Pension Plan and Employee Benefits, Amounts Recognized in Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 330,193		$ 292,529
Amounts recognized in other comprehensive income [Abstract]
Net actuarial loss (gain) occurring during year	20,389		14,001
Net actuarial loss (gain) amortized during year	5,556		3,156
Transition obligation (asset) amortized during year	0		0
Prior service cost (credit) amortized during year	(71)		(71)
Amounts in accumulated other comprehensive income to be recognized in next fiscal year [Abstract]
Net actuarial loss (gain)	7,750
Transition obligation (asset)	0
Prior service cost (credit)	71
Amounts in accumulated other comprehensive income [Abstract]
Net actuarial loss (gain)	133,186		118,353
Transition obligation (asset)	0		0
Prior service cost (credit)	(630)		(702)
Other Benefits [Member]
Amounts recognized in other comprehensive income [Abstract]
Net actuarial loss (gain) occurring during year	141		1,231
Net actuarial loss (gain) amortized during year	1,011		972
Transition obligation (asset) amortized during year	20		20
Prior service cost (credit) amortized during year	(206)		(2,021)
Amounts in accumulated other comprehensive income to be recognized in next fiscal year [Abstract]
Net actuarial loss (gain)	876	[1]
Transition obligation (asset)	20
Prior service cost (credit)	0
Amounts in accumulated other comprehensive income [Abstract]
Net actuarial loss (gain)	12,620		13,491
Transition obligation (asset)	55		76
Prior service cost (credit)	0		(206)
Estimated Medicare Part D subsidy through 2012 in net actuarial loss	(139)
SERP Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	42,410		38,337
Amounts recognized in other comprehensive income [Abstract]
Net actuarial loss (gain) occurring during year	2,529		2,878
Net actuarial loss (gain) amortized during year	940		925
Prior service cost (credit) amortized during year	54		54
Amounts in accumulated other comprehensive income to be recognized in next fiscal year [Abstract]
Net actuarial loss (gain)	1,195
Prior service cost (credit)	54
Amounts in accumulated other comprehensive income [Abstract]
Net actuarial loss (gain)	15,588		13,969
Prior service cost (credit)	$ 334		$ 387

[1] )Net of the estimated Medicare Part D subsidy through 2012 of $139 thousand