Subsequent Events (Details) $ / shares in Units, shares in Thousands											12 Months Ended
	Dec. 07, 2021 USD ($)	Feb. 09, 2021 $ / shares	Jan. 28, 2021 USD ($)	Jan. 15, 2021 USD ($)	Jan. 12, 2021 shares	Jan. 04, 2021 USD ($)	Sep. 22, 2020	Sep. 01, 2020 USD ($)	May 29, 2020 USD ($)	Dec. 12, 2019	Dec. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Feb. 19, 2021 USD ($)	Feb. 02, 2021 USD ($)	Jan. 07, 2021 USD ($)	Nov. 01, 2020 USD ($)	Oct. 30, 2020 USD ($)	Jul. 01, 2020 USD ($)	Mar. 02, 2020 USD ($)	Jan. 28, 2020 USD ($)	Jan. 10, 2020 USD ($)	May 15, 2019 USD ($)	Dec. 11, 2018 USD ($)	Jul. 16, 2018 USD ($)	Mar. 07, 2018 USD ($)	Nov. 28, 2017 USD ($)	Sep. 18, 2017 USD ($)	Jun. 23, 2017 USD ($)	Feb. 07, 2017 USD ($)	Jun. 17, 2016 USD ($)	Feb. 25, 2016 USD ($)
Subsequent Event [Line Items]
Dispositions of real estate investments, net of selling costs											$ 96,459,000	$ 32,944,000	$ 34,673,000
Indebtedness, net											963,845,000	950,537,000
Total principal balances											962,812,000	960,819,000
Notional amount											874,606,000	496,642,000
Aggregate cash dividends and distributions, paid											$ 47,603,000	$ 61,504,000	$ 50,897,000
Dividend declared (in dollars per share) | $ / shares											$ 0.44	$ 0.84	$ 0.80
Common stock
Subsequent Event [Line Items]
Aggregate cash dividends and distributions, paid											$ 25,300,000	$ 45,400,000	$ 38,700,000
Series A Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Dividends declared (in dollars per share) | $ / shares											$ 1.687500	$ 0.970315
Interest rate caps
Subsequent Event [Line Items]
Notional amount																		$ 100,000
Unsecured Debt
Subsequent Event [Line Items]
Total principal balances											$ 215,000,000	$ 315,000,000
Revolving Credit Facility | Unsecured Debt
Subsequent Event [Line Items]
Total principal balances											10,000,000	$ 110,000,000
LIBOR
Subsequent Event [Line Items]
Stated interest rate, basis spread on variable rate										3.17%
LIBOR | Interest rate caps
Subsequent Event [Line Items]
Notional amount																	$ 84,375,000		$ 100,000,000	$ 100,000,000	$ 50,000,000	$ 50,000,000	$ 100,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 50,000,000	$ 70,000,000	$ 75,000,000
Strike rate																			0.50%	1.50%	1.75%	1.75%	2.50%	2.75%	2.50%	2.25%	1.50%	1.50%	1.50%	1.50%	1.00%	1.50%
Premium paid											$ 2,816,000						$ 91,000		$ 232,000	$ 111,000	$ 62,000	$ 87,000	$ 288,000	$ 210,000	$ 319,000	$ 310,000	$ 359,000	$ 199,000	$ 154,000	$ 187,000	$ 150,000	$ 57,000
Subsequent Event
Subsequent Event [Line Items]
Dividend declared (in dollars per share) | $ / shares		$ 0.15
Increase from prior dividend		36.00%
Subsequent Event | Harbor Point Parcel 3 Partnership
Subsequent Event [Line Items]
Outstanding letters of credit																$ 15,000,000.0
Subsequent Event | Common stock
Subsequent Event [Line Items]
Aggregate cash dividends and distributions, paid	$ 6,500,000
Subsequent Event | Class A units
Subsequent Event [Line Items]
Aggregate cash dividends and distributions, paid	$ 2,300,000
Subsequent Event | Common Class A | Stock Issuance - Shares From Existing Shareholder
Subsequent Event [Line Items]
Number of shares issued in public offering | shares					12
Subsequent Event | Series A Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Aggregate cash dividends and distributions, paid				$ 2,900,000
Dividends declared (in dollars per share) | $ / shares		$ 0.421875
Subsequent Event | Revolving Credit Facility | Unsecured Debt
Subsequent Event [Line Items]
Total principal balances														$ 25,000,000.0
Subsequent Event | LIBOR | Interest rate caps
Subsequent Event [Line Items]
Notional amount															$ 100,000,000.0
Strike rate															0.50%
Premium paid															$ 100,000
Discontinued Operations, Disposed of by Sale
Subsequent Event [Line Items]
Gain (loss) on disposition of property									$ 2,800,000
Hanbury Village | Discontinued Operations, Disposed of by Sale
Subsequent Event [Line Items]
Dispositions of real estate investments, net of selling costs								$ 7,000,000.0
Gain (loss) on disposition of property								$ 3,600,000
Hanbury Village | Discontinued Operations, Disposed of by Sale | Subsequent Event
Subsequent Event [Line Items]
Dispositions of real estate investments, net of selling costs						$ 2,800,000
Gain (loss) on disposition of property						2,400,000
4225 Main Street and Encore Apartments | Subsequent Event
Subsequent Event [Line Items]
Debt, face value				$ 57,000,000.0
Interest rate				2.93%
Nexton Square | LIBOR
Subsequent Event [Line Items]
Stated interest rate, basis spread on variable rate							2.25%
Nexton Square | Subsequent Event
Subsequent Event [Line Items]
Repayment of debt			$ 2,000,000.0
Indebtedness, net			$ 20,100,000
Floor interest rate			0.0025
Nexton Square | Subsequent Event | LIBOR
Subsequent Event [Line Items]
Stated interest rate, basis spread on variable rate			2.25%
Nexton Square | Discontinued Operations, Disposed of by Sale | Subsequent Event
Subsequent Event [Line Items]
Dispositions of real estate investments, net of selling costs						$ 900,000