Securities Carried at Fair Value - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Fair Value Disclosures [Abstract]
Proceeds from sale of securities carried at fair value	$ 3,255,000	$ 0	$ 12,345,000	$ 4,614,000
Realized gain (loss) on sale of securities carried at fair value	(31,000)		(133,000)	41,000
Net unrealized gain on securities carried at fair value	$ 0	$ 3,484,000	$ 73,000	$ 7,701,000