Employee Benefits (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Pension Plan [Member]
Net periodic benefit cost
Service cost	$ 1,777,000	$ 792,000	$ 3,846,000	$ 2,375,000
Interest cost	1,263,000	1,190,000	3,787,000	3,570,000
Expected return on plan assets	(1,341,000)	(1,322,000)	(4,023,000)	(3,966,000)
Amortization of prior service cost	2,000	2,000	5,000	8,000
Amortization of net loss	1,035,000	592,000	3,311,000	1,776,000
Net periodic benefit cost	2,736,000	1,254,000	6,926,000	3,763,000
2012 Pension Plan Contribution Estimated and Disclosed in Prior Year 10K					7,000,000
Contribution by Employer			5,000,000
Postretirement Benefit Plan [Member]
Net periodic benefit cost
Service cost	496,000	496,000	1,488,000	1,489,000
Interest cost	398,000	398,000	1,194,000	1,193,000
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	(8,000)	(8,000)	(24,000)	(24,000)
Amortization of net loss	56,000	56,000	168,000	168,000
Net periodic benefit cost	942,000	942,000	2,826,000	2,826,000
Mercer Insurance Group [Member]
Net periodic benefit cost
Net periodic benefit cost	$ 600,000		$ 600,000