Fair Value Measurements - Summary of Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financial assets:
Preferred equity investment - face value	$ 2,327	$ 4,531
Mortgage loans receivable
Financial assets:
Mortgage loans receivable - face value	41,773	12,375
Senior unsecured notes payable
Financial liabilities:
Senior unsecured notes payable - face value	300,000	300,000
Carrying Amount | Level 2 | Senior unsecured notes payable
Financial liabilities:
Senior unsecured notes payable	295,721	295,153
Carrying Amount | Level 3
Financial assets:
Preferred equity investments	3,079	5,746
Carrying Amount | Level 3 | Mortgage loans receivable
Financial assets:
Mortgage loans receivable	41,728	12,299
Fair Value | Level 2 | Senior unsecured notes payable
Financial liabilities:
Senior unsecured notes payable	309,750	289,500
Fair Value | Level 3
Financial assets:
Preferred equity investments	3,540	6,246
Fair Value | Level 3 | Mortgage loans receivable
Financial assets:
Mortgage loans receivable	$ 41,773	$ 12,375