Pension Plan and Other Postretirement Benefits (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Plan and Other Postretirement Benefits
Cash payments by the entity related to pension plans and other postretirement benefits			$ 17,800,000	$ 15,800,000
Pension Plan
Components of the pension plans and other postretirement benefits
Estimated cash contributions to benefit plans in the current fiscal year			31,300,000
Service cost	4,658,000	3,709,000	9,316,000	7,725,000
Interest cost	4,063,000	3,864,000	8,126,000	7,643,000
Expected return on plan assets	(3,565,000)	(2,886,000)	(7,130,000)	(5,779,000)
Amortization of prior service cost	1,541,000	1,570,000	3,082,000	3,141,000
Recognized net actuarial loss	2,224,000	2,075,000	4,448,000	4,001,000
Net periodic benefit cost	8,921,000	8,332,000	17,842,000	16,731,000
Other Benefits
Components of the pension plans and other postretirement benefits
Estimated cash contributions to benefit plans in the current fiscal year			9,600,000
Service cost	1,695,000	1,330,000	3,390,000	2,747,000
Interest cost	1,109,000	1,005,000	2,218,000	1,972,000
Expected return on plan assets	(598,000)	(448,000)	(1,196,000)	(916,000)
Recognized net initial APBO	2,000	69,000	4,000	138,000
Amortization of prior service cost	20,000	29,000	40,000	58,000
Recognized net actuarial loss	916,000	822,000	1,832,000	1,586,000
Net periodic benefit cost	$ 3,144,000	$ 2,807,000	$ 6,288,000	$ 5,585,000