Benefit Plans (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Incentive Savings Plan
Employee maximum contribution of pre-tax base salary, percentage	15.00%
Employee maximum contribution of pre-tax base salary limit	$ 17,000
Employee vesting in employer contributions after period of time	1 year
Employee Stock Ownership Plan disclosures
ESOP loans interest rate (as a percent)	6.00%
ESOP loans outstanding principal balance	5,900,000	12,100,000
Shares allocated to participants	1,075,354	1,398,763	863,505
Shares allocated to participants to date	14,101,549
Shares not allocated to participants	967,013	2,042,367
Fair value of shares not allocated to participants	9,100,000
Cash contribution to participant accounts	513,000	1,800,000	2,200,000
Compensation expense related to ESOP	$ 10,700,000	$ 18,200,000	$ 13,800,000