Schedule of Per Share Distributions to Stockholders (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Income Tax [Line Items]
Common share distribution	$ 0.800000		$ 0.800000		$ 0.800000
Ordinary income	$ 0.601216		$ 0.300844		$ 0.388128
Capital gains	$ 0.117584	[1]	$ 0.031396	[1]	$ 0.027724	[1]
Unrecaptured Sec. 1250 gain	$ 0.086976		$ 0.031396		$ 0.022784
Return of capital	$ 0.081200		$ 0.467760		$ 0.384148
Allocable to next year

[1] Capital gains include unrecaptured Sec. 1250 gains.