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Benefit Plans (Details) (USD $)
In Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
Benefit Plans (Textuals)        
Contributions to qualified and non qualified pension plans     $ 21,500 $ 13,381
Pension Benefits [Member]
       
Components of net periodic benefit cost        
Service cost 2,713 2,499 5,426 4,998
Interest cost 7,872 7,681 15,744 15,362
Expected return on plan assets (10,184) (9,603) (20,367) (19,206)
Amortization of prior service cost 64 49 129 97
Recognized net actuarial loss 2,394 1,344 4,800 2,717
Net periodic pension benefit cost 2,859 1,970 5,732 3,968
Other Benefits [Member]
       
Components of net periodic benefit cost        
Interest cost 232 248 465 496
Amortization of prior service cost (129) (129) (258) (258)
Recognized net actuarial loss 97 71 194 142
Net periodic pension benefit cost $ 200 $ 190 $ 401 $ 380