Debt (Schedule of Cash and Non-Cash Interest Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Debt Instrument [Line Items]
Cash Interest	$ 93,639	$ 78,456	$ 182,562	$ 156,058
Non-cash Interest	638	717	1,370	1,421
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Cash Interest	1,589	1,406	3,191	4,176
2014 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	9,141	9,141	18,281	18,281
Non-cash Interest	189	180	376	357
2016 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	13,406	13,406	26,813	26,813
Non-cash Interest	249	237	495	471
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	7,500		15,000
2012 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest		806		5,331
2013 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,396	10,804	14,871	21,609
2014 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	12,785	12,785	25,569	25,569
2015-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	3,985	3,985	7,969	7,969
2016-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,090	5,090	10,181	10,181
2017-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	6,088	5,001	12,173	5,001
2018-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,570		6,932
2014 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest	1,603	12,043	15,550	23,327
Non-cash Interest	15	131	146	259
2015 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest	540	4,056	5,237	7,855
Non-cash Interest	19	169	187	334
2018 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest	21,207		21,207
Non-cash Interest	166		166
Other [Member]
Debt Instrument [Line Items]
Cash Interest	$ (261)	$ (67)	$ (412)	$ (54)