Equity Incentive Compensation Plans and Other Benefit Plans (Director Fees and Other Employee Benefits-401(k) Plan) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Other Employee Benefits—401(k) Plan
Company currently matches employee's contributions (as a percent)	100.00%
Contributions to 401(k) Plan, net of forfeitures	$ 2.1	$ 1.8	$ 1.5
Employees participating in 401(k) Plan (as a percent)	94.00%
Maximum
Other Employee Benefits—401(k) Plan
Company matches employee's eligible compensation (as a percent)	8.00%
Non-employee directors
Director Fees
Shares earned and deferred in accordance with the plan (in shares)	12,797	13,647	38,462