Employee Benefit Plans (Details 2)	12 Months Ended
	Dec. 31, 2011 company industry	Dec. 31, 2010	Dec. 31, 2009
Weighted-average assumptions used to determine benefit obligations
Discount rate (as a percent)	4.80%	5.50%
Rate of compensation increase (as a percent)		4.00%
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate (as a percent)	4.70%	6.00%	6.00%
Original discount rate (as a percent)	5.50%
Long-term rate of return on assets (as a percent)	7.75%	8.50%	8.50%
Rate of compensation increase (as a percent)		4.00%	4.00%
Weighted average asset allocations by asset category
Equity securities (as a percent)	13.40%	42.50%
Debt securities (as a percent)	77.40%	40.20%
Other (as a percent)	9.20%	17.30%
Total (as a percent)	100.00%	100.00%
Guidelines regarding allocation of assets
Fixed income securities, preferred allocation	80.00%
Equity securities and other investments (as a percent)	20.00%
Allocation target in 2012, minimum (as a percent)	90.00%
Number of companies or government agencies in which the allocation of assets should not exceed 10% of the total fund	1
Maximum allocation of assets in the securities of any one company or government agency (as a percent)	10.00%
Maximum allocation of assets in any one industry (as a percent)	20.00%
Number of industries in which the allocation of assets should be no more than 20% of the total fund	1
Individual treasury securities (as a percent)	50.00%
Treasury bonds and notes, maximum (as a percent)	100.00%