronouncements (Recent Accounting Pronouncements)(Details 2) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Item Effected [Line Items]
Income from Operations	$ 29,054	$ 51,872
Income before income taxes	23,786	60,615
As reported [Member]
Item Effected [Line Items]
Income from Operations	29,054	51,872	$ 303,534
Non-operating pension and postretirement income	0	0	0
Income before income taxes	23,786	60,615	250,658
Adjustment [Member]
Item Effected [Line Items]
Income from Operations	(18,801)	(15,677)	(80,665)
Non-operating pension and postretirement income	18,801	15,677	80,665
Income before income taxes	0	0	0
Upon Adoption [Member]
Item Effected [Line Items]
Income from Operations	10,253	36,195	222,869
Non-operating pension and postretirement income	18,801	15,677	80,665
Income before income taxes	$ 23,786	$ 60,615	$ 250,658