Pension Plan and Other Postretirement Benefits (Details) (USD $)			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Pension Benefits [Member]	Mar. 31, 2012 Pension Benefits [Member]	Mar. 31, 2013 Other Postretirement Benefits [Member]	Mar. 31, 2012 Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 3,447,000	$ 2,736,000	$ 574,000	$ 458,000
Interest cost			1,026,000	1,013,000	110,000	100,000
Expected return on plan assets			(1,534,000)	(1,357,000)
Amortization of transition obligation						16,000
Amortization of prior service cost			26,000	71,000	4,000	3,000
Amortization of net loss			385,000	305,000	30,000	23,000
Net periodic benefit cost			3,350,000	2,768,000	718,000	600,000
Defined benefit plan, Expected employer contributions			12,000,000		100,000
Employer contributions			$ 3,000,000		$ 100,000
Common stock purchased under non-qualified plan, Treasury stock, Shares	14,223	64,715