Employee Benefit Plans (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,190,000	$ 1,985,000	$ 6,380,000	$ 3,970,000
Interest cost	1,204,000	950,000	2,407,000	1,899,000
Expected return on plan assets	(1,176,000)	(1,022,000)	(2,352,000)	(2,043,000)
Amortization of prior service cost (credit)	77,000	77,000	154,000	154,000
Amortization of actuarial loss	826,000	151,000	1,653,000	302,000
Net periodic benefit cost	4,121,000	2,141,000	8,242,000	4,282,000
Contributions estimated to be paid in 2012	13,300,000		13,300,000
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	137,000	91,000	275,000	182,000
Interest cost	258,000	260,000	515,000	519,000
Amortization of prior service cost (credit)	(211,000)	(213,000)	(424,000)	(426,000)
Amortization of actuarial loss	161,000	62,000	322,000	125,000
Net periodic benefit cost	345,000	200,000	688,000	400,000
Contributions estimated to be paid in 2012	$ 300,000		$ 300,000