Employee Benefits (Net Periodic Benefit Costs) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 8,530	$ 6,590	$ 5,888
Interest cost	12,594	12,871	12,507
Amendments	0	0	0
Expected return on plan assets	(14,443)	(14,095)	(13,867)
Amortization of:
Net loss	10,729	6,190	3,331
Prior service cost	21	21	21
Net periodic benefit cost	17,431	11,577	7,880
Non-Qualified Retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	299	260	176
Interest cost	963	1,116	1,122
Amendments	0	0	838
Expected return on plan assets	0	0	0
Amortization of:
Net loss	627	354	218
Prior service cost	94	94	94
Net periodic benefit cost	$ 1,983	$ 1,824	$ 2,448