Debt (Details Textual 1) (USD $)	1 Months Ended	6 Months Ended		3 Months Ended			3 Months Ended			6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Dec. 31, 2007	Jun. 30, 2011 6.30% notes due 2013 [Member]	Jun. 30, 2012 6.30% notes due 2013 [Member]	Dec. 31, 2011 6.30% notes due 2013 [Member]	Jun. 30, 2011 5.60% notes due 2012 [Member]	Jun. 30, 2012 5.60% notes due 2012 [Member]	Dec. 31, 2011 5.60% notes due 2012 [Member]	Jun. 30, 2011 5.60% notes due 2012 [Member] 6.30% notes due 2013 [Member]	Jun. 30, 2012 10.125% notes due 2015 [Member]	Dec. 31, 2011 10.125% notes due 2015 [Member]	Jun. 30, 2011 10.125% notes due 2015 [Member]	Jun. 30, 2012 6.50% notes due 2016 [Member]	Dec. 31, 2011 6.50% notes due 2016 [Member]	Jun. 30, 2011 6.50% notes due 2016 [Member]	Jun. 30, 2012 6.40% notes due 2017 [Member]	Dec. 31, 2011 6.40% notes due 2017 [Member]	Jun. 30, 2011 6.40% notes due 2017 [Member]	Jun. 30, 2012 7.00% notes due 2018 [Member]	Dec. 31, 2011 7.00% notes due 2018 [Member]	Jun. 30, 2011 7.00% notes due 2018 [Member]	Jun. 30, 2012 10.375% notes due 2018 [Member]	Dec. 31, 2011 10.375% notes due 2018 [Member]	Jun. 30, 2011 10.375% notes due 2018 [Member]	Jun. 30, 2012 7.50% notes due 2021 [Member]	Dec. 31, 2011 7.50% notes due 2021 [Member]	Jun. 30, 2011 7.50% notes due 2021 [Member]	Jun. 30, 2012 7.15% notes due 2037 [Member]	Dec. 31, 2011 7.15% notes due 2037 [Member]	Jun. 30, 2011 7.15% notes due 2037 [Member]	Jun. 30, 2011 Floating-rate term loan due 2015 [Member]
Debt (Textual)
Coupon rate of notes				6.30%	6.30%	6.30%	5.60%	5.60%	5.60%		10.125%	10.125%	10.125%	6.50%	6.50%	6.50%	6.40%	6.40%	6.40%	7.00%	7.00%	7.00%	10.375%	10.375%	10.375%	7.50%	7.50%	7.50%	7.15%	7.15%	7.15%
Decrease in unamortized discounts				$ 122,000	$ 62,000	$ 92,000	$ 74,000	$ 22,000	$ 49,000		$ 302,000	$ 338,000	$ 372,000	$ 16,701,000	$ 18,293,000		$ 122,000	$ 131,000	$ 139,000	$ 289,000	$ 307,000	$ 325,000	$ 1,401,000	$ 1,474,000	$ 1,543,000				$ 639,000	$ 643,000	$ 646,000
Increase (decrease) in unamortized deferred gain realized											3,402,000	3,802,000
Effective interest rate					7.48%			6.57%			9.59%			6.02%			7.41%			7.87%			10.62%			7.75%			8.05%
Purchase of long term notes				109,556,000			165,443,000
Total consideration paid for debt										294,533,000
Premium paid for purchase of debt										19,534,000
Long-term notes face amount	1,100,000,000	1,100,000,000	325,000,000							274,999,000						500,000,000												600,000,000				450,000,000
Outstanding amount under revolving credit facility repaid	275,000,000
Recognition of unamortized deferred financing costs		2,423,000
Expenses related to partial termination of debt	4,711,000
Combined expense	$ 24,245,000