Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Interest expense	$ 991		$ 1,131	$ 1,970		$ 2,270
Income tax provision	1,300		1,567	2,741		2,661
Prior service credits	(236)		(236)	(472)		(472)
Actuarial loss	98		120	196		240
Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Total reclassifications of period, net of tax	103			205
Gains and Losses on Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Interest expense	34			66
Income tax provision	(14)			(27)
Net of tax	20			39
Amortization of Benefit Pension Items [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Prior service credits	236	[1]		472	[1]
Actuarial loss	(98)	[1]		(196)	[1]
Total before tax	138			276
Income tax provision	(55)			(110)
Net of tax	$ 83			$ 166

[1] These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. See Note 10 "Employee Post-Retirement Benefits."