Pension Plan and Postretirement Benefits Other Than Pension (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits
Components of net periodic benefit cost:
Service cost	$ 9,373,000	$ 7,101,000	$ 6,140,000
Interest cost	7,570,000	7,195,000	6,596,000
Expected return on plan assets	(8,799,000)	(8,764,000)	(7,499,000)
Actuarial loss amortization	4,563,000	1,805,000	1,617,000
Prior service cost amortization	555,000	555,000	555,000
Transition obligation amortization	5,000	5,000	5,000
Net periodic benefit cost	13,267,000	7,897,000	7,414,000
Net periodic pension benefit cost related to discontinued operations	738,000	525,000	489,000
Amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost in next fiscal year
Estimated net loss that will be amortized from accumulated other comprehensive income into net periodic benefit cost	4,400,000
Estimated prior service cost that will be amortized from accumulated other comprehensive income into net periodic benefit cost	555,000
Estimated transition obligation that will be amortized from accumulated other comprehensive income into net periodic benefit cost	5,000
Weighted average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	4.99%	6.00%	6.25%
Expected return on plan assets (as a percent)	7.75%	7.75%	7.75%
Rate of compensation increase (as a percent)	4.04%	3.86%	3.86%
Expected benefit payments
2013	7,985,000
2014	9,567,000
2015	8,022,000
2016	10,691,000
2017	10,147,000
2018 through 2022	60,647,000
Total	107,059,000
Expected contribution in the next fiscal year	10,000,000
Pension Benefits | Maximum
Expected benefit payments
Expected contribution in the next fiscal year	20,000,000
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	693,000	558,000	443,000
Interest cost	400,000	402,000	364,000
Actuarial loss amortization	12,000
Prior service cost amortization	55,000	55,000	45,000
Net periodic benefit cost	1,160,000	1,015,000	852,000
Net periodic pension benefit cost related to discontinued operations	11,000	18,000	20,000
Amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost in next fiscal year
Estimated prior service cost that will be amortized from accumulated other comprehensive income into net periodic benefit cost	55,000
Weighted average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	5.00%	6.00%	6.25%
Expected benefit payments
2013	304,000
2014	317,000
2015	349,000
2016	377,000
2017	402,000
2018 through 2022	2,961,000
Total	4,710,000
Contributions by participants	$ 337,000	$ 359,000	$ 237,000