Debt (Schedule of Cash and Non-Cash Interest Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Debt Instrument [Line Items]
Cash Interest	$ 98,667	$ 88,923
Non-cash Interest	641	733
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Cash Interest	2,836	1,601
2014 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	9,141	9,141
Non-cash Interest	196	187
2016 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	13,406	13,406
Non-cash Interest	259	246
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Cash Interest	7,500	7,500
2013 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,396	9,475
2014 Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	12,785	12,785
2015-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	3,985	3,985
2016-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,090	5,090
2017-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	6,085	6,085
2018-1C Tower Securities [Member]
Debt Instrument [Line Items]
Cash Interest	5,570	1,362
2014 Term Loan [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Cash Interest		13,947
Non-cash Interest		131
2015 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest		4,697
Non-cash Interest		169
2018 Term Loan [Member]
Debt Instrument [Line Items]
Cash Interest	26,922
Non-cash Interest	186
Other [Member]
Debt Instrument [Line Items]
Cash Interest	$ (49)	$ (151)