Loans and Investments (Details 2) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Loans and Investments
Unpaid Principal Balance	1,587,429,498	1,660,195,301
Percentage of Portfolio	100.00%abr_MortgageLoansOnRealEstatePercentage	100.00%abr_MortgageLoansOnRealEstatePercentage
First Dollar LTV Ratio (as percent)	13.00%abr_FirstDollarLTVRatio	17.00%abr_FirstDollarLTVRatio
Last Dollar LTV Ratio (as percent)	76.00%abr_LastDollarLTVRatio	77.00%abr_LastDollarLTVRatio
Loans and investments portfolio \| New York
Loans and Investments
Concentration risk, percentage	28.00%	36.00%
Loans and investments portfolio \| Florida
Loans and Investments
Concentration risk, percentage	14.00%	8.00%
Loans and investments portfolio \| Texas
Loans and Investments
Concentration risk, percentage	10.00%	10.00%
Credit risk concentration
Loans and Investments
Unpaid Principal Balance	1,587,429,498	1,660,195,301
Percentage of Portfolio	100.00%	100.00%
First Dollar LTV Ratio (as percent)	13.00%	17.00%
Last Dollar LTV Ratio (as percent)	76.00%	77.00%
Credit risk concentration \| Weighted average
Loans and Investments
Wtd. Avg. Internal Risk Rating	3.1	3.3
Credit risk concentration \| Multifamily
Loans and Investments
Unpaid Principal Balance	1,157,462,400	1,068,529,815
Percentage of Portfolio	72.90%	64.40%
First Dollar LTV Ratio (as percent)	10.00%	14.00%
Last Dollar LTV Ratio (as percent)	73.00%	75.00%
Credit risk concentration \| Multifamily \| Weighted average
Loans and Investments
Wtd. Avg. Internal Risk Rating	2.9	3.3
Credit risk concentration \| Office
Loans and Investments
Unpaid Principal Balance	230,491,164	358,832,526
Percentage of Portfolio	14.50%	21.60%
First Dollar LTV Ratio (as percent)	29.00%	32.00%
Last Dollar LTV Ratio (as percent)	79.00%	82.00%
Credit risk concentration \| Office \| Weighted average
Loans and Investments
Wtd. Avg. Internal Risk Rating	3.3	3.2
Credit risk concentration \| Land
Loans and Investments
Unpaid Principal Balance	128,367,601	116,751,563
Percentage of Portfolio	8.10%	7.00%
First Dollar LTV Ratio (as percent)	6.00%	3.00%
Last Dollar LTV Ratio (as percent)	88.00%	88.00%
Credit risk concentration \| Land \| Weighted average
Loans and Investments
Wtd. Avg. Internal Risk Rating	3.9	4.0
Credit risk concentration \| Hotel
Loans and Investments
Unpaid Principal Balance	66,250,000	69,181,252
Percentage of Portfolio	4.20%	4.20%
First Dollar LTV Ratio (as percent)	32.00%	26.00%
Last Dollar LTV Ratio (as percent)	83.00%	84.00%
Credit risk concentration \| Hotel \| Weighted average
Loans and Investments
Wtd. Avg. Internal Risk Rating	3.5	3.8
Credit risk concentration \| Commercial
Loans and Investments
Unpaid Principal Balance	1,700,000	24,900,145
Percentage of Portfolio	0.10%	1.50%
First Dollar LTV Ratio (as percent)	63.00%	3.00%
Last Dollar LTV Ratio (as percent)	67.00%	49.00%
Credit risk concentration \| Commercial \| Weighted average
Loans and Investments
Wtd. Avg. Internal Risk Rating	3.5	3.0
Credit risk concentration \| Condo
Loans and Investments
Unpaid Principal Balance		15,250,000
Percentage of Portfolio		0.90%
First Dollar LTV Ratio (as percent)		41.00%
Last Dollar LTV Ratio (as percent)		65.00%
Credit risk concentration \| Condo \| Weighted average
Loans and Investments
Wtd. Avg. Internal Risk Rating		3.7
Credit risk concentration \| Retail
Loans and Investments
Unpaid Principal Balance	3,158,333	6,750,000
Percentage of Portfolio	0.20%	0.40%
First Dollar LTV Ratio (as percent)	72.00%	0.00%
Last Dollar LTV Ratio (as percent)	80.00%	63.00%
Credit risk concentration \| Retail \| Weighted average
Loans and Investments
Wtd. Avg. Internal Risk Rating	2.5	2.5

Represents the individual ratings assigned to credit risk during the loan valuation and risk assessment process.

No definition available.

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- Definition

Represents the First Dollar LTV Ratio that is calculated by comparing the total of the company's senior most dollar and all senior lien positions within the capital stack to the fair value of the underlying collateral to determine the point at which the company will absorb a total loss of its position.

+ References

No definition available.

+ Details

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- Definition

Represents the weighted average loan to value ratio that is calculated by comparing the total of the carrying value of the company's loan and all senior lien positions within the capital stack to the fair value of the underlying collateral to determine the point at which the company will initially absorb a loss.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Represents a category of loans on real estate expressed as a percentage of total loans on real estate.

+ References

No definition available.

+ Details

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

+ Details

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- Definition

The carrying amount of the outstanding balance due under the mortgage loan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule IV)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 29

-Article 12

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule IV

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 310

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-29)

-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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- Details

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- Details

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