Benefit Plans Net Periodic Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4,288	$ 3,516	$ 3,171
Interest cost	5,349	5,313	5,231
Expected return on assets	(4,442)	(4,289)	(3,599)
Amortization of transition obligation	0	0	0
Amortization of prior service cost	414	450	470
Recognized actuarial loss	3,857	2,147	2,129
Net periodic pension cost	9,466	7,137	7,402
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	339	273	229
Interest cost	452	467	433
Expected return on assets	(151)	(129)	(130)
Amortization of transition obligation	1	57	57
Amortization of prior service cost	197	197	197
Recognized actuarial loss	195	96	48
Net periodic pension cost	$ 1,033	$ 961	$ 834