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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Fair Value of Financial Instruments (Schedule of Estimated Fair Value of Financial Instruments, by Balance Sheet Grouping) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Assets:
Cash and cash equivalents	$ 285,048	$ 387,813	$ 129,298	$ 129,865
Cash and cash equivalents, fair value disclosure	285,048	387,813
Available-for-sale securities	59,394	56,376
Available-for-sale securities, fair value disclosure	59,394	56,376
Trading securities	38,932	34,696
Trading securities, fair value disclosure	38,932	34,696
Credit Facility, Type of Debt [Member] \| Credit Facility, Name [Member]
Liabilities:
Credit Facility	4,125,084	4,331,562
Credit Facility, fair value disclosure	4,153,531	4,357,910
Senior Notes [Member] \| Senior Notes at 8.0, Due 2019 [Member]
Liabilities:
Senior notes	2,022,228	2,022,829
Senior notes, fair value disclosure	2,216,980	2,185,220
Senior Notes [Member] \| Senior Notes at 7.125, Due 2020 [Member]
Liabilities:
Senior notes	1,200,000	1,200,000
Senior notes, fair value disclosure	1,306,800	1,285,848
Senior Secured Notes [Member] \| Senior Secured Notes At 5.125 Due 2018 [Member]
Liabilities:
Senior notes	1,600,000	1,600,000
Senior notes, fair value disclosure	1,679,040	1,674,480
Receivables Facility and Other Debt, Type [Member] \| Receivables Facility and Unsecured Debt [Member]
Liabilities:
Other debt	543,835	338,963
Other debt, fair value disclosure	$ 543,835	$ 338,963