Stock Based Compensation Summary of Non Vested Restricted Stock Awards (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Stock-Based Compensation [Abstract]
Nonvested shares, beginning of year (in shares)	2,385
Nonvested shares, beginning of year (in dollars per share)	$ 26.07
Shares awarded (in shares)	558
Shares awarded (in dollars per share)	$ 27.77
Shares vested (in shares)	(717)
Shares vested (in dollars per share)	$ 26.02
Shares forfeited (in shares)	(139)
Shares forfeited (in dollars per share)	$ 27.85
Nonvested shares, end of year (in shares)	2,087
Nonvested shares, end of year (in dollars per share)	$ 26.42