Components of Net Periodic Benefit Cost (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Defined contribution plans
Defined contribution plan, costs recognized	$ 4,800,000	$ 4,400,000	$ 9,900,000	$ 8,300,000
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost - benefits earned during the period	3,395,000	3,348,000	6,782,000	6,596,000
Interest cost on projected benefit obligation	8,836,000	8,651,000	17,701,000	17,476,000
Expected return on plan assets	(10,117,000)	(9,986,000)	(20,189,000)	(20,108,000)
Amortization of unrecognized transition obligation	67,000	56,000	128,000	118,000
Amortization of prior service cost	521,000	658,000	1,040,000	1,306,000
Recognized actuarial net (gain) or loss	5,856,000	4,055,000	11,712,000	8,110,000
Settlement loss (gain)	(2,491,000)	31,000	(2,491,000)	31,000
Net periodic benefit cost	6,067,000	6,813,000	14,683,000	13,529,000
Other Benefits
Components of Net Periodic Benefit Cost
Service cost - benefits earned during the period	81,000	71,000	163,000	132,000
Interest cost on projected benefit obligation	122,000	137,000	220,000	275,000
Amortization of prior service cost	(134,000)	(138,000)	(321,000)	(276,000)
Recognized actuarial net (gain) or loss	(107,000)	(113,000)	(218,000)	(225,000)
Net periodic benefit cost	$ (38,000)	$ (43,000)	$ (156,000)	$ (94,000)