Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Taxes [Line Items]
Minimum Distribution Percentage of Taxable Income to Qualify for Real Estate Investment Trust			90.00%
Income tax expense	$ (2,673,000)	$ (1,622,000)	$ (8,400,000)	$ (5,447,000)
Liabilities for uncertain tax positions	$ 0		$ 0