Credit Facilities, Short-term Borrowings and Long-term Debt (Details Textual) (USD $)	1 Months Ended	6 Months Ended	9 Months Ended																		1 Months Ended				3 Months Ended				6 Months Ended							3 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Sep. 30, 2011 6.50% notes due 2016 [Member]	Jun. 30, 2011 6.50% notes due 2016 [Member]	Dec. 31, 2010 6.50% notes due 2016 [Member]	Sep. 30, 2010 6.50% notes due 2016 [Member]	Sep. 30, 2011 7.50% notes due 2021 [Member]	Jun. 30, 2011 7.50% notes due 2021 [Member]	Dec. 31, 2010 7.50% notes due 2021 [Member]	Sep. 30, 2010 7.50% notes due 2021 [Member]	Jul. 07, 2010 Floating-rate term loan due 2015 [Member]	Sep. 30, 2011 10.125% notes due 2015 [Member]	Dec. 31, 2010 10.125% notes due 2015 [Member]	Sep. 30, 2010 10.125% notes due 2015 [Member]	Sep. 30, 2011 10.375% notes due 2018 [Member]	Dec. 31, 2010 10.375% notes due 2018 [Member]	Sep. 30, 2010 10.375% notes due 2018 [Member]	Jul. 31, 2010 Floating-rate term loan due in 2011 [Member]	Sep. 30, 2011 7.00% notes due 2018 [Member]	Dec. 31, 2010 7.00% notes due 2018 [Member]	Sep. 30, 2010 7.00% notes due 2018 [Member]	Jun. 30, 2011 5.60% notes due 2012 [Member]	Sep. 30, 2011 5.60% notes due 2012 [Member]	Dec. 31, 2010 5.60% notes due 2012 [Member]	Sep. 30, 2010 5.60% notes due 2012 [Member]	Jun. 30, 2011 5.60% notes due 2012 [Member] 6.30% notes due 2013 [Member]	Sep. 30, 2011 6.40% notes due 2017 [Member]	Dec. 31, 2010 6.40% notes due 2017 [Member]	Sep. 30, 2010 6.40% notes due 2017 [Member]	Sep. 30, 2011 7.15% notes due 2037 [Member]	Dec. 31, 2010 7.15% notes due 2037 [Member]	Sep. 30, 2010 7.15% notes due 2037 [Member]	Jun. 30, 2011 6.30% notes due 2013 [Member]	Sep. 30, 2011 6.30% notes due 2013 [Member]	Dec. 31, 2010 6.30% notes due 2013 [Member]	Sep. 30, 2010 6.30% notes due 2013 [Member]
Credit Facilities, Short-term Borrowings and Long-term Debt (Textuals)
Decrease in unamortized discounts															$ 355,000	$ 403,000	$ 418,000	$ 1,509,000	$ 1,609,000	$ 1,640,000		$ 316,000	$ 342,000	$ 351,000		$ 61,000	$ 227,000	$ 254,000		$ 135,000	$ 148,000	$ 152,000	$ 644,000	$ 676,000	$ 678,000		$ 107,000	$ 271,000	$ 296,000
Increase in unamortized deferred gain realized						19,072,000									3,995,000
Effective interest rate						6.01%				7.74%					9.59%	9.59%	9.59%	10.58%	10.58%	10.58%		7.87%	7.87%	7.87%		6.57%	6.57%	6.57%		7.41%	7.41%	7.41%	8.06%	8.06%	8.06%		7.48%	7.48%	7.48%
Coupon rate of notes						6.50%	6.50%	6.50%	6.50%	7.50%	7.50%	7.50%	7.50%		10.125%	10.125%	10.125%	10.375%	10.375%	10.375%		7.00%	7.00%	7.00%	5.60%	5.60%	5.60%	5.60%		6.40%	6.40%	6.40%	7.15%	7.15%	7.15%	6.30%	6.30%	6.30%	6.30%
Long-term notes face amount	1,100,000,000	1,100,000,000					500,000,000				600,000,000			450,000,000															274,999,000
Purchase of long term notes																									165,443,000											109,556,000
Total consideration paid for debt																													294,533,000
Premium paid for purchase of debt																													19,534,000
Amount of outstanding balance of loan repaid																					100,000,000
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
Maximum total debt as a percentage of total capital			65.00%
Total debt as a percentage of total capital			42.10%	40.70%	40.70%