Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Taxes [Line Items]
Minimum Distribution Percentage of Taxable Income to Qualify for Real Estate Investment Trust			90.00%
Income tax expense	$ (3,242,000)	$ (2,665,000)	$ (5,727,000)	$ (3,825,000)
Liabilities for uncertain tax positions	$ 0		$ 0