Equity - Additional Information (Details)																	1 Months Ended	3 Months Ended						9 Months Ended
	Oct. 15, 2019 USD ($)	Oct. 03, 2019 USD ($)	Oct. 01, 2019 shares	Sep. 20, 2019 USD ($) shares	Aug. 20, 2019 USD ($) shares	Aug. 07, 2019 $ / shares	Aug. 06, 2019 USD ($)	Jul. 03, 2019 USD ($)	Jul. 01, 2019 shares	Jun. 18, 2019 USD ($) ft² $ / shares shares	May 30, 2019 USD ($) shares	May 23, 2019 USD ($) shares	Apr. 04, 2019 USD ($)	Jan. 03, 2019 USD ($)	Jan. 02, 2019 shares	Feb. 26, 2018 USD ($)	Oct. 31, 2019 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 $ / shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) $ / shares shares
Class of Stock
Net proceeds from issuance of common and preferred stock																		$ 34,045,000	$ 7,498,000	$ 30,206,000	$ 10,548,000	$ 48,981,000
Preferred stock issued (in shares) | shares																		2,530,000						2,530,000		0
Preferred stock, par value (in dollars per share) | $ / shares																		$ 0.01						$ 0.01		$ 0.01
Percentage of operating partnership held																		72.20%						72.20%		74.50%
Aggregate cash dividends and distributions, paid																								$ 43,537,000	$ 37,550,000
Dividends and distributions declared per common share and unit (in dollars per share) | $ / shares																		$ 0.21	$ 0.21	$ 0.21	$ 0.20	$ 0.20	$ 0.20
Class A units
Class of Stock
Class A Units not held by Company (in shares) | shares																		21,167,104						21,167,104
Class A units | Operating Partnership
Class of Stock
Number of shares issued (in shares) | shares				73,666	40,864						60,000	4,125,759
Business acquisition, equity interest issued or issuable, value assigned				$ 1,300,000	$ 700,000						$ 1,000,000.0	$ 68,100,000
Business acquisition, percentage of voting interests acquired											35.00%
Aggregate cash dividends and distributions, paid								$ 4,400,000					$ 3,600,000	$ 3,400,000
Common stock
Class of Stock
Shares issued (in shares) | shares									125,118						118,471
Net proceeds from issuance of common and preferred stock																		$ 20,000	$ 4,000	$ 21,000	$ 7,000	$ 35,000
Aggregate cash dividends and distributions, paid								$ 11,100,000					$ 11,000,000.0	$ 10,000,000.0
Dividends and distributions declared per common share and unit (in dollars per share) | $ / shares						$ 0.21
New ATM Program | Common stock
Class of Stock
Maximum aggregate offering price of shares to be sold (up to)							$ 180,700,000									$ 125,000,000.0
Net proceeds from issuance of common and preferred stock							105,700,000
Remaining authorized repurchase amount							$ 75,000,000.0
The Amendments
Class of Stock
Consideration received on transaction																								$ 71,900,000
The Amendments | Common stock
Class of Stock
Shares issued (in shares) | shares																								4,476,565
Weighted average price (in dollars per share) | $ / shares																		$ 16.28						$ 16.28
Subsequent Event | Class A units | Operating Partnership
Class of Stock
Aggregate cash dividends and distributions, paid		$ 4,400,000
Subsequent Event | Common stock
Class of Stock
Shares issued (in shares) | shares			4,896
Aggregate cash dividends and distributions, paid		$ 11,500,000
Subsequent Event | New ATM Program
Class of Stock
Consideration received on transaction																	$ 9,700,000
Subsequent Event | New ATM Program | Common stock
Class of Stock
Shares issued (in shares) | shares																	543,513
Weighted average price (in dollars per share) | $ / shares																	$ 18.14
Noncontrolling interests in investment entities
Class of Stock
Liquidation preference																		$ 63,300,000						$ 63,300,000
Consolidated Entities Under Development Or Construction | Operating Partnership
Class of Stock
Ownership interest percentage in properties																										$ 0
Redeemable convertible preferred stock
Class of Stock
Net proceeds from issuance of common and preferred stock																			$ 61,001,000
Preferred stock issued (in shares) | shares										2,530,000
Preferred Stock dividend rate percentage						6.75%				6.75%														6.75%
Preferred stock, par value (in dollars per share) | $ / shares										$ 0.01
Preferred stock, liquidation preference (in dollars per share) | $ / shares										$ 25.00
Proceeds from issuance of preferred stock										$ 61,300,000
Dividends and distributions declared per common share and unit (in dollars per share) | $ / shares						$ 0.54844
Preferred stock, redemption price (in usd per share) | $ / shares																		$ 25.00						$ 25.00
Redeemable convertible preferred stock | Over-Allotment Option
Class of Stock
Preferred stock issued (in shares) | shares										330,000
Redeemable convertible preferred stock | Subsequent Event
Class of Stock
Aggregate cash dividends and distributions, paid	$ 1,400,000
Series A Cumulative Redeemable Perpetual Preferred Units
Class of Stock
Preferred stock issued (in shares) | shares										2,530,000
Preferred Stock dividend rate percentage										6.75%
Thames Street Wharf
Class of Stock
Area of real estate property | ft²										263,426
1405 Point | Noncontrolling interests in investment entities | Operating Partnership
Class of Stock
Ownership interest percentage in properties																		$ 5,500,000						$ 5,500,000