Transactions With Related Parties - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Person Year	Jun. 30, 2011	Dec. 31, 2011
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	$ 4,312,000	$ 3,531,000	$ 8,154,000	$ 6,623,000
Reimbursable expense	354,000	0	626,000	0
Management fee payable	1,591,000		1,591,000		1,171,000
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