Retirement and Employee Benefit Plans (Pension and Other Postretirement Benefit Costs) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 13,789	$ 10,942	$ 9,323
Interest cost	4,104	4,050	3,671
Expected return on plan assets	(6,136)	(5,426)	(4,398)
Amortization of prior service cost	103	286	344
Amortization of net loss	1,541	1,220	856
Net periodic benefit cost	13,401	11,072	9,796
Settlements and curtailments	70
Total benefit cost	13,471	11,072	9,796
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,296	1,832	1,354
Interest cost	441	398	252
Amortization of transition obligation		64	64
Amortization of prior service cost	14	14	14
Amortization of net loss	120	93	11
Net periodic benefit cost	2,871	2,401	1,695
Total benefit cost	$ 2,871	$ 2,401	$ 1,695