Acquisitions (Schedule of Consideration Paid and Net Assets Acquired, Business Acquisitions - WesTower) (Details) - USD ($) $ in Thousands	Oct. 01, 2014	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Identifiable assets acquired and liabilities assumed:
Goodwill		$ 1,082,466	$ 1,000,024	$ 983,133	$ 912,885	$ 902,044	$ 826,600
WesTower [Member]
Acquisition consideration:
Cash	$ 198,000
Acquisition consideration	198,000
Identifiable assets acquired and liabilities assumed:
Accounts receivable	180,600
Other current assets, including $18.0 million of cash acquired	50,300
Business combinations, cash acquired	18,000
Property, equipment and other long-term assets, including deferred tax asset	18,000
Finite-lived intangible assets	42,600
Billings in excess of costs and earnings	(33,300)
Other current liabilities, including current portion of capital lease obligations	(89,800)
Long-term liabilities, including capital lease obligations	(21,100)
Total identifiable net assets	147,300
Goodwill	50,700
Total net assets acquired, including goodwill	$ 198,000