Pension Benefits (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net periodic benefit cost:
Service cost	$ 288,000	$ 263,000	$ 863,000	$ 788,000
Interest cost	2,307,000	2,435,000	6,920,000	7,306,000
Expected return on plan assets	(2,746,000)	(2,666,000)	(8,237,000)	(7,997,000)
Amortization of net actuarial loss	166,000		499,000
Total net periodic benefit cost	15,000	32,000	45,000	97,000
Weighted average assumptions used to determine net costs
Discount rate (as a percent)	4.30%	5.40%	4.30%	5.40%
Expected return on plan assets (as a percent)	7.50%	7.50%	7.50%	7.50%
Employer contributions			$ 6,100,000	$ 2,700,000