Employee Benefit Plans (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pension Plans
Components of net periodic benefit cost:
Service cost	$ 2,632,000	$ 2,293,000	$ 7,895,000	$ 6,879,000
Interest cost	2,700,000	2,740,000	8,101,000	8,220,000
Expected long-term return on assets	(3,563,000)	(3,868,000)	(10,689,000)	(11,603,000)
Actuarial loss	2,099,000	1,609,000	6,297,000	4,826,000
Prior service cost amortization	129,000	124,000	388,000	372,000
Net periodic expense	3,997,000	2,898,000	11,992,000	8,694,000
Estimated Future Employer Contributions in Current Fiscal Year	12,800,000		12,800,000
Benefit Payments Made in Current Fiscal Year	36,000		2,300,000
Estimated Future Benefit Payments in Current Fiscal Year			36,000
Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost	463,000	442,000	1,390,000	1,327,000
Interest cost	1,062,000	1,111,000	3,186,000	3,332,000
Expected long-term return on assets	(1,109,000)	(1,104,000)	(3,328,000)	(3,314,000)
Actuarial loss	9,000	0	27,000	0
Transition amortization	479,000	479,000	1,438,000	1,438,000
Net periodic expense	904,000	928,000	2,713,000	2,783,000
Estimated Future Employer Contributions in Current Fiscal Year	900,000		900,000
Contributions by Employer in Current Fiscal Year	900,000		2,700,000
Maximum [Member] | Pension Plans
Components of net periodic benefit cost:
Estimated Future Employer Contributions in Current Fiscal Year	$ 2,100,000		$ 2,100,000