Equity - Additional Information (Details) - USD ($)											1 Months Ended	3 Months Ended
	Apr. 17, 2018	Apr. 05, 2018	Apr. 02, 2018	Feb. 26, 2018	Feb. 22, 2018	Jan. 29, 2018	Jan. 04, 2018	Jan. 02, 2018	Jan. 10, 2017	Jul. 10, 2015	Apr. 30, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Class of Stock
Authorized capital shares of common stock (in shares)												500,000,000		500,000,000
Authorized capital shares of preferred stock (in shares)												100,000,000		100,000,000
Common stock, shares issued (in shares)												45,205,575		44,937,763
Common stock, shares outstanding (in shares)												45,205,575		44,937,763
Preferred stock issued (in shares)												0		0
Preferred stock outstanding (in shares)												0		0
Percentage of Operating Partnership held												72.20%		72.00%
Aggregate cash dividends and distributions, paid												$ 11,808,000	$ 9,726,000
Dividends and distributions declared per common share and unit (in dollars per share)					$ 0.2							$ 0.2	$ 0.19
Parkway Centre
Class of Stock
Acquisition, common units/shares issued or to be issued (in shares)						117,228
Class A units
Class of Stock
Class A Units not held by Company (in shares)												17,440,861
Class A units | Operating Partnership
Class of Stock
Aggregate cash dividends and distributions, paid							$ 3,300,000
Class B units | Columbus Village
Class of Stock
Acquisition, common units/shares issued or to be issued (in shares)										1,000,000
Class C units | Columbus Village
Class of Stock
Acquisition, common units/shares issued or to be issued (in shares)									275,000
Common Stock
Class of Stock
Shares issued (in shares)								163,000				163,000
Common stock, shares outstanding (in shares)												45,205,575		44,937,763
Aggregate cash dividends and distributions, paid							$ 8,500,000
Common Stock | New ATM Program
Class of Stock
Maximum aggregate offering price of shares to be sold (up to)				$ 125,000,000
Shares issued (in shares)												0
Subsequent Event | Class A units
Class of Stock
Units redeemed (in shares)			187,142
Payments for redemption of partnership units			$ 2,500,000
Subsequent Event | Class A units | Operating Partnership
Class of Stock
Aggregate cash dividends and distributions, paid		$ 3,500,000
Subsequent Event | Common Stock
Class of Stock
Aggregate cash dividends and distributions, paid		$ 9,000,000
Subsequent Event | Common Stock | New ATM Program
Class of Stock
Shares issued (in shares)											31,468
Number of shares issued and sold, weighted average price per share (in dollars per share)											$ 13.79
Net proceeds after offering costs and commissions from sale of shares											$ 400,000
Johns Hopkins Village | Subsequent Event | Noncontrolling interests | Class A units
Class of Stock
Shares issued (in shares)	36,684
Consolidated Entities Under Development Or Construction | Operating Partnership
Class of Stock
Ownership interest percentage in properties												$ 0		$ 0