Employees, Retirement and Incentive Plans Performance Units (Details) (USD $)	12 Months Ended									3 Months Ended		12 Months Ended							3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2012 Performance Units [Member]	Dec. 31, 2012 Retirement Costs [Member]	Dec. 31, 2011 Retirement Costs [Member]	Dec. 31, 2010 Retirement Costs [Member]	Dec. 31, 2012 Selected Executives [Member] Performance Units [Member]	Dec. 31, 2012 Certain Officers [Member] Performance Units [Member]	Dec. 31, 2012 Long-term Incentive Plan [Member]	Dec. 31, 2012 Long-term Incentive Plan [Member] Performance Units [Member]	Dec. 31, 2011 Long-term Incentive Plan [Member] Performance Units [Member]	Dec. 31, 2010 Long-term Incentive Plan [Member] Performance Units [Member]	Dec. 31, 2012 Long-term Incentive Plan [Member] Certain Officers [Member] Performance Units [Member]	Dec. 31, 2011 Long-term Incentive Plan [Member] Certain Officers [Member] Performance Units [Member]	Dec. 31, 2010 Long-term Incentive Plan [Member] Certain Officers [Member] Performance Units [Member]	Dec. 31, 2012 Maximum [Member] Performance Share Units Member
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Benefits and Share-based Compensation	$ 6,900,000	$ 3,600,000		$ 2,900,000			$ 4,300,000	$ 2,200,000	$ 1,500,000
Award vesting period										3 years	3 years								3 years
Estimated share payouts, outstanding nonvested performance unit awards (percent)										110.00%
Grants in period																11,436
Range of performance units earned, based on performance units granted, minimum (percent)																50.00%
Range of performance units earned, based on performance units granted, maximum (percent)																150.00%
Grants in period, weighted average grant date fair value																$ 30.61	$ 29.83	$ 21.30
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Outstanding at January 1, 2012 (nonvested)						85,982
Granted						11,436
Vesting and transfer of full ownership to recipients						(42,920)
Outstanding at June 30, 2012 (nonvested)						54,498
Fair value of vested units transferred to recipients													500,000	900,000	600,000
Weighted average fair value, units vested and transferred to recipients													$ 26.06
Total unrecognized compensation related to nonvested units													500,000
Weighted average remaining contractual term (years)													7 months 6 days
Purchase of units for incentive grants	$ (4,919,000)	$ (1,641,000)	[1]	$ (2,704,000)	[1]							$ 4,900,000

[1] (1) Restated as described in Note 2.