Pension Plan and Other Postretirement Benefits (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension Plan and Other Postretirement Benefits
Cash payments by the entity related to pension plans and other postretirement benefits			$ 28,100,000	$ 25,500,000
Pension Plan
Components of the pension plans and other postretirement benefits
Estimated cash contributions in the current fiscal year			31,100,000
Service cost	4,019,000	3,863,000	13,335,000	11,588,000
Interest cost	4,140,000	3,822,000	12,266,000	11,465,000
Expected return on plan assets	(3,559,000)	(2,890,000)	(10,689,000)	(8,669,000)
Amortization of prior service cost	1,542,000	1,571,000	4,624,000	4,712,000
Recognized net actuarial loss	2,404,000	2,000,000	6,852,000	6,001,000
Net periodic benefit cost	8,546,000	8,366,000	26,388,000	25,097,000
Other Benefits
Components of the pension plans and other postretirement benefits
Estimated cash contributions in the current fiscal year			7,200,000
Service cost	1,636,000	1,374,000	5,025,000	4,121,000
Interest cost	1,121,000	986,000	3,339,000	2,958,000
Expected return on plan assets	(600,000)	(458,000)	(1,796,000)	(1,374,000)
Recognized net initial APBO	3,000	69,000	7,000	207,000
Amortization of prior service cost	21,000	29,000	61,000	87,000
Recognized net actuarial loss	961,000	793,000	2,794,000	2,379,000
Net periodic benefit cost	$ 3,142,000	$ 2,793,000	$ 9,430,000	$ 8,378,000