Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

+ Details

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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- Definition

The average forward price on the group of price risk forward or futures contracts, such as gas futures contracts.

+ References

No definition available.

+ Details

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- Definition

Cap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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- Definition

The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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- Definition

The time remaining until the derivative matures.

+ References

No definition available.

+ Details

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- Definition

Aggregate notional amount of all interest rate derivatives designated as hedging instruments in cash flow hedges. Notional amount refers to the monetary amount specified in the interest rate derivative contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5579245-113959

+ Details

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Period Type:	instant

- Definition

Number of monthly interest payments required under an equipment financing arrangement.

+ References

No definition available.

+ Details

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- Definition

Number of monthly interest payments, which are protected against the variability in expected future cash flows attributable to changes in the benchmark interest rate.

+ References

No definition available.

+ Details

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Namespace Prefix:	wlt_
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Derivative Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended		1 Months Ended		1 Months Ended
	Jun. 30, 2011 Interest rate swap - June 2011	Jun. 27, 2011 Interest rate swap - June 2011	Dec. 31, 2008 Interest rate swap - December 2008 M	Dec. 30, 2008 Interest rate swap - December 2008	Jun. 30, 2011 Interest rate cap	Jun. 27, 2011 Interest rate cap	Jun. 07, 2011 Natural Gas Hedge DollarPerMMBtu MMBTU
Fair Value of Financial Instruments
Notional value		$ 450.0		$ 31.5		$ 255.0
Debt instrument, description of variable rate basis	3-month LIBOR		1-month LIBOR		3-month LIBOR
Agreement period (in years)		3 years				3 years	1 year
Fixed rate (as a percent)		1.17%		1.84%
Number of monthly interest payments, hedged			62
Number of monthly interest payments			64
Fixed rate (as a percent)						2.00%
Amount hedged (in mmbtus)							4,200,000
Price per mmbtu of forecasted natural gas (in dollars per mmbtu)							5.00
Percentage of forecasted natural gas to be hedged							35.00%