Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Licenses
Balance, beginning of period	$ 1,456,794	$ 1,470,769
Acquisitions	14,150	11,096
Balance, end of period	$ 1,470,944	$ 1,481,865