Debt (Schedule of Cash and Non-Cash Interest Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Debt Instrument [Line Items]
Cash Interest	$ 97,447	$ 93,639	$ 196,114	$ 182,562
Non-cash Interest	651	638	1,292	1,370
2014 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	9,141	9,141	18,281	18,281
Non-cash Interest	199	189	395	376
2016 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	13,406	13,406	26,813	26,813
Non-cash Interest	262	249	521	495
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	7,500	7,500	15,000	15,000
2013 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,396	5,396	10,792	14,871
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	6,088	12,173	12,173
2018-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,570	5,570	11,141	6,932
2018-1C Tower Securities [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Cash Interest	1,564	1,589	4,401	3,191
2014 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest		1,603		15,550
Non-cash Interest		15		146
2015 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest		540		5,237
Non-cash Interest		19		187
2018 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest	26,944	21,207	53,866	21,207
Non-cash Interest	190	166	376	166
Other [Member]
Debt Instrument [Line Items]
Cash Interest	$ (22)	$ (261)	$ (72)	$ (412)