Long-Term Debt (Senior Notes) (Details) (USD $)	12 Months Ended				0 Months Ended	9 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jan. 17, 2006 6.125% Notes, Payable January 15, 2016 [Member]	Sep. 29, 2012 6.125% Notes, Payable January 15, 2016 [Member]	Dec. 31, 2012 6.125% Notes, Payable January 15, 2016 [Member]	Dec. 31, 2011 6.125% Notes, Payable January 15, 2016 [Member]	Apr. 16, 2012 7.20% Senior Notes, Payable April 15, 2012 [Member]	Dec. 31, 2012 7.20% Senior Notes, Payable April 15, 2012 [Member]	Dec. 31, 2011 7.20% Senior Notes, Payable April 15, 2012 [Member]	Dec. 31, 2002 7.20% Senior Notes, Payable April 15, 2012 [Member]	Sep. 29, 2012 7.20% Senior Notes, Payable April 15, 2012 [Member]	Dec. 31, 2012 Subsequent Event [Member] 3.850% Senior Notes Due, Payable January 15, 2016 [Member]	Jan. 31, 2013 Subsequent Event [Member] 3.850% Senior Notes Due, Payable January 15, 2016 [Member]
Debt Instrument [Line Items]
Increase (Decrease) on Interest Rate	0.05%			(0.75%)
Aggregate principal amount of debts					$ 900,000,000							$ 400,000,000			$ 600,000,000
Interest rate percentage					6.125%		6.125%	6.125%		7.20%	7.20%	7.20%	7.20%		3.85%
Redemption rate to the aggregate principal of notes outstanding and accrued and unpaid interest, percent														101.00%
Notes payable, maturity date					Jan. 15, 2016		Jan. 15, 2016	Jan. 15, 2016		Apr. 15, 2012	Apr. 15, 2012	Apr. 15, 2012
Increase in interest rate from rating agency downgrade						0.25%
Maximum increase in interest rate per agency from rating agency downgrade						1.00%
Increase in interest expense per quarter for .25% increase in notes per $100,000 of outstanding notes	74,713,000	101,617,000	133,151,000			100,000
Incremental increase in outstanding notes						100,000,000
Remaining outstanding senior notes repaid											63,730,000
Repurchase price as percentage of principal amount of senior notes										102.72%
Repayments of secured debt									336,270,000
Increase accrued interest									$ 12,106,000