Pension Plan and Other Postretirement Benefits (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension plans
Pension Plan and Other Postretirement Benefits
Cash payments by the entity related to pension plans and other postretirement benefits			$ 14,000,000	$ 23,400,000
Estimated cash contributions in the current fiscal year			26,800,000
Components of the pension plans and other postretirement benefits
Service cost	3,539,000	4,019,000	11,973,000	13,335,000
Interest cost	4,737,000	4,140,000	14,190,000	12,266,000
Expected return on plan assets	(4,091,000)	(3,559,000)	(12,449,000)	(10,689,000)
Amortization of prior service cost	1,527,000	1,542,000	4,547,000	4,624,000
Recognized net actuarial loss	1,002,000	2,404,000	3,008,000	6,852,000
Net periodic benefit cost	6,714,000	8,546,000	21,269,000	26,388,000
Other Benefits
Pension Plan and Other Postretirement Benefits
Cash payments by the entity related to pension plans and other postretirement benefits			2,400,000	4,700,000
Estimated cash contributions in the current fiscal year			9,600,000
Components of the pension plans and other postretirement benefits
Service cost	1,398,000	1,636,000	4,637,000	5,025,000
Interest cost	1,321,000	1,121,000	3,995,000	3,339,000
Expected return on plan assets	(832,000)	(600,000)	(2,339,000)	(1,796,000)
Recognized net initial APBO		3,000		7,000
Amortization of prior service cost	11,000	21,000	33,000	61,000
Recognized net actuarial loss	656,000	961,000	2,206,000	2,794,000
Net periodic benefit cost	$ 2,554,000	$ 3,142,000	$ 8,532,000	$ 9,430,000