Pension Plan and Other Postretirement Benefits (Details) (USD $)			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Pension Benefits [Member]	Sep. 30, 2011 Pension Benefits [Member]	Sep. 30, 2012 Pension Benefits [Member]	Sep. 30, 2011 Pension Benefits [Member]	Sep. 30, 2012 Other Postretirement Benefits [Member]	Sep. 30, 2011 Other Postretirement Benefits [Member]	Sep. 30, 2012 Other Postretirement Benefits [Member]	Sep. 30, 2011 Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 2,736,000	$ 2,330,000	$ 8,207,000	$ 6,992,000	$ 458,000	$ 338,000	$ 1,374,000	$ 1,015,000
Interest cost			1,013,000	918,000	3,038,000	2,753,000	100,000	63,000	299,000	189,000
Expected return on plan assets			(1,356,000)	(1,099,000)	(4,069,000)	(3,298,000)
Amortization of transition obligation							16,000	16,000	48,000	48,000
Amortization of prior service cost			71,000	86,000	214,000	258,000	4,000	4,000	11,000	11,000
Amortization of net loss			305,000	214,000	915,000	642,000	23,000	2,000	69,000	8,000
Net periodic benefit cost			2,769,000	2,449,000	8,305,000	7,347,000	601,000	423,000	1,801,000	1,271,000
Employer contributions					$ 11,000,000				$ 100,000
Common stock purchased under non-qualified plan, Treasury stock, Shares	66,791	98,889