Pension Benefits (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension plan
Assets measured at fair value	$ 176,706	$ 164,048	$ 146,630
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.50%	7.50%	7.50%
Rollforward of the balances of plan assets that are valued using level 3 inputs (in thousands)
Beginning balance	164,048	146,630	143,818
Actual return on plan assets:
Fair value of plan assets at end of period	176,706	164,048	146,630
Estimated Future Employer Contributions
2014	6,000
Expected benefit payments:
2014	8,460
2015	8,975
2016	9,450
2017	9,894
2018	10,610
2019	59,633
Total benefit payments	107,022
Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	167,187	141,430
Actual return on plan assets:
Fair value of plan assets at end of period	167,187	141,430
Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	9,519	22,618
Actual return on plan assets:
Fair value of plan assets at end of period	9,519	22,618
Domestic equity securities
Pension plan
Target allocation (as a percent)	18.00%
Fixed income securities
Pension plan
Target allocation (as a percent)	47.00%
International equity
Pension plan
Target allocation (as a percent)	14.00%
Assets measured at fair value	25,753
Rollforward of the balances of plan assets that are valued using level 3 inputs (in thousands)
Beginning balance	21,618
Actual return on plan assets:
Fair value of plan assets at end of period	25,753
International equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	25,753	21,618
Actual return on plan assets:
Fair value of plan assets at end of period	25,753	21,618
International equity | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
International equity | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Alternatives
Pension plan
Target allocation (as a percent)	21.00%
Large-Cap Disciplined Equity
Pension plan
Assets measured at fair value	35,446	37,942
Actual return on plan assets:
Fair value of plan assets at end of period	35,446	37,942
Large-Cap Disciplined Equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	35,446	37,942
Actual return on plan assets:
Fair value of plan assets at end of period	35,446	37,942
Large-Cap Disciplined Equity | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Large-Cap Disciplined Equity | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Small/Mid-Cap Equity
Pension plan
Assets measured at fair value	5,668	9,212
Actual return on plan assets:
Fair value of plan assets at end of period	5,668	9,212
Small/Mid-Cap Equity | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	5,668	9,212
Actual return on plan assets:
Fair value of plan assets at end of period	5,668	9,212
Small/Mid-Cap Equity | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Small/Mid-Cap Equity | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Long Duration Fixed Income
Pension plan
Assets measured at fair value	67,298	46,084
Actual return on plan assets:
Fair value of plan assets at end of period	67,298	46,084
Long Duration Fixed Income | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	67,298	46,084
Actual return on plan assets:
Fair value of plan assets at end of period	67,298	46,084
Long Duration Fixed Income | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Long Duration Fixed Income | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Core Fixed Income
Pension plan
Assets measured at fair value		3,081
Actual return on plan assets:
Fair value of plan assets at end of period		3,081
Core Fixed Income | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value		3,081
Actual return on plan assets:
Fair value of plan assets at end of period		3,081
Core Fixed Income | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value		0
Actual return on plan assets:
Fair value of plan assets at end of period		0
Core Fixed Income | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value		0
Actual return on plan assets:
Fair value of plan assets at end of period		0
High Yield
Pension plan
Assets measured at fair value	8,764	6,145
Actual return on plan assets:
Fair value of plan assets at end of period	8,764	6,145
High Yield | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	8,764	6,145
Actual return on plan assets:
Fair value of plan assets at end of period	8,764	6,145
High Yield | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
High Yield | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Emerging Markets Debt
Pension plan
Assets measured at fair value	6,583	4,638
Actual return on plan assets:
Fair value of plan assets at end of period	6,583	4,638
Emerging Markets Debt | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	6,583	4,638
Actual return on plan assets:
Fair value of plan assets at end of period	6,583	4,638
Emerging Markets Debt | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Emerging Markets Debt | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Hedge Fund of Funds
Pension plan
Assets measured at fair value	9,519	22,618
Actual return on plan assets:
Fair value of plan assets at end of period	9,519	22,618
Hedge Fund of Funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Hedge Fund of Funds | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Hedge Fund of Funds | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	9,519	22,618
Rollforward of the balances of plan assets that are valued using level 3 inputs (in thousands)
Beginning balance	22,618	21,596
Actual return on plan assets:
Relating to assets still held at the reporting date	446	1,022
Relating to assets sold during the period	181
Purchases, sales and settlements, net	(13,726)
Fair value of plan assets at end of period	9,519	22,618
Cash
Pension plan
Assets measured at fair value	8,867	4,510
Actual return on plan assets:
Fair value of plan assets at end of period	8,867	4,510
Cash | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	8,867	4,510
Actual return on plan assets:
Fair value of plan assets at end of period	8,867	4,510
Cash | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Cash | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Other Investments
Pension plan
Assets measured at fair value	8,808	8,200
Actual return on plan assets:
Fair value of plan assets at end of period	8,808	8,200
Other Investments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension plan
Assets measured at fair value	8,808	8,200
Actual return on plan assets:
Fair value of plan assets at end of period	8,808	8,200
Other Investments | Significant Observable Inputs (Level 2)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	0	0
Other Investments | Significant Unobservable Inputs (Level 3)
Pension plan
Assets measured at fair value	0	0
Actual return on plan assets:
Fair value of plan assets at end of period	$ 0	$ 0