Debt (Schedule of Cash and Non-Cash Interest Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Cash Interest	$ 95,717	$ 81,357	$ 278,278	$ 237,415
Non-cash Interest	632	725	2,002	2,146
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Cash Interest	1,721	2,673	4,911	6,848
2014 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	9,141	9,141	27,422	27,422
Non-cash Interest	191	182	567	540
2016 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	13,406	13,406	40,219	40,219
Non-cash Interest	252	240	748	711
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	7,500		22,500
2012 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest				5,331
2013 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,396	10,804	20,267	32,413
2014 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	12,785	12,785	38,354	38,354
2015-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	3,985	3,985	11,954	11,954
2016-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,090	5,090	15,271	15,271
2017-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	6,096	6,096	18,268	11,098
2018-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,570		12,502
2014 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest		12,964	15,550	36,291
Non-cash Interest		133	146	391
2015 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest		4,366	5,237	12,221
Non-cash Interest		170	187	504
2018 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest	25,096		46,303
Non-cash Interest	189		354
Other [Member]
Debt Instrument [Line Items]
Cash Interest	$ (69)	$ 47	$ (480)	$ (7)