Debt And Interest Expense Debt and Interest Expense (Senior Notes) (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended	12 Months Ended
	Mar. 27, 2015	Apr. 30, 2013	Aug. 31, 2007	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Apr. 16, 2013	Aug. 15, 2007
Debt Disclosure [Abstract]
Debt Instrument, Offering Date	Mar. 27, 2015	Apr. 16, 2013
Debt Instrument, Face Amount	$ 500,000				$ 1,250,000	$ 1,250,000	$ 750,000	$ 1,250,000
Debt Instrument, Interest Rate, Stated Percentage	5.25%						4.625%	3.25%
Debt Instrument, Maturity Date	Apr. 01, 2025	May 01, 2023		Apr. 01, 2020
issuance cost on senior note	$ 6,500						$ 12,000
Net proceeds from issuance of convertible debenture			$ 1,224,223
Debt Instrument, Term Length					10 years