Retirement and Employee Benefit Plans (Pension and Other Postretirement Benefit Costs) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10,942	$ 9,323	$ 7,096
Interest cost	4,050	3,671	3,249
Expected return on plan assets	(5,426)	(4,398)	(3,503)
Amortization of prior service cost	286	344	346
Amortization of net loss	1,220	856	806
Net Periodic Benefit Cost	11,072	9,796	7,994
Settlements and curtailments			223
Defined Benefit Plan, Net Periodic Benefit Cost	11,072	9,796	8,217
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,832	1,354	1,089
Interest cost	398	252	195
Amortization of transition obligation	64	64	65
Amortization of prior service cost	14	14	14
Amortization of net loss	93	11	21
Net Periodic Benefit Cost	2,401	1,695	1,384
Defined Benefit Plan, Net Periodic Benefit Cost	$ 2,401	$ 1,695	$ 1,384