Income Taxes - Additional Information (Detail) - Entity [Domain] - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 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) benefit	$ (2,653,000)	$ (2,052,000)	$ (4,038,000)	$ (3,419,000)
Percentage of likelihood required for a tax position to be measured			50.00%
Liabilities for uncertain tax positions	$ 0		$ 0