Benefit Plans (Net Periodic Pension Expense) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Benefit Plans [Abstract]
Service cost	$ 5,951	$ 5,544	$ 5,216
Interest cost	6,147	5,709	5,059
Expected return on plan assets	(6,698)	(6,214)	(6,040)
Amortization of prior service cost	707	643	640
Amortization of actuarial loss	1,525	1,098	858
Total net periodic pension expense	$ 7,632	$ 6,780	$ 5,733