Fair Value Measurements - Narrative (Details) - Level 2 - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Market Approach Valuation Technique | Junior subordinated notes
Financial Instruments Not Measured at Fair Value
Market interest rate (as a percent)	4.74%	6.41%
Market Approach Valuation Technique | Mortgages payable | Minimum
Financial Instruments Not Measured at Fair Value
Market interest rate (as a percent)	2.69%	3.89%
Market Approach Valuation Technique | Mortgages payable | Maximum
Financial Instruments Not Measured at Fair Value
Market interest rate (as a percent)	3.04%	4.33%
Carrying and Fair Value | Junior subordinated notes
Financial Instruments Not Measured at Fair Value
Estimated fair value (lower) higher than carrying value	$ 10,542	$ 9,589
Carrying and Fair Value | Mortgages payable
Financial Instruments Not Measured at Fair Value
Estimated fair value (lower) higher than carrying value	$ 5,258	$ 321