Postretirement Benefits (Details 2)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assumptions used to determine net periodic benefit cost:
Number of economic assumptions that have the most impact on the postretirement benefit expense	2
Employee pension plan
Assumptions used to determine benefit obligations:
Discount rate (as a percent)	4.19%	4.99%	5.69%	6.11%
Compensation increase (as a percent)	4.15%	4.15%	4.15%	4.15%
Assumptions used to determine net periodic benefit cost:
Discount rate (as a percent)	4.99%	5.69%	6.11%
Expected return on assets (as a percent)	7.50%	8.00%	8.00%	8.25%
Rate of compensation increase (as a percent)	4.15%	4.15%	4.15%
Supplemental employee retirement plan (SERP)
Assumptions used to determine benefit obligations:
Pre-retirement discount rate (as a percent)	4.19%	4.99%	5.69%	6.11%
Post-retirement discount rate (as a percent)	3.69%	4.49%	5.19%	5.00%
Compensation increase (as a percent)	6.00%	6.00%	6.00%	6.00%
Assumptions used to determine net periodic benefit cost:
Pre-retirement discount rate (as a percent)	4.99%	5.69%	6.11%
Post-retirement discount rate (as a percent)	4.49%	5.19%	5.00%
Rate of compensation increase (as a percent)	6.00%	6.00%	6.00%