Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Licenses
Balance, beginning of period	$ 1,401,126	$ 1,456,794
Acquisitions	9,100	14,150
Exchanges, net	15,719
Balance, end of period	$ 1,425,945	$ 1,470,944