Benefit Plans (Details 2) (Pension Plans [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair values of pension plan assets
Fair value of pension plan assets	$ 636,648	$ 630,303	$ 493,646
Debt Securities [Member]
Fair values of pension plan assets
Fair value of pension plan assets	152,240	127,501
Commodity funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	26,498	29,270
Equity funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	347,516	361,318
Short term funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	3,593	15,967
Venture Capital and Partnerships [Member]
Fair values of pension plan assets
Fair value of pension plan assets	106,801	96,244
Other pension plan assets [Member]
Fair values of pension plan assets
Fair value of pension plan assets		3
Level 1 [Member]
Fair values of pension plan assets
Fair value of pension plan assets	4,477	130
Level 1 [Member] | Debt Securities [Member]
Fair values of pension plan assets
Fair value of pension plan assets	0	0
Level 1 [Member] | Commodity funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	0	0
Level 1 [Member] | Equity funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	884	128
Level 1 [Member] | Short term funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	3,593	2
Level 1 [Member] | Venture Capital and Partnerships [Member]
Fair values of pension plan assets
Fair value of pension plan assets	0	0
Level 1 [Member] | Other pension plan assets [Member]
Fair values of pension plan assets
Fair value of pension plan assets		0
Level 2 [Member]
Fair values of pension plan assets
Fair value of pension plan assets	525,370	533,621
Level 2 [Member] | Debt Securities [Member]
Fair values of pension plan assets
Fair value of pension plan assets	152,240	127,193
Level 2 [Member] | Commodity funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	26,498	29,270
Level 2 [Member] | Equity funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	346,632	361,190
Level 2 [Member] | Short term funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	0	15,965
Level 2 [Member] | Venture Capital and Partnerships [Member]
Fair values of pension plan assets
Fair value of pension plan assets	0	0
Level 2 [Member] | Other pension plan assets [Member]
Fair values of pension plan assets
Fair value of pension plan assets		3
Level 3 [Member]
Fair values of pension plan assets
Fair value of pension plan assets	106,801	96,552	93,582
Level 3 [Member] | Debt Securities [Member]
Fair values of pension plan assets
Fair value of pension plan assets	0	308	320
Level 3 [Member] | Commodity funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	0	0
Level 3 [Member] | Equity funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	0	0
Level 3 [Member] | Short term funds [Member]
Fair values of pension plan assets
Fair value of pension plan assets	0	0
Level 3 [Member] | Venture Capital and Partnerships [Member]
Fair values of pension plan assets
Fair value of pension plan assets	106,801	96,244	93,262
Level 3 [Member] | Other pension plan assets [Member]
Fair values of pension plan assets
Fair value of pension plan assets		$ 0