Debt (Schedule of Cash and Non-Cash Interest Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Cash Interest	$ 96,567	$ 95,717	$ 292,681	$ 278,278
Non-cash Interest	662	632	1,954	2,002
2014 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	9,141	9,141	27,422	27,422
Non-cash Interest	201	191	596	567
2016 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	13,406	13,406	40,219	40,219
Non-cash Interest	265	252	786	748
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	7,500	7,500	22,500	22,500
2013 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,396	5,396	16,188	20,267
2014 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	11,439	12,785	37,009	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	18,269	18,268
2018-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,570	5,570	16,711	12,502
2018-1C Tower Securities [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Cash Interest	1,009	1,721	5,409	4,911
2019-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	1,671		1,671
2014 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest				15,550
Non-cash Interest				146
2015 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest				5,237
Non-cash Interest				187
2018 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest	26,243	25,096	79,959	46,303
Non-cash Interest	196	189	572	354
Other [Member]
Debt Instrument [Line Items]
Cash Interest	$ 21	$ (69)	$ 99	$ (480)