Pension Benefit and Retirement Health and Life Insurance Benefits (Obligations and Funded Status) (Details) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions			$ 1,700,000	$ 1,700,000	$ 1,500,000
Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year			193,715,000	157,340,000
Service cost			4,596,000	3,922,000	3,563,000
Interest cost			8,420,000	8,535,000	8,345,000
Actuarial (gain) loss			16,636,000	30,616,000
Defined Benefit Plan, Benefits Paid			(6,800,000)	(6,874,000)
Defined Benefit Plan, Settlement Charge	2,073,000		(6,723,000)
Special termination benefit				(176,000)
Benefit obligation at end of year	209,844,000		209,844,000	193,715,000	157,340,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year			120,565,000	125,261,000
Actual return on plan assets			13,775,000	(2,849,000)
Employer contributions	0	0	22,723,000	5,027,000
Fair value of plan assets at the end of the year	143,540,000		143,540,000	120,565,000	125,261,000
Funded status	(66,304,000)		(66,304,000)	(73,150,000)
Retirement Health and Life Insurance Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year			10,495,000	9,149,000
Service cost			630,000	693,000	661,000
Interest cost			364,000	413,000	398,000
Actuarial (gain) loss			(395,000)	1,117,000
Defined Benefit Plan, Benefits Paid			(795,000)	(877,000)
Defined Benefit Plan, Settlement Charge
Special termination benefit			(1,592,000)
Benefit obligation at end of year	11,891,000		11,891,000	10,495,000	9,149,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year			0	0
Actual return on plan assets			0	0
Employer contributions			795,000	877,000
Fair value of plan assets at the end of the year	0		0	0	0
Funded status	$ (11,891,000)		$ (11,891,000)	$ (10,495,000)