Distributions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	12 Months Ended
	Jan. 31, 2018	Jan. 15, 2018	Jan. 02, 2018	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dividends [Line Items]
Common stock issued, discount rate					3.00%
Common stock distributions (in usd per share)					$ 2.04	$ 1.84	$ 1.69
Dividends declared per common share outstanding (in usd per share)				$ 0.52
Distribution to limited partnership unitholders					$ 15,268	$ 13,533	$ 12,228
Dividend Income
Dividends [Line Items]
Common stock distributions (in usd per share)					$ 1.7	$ 1.75	$ 1.69
Return on Invested Capital
Dividends [Line Items]
Return of capital (in usd per share)				$ 0.34	0.34	0.09
Series C Preferred Stock
Dividends [Line Items]
Preferred stock dividend (in usd per share)					$ 1.72	$ 1.72	$ 1.72
Subsequent Event
Dividends [Line Items]
Common stock dividend paid	$ 11,500
Distribution to limited partnership unitholders	$ 3,900
Distributions partnership units (in usd per share)	$ 0.52
Subsequent Event | Series C Preferred Stock
Dividends [Line Items]
Dividends declared per preferred share outstanding (in usd per share)			$ 0.4297
Preferred stock distributions		$ 3,100