Employee Benefit Plans (Schedule of Defined Benefit Plans Disclosures) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Value of Plan Assets at beginning of year	$ 336,709
Value of Plan Assets at end of year		$ 336,709
Pension Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligations at beginning of year	353,736	355,468
Service cost	9	21,478	$ 27,065
Interest cost	14,604	17,070	16,207
Re-entry of former Magnum employees	0	0
Plan amendments	0	(23)
Curtailments	0	(25,787)
Benefits paid	(61,955)	(53,974)
Other-primarily actuarial loss (gain)	(5,102)	39,504
Benefit Obligations at end of year	301,292	353,736	355,468
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Value of Plan Assets at beginning of year	336,709	347,952
Actual return on plan assets	(1,679)	36,130
Employer contributions	424	6,601
Benefits paid	(61,955)	(53,974)
Value of Plan Assets at end of year	273,499	336,709	347,952
Accrued benefit cost	(27,793)	(17,027)
Prior service credit (cost)	0	0
Accumulated gain (loss)	16,769	11,332
Total not yet recognized as a component of net periodic benefit cost	(16,769)	(11,332)
Current liability	(420)	(767)
Noncurrent liability	(27,373)	(16,260)
Pension and Other Postretirement Defined Benefit Plans, Liabilities	(27,793)	(17,027)
Other Postretirement Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligations at beginning of year	36,098	42,531
Service cost	866	1,649	2,027
Interest cost	1,904	1,841	1,739
Re-entry of former Magnum employees	85,843	0
Plan amendments	0	0
Curtailments	0	0
Benefits paid	(3,646)	(3,431)
Other-primarily actuarial loss (gain)	(17,605)	(6,492)
Benefit Obligations at end of year	103,460	36,098	42,531
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Value of Plan Assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	3,646	3,431
Benefits paid	(3,646)	(3,431)
Value of Plan Assets at end of year	0	0	$ 0
Accrued benefit cost	(103,460)	(36,098)
Prior service credit (cost)	26,944	21,972
Accumulated gain (loss)	(11,313)	(9,125)
Total not yet recognized as a component of net periodic benefit cost	38,257	31,097
Current liability	(3,650)	(3,430)
Noncurrent liability	(99,810)	(32,668)
Pension and Other Postretirement Defined Benefit Plans, Liabilities	$ (103,460)	$ (36,098)