Employee Benefit Plans (Details) (USD $)	3 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended
	Mar. 31, 2010	Jun. 30, 2011 Pension Plans	Jun. 30, 2010 Pension Plans	Jun. 30, 2011 Pension Plans	Jun. 30, 2010 Pension Plans	Jun. 30, 2011 Postretirement Benefit Plans	Jun. 30, 2010 Postretirement Benefit Plans	Jun. 30, 2011 Postretirement Benefit Plans	Jun. 30, 2010 Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost		$ 2,293,000	$ 2,144,000	$ 4,586,000	$ 4,287,000	$ 442,000	$ 516,000	$ 885,000	$ 1,032,000
Interest cost		2,740,000	2,841,000	5,480,000	5,683,000	1,111,000	1,208,000	2,222,000	2,417,000
Expected long-term return on assets		(3,868,000)	(3,229,000)	(7,736,000)	(6,458,000)	(1,104,000)	(996,000)	(2,209,000)	(1,993,000)
Actuarial loss		1,609,000	1,443,000	3,218,000	2,887,000
Prior service cost amortization		124,000	124,000	248,000	248,000
Transition amortization						479,000	479,000	958,000	958,000
Net periodic expense		2,898,000	3,323,000	5,796,000	6,647,000	928,000	1,207,000	1,856,000	2,414,000
Estimated Future Employer Contributions in Current Fiscal Year		7,200,000		7,200,000		1,900,000		1,900,000
Benefit Payments Made in Current Fiscal Year		36,000		2,200,000
Estimated Future Benefit Payments in Current Fiscal Year		71,000
Contributions by Employer in Current Fiscal Year						900,000		1,900,000
Income Tax Expense, Tax Treatement for Medicare Part D subsidy	$ 128,000