Fair Value of Financial Instruments (Narrative) (Details)	6 Months Ended
	Jun. 30, 2011
Senior Notes [Member] | 5.50% Senior Notes [Member]
Senior notes, interest rate	5.50%
Debt instrument interest rate traded percentage	100.90%
Debt instrument interest rate effective yield percentage	5.40%
Senior Notes [Member] | 7.50% Senior Notes [Member]
Senior notes, interest rate	7.50%
Debt instrument interest rate traded percentage	115.10%
Debt instrument interest rate effective yield percentage	4.20%
5.50% Senior Notes [Member]
Senior notes, interest rate	5.50%
7.50% Senior Notes [Member]
Senior notes, interest rate	7.50%