Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Taxes [Line Items]
Minimum Distribution Percentage of Taxable Income to Qualify for Real Estate Investment Trust			90.00%
Minimum distribution Percentage of Taxable Income to avoid Federal Income Taxes			100.00%
Income tax expense	$ (2,658,000)	$ (2,071,000)	$ (6,696,000)	$ (5,490,000)
Percentage of likelihood required for a tax position to be measured			50.00%
Liabilities for uncertain tax positions	$ 0		$ 0