Maximum Potential Total of Future Payments Under Commitment Instruments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	$ 661,860
Maximum potential total of future payments under commitments	1,039,476
Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	258,177
Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	63,837
Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	3,059
Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	191,281
Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	672,997
Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	115,353
Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	535,738
Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	21,906
Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	108,302
Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	74,902
Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	$ 33,400
Earl Kennedy [Member]
Loss Contingencies [Line Items]
Loss Contingency, Damages Sought	20000
Balance on First Anniversary [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	$ 935,904
Balance on First Anniversary [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	233,266
Balance on First Anniversary [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	55,524
Balance on First Anniversary [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Balance on First Anniversary [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	177,742
Balance on First Anniversary [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	629,128
Balance on First Anniversary [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	114,053
Balance on First Anniversary [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	494,210
Balance on First Anniversary [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	20,865
Balance on First Anniversary [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	73,510
Balance on First Anniversary [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	40,110
Balance on First Anniversary [Member] | Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	33,400
More Than One And Within Three Years From Balance Sheet Date [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	83,333
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	24,911
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	8,313
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	3,059
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	13,539
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	43,869
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	1,300
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	41,528
More Than One And Within Three Years From Balance Sheet Date [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	1,041
More Than One And Within Three Years From Balance Sheet Date [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	14,553
More Than One And Within Three Years From Balance Sheet Date [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	14,553
More Than One And Within Three Years From Balance Sheet Date [Member] | Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	12,405
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
More Than Three And Within Five Years From Balance Sheet Date [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	12,405
More Than Three And Within Five Years From Balance Sheet Date [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	12,405
More Than Three And Within Five Years From Balance Sheet Date [Member] | Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	7,834
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member] | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member] | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bond [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds:
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds: | Employee-Related
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds: | Environmental
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Surety Bonds: | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	0
Beyond Five Years of Balance Sheet Date [Member] | Guarantees [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	7,834
Beyond Five Years of Balance Sheet Date [Member] | Guarantees [Member] | Other Commitments
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	7,834
Beyond Five Years of Balance Sheet Date [Member] | Guarantees [Member] | Coal Segment [Member]
Loss Contingencies [Line Items]
Maximum potential total of future payments under commitments	$ 0