Employee Benefit Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Increase (Decrease) in net periodic benefit costs for the pension plans	$ 2,000,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3,190,000	1,985,000
Interest cost	1,203,000	949,000
Expected return on plan assets	(1,176,000)	(1,021,000)
Amortization of prior service cost (credit)	77,000	77,000
Amortization of actuarial loss	827,000	151,000
Net periodic benefit cost	4,121,000	2,141,000
Contributions estimated to be paid in 2012	12,700,000
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	138,000	91,000
Interest cost	257,000	259,000
Expected return on plan assets
Amortization of prior service cost (credit)	(213,000)	(213,000)
Amortization of actuarial loss	161,000	63,000
Net periodic benefit cost	343,000	200,000
Contributions estimated to be paid in 2012	$ 600,000