Pension and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 5,551	$ 6,030	$ 16,654	$ 18,089
Interest cost	6,704	5,979	20,113	17,936
Expected return on plan assets	(6,656)	(5,977)	(19,968)	(17,931)
Amortization of: Net actuarial loss	4,410	6,593	13,229	19,778
Amortization of: Prior service cost (gain)	238	343	714	1,031
Settlement loss			789	0
Net periodic benefit cost	10,247	12,968	31,531	38,903
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	614	661	1,841	1,983
Interest cost	834	718	2,502	2,154
Expected return on plan assets	0	0	0	0
Amortization of: Net actuarial loss	317	449	951	1,346
Amortization of: Prior service cost (gain)	(545)	(545)	(1,635)	(1,635)
Settlement loss			0	0
Net periodic benefit cost	$ 1,220	$ 1,283	$ 3,659	$ 3,848