Investment in Securities (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012		Dec. 31, 2011
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	$ 924,226
Total investments in securities, Net Fair Value Adjustments	(266,443)
Investments in securities and security-related receivables, Carrying Amount	657,783		647,461
Total investments in securities, Weighted Average Coupon	4.60%
Total investments in securities, Weighted Average Years to Maturity	21 years 9 months 18 days
Trading securities [Member]
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	648,674
Total investments in securities, Net Fair Value Adjustments	(158,504)
Investments in securities and security-related receivables, Carrying Amount	490,170
Total trading securities, Weighted Average Coupon	4.20%
Total investments in securities, Weighted Average Years to Maturity	22 years 4 months 24 days
Trading securities [Member] | TruPS [Member]
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	637,376
Total trading Securities, Net Fair Value Adjustments	(147,206)
Total trading securities, Estimated Fair Value	490,170
Investments in securities and security-related receivables, Carrying Amount	490,170
Total trading securities, Weighted Average Coupon	4.20%
Total investments in securities, Weighted Average Years to Maturity	22 years 1 month 6 days
Trading securities [Member] | Other Securities [Member]
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	11,298
Total trading Securities, Net Fair Value Adjustments	(11,298)
Investments in securities and security-related receivables, Carrying Amount	0
Total trading securities, Weighted Average Coupon	5.00%
Total investments in securities, Weighted Average Years to Maturity	40 years 4 months 24 days
Trading securities [Member] | Other securities [Member]
Trading Securities [Abstract]
Estimated Fair Value	0
Security-related receivables [Member]
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	271,952
Estimated Fair Value	167,611
Total investments in securities, Net Fair Value Adjustments	(104,341)
Total investments in securities, Weighted Average Coupon	5.80%
Total investments in securities, Weighted Average Years to Maturity	20 years
Security-related receivables [Member] | TruPS Receivables [Member]
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	111,025
Estimated Fair Value	86,508
Total investments in securities, Net Fair Value Adjustments	(24,517)
Investments in securities and security-related receivables, Carrying Amount	86,508
Total investments in securities, Weighted Average Coupon	6.50%
Total investments in securities, Weighted Average Years to Maturity	10 years 6 months
Security-related receivables [Member] | Unsecured REIT note receivables [Member]
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	30,000
Estimated Fair Value	31,697
Total investments in securities, Net Fair Value Adjustments	1,697
Investments in securities and security-related receivables, Carrying Amount	31,697
Total investments in securities, Weighted Average Coupon	6.70%
Total investments in securities, Weighted Average Years to Maturity	4 years 7 months 6 days
Security-related receivables [Member] | CMBS receivables [Member]
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	84,780	[1]
Estimated Fair Value	39,300	[1]
Total investments in securities, Net Fair Value Adjustments	(45,480)	[1]
Investments in securities and security-related receivables, Carrying Amount	39,300
Total investments in securities, Weighted Average Coupon	5.60%
Total investments in securities, Weighted Average Years to Maturity	31 years 2 months 12 days	[1]
Security-related receivables [Member] | Other securities [Member]
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	46,147
Estimated Fair Value	10,106
Total investments in securities, Net Fair Value Adjustments	(36,041)
Investments in securities and security-related receivables, Carrying Amount	10,106
Total investments in securities, Weighted Average Coupon	3.60%
Total investments in securities, Weighted Average Years to Maturity	32 years 3 months 18 days
Available-for-sale securities [Member]
Trading Securities [Abstract]
Total investments in securities, Amortized Cost	3,600
Estimated Fair Value	2
Available-for-sale Securities, Net Fair Value Adjustments	(3,598)
Investments in securities and security-related receivables, Carrying Amount	$ 2
Available-for-sale securities, Weighted Average Coupon	2.30%
Total investments in securities, Weighted Average Years to Maturity	30 years 4 months 24 days

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