Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 171	$ 193
Interest cost	518	488
Expected return on plan assets	(754)	(756)
Amortization of net actuarial loss	323	328
Accretion of prior service cost	(71)	(70)
Net periodic benefit cost	187	183
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	12	15
Interest cost	33	28
Expected return on plan assets	0	0
Amortization of net actuarial loss	6	13
Accretion of prior service cost	0	0
Net periodic benefit cost	$ 51	$ 56