Employee Benefit Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended										12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Employee Thrift Plan [Member]	Dec. 31, 2010 Employee Thrift Plan [Member]	Dec. 31, 2009 Employee Thrift Plan [Member]	Dec. 31, 2011 Salary Deferral Plan [Member]	Dec. 31, 2010 Salary Deferral Plan [Member]	Jan. 01, 1997 Separation Plan [Member] weeks years	May 05, 2004 Special Separation Benefit Plan [Member] years	Dec. 31, 2011 Change Of Control Contracts [Member] years	Dec. 31, 2011 Plan 401k [Member] years
Defined Benefit Plan Disclosure [Line Items]
Contribution of shares, common stock				71,742	74,205	202,655
Recognized expense, common stock				$ 4.3	$ 3.6	$ 3.6
Liability recorded under deferral plan							2.5	2.4
Service period, years									20	20
Maximum period benefit, weeks									104
Age limit										65
Separation benefit plans expense	$ 1.9	$ 1.6	$ 1.5
Employee contract period, years											3
Multiple for determination compensation											2.9
Additional period for 401k, years												3