Pension Plan and Other Postretirement Benefits (Details) (USD $)			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Pension Benefits [Member]	Jun. 30, 2011 Pension Benefits [Member]	Jun. 30, 2012 Pension Benefits [Member]	Jun. 30, 2011 Pension Benefits [Member]	Jun. 30, 2012 Other Postretirement Benefits [Member]	Jun. 30, 2011 Other Postretirement Benefits [Member]	Jun. 30, 2012 Other Postretirement Benefits [Member]	Jun. 30, 2011 Other Postretirement Benefits [Member]
Service cost			$ 2,735,000	$ 2,331,000	$ 5,471,000	$ 4,662,000	$ 458,000	$ 339,000	$ 916,000	$ 677,000
Interest cost			1,012,000	918,000	2,025,000	1,835,000	99,000	63,000	199,000	126,000
Expected return on plan assets			(1,356,000)	(1,100,000)	(2,713,000)	(2,199,000)
Amortization of transition obligation							16,000	16,000	32,000	32,000
Amortization of prior service cost			72,000	86,000	143,000	172,000	4,000	3,000	7,000	7,000
Amortization of net loss			305,000	214,000	610,000	428,000	23,000	3,000	46,000	6,000
Net periodic benefit cost			2,768,000	2,449,000	5,536,000	4,898,000	600,000	424,000	1,200,000	848,000
Defined benefit plan, Expected employer contributions			10,000,000		10,000,000		100,000		100,000
Employer contributions					$ 9,500,000				$ 100,000
Common stock purchased under non-qualified plan, Treasury stock, Shares	101,659	98,889