Equity - Additional Information (Details)																						12 Months Ended
	Feb. 20, 2020 $ / shares	Jan. 15, 2020 USD ($)	Jan. 02, 2020 USD ($)	Dec. 16, 2019 USD ($) shares	Oct. 01, 2019 shares	Sep. 20, 2019 USD ($) shares	Aug. 20, 2019 USD ($) shares	Aug. 06, 2019 USD ($)	Aug. 05, 2019 USD ($)	Jul. 01, 2019 shares	Jun. 18, 2019 USD ($) ft² $ / shares shares	May 30, 2019 USD ($) shares	May 23, 2019 USD ($) shares	Jan. 02, 2019 shares	Apr. 17, 2018 $ / shares shares	Jan. 29, 2018 shares	Dec. 21, 2017 USD ($)	May 12, 2017 USD ($) $ / shares shares	Jan. 10, 2017 shares	May 04, 2016 USD ($)	Jul. 10, 2015 shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 20, 2017 USD ($)
Class of Stock [Line Items]
Authorized capital shares of common stock (in shares) | shares																						500,000,000	500,000,000
Preferred stock, shares authorized (in shares) | shares																						100,000,000	100,000,000
Common stock, shares issued (in shares) | shares																						56,277,971	50,013,731
Common stock, shares outstanding (in shares) | shares																						56,277,971	50,013,731
Preferred stock, shares issued (in shares) | shares																						2,530,000	0
Preferred stock, shares outstanding (in shares) | shares																						2,530,000	0
Proceeds from issuance of common stock, net																						$ 96,845,000	$ 65,244,000	$ 91,381,000
Redeemable noncontrolling interest, equity percentage																									20.00%
Redeemable noncontrolling interest																	$ 2,000,000.0
Noncontrolling interest change in redemption value																	$ 500,000
Percentage of operating partnerships held																						72.60%	74.50%
Operating partnership units redemption ratio																						1
Aggregate cash dividends and distributions, paid																						$ 61,504,000	$ 50,897,000	$ 43,616,000
Preferred stock, par value (in dollars per share) | $ / shares																						$ 0.01	$ 0.01
Dividend declared (in dollars per share) | $ / shares																						$ 0.84	$ 0.80	$ 0.76
Dividends, cash paid																						$ 2,455,000
Johns Hopkins Village
Class of Stock [Line Items]
Redeemable noncontrolling interest carrying amount																									$ 2,000,000.0
Class A units
Class of Stock [Line Items]
Units not held by company | shares																						21,272,962
Class A units | Operating Partnership
Class of Stock [Line Items]
Acquisition, common units/shares issued (in shares) | shares				110,754		73,666	40,864					60,000	4,125,759
Acquisition, contract price				$ 2,100,000		$ 1,300,000	$ 700,000					$ 1,000,000.0	$ 68,100,000
Noncontrolling interest ownership percentage in properties												35.00%
Aggregate cash dividends and distributions, paid																						$ 16,900,000	$ 13,800,000	$ 12,600,000
Class A units | Operating Partnership | Subsequent Event
Class of Stock [Line Items]
Aggregate cash dividends and distributions, paid			$ 4,500,000
Common stock
Class of Stock [Line Items]
Shares issued through public offering (in shares) | shares					4,896					125,118				118,471
Aggregate cash dividends and distributions, paid																						$ 45,400,000	$ 38,700,000	$ 31,100,000
Common stock | Subsequent Event
Class of Stock [Line Items]
Aggregate cash dividends and distributions, paid			$ 11,800,000
Columbus Village | Class B units
Class of Stock [Line Items]
Acquisition, common units/shares issued (in shares) | shares																					1,000,000
Columbus Village | Class C units
Class of Stock [Line Items]
Acquisition, common units/shares issued (in shares) | shares																			275,000
Parkway Centre | Class A units
Class of Stock [Line Items]
Acquisition, common units/shares issued (in shares) | shares																117,228
2016 ATM Program | Common stock
Class of Stock [Line Items]
Maximum aggregate offering price of shares to be sold (up to)																				$ 75,000,000.0
Shares issued through public offering (in shares) | shares																								450,890
Net proceeds after offering costs and commissions from sale of shares																								$ 6,200,000
2018 ATM Program | Common stock
Class of Stock [Line Items]
Maximum aggregate offering price of shares to be sold (up to)								$ 180,700,000	$ 125,000,000.0
Shares issued through public offering (in shares) | shares																						5,871,519	4,617,409
Net proceeds after offering costs and commissions from sale of shares																						$ 97,000,000.0	$ 65,200,000
Underwritten Public Offering
Class of Stock [Line Items]
Number of shares issued in public offering | shares																		6,900,000
Issuance of common stock, price per share (in dollars per share) | $ / shares																		$ 13.00
Proceeds from issuance of common stock, net																		$ 85,300,000
Thames Street Wharf
Class of Stock [Line Items]
Area of retail space | ft²											263,426
Johns Hopkins Village | Noncontrolling interests in Operating Partnership | Class A units
Class of Stock [Line Items]
Shares issued through public offering (in shares) | shares															36,684
Share price (in dollars per share) | $ / shares															$ 13.77
Weighted Average | 2016 ATM Program | Common stock
Class of Stock [Line Items]
Issuance of common stock, price per share (in dollars per share) | $ / shares																								$ 14.08
Weighted Average | 2018 ATM Program | Common stock
Class of Stock [Line Items]
Issuance of common stock, price per share (in dollars per share) | $ / shares																						$ 16.76	$ 14.39
Redeemable convertible preferred stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares) | shares											2,530,000
Dividend rate											6.75%											6.75%
Preferred stock, redemption price (in dollars per share) | $ / shares																						$ 25.00
Preferred stock, par value (in dollars per share) | $ / shares											$ 0.01
Liquidation preference (in dollars per share) | $ / shares											$ 25.00
Proceeds from issuance of preferred stock and preference stock											$ 61,300,000
Dividends declared (in dollars per share) | $ / shares																						$ 0.970315
Dividends, cash paid																						$ 2,500,000
Redeemable convertible preferred stock | Subsequent Event
Class of Stock [Line Items]
Aggregate cash dividends and distributions, paid		$ 1,100,000
Dividends declared (in dollars per share) | $ / shares	$ 0.421875
Redeemable convertible preferred stock | Over-Allotment Option
Class of Stock [Line Items]
Preferred stock, shares issued (in shares) | shares											330,000
Common stock | Subsequent Event
Class of Stock [Line Items]
Dividend declared (in dollars per share) | $ / shares	$ 0.22
Increase from prior dividend	4.80%
Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares) | shares											2,530,000
Dividend rate											6.75%
Noncontrolling interests in Operating Partnership
Class of Stock [Line Items]
Liquidation preference																						63,300,000
Noncontrolling interests in Operating Partnership | 1405 Point | Operating Partnership
Class of Stock [Line Items]
Nonredeemable noncontrolling interest																						$ 4,500,000