Fair Value Measurements - Summary of Fair Value of Financial Instruments (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Financial assets:
Preferred equity investment - face value	$ 0	$ 2,327,000
Mortgage loan receivable
Financial assets:
Mortgage loans receivable - face value	0	29,500,000
Senior unsecured notes payable
Financial liabilities:
Senior unsecured notes payable - face value	300,000,000	300,000,000
Carrying Amount | Level 2 | Senior unsecured notes payable
Financial liabilities:
Senior unsecured notes payable	296,479,000	295,911,000
Carrying Amount | Level 3
Financial assets:
Preferred equity investments	0	3,800,000
Carrying Amount | Level 3 | Mortgage loan receivable
Financial assets:
Mortgage loans receivable	0	29,500,000
Fair Value | Level 2 | Senior unsecured notes payable
Financial liabilities:
Senior unsecured notes payable	309,000,000	312,750,000
Fair Value | Level 3
Financial assets:
Preferred equity investments	0	3,674,000
Fair Value | Level 3 | Mortgage loan receivable
Financial assets:
Mortgage loans receivable	$ 0	$ 29,500,000