Fair Value of Financial Instruments (Details) (USD $)			3 Months Ended	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 CMBS	Sep. 30, 2013 CMBS	Sep. 30, 2013 Fair value measurements on recurring basis Total fair value	Dec. 31, 2012 Fair value measurements on recurring basis Total fair value	Sep. 30, 2013 Fair value measurements on recurring basis Total fair value Domestic Servicing Rights	Dec. 31, 2012 Fair value measurements on recurring basis Total fair value Foreign exchange contracts	Dec. 31, 2012 Fair value measurements on recurring basis Total fair value Interest rate contracts	Dec. 31, 2012 Fair value measurements on recurring basis Total fair value Available-for-sale debt securities	Sep. 30, 2013 Fair value measurements on recurring basis Total fair value RMBS	Dec. 31, 2012 Fair value measurements on recurring basis Total fair value RMBS	Sep. 30, 2013 Fair value measurements on recurring basis Total fair value CMBS	Dec. 31, 2012 Fair value measurements on recurring basis Total fair value CMBS	Dec. 31, 2012 Fair value measurements on recurring basis Total fair value Available-for-sale equity securities, Real estate industry	Sep. 30, 2013 Fair value measurements on recurring basis Total fair value Total available-for-sale equity securities	Dec. 31, 2012 Fair value measurements on recurring basis Total fair value Total available-for-sale equity securities	Sep. 30, 2013 Fair value measurements on recurring basis Level I	Dec. 31, 2012 Fair value measurements on recurring basis Level I	Dec. 31, 2012 Fair value measurements on recurring basis Level I Available-for-sale equity securities, Real estate industry	Sep. 30, 2013 Fair value measurements on recurring basis Level I Total available-for-sale equity securities	Dec. 31, 2012 Fair value measurements on recurring basis Level I Total available-for-sale equity securities	Sep. 30, 2013 Fair value measurements on recurring basis Level II	Dec. 31, 2012 Fair value measurements on recurring basis Level II	Dec. 31, 2012 Fair value measurements on recurring basis Level II Foreign exchange contracts	Dec. 31, 2012 Fair value measurements on recurring basis Level II Interest rate contracts	Dec. 31, 2012 Fair value measurements on recurring basis Level II Available-for-sale debt securities	Dec. 31, 2012 Fair value measurements on recurring basis Level II CMBS	Sep. 30, 2013 Fair value measurements on recurring basis Level III	Dec. 31, 2012 Fair value measurements on recurring basis Level III	Sep. 30, 2013 Fair value measurements on recurring basis Level III Domestic Servicing Rights	Dec. 31, 2012 Fair value measurements on recurring basis Level III Available-for-sale debt securities	Sep. 30, 2013 Fair value measurements on recurring basis Level III RMBS	Dec. 31, 2012 Fair value measurements on recurring basis Level III RMBS	Sep. 30, 2013 Fair value measurements on recurring basis Level III CMBS
Assets and liabilities measured at fair value
Loans held-for-sale, fair value option	$ 279,121,000	$ 0			$ 279,121,000																								$ 279,121,000
Available-for-sale securities										862,587,000	316,261,000	333,153,000	198,146,000	529,434,000	21,667,000	15,016,000	21,667,000			21,667,000	15,016,000	21,667,000					529,434,000	529,434,000				333,153,000	316,261,000	333,153,000	198,146,000
Intangible assets - servicing rights at fair value	158,023,000	0					158,023,000																								158,023,000
Total investments						884,254,000													21,667,000					529,434,000						333,153,000
Derivative assets	9,513,000	9,227,000			9,513,000			4,335,000	4,892,000														9,513,000		4,335,000	4,892,000
VIE assets	97,359,666,000				97,359,666,000																								97,359,666,000
Total					98,335,746,000													15,016,000					9,513,000						98,311,217,000
Derivative liabilities					(32,252,000)			(23,427,000)	(4,343,000)														(32,252,000)		(23,427,000)	(4,343,000)
VIE liabilities	96,934,006,000				96,934,006,000																		95,150,366,000						1,783,640,000
Total					96,966,258,000																		95,182,618,000						1,783,640,000
Total derivatives						(18,543,000)																		(18,543,000)
Total						865,711,000													21,667,000					510,891,000						333,153,000
Transfer of investment from Level II to Level III			$ 5,100,000	$ 117,400,000