Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 193	$ 137	$ 386	$ 273
Interest cost	488	475	976	950
Expected return on plan assets	(756)	(745)	(1,512)	(1,490)
Amortization of net actuarial loss	326	165	654	326
Accretion of prior service cost	(70)	(71)	(140)	(141)
Net periodic benefit cost (income)	181	(39)	364	(82)
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	14	18	29	37
Interest cost	27	31	55	67
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss	14	2	27	5
Accretion of prior service cost	0	2	0	(3)
Net periodic benefit cost (income)	$ 55	$ 53	$ 111	$ 106