The percentage of the required distribution for such calendar year.

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Annual Limitation Net Operating Losses And Net Capital Losses

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The percentage of tax on the excess (if any) of the required distribution for such calendar year, over the distributed amount for such calendar year.

+ References

No definition available.

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The percentage of net taxable income for such calendar year.

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No definition available.

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The expiration date of each operating loss carryforward included in total operating loss carryforwards, or the applicable range of such expiration dates.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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

-Publisher FASB

-Name Accounting Standards Codification

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Amount of deferred tax liability attributable to taxable temporary differences.

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-Publisher FASB

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Tax year that remains open to examination under enacted tax laws, in CCYY format.

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Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended
Income Taxes - Additional Information (Detail) (USD $)	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	May 31, 2013
Tax Credit Carryforward [Line Items]
Annual distribution of net taxable income for U.S. federal income tax not to apply to our earnings that we distribute (percent)	90.00%
Net taxable income subject to distribution (percent)	100.00%
Excise tax rate	4.00%bxmt_ExciseTaxRate
Income tax provision	$ 245,000us-gaap_IncomeTaxExpenseBenefit	$ 531,000us-gaap_IncomeTaxExpenseBenefit
Deferred tax assets	0us-gaap_DeferredTaxAssetsGross		0us-gaap_DeferredTaxAssetsGross
Deferred tax liabilities	0us-gaap_DeferredIncomeTaxLiabilities		0us-gaap_DeferredIncomeTaxLiabilities
Common stock, shares issued	58,451,077us-gaap_CommonStockSharesIssued		58,269,889us-gaap_CommonStockSharesIssued
Net operating losses carried forward			159,000,000us-gaap_OperatingLossCarryforwards
Net capital losses carried forward			32,000,000us-gaap_TaxCreditCarryforwardAmount
NOLs expiration date	Expire in 2029
Capital Loss Carryforwards Expiring 2014 [Member]
Tax Credit Carryforward [Line Items]
Net capital losses carried forward	31,400,000
Capital Loss Carryforwards Expiring 2015 [Member]
Tax Credit Carryforward [Line Items]
Net capital losses carried forward	602,000
Internal Revenue Service [Member]
Tax Credit Carryforward [Line Items]
Net operating losses and net capital losses	$ 2,000,000
Class A Common Stock [Member]
Tax Credit Carryforward [Line Items]
Common stock, shares issued				25,875,000
Earliest Tax Year [Member]
Tax Credit Carryforward [Line Items]
Open tax year	2010
Latest Tax Year [Member]
Tax Credit Carryforward [Line Items]
Open tax year	2014