Benefit Obligations (Details 11) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	$ 10,637	$ 10,488
Level 1 [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	10,637	10,488
Level 2 [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	0	0
Level 3 [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	0	0
Money-market funds [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	1,353	2,061
Money-market funds [Member] | Level 1 [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	1,353	2,061
Money-market funds [Member] | Level 2 [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	0	0
Money-market funds [Member] | Level 3 [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	0	0
Mutual funds [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	9,284	8,427
Mutual funds [Member] | Level 1 [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	9,284	8,427
Mutual funds [Member] | Level 2 [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	0	0
Mutual funds [Member] | Level 3 [Member]
Fair values of the assets for the non-qualified supplemental pension plan by asset category
Total	$ 0	$ 0