Retirement and Employee Benefit Plans (Changes in the Plans Benefit Obligations, Fair Value of Assets, and Funded Status) (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
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,296	1,832	1,354
Interest cost	441	398	252
Change In Benefit Obligation [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at January 1	105,432	81,738
Service cost	13,789	10,942
Interest cost	4,104	4,050
Actuarial loss	(11,107)	14,981
Benefits paid	(8,492)	(6,951)
Plan amendments		672
Settlements	(520)
Benefit obligation at December 31	103,206	105,432
Change In Benefit Obligation [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at January 1	11,464	6,793
Service cost	2,296	1,832
Interest cost	441	398
Participant contributions	24	21
Actuarial loss	(1,706)	2,525
Benefits paid	(139)	(105)
Benefit obligation at December 31	12,380	11,464
Change In Plan Assets [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	12,520	11,084
Benefits paid	(8,492)	(6,951)
Settlements	(507)
Fair value of plan assets at January 1	83,347	68,023
Fair value of plan assets at December 31	99,339	83,347
Actual return/(loss) on plan assets	12,471	11,191
Funded status of plans at December 31	(3,867)	(22,085)
Change In Plan Assets [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	115	84
Participant contributions	24	21
Benefits paid	(139)	(105)
Funded status of plans at December 31	$ (12,380)	$ (11,464)