Defined Benefit Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Benefits [Member]
Components of net periodic (benefit) cost [Abstract]
Service cost	$ 655	$ 587	$ 1,310	$ 1,174
Interest cost	998	1,040	1,996	2,080
Expected return on plan assets	(2,150)	(2,175)	(4,300)	(4,350)
Net amortization	546	25	1,092	50
Total cost (benefit)	49	(523)	98	(1,046)
Other Benefits [Member]
Components of net periodic (benefit) cost [Abstract]
Service cost	4	4	8	8
Interest cost	91	90	182	180
Expected return on plan assets	0	0	0	0
Net amortization	15	(6)	30	(12)
Total cost (benefit)	$ 110	$ 88	$ 220	$ 176