Long-Term Debt (Details Textual) (USD $) In Thousands, unless otherwise specified	1 Months Ended	12 Months Ended				12 Months Ended			12 Months Ended		1 Months Ended	12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Aug. 20, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2012 Revolving Credit Facility [Member]	Dec. 21, 2011 Revolving Credit Facility [Member]	Dec. 31, 2012 Letter of Credit [Member]	Dec. 31, 2012 Maximum [Member] Revolving Credit Facility [Member]	Dec. 31, 2012 Minimum [Member] Revolving Credit Facility [Member]	Nov. 30, 2012 6 3/4% Senior Notes due May 30, 2013 [Member]	Dec. 31, 2012 6 3/4% Senior Notes due May 30, 2013 [Member]	Dec. 31, 2011 6 3/4% Senior Notes due May 30, 2013 [Member]	Dec. 31, 2012 8% Senior Notes due November 15, 2016 [Member]	Dec. 31, 2011 8% Senior Notes due November 15, 2016 [Member]	Dec. 31, 2012 7 3/4% Senior Debenture due June 1, 2027 [Member]	Dec. 31, 2011 7 3/4% Senior Debenture due June 1, 2027 [Member]	Dec. 31, 2012 7 1/4% Senior Debenture due September 15, 2027 [Member]	Dec. 31, 2011 7 1/4% Senior Debenture due September 15, 2027 [Member]
Long-Term Debt (Additional Textual) [Abstract]
Weighted average interest rate for debt instruments		7.50%	7.50%			2.70%
Weighted average effective interest rate for the fixed rate debt		7.70%	7.50%
Debt instruments, Stated Percentage												6.75%		8.00%		7.75%		7.25%
Redemption premium paid on redemption of Senior notes											$ 5,529
Write off of Deferred Debt Issuance Cost											173
Fixed Rate Interest Debt, Maturity Date												May 30, 2013		Nov. 15, 2016		Jun. 01, 2027		Sep. 15, 2027
Credit Agreement, Revolving credit facility, maximum Amount	205,000				460,750		200,000
Extended maturity date of credit agreement						Aug. 15, 2016
Ownership Interest in subsidiary						100.00%
Percent of Commitment fees on unused funds						0.625%
Credit Agreement, Interest Coverage Ratio										2.0
Credit Agreement, Senior Leverage Ratio									1.0
Credit Agreement, dividends and repurchase annual maximum						100,000
Credit Agreement, Dividends and repurchase shares covenants leverage ratio									4.5
Credit Agreement, Minimum Liquidity Amount						75,000
Due of repurchases of bonds 2016						2016
Due of repurchases of bonds 2027						2027
Letters of credit Outstanding						21,000		4,726
Leverage Ratio						2.8
Interest coverage ratio						3.8
Senior leverage ratio						0.1
Redemption of Senior notes principal amount											175,925
Long-Term Debt (Textual) [Abstract]
Estimated fair value of fixed-rate debt		769,541	865,921
Date of Company's bonds retired		Nov. 30, 2012
Redemption of the Company's bonds exempt per year limitation		100,000
Redemption of the Company's bonds exempt liquidity restriction		75,000
Expected Due period of the Company's bonds		2013
Senior notes principal amount		712,025	887,003										175,748	272,025	271,255	200,000	200,000	240,000	240,000
Interest coverage ratio						3.8
Senior leverage ratio						0.1
Charge related to the write-off of debt issuance costs	1,225
Interest paid, net of amounts capitalized		$ 68,051	$ 68,607	$ 71,993