Pension Plan and Other Postretirement Benefits (Details) (USD $)			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Pension Benefits [Member]	Sep. 30, 2012 Pension Benefits [Member]	Sep. 30, 2013 Pension Benefits [Member]	Sep. 30, 2012 Pension Benefits [Member]	Sep. 30, 2013 Other Postretirement Benefits [Member]	Sep. 30, 2012 Other Postretirement Benefits [Member]	Sep. 30, 2013 Other Postretirement Benefits [Member]	Sep. 30, 2012 Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 3,447,000	$ 2,736,000	$ 10,342,000	$ 8,207,000	$ 574,000	$ 458,000	$ 1,722,000	$ 1,374,000
Interest cost			1,026,000	1,013,000	3,078,000	3,038,000	111,000	100,000	331,000	299,000
Expected return on plan assets			(1,534,000)	(1,356,000)	(4,602,000)	(4,069,000)
Amortization of transition obligation								16,000		48,000
Amortization of prior service cost			25,000	71,000	77,000	214,000	4,000	4,000	11,000	11,000
Amortization of net loss			386,000	305,000	1,156,000	915,000	30,000	23,000	90,000	69,000
Net periodic benefit cost			3,350,000	2,769,000	10,051,000	8,305,000	719,000	601,000	2,154,000	1,801,000
Defined benefit plan, Expected employer contributions			3,000,000		3,000,000
Employer contributions					$ 9,000,000				$ 100,000
Common stock purchased under non-qualified plan, Treasury stock, Shares	14,625	64,715