Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 193	$ 137	$ 579	$ 410
Interest cost	488	476	1,463	1,426
Expected return on plan assets	(756)	(746)	(2,268)	(2,236)
Amortization of net actuarial loss	328	164	982	490
Accretion of prior service cost	(70)	(71)	(210)	(212)
Net periodic benefit cost (income)	183	(40)	546	(122)
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	15	19	44	56
Interest cost	28	32	83	99
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss	13	4	40	9
Accretion of prior service cost	0	(1)	0	(4)
Net periodic benefit cost (income)	$ 56	$ 54	$ 167	$ 160