Pension and Postretirement Benefits - Amounts recognized in accumulated other comprehensive income (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Amounts recognized in accumulated other comprehensive income
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	$ 15,144	$ 20,306
Prior service credit	(2,038)	(2,900)
Subtotal	13,106	17,406
Less tax effect	(4,970)	(6,601)
Total	8,136	10,805
Funded Plans
Amounts recognized in accumulated other comprehensive income
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	6,972	9,052
Prior service credit	0	0
Subtotal	6,972	9,052
Less tax effect	(2,644)	(3,433)
Total	4,328	5,619
Unfunded Pension Plans
Amounts recognized in accumulated other comprehensive income
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	3,480	4,548
Prior service credit	0	0
Subtotal	3,480	4,548
Less tax effect	(1,320)	(1,725)
Total	2,160	2,823
US Postretirement Benefit Plans
Amounts recognized in accumulated other comprehensive income
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	4,692	6,706
Prior service credit	(2,038)	(2,900)
Subtotal	2,654	3,806
Less tax effect	(1,006)	(1,443)
Total	$ 1,648	$ 2,363