Defined Benefit Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits [Member]
Components of net periodic (benefit) cost [Abstract]
Service cost	$ 560	$ 655	$ 1,120	$ 1,310
Interest cost	1,051	998	2,102	1,996
Expected return on plan assets	(1,835)	(2,150)	(3,670)	(4,300)
Net amortization	483	546	966	1,092
Total cost (benefit)	259	49	518	98
Other Benefits [Member]
Components of net periodic (benefit) cost [Abstract]
Service cost	4	4	8	8
Interest cost	94	91	188	182
Expected return on plan assets	0	0	0	0
Net amortization	29	15	58	30
Total cost (benefit)	$ 127	$ 110	$ 254	$ 220