Debt (Schedule Of Cash And Non-Cash Interest Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 13, 2017	Apr. 17, 2017	Aug. 15, 2016	Jul. 07, 2016	Oct. 14, 2015	Sep. 28, 2012	Aug. 09, 2012	Jul. 13, 2012
Debt Instrument [Line Items]
Cash Interest	$ 323,749	$ 329,171	$ 322,366
Non-cash Interest	2,879	2,203	1,505
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Cash Interest	$ 8,046	4,167	5,552
5.625% Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest		21,094	28,125
Debt instrument, interest rate, stated percentage	5.625%								5.625%
5.75% Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest		28,494	46,000
Debt instrument, interest rate, stated percentage	5.75%										5.75%
2014 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	$ 36,563	36,563	36,563
Non-cash Interest	724	689	655
2016 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	53,625	20,258
Non-cash Interest	954	348
Debt instrument, interest rate, stated percentage						4.875%
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	6,500
Debt instrument, interest rate, stated percentage				4.00%
2010 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest		15,213	28,230
2012-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,330	18,107	18,111
Debt instrument, interest rate, stated percentage										2.933%
2013 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	43,217	43,217	43,217
2014 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	51,138	51,138	51,138
2015-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	15,939	15,939	3,453
Debt instrument, interest rate, stated percentage								3.156%
2016-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	20,361	9,898
Debt instrument, interest rate, stated percentage							2.877%
2017-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	17,182
Debt instrument, interest rate, stated percentage					3.168%
2012-1 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest			3,959
2014 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest	49,414	48,962	48,992
Non-cash Interest	525	510	492
2015 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest	16,641	16,487	9,243
Non-cash Interest	676	656	358
Capitalized Interest And Other [Member]
Debt Instrument [Line Items]
Cash Interest	$ (207)	$ (366)	$ (217)