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Equity - Additional Information (Details) - USD ($)													3 Months Ended		6 Months Ended
Equity - Additional Information (Details) - USD ($)	Jul. 05, 2018	Jul. 02, 2018	May 03, 2018	Apr. 17, 2018	Apr. 05, 2018	Apr. 02, 2018	Feb. 26, 2018	Jan. 29, 2018	Jan. 04, 2018	Jan. 02, 2018	Jan. 10, 2017	Jul. 10, 2015	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Class of Stock
Authorized capital shares of common stock (in shares)													500,000,000		500,000,000		500,000,000
Authorized capital shares of preferred stock (in shares)													100,000,000		100,000,000		100,000,000
Common stock, shares issued (in shares)													48,768,363		48,768,363		44,937,763
Common stock, shares outstanding (in shares)													48,768,363		48,768,363		44,937,763
Preferred stock issued (in shares)													0		0		0
Preferred stock outstanding (in shares)													0		0		0
Percentage of Operating Partnership held													73.80%		73.80%		72.00%
Aggregate cash dividends and distributions, paid															$ 24,337,000	$ 20,097,000
Dividends and distributions declared per common share and unit (in dollars per share)			$ 0.20										$ 0.2	$ 0.19	$ 0.4	$ 0.38
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)													17,290,403		17,290,403
Units redeemed (in shares)						187,142
Payments for redemption of partnership units						$ 2,500,000
Class A units \| Operating Partnership
Class of Stock
Aggregate cash dividends and distributions, paid					$ 3,500,000				$ 3,300,000
Class C units \| Columbus Village
Class of Stock
Acquisition, common units/shares issued or to be issued (in shares)											275,000
Class B units \| Columbus Village
Class of Stock
Acquisition, common units/shares issued or to be issued (in shares)												1,000,000
New ATM Program
Class of Stock
Consideration received on transaction															$ 49,100,000
Common Stock
Class of Stock
Shares issued (in shares)										163,000					3,542,178
Common stock, shares outstanding (in shares)													48,768,363		48,768,363		44,937,763
Aggregate cash dividends and distributions, paid					$ 9,000,000				$ 8,500,000
Units redeemed (in shares)															(163,000)
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)															3,542,178
Weighted average price (in dollars per share)													$ 14.07		$ 14.07
Subsequent Event \| Class A units
Class of Stock
Units redeemed (in shares)		123,504
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	$ 9,700,000
Johns Hopkins Village \| 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		$ 0