Transactions with Related Parties - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013 Y Person	Dec. 31, 2012
Related Party Transaction [Line Items]
Number of independent directors	4
Management agreement initial expiration date	February 23, 2015
Management agreement additional term of expiration (in years)	1
Prior notice for uncertain termination (in days)	180 days
Proportion of average annual management fee	4
Period of annual management fees earned (in years)	2
Management fee payable	$ 2,152,000	$ 2,120,000
Company's Equity Up To $250 Million
Related Party Transaction [Line Items]
Management fee bases per annum	1.50%
Company's Equity Up To $250 Million | Maximum
Related Party Transaction [Line Items]
Management fee payable	250,000,000
Company's Equity In Excess Of $250 Million And Up To $500 Million
Related Party Transaction [Line Items]
Management fee bases per annum	1.10%
Company's Equity In Excess Of $250 Million And Up To $500 Million | Maximum
Related Party Transaction [Line Items]
Management fee payable	500,000,000
Company's Equity In Excess Of $250 Million And Up To $500 Million | Minimum
Related Party Transaction [Line Items]
Management fee payable	250,000,000
Company's Equity In Excess Of $500 Million And Up To $750 Million
Related Party Transaction [Line Items]
Management fee bases per annum	0.80%
Company's Equity In Excess Of $500 Million And Up To $750 Million | Maximum
Related Party Transaction [Line Items]
Management fee payable	750,000,000
Company's Equity In Excess Of $500 Million And Up To $750 Million | Minimum
Related Party Transaction [Line Items]
Management fee payable	500,000,000
Company's Equity In Excess Of $750
Related Party Transaction [Line Items]
Management fee bases per annum	0.50%
Company's Equity In Excess Of $750 | Minimum
Related Party Transaction [Line Items]
Management fee payable	$ 750,000,000