Investments in Securities and Security-Related Receivables (Parenthetical) (Detail) (CMBS receivables, Security-related receivables, USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Standard & Poor's AAA and A- Rating
Investment Securities [Line Items]
Securities, fair value	$ 12,122	$ 8,228
Standard & Poor's BBB+ and B- Rating
Investment Securities [Line Items]
Securities, fair value	22,667	26,594
Standard & Poor's, CCC Rating
Investment Securities [Line Items]
Securities, fair value		8,164
Standard & Poor's, D Rating
Investment Securities [Line Items]
Securities, fair value	$ 1,646	$ 1,132