Employee Benefit Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Plans
Components of net periodic benefit cost:
Service cost	$ 2,632,000	$ 2,293,000
Interest cost	2,700,000	2,740,000
Expected long-term return on assets	(3,563,000)	(3,868,000)
Actuarial loss	2,099,000	1,609,000
Prior service cost amortization	129,000	124,000
Net periodic expense	3,997,000	2,898,000
Estimated Future Employer Contributions in Current Fiscal Year	12,800,000
Benefit Payments Made in Current Fiscal Year	2,300,000
Estimated Future Benefit Payments in Current Fiscal Year	100,000
Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost	463,000	442,000
Interest cost	1,062,000	1,111,000
Expected long-term return on assets	(1,109,000)	(1,104,000)
Actuarial loss	9,000	0
Transition amortization	479,000	479,000
Net periodic expense	904,000	928,000
Estimated Future Employer Contributions in Current Fiscal Year	2,700,000
Contributions by Employer in Current Fiscal Year	$ 900,000