Benefit Plans Benefit Plans - Allocation of Plan Assets (Additional Information) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Private equity funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	5,529	5,618
Commercial Real Estate [Member] | Real estate common collective trusts [Member] | Common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	43.00%	46.00%
Residential Real Estate [Member] | Real estate common collective trusts [Member] | Common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	21.00%	23.00%
Retail Site [Member] | Real estate common collective trusts [Member] | Common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	17.00%	19.00%
Industrial, Cash and Other [Member] | Real estate common collective trusts [Member] | Common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	19.00%	12.00%
Fixed income securities [Member] | Other [Member] | Common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	60.00%	64.00%
Collateralized Mortgage Backed Securities [Member] | Other [Member] | Common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	27.00%	35.00%
Corporate Bond Securities [Member] | Other [Member] | Common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	42.00%	45.00%
U.S. Treasury and Other [Member] | Other [Member] | Common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	31.00%	20.00%
Russell 1000 Fund Large Cap Index Funds [Member] | Other [Member] | Common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	40.00%	36.00%
Arbitrage and Event Investments [Member] | Hedge Funds, Multi-strategy [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	40.00%	35.00%
Directional Trading, Fixed Income and Other Investments [Member] | Hedge Funds, Multi-strategy [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	25.00%	30.00%
Buyout Private Equity Funds [Member] | Private equity funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	50.00%	50.00%
Special Situation Private Equity and Debt Funds [Member] | Private equity funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	25.00%	30.00%
Venture Private Equity Funds [Member] | Private equity funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	25.00%	20.00%
Long Short Equity [Member] | Hedge Funds, Multi-strategy [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	35.00%	35.00%
Hedge Funds, Multi-strategy [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets Redemptions per Period	0.5
Plan Asset Underlying Investment Redemption Notice	95 days
Real estate common collective trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets Redemptions per Period	0.25
Plan Asset Underlying Investment Redemption Notice	45 days
Arbitrage and Event Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	40.00%	35.00%
Directional Trading, Fixed Income and Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Asset Underlying Investment Portfolio Holdings Percentage	25.00%	30.00%