Pension Plan and Other Postretirement Benefits (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Pension Plan and Other Postretirement Benefits
Cash payments by the entity related to pension plans and other postretirement benefits			$ 8,100,000	$ 6,600,000
Pension plans
Components of the pension plans and other postretirement benefits
Estimated contributions to benefit plans in current fiscal year			24,600,000
Service cost	2,716,000	2,451,000	5,857,000	4,902,000
Interest cost	3,600,000	3,332,000	7,342,000	6,664,000
Expected return on plan assets	(2,231,000)	(2,051,000)	(4,475,000)	(4,102,000)
Amortization of prior service cost	1,579,000	1,649,000	3,159,000	3,298,000
Recognized net actuarial loss	955,000	524,000	2,034,000	1,048,000
Net periodic benefit cost	6,619,000	5,905,000	13,917,000	11,810,000
Other Benefits
Components of the pension plans and other postretirement benefits
Estimated contributions to benefit plans in current fiscal year			7,000,000
Service cost	1,002,000	793,000	1,981,000	1,586,000
Interest cost	955,000	783,000	1,788,000	1,566,000
Expected return on plan assets	(347,000)	(279,000)	(688,000)	(558,000)
Recognized net initial APBO	69,000	69,000	138,000	138,000
Amortization of prior service cost	29,000	29,000	58,000	58,000
Recognized net actuarial loss	583,000	392,000	1,008,000	784,000
Net periodic benefit cost	$ 2,291,000	$ 1,787,000	$ 4,285,000	$ 3,574,000