Benefit Plans (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Pension Benefits [Member]
Components of net periodic benefit expense
Service cost	$ 5,412	$ 5,051	$ 16,238	$ 15,153
Interest cost	7,518	7,217	22,554	21,651
Expected return on plan assets	(10,822)	(10,528)	(32,468)	(31,584)
Amortization of transition asset	(1)	1	(3)	5
Amortization of prior service cost	(1,442)	(1,442)	(4,326)	(4,326)
Amortization of gains	5,873	3,748	17,621	11,242
Settlements	1,750	3,925	5,250	7,375
Benefit expense	8,288	7,972	24,866	19,516
Post Retirement Benefits [Member]
Components of net periodic benefit expense
Service cost	0	0	0	0
Interest cost	404	433	1,214	1,299
Expected return on plan assets	0	0	0	0
Amortization of transition asset	0	0	0	0
Amortization of prior service cost	(338)	(339)	(1,014)	(1,014)
Amortization of gains	(106)	(174)	(318)	(525)
Settlements	0	0	0	0
Benefit expense	$ (40)	$ (80)	$ (118)	$ (240)