Employee Benefits (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Interest perrcentage accrued on employees account balances (in hundredths)	5.25%
Defined Benefit Plan, Interest Percentage Accrued On Employee Account Balances, Next Fiscal Year (Rate to Add to Treasury Securities Rate)	1.50%
Defined Benefit Plan Interest Percentage Accrued On Employee Account Balances, Next Fiscal Year (Minimum)	2.50%
Defined Benefit Plan Interest Percentage Accrued on Employee Account Balances, Next Fiscal Year (Maximum)	5.00%
Thrift Plan - Defined Contribution [Abstract]
Employee base compensation company match employee contributions (in hundredths)	6.00%
Employer matching rate for employee contributions minimum (in hundredths)	50.00%
Minimum years of service for employees to obtain maximum employer matching (in years)	P4Y
Employer matching rate for employee contributions maximum (in hundredths)	200.00%
Maximum years of service for employees to obtain minimum employer matching (in years)	15 years
Non-elective annual contribution for qualified employees	$ 750
Annual base employee compensation to qualify for non-elective employer contributions maximum	40,000
Defined Contribution Plan, Employer Discretionary Contribution Amount	802,000		933,000		1,000,000
Vesting period for employer contributions (in years)	5 years
Thrift Plan expenses	16,800,000		15,400,000		14,300,000
Incentive compensation plans [Abstract]
Charge to earnings for incentive compensation plan	153,900,000		117,800,000		104,000,000
Pension Plan [Member]
Change in projected benefit obligation [Roll Forward]
Projected benefit obligation at beginning of year	50,213,000	[1],[2]	48,373,000
Interest cost	1,925,000		2,157,000
Actuarial loss	2,786,000		2,461,000
Benefits paid	2,194,000		2,778,000
Plan amendments	(4,702,000)		0
Projected benefit obligation at end of year	48,028,000	[1],[2]	50,213,000	[1],[2]
Change in plan assets [Roll Forward]
Plan assets at fair value at beginning of year	43,859,000		44,477,000
Actual return on plan assets	4,255,000		2,160,000
Plan assets at fair value at end of year	45,920,000		43,859,000
Defined Benefit Plan, Funded Status of Plan [Abstract]
Funded status of the plan	(2,108,000)		(6,354,000)
Components of net periodic benefit costs [Abstract]
Interest cost	1,925,000		2,157,000
Expected return on plan assets	(2,062,000)		(1,957,000)
Amortization of unrecognized net loss	3,461,000		3,659,000
Net periodic pension cost (benefit)	3,324,000		3,859,000
Weighted-average assumptions [Abstract]
Discount rate (in hundredths)	3.36%		4.11%
Expected return on plan assets (in hundredths)	5.25%		5.25%
Estimated Future Benefit Payments [Abstract]
2013	3,629,000
2014	3,298,000
2015	3,372,000
2016	3,771,000
2017	3,488,000
Thereafter	16,227,000
Total estimated future benefit payments	(33,785,000)
Defined Benefit Plan, Information about Plan Assets [Abstract]
Defined Benefit Plan, Plan Assets, Inception to date return (in hundredths)	6.96%
Defined Benefit Plan, Plan contributions, Maximum allowed	28,000,000
Net pension costs currently in accumulated other comprehensive income to be recognized as net periodic pension cost in next fiscal year	1,300,000
Post-retirement employee medical plan [Member]
Change in projected benefit obligation [Roll Forward]
Projected benefit obligation at beginning of year	2,200,000
Projected benefit obligation at end of year	$ 1,100,000
Thrift Plan - Defined Contribution [Abstract]
Annual medical insurance premiums paid for retirees (in hundredths)	50.00%
Age of current retirees and certain employees at the time the plan was frozen (in years)	60
Change in medical expense trends not significantly affecting net obligations or cost of the plan (in hundredths)	1.00%
Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Percentage of equities included in portfolio mix of fund used for defined benefit plan (in hundredths)	60.00%
Bonds [Member] | Pension Plan [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Percentage of equities included in portfolio mix of fund used for defined benefit plan (in hundredths)	40.00%

[1] 1 Projected benefit obligation equals accumulated benefit obligation.

[2] 2 Projected benefit obligation is based on January 1 measurement date.