Pension and Other Postretirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Benefits [Member]
Components of net periodic cost (benefit):
Service cost	$ 1,878	$ 1,536	$ 5,715	$ 4,609
Interest cost	3,594	3,367	10,936	10,102
Expected return on assets	(5,930)	(5,467)	(18,045)	(16,402)
Amortization of:
Prior service (benefit) cost	6	51	18	152
Actuarial loss	1,393	180	4,240	539
Net periodic cost (benefit)	941	(333)	2,864	(1,000)
Postretirement Benefits [Member]
Components of net periodic cost (benefit):
Service cost	194	241	580	722
Interest cost	392	564	1,176	1,691
Expected return on assets	(355)	(478)	(1,063)	(1,432)
Amortization of:
Transition obligation	0	1	1	2
Prior service (benefit) cost	(337)	(487)	(1,009)	(1,462)
Actuarial loss	133	28	397	86
Net periodic cost (benefit)	$ 27	$ (131)	$ 82	$ (393)