Pension and Other Post Retirement Benefit Plans Pension and Other Post Retirement Benefit Plans - Retirement and Income Savings Plan (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Defined Contribution Plans Disclosures [Line Items]
Amount of discretionary contributions made by employer to defined contribution plan, percent	50.00%
Maximum Annual Contribution Per Employee, Percent	6.00%
Requisite Service Period	1000 hours
Vesting Period	5 years
Expense Recognized In The Period	$ 2,914	$ 2,824	$ 2,728
Minimum
Schedule of Defined Contribution Plans Disclosures [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution, Percent	2.00%
Maximum
Schedule of Defined Contribution Plans Disclosures [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution, Percent	7.00%