Unrecorded Unconditional Purchase Obligation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Unrecorded Unconditional Purchase Obligation [Line Items]
Total costs related to purchase obligations	$ 69,632	$ 57,427	$ 261,619	$ 164,169
Guarantor Obligations, Maximum Exposure, Undiscounted	1,465,065		1,465,065
Purchase Commitment [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Less than 1 year	240,865		240,865
1 - 3 years	371,127		371,127
3 - 5 years	224,394		224,394
More than 5 years	492,825		492,825
Total Purchase Obligations	1,329,211		1,329,211
Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	1,175,533		1,175,533
More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	270,384		270,384
More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	8,446		8,446
Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	10,702		10,702
Standby Letters of Credit [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	326,474		326,474
Standby Letters of Credit [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	165,759		165,759
Standby Letters of Credit [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	160,715		160,715
Standby Letters of Credit [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Standby Letters of Credit [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Surety Bonds [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	891,760		891,760
Surety Bonds [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	849,550		849,550
Surety Bonds [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	42,209		42,209
Surety Bonds [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Surety Bonds [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	1		1
Guarantees [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	246,831		246,831
Guarantees [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	160,224		160,224
Guarantees [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	67,460		67,460
Guarantees [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	8,446		8,446
Guarantees [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	10,701		10,701
Employee Related Commitments [Member] | Standby Letters of Credit [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	151,302		151,302
Employee Related Commitments [Member] | Standby Letters of Credit [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	71,915		71,915
Employee Related Commitments [Member] | Standby Letters of Credit [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	79,387		79,387
Employee Related Commitments [Member] | Standby Letters of Credit [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Employee Related Commitments [Member] | Standby Letters of Credit [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Employee Related Commitments [Member] | Surety Bonds [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	204,884		204,884
Employee Related Commitments [Member] | Surety Bonds [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	204,884		204,884
Employee Related Commitments [Member] | Surety Bonds [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Employee Related Commitments [Member] | Surety Bonds [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Employee Related Commitments [Member] | Surety Bonds [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Environment Related Commitments [Member] | Standby Letters of Credit [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	39,363		39,363
Environment Related Commitments [Member] | Standby Letters of Credit [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	37,635		37,635
Environment Related Commitments [Member] | Standby Letters of Credit [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	1,728		1,728
Environment Related Commitments [Member] | Standby Letters of Credit [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Environment Related Commitments [Member] | Standby Letters of Credit [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Environment Related Commitments [Member] | Surety Bonds [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	661,191		661,191
Environment Related Commitments [Member] | Surety Bonds [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	619,041		619,041
Environment Related Commitments [Member] | Surety Bonds [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	42,150		42,150
Environment Related Commitments [Member] | Surety Bonds [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Environment Related Commitments [Member] | Surety Bonds [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Other Commitments [Member] | Standby Letters of Credit [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	135,809		135,809
Other Commitments [Member] | Standby Letters of Credit [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	56,209		56,209
Other Commitments [Member] | Standby Letters of Credit [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	79,600		79,600
Other Commitments [Member] | Standby Letters of Credit [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Other Commitments [Member] | Standby Letters of Credit [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Other Commitments [Member] | Surety Bonds [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	25,685		25,685
Other Commitments [Member] | Surety Bonds [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	25,625		25,625
Other Commitments [Member] | Surety Bonds [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	59		59
Other Commitments [Member] | Surety Bonds [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Other Commitments [Member] | Surety Bonds [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	1		1
Other Commitments [Member] | Guarantees [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	63,131		63,131
Other Commitments [Member] | Guarantees [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	34,974		34,974
Other Commitments [Member] | Guarantees [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	9,010		9,010
Other Commitments [Member] | Guarantees [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	8,446		8,446
Other Commitments [Member] | Guarantees [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	10,701		10,701
Coal Segment [Member] | Guarantees [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	183,700		183,700
Coal Segment [Member] | Guarantees [Member] | Balance on First Anniversary [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	125,250		125,250
Coal Segment [Member] | Guarantees [Member] | More Than One And Within Three Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	58,450		58,450
Coal Segment [Member] | Guarantees [Member] | More Than Three And Within Five Years From Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Coal Segment [Member] | Guarantees [Member] | Beyond Five Years of Balance Sheet Date [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	0		0
Murray Energy [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Contractual Obligation	$ 3,000		$ 3,000