BORROWINGS (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Dec. 31, 2012
2015 Facility
Details of Company's borrowings
Credit facility term	3 years
Current borrowing capacity under line of credit facility	$ 150.0
Maximum borrowing capacity	350.0
Amount outstanding	0	0
2015 Facility \| LIBOR
Details of Company's borrowings
Debt, variable interest rate basis	LIBOR
Percentage of margin added to reference rate to determine interest rate on debt	2.25%
2015 Facility \| Alternate base rate
Details of Company's borrowings
Debt, variable interest rate basis	alternate base rate
Percentage of margin added to reference rate to determine interest rate on debt	1.25%
2015 Natural Resources Facility
Details of Company's borrowings
Credit facility term	5 years
Current borrowing capacity under line of credit facility	126.1
Amount outstanding	46.1	107.8
Debt, variable interest rate basis	LIBOR
2015 Natural Resources Facility \| Minimum \| LIBOR
Details of Company's borrowings
Percentage of margin added to reference rate to determine interest rate on debt	1.75%
2015 Natural Resources Facility \| Maximum \| LIBOR
Details of Company's borrowings
Percentage of margin added to reference rate to determine interest rate on debt	2.75%
2018 Natural Resources Facility
Details of Company's borrowings
Credit facility term	5 years
Maximum borrowing capacity	6.0
Amount outstanding	$ 0
Debt, variable interest rate basis	LIBOR
2018 Natural Resources Facility \| Minimum \| LIBOR
Details of Company's borrowings
Percentage of margin added to reference rate to determine interest rate on debt	1.75%
2018 Natural Resources Facility \| Maximum \| LIBOR
Details of Company's borrowings
Percentage of margin added to reference rate to determine interest rate on debt	2.75%

Represents the term for the credit facility.

No definition available.

Name:	kfn_LineOfCreditFacilityTerm
Namespace Prefix:	kfn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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

- 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

Name:	us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount borrowed under the credit facility as of the balance sheet date.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant