Subordinate Loans - Company's Subordinate Loan Portfolio (Details) (USD $)	1 Months Ended	9 Months Ended	12 Months Ended			9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended		12 Months Ended	9 Months Ended		12 Months Ended	9 Months Ended		12 Months Ended		9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended		12 Months Ended	9 Months Ended					12 Months Ended	9 Months Ended		12 Months Ended	9 Months Ended									1 Months Ended
	Jan. 31, 2013	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2012 Senior Mezz - Retail - Various	Dec. 31, 2012 Junior Mezz - Retail - Various	Sep. 30, 2013 Office - Michigan	Dec. 31, 2012 Office - Michigan	Sep. 30, 2013 Ski Resort - California	Dec. 31, 2012 Ski Resort - California	Sep. 30, 2013 Hotel Portfolio – New York option		Dec. 31, 2012 Hotel Portfolio – New York option	Sep. 30, 2013 Retail Center – Virginia option		Dec. 31, 2012 Retail Center – Virginia option	Sep. 30, 2013 Hotel– New York		Dec. 31, 2012 Hotel– New York	Dec. 31, 2012 Hotel– New York option	Sep. 30, 2013 Mixed Use – North Carolina	Dec. 31, 2012 Mixed Use – North Carolina	Sep. 30, 2013 Office Complex - Missouri	Dec. 31, 2012 Office Complex - Missouri	Sep. 30, 2013 Hotel Portfolio – Various		Dec. 31, 2012 Hotel Portfolio – Various	Sep. 30, 2013 Multifamily Conversion – NY, NY; One-year Extension Option		Sep. 30, 2013 Hotel Portfolio – Rochester, MN	Sep. 30, 2013 Condo Conversion – NY, NY option		Dec. 31, 2012 Condo Conversion – NY, NY	Sep. 30, 2013 Condo Construction - NY, NY		Dec. 31, 2012 Condo Construction - NY, NY option	Sep. 30, 2013 Warehouse Portfolio - Various	Sep. 30, 2013 Multifamily Conversion – NY, NY; Three-month Extension Option		Sep. 30, 2013 Office Condo - NY, NY [Member]		Sep. 30, 2013 Condo Conversion - NY, NY		Sep. 30, 2013 Mixed Use - Pittsburgh, PN [Member] option		Jun. 30, 2013 Mezzanine loans [Member]	Feb. 28, 2013 Mezzanine loans [Member] loan
Mortgage Loans on Real Estate [Line Items]
Date of Investment				Dec-09	Dec-09	May-10	May-10	Apr-11	Apr-11	Aug-11	[1]	Aug-11	Oct-11	[2]	Oct-11	Jan-12	[3]	Jan-12	Mar-12	Jul-12	Jul-12	Sept-12	Sept-12	Nov-12	[4]	Nov-12	Jan-13	[5]	Jan-13	Dec-12	[6]	Dec-12	Jan-13	[7]		May-13	May-13	[8]	Jul-13		Aug-13		Aug-13
Maturity Date				Dec-19	Dec-19	Jun-20	Jun-20	May-17	May-17	July-14	[1]	July-13	Oct-14	[2]	Oct-14	Feb-14	[3]	Feb-14	Mar-14	Jul-22	Jul-22	Oct-22	Oct-22	Nov-15	[4]	Nov-15	Dec-14	[5]	Feb-18	Jan-15	[6]	Jan-15	Jul-17	[7]		May-23	Jun-14	[8]	Jul-22		Sept-15		Aug-16
Original Face Amount		$ 396,669,000	$ 245,875,000	$ 30,000,000	$ 20,000,000	$ 9,000,000	$ 9,000,000	$ 40,000,000	$ 40,000,000	$ 25,000,000	[1]	$ 25,000,000	$ 25,000,000	[2]	$ 25,000,000	$ 15,000,000	[3]	$ 15,000,000	$ 15,000,000	$ 6,525,000	$ 6,525,000	$ 10,000,000	$ 10,000,000	$ 50,000,000	[4]	$ 50,000,000	$ 18,000,000	[5]	$ 25,000,000	$ 350,000	[6]	$ 350,000	$ 60,000,000	[7]		$ 32,000,000	$ 44,000,000	[8]	$ 14,000,000	[8]	$ 294,000	[8]	$ 22,500,000	[8]
Current Face Amount		396,796,000	246,959,000	30,000,000	20,000,000	8,879,000	8,912,000	40,000,000	40,000,000	25,000,000	[1]	25,000,000	22,216,000	[2]	26,243,000	15,000,000	[3]	15,000,000	15,000,000	6,525,000	6,525,000	9,883,000	9,979,000	48,697,000	[4]	49,950,000	18,000,000	[5]	24,840,000	350,000	[6]	350,000	64,612,000	[7]		32,000,000	44,000,000	[8]	14,000,000	[8]	294,000	[8]	22,500,000	[8]
Carrying Value		394,554,000	246,246,000	30,000,000	20,000,000	8,879,000	8,912,000	39,812,000	39,831,000	25,000,000	[1]	25,000,000	22,216,000	[2]	26,243,000	15,156,000	[3]	15,013,000	15,000,000	6,525,000	6,525,000	9,883,000	9,979,000	48,616,000	[4]	49,743,000	17,889,000	[5]	24,840,000		[6]		64,094,000	[7]		32,000,000	43,781,000	[8]	13,557,000	[8]		[8]	22,306,000	[8]
Coupon				Fixed	Fixed	Fixed	Fixed	Fixed	Fixed	Floating	[1]	Floating	Fixed	[2]	Fixed	Fixed	[3]	Fixed	Floating	Fixed	Fixed	Fixed	Fixed	Floating	[4]	Floating	Floating	[5]	Fixed	Floating	[6]	Floating	Fixed	[7]		Fixed	Floating	[8]	Fixed		Floating		Floating
Coupon		12.04%	12.46%
Number of options to extend loan agreement										2		3	2		2			2	2											2					2								2
Option to extend loan agreement, term										1 year		1 year	1 year		1 year	1 year		1 year	1 year							1 year				1 year					1 year		3 months				1 year		1 year
Unfunded loan commitments																														34,650,000					34,650,000						29,106,000
Number of loans for which principal amount received																																														2
Principal Prepayment On Mortgage Debt																																													15,000,000	50,000,000
Yield maintenance payment																																													$ 1,233,000	$ 2,500,000
IRR on loan investment	17.00%																																												19.00%	15.00%

[1] Includes two one-year extension options subject to certain conditions and the payment of a fee for the fourth and fifth year extensions.

[2] Includes two one-year extension options subject to certain conditions.

[3] Includes a one-year extension option subject to certain conditions and the payment of an extension fee.

[4] (4)Includes two one-year extension options subject to certain conditions and the payment of a fee for each extension. As of September 30, 2013, the Company had $34,650 of unfunded loan commitments related to this loan.

[5] (7)Includes two one-year extension options subject to certain conditions and the payment of a fee for each extension.

[6] Includes two one-year extension options subject to certain conditions and the payment of a fee for each extension. As of September 30, 2013, the Company had $34,650 of unfunded loan commitments related to this loan.

[7] (6)Includes a one-year extension option subject to certain conditions and the payment of an extension fee. As of September 30, 2013, the Company had $29,106 of unfunded loan commitments related to this loan.

[8] Includes a three-month extension option subject to certain conditions and the payment of an extension fee.