Major Customers And Segment Information (Revenues Attributed By Geographical Region) (Details) - USD ($) $ 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
Segment Reporting Information [Line Items]
Operating Revenues	$ 213,036	$ 206,983	$ 197,038	$ 213,928	$ 250,631	$ 261,852	$ 281,609	$ 260,644	$ 830,985	$ 1,054,736	$ 1,319,394
Non-US [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Percentage									29.00%	29.00%	30.00%
UNITED STATES
Segment Reporting Information [Line Items]
Operating Revenues									$ 590,310	$ 751,548	$ 925,750
Africa Primarily West Africa [Member]
Segment Reporting Information [Line Items]
Operating Revenues									37,764	57,268	70,743
Europe Primarily North Sea [Member]
Segment Reporting Information [Line Items]
Operating Revenues									82,730	104,042	112,644
Middle East and Asia [Member]
Segment Reporting Information [Line Items]
Operating Revenues									54,950	65,045	69,598
Brazil, Mexico Central And South America [Member]
Segment Reporting Information [Line Items]
Operating Revenues									64,837	76,404	140,460
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenues									$ 394	$ 429	$ 199