Noncontrolling Interests - Holders of Convertible Limited Partnership Units in Operating Partnership - Additional Information (Detail) - Noncontrolling Interests	12 Months Ended
	Dec. 31, 2017 shares	Dec. 31, 2016 shares	Dec. 31, 2015 shares
Noncontrolling Interest [Line Items]
Percentage of ownership interest of noncontrolling interest	25.60%
Limited partnership units (in shares)	7,541,867
Limited partnership units, conversion ratio	1
Outstanding stock percent that should be acquired for rights to be exercised	39.90%
Limited partnership units convertible to shares of common stock, eligible for conversion (in partnership units)	740,000
Fully converted partnership units and diluted weighted average shares outstanding (in shares)	29,510,900	28,989,900	28,449,400