Accumulated Other Comprehensive Loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Changes in accumulated other comprehensive loss, net of tax
Balance at the beginning of the period	$ (91,096)
Amount reclassified from other comprehensive loss	1,000
Balance at the end of the period	(90,096)
Accumulated other comprehensive loss, net of tax
Tax provision	17,426	(906)
Reclassifications for the period, Net of tax	1,000
Pension and other post-retirement benefit obligation changes | Amounts reclassified out of accumulated other comprehensive loss
Changes in accumulated other comprehensive loss, net of tax
Amount reclassified from other comprehensive loss	1,000
Accumulated other comprehensive loss, net of tax
Amortization of prior service benefit	(490)
Amortization of actuarial losses	2,103
Total recognized in other comprehensive loss	1,613
Tax provision	613
Reclassifications for the period, Net of tax	$ 1,000