Fair Value Measurements - Summary of the Face Value, Carrying Amount and Fair Value of Financial Instruments (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Financial assets:
Preferred equity investment	$ 5,400,000
Financial liabilities:
Senior unsecured notes payable, net	294,221,000	$ 255,294,000
Level 2 | Senior unsecured notes payable
Financial liabilities:
Financial liabilities - face value	300,000,000	260,000,000
Level 2 | Carrying Amount
Financial liabilities:
Senior unsecured notes payable, net	294,221,000	255,294,000
Level 2 | Fair Value
Financial liabilities:
Senior unsecured notes payable, net	309,750,000	265,850,000
Level 3
Financial assets:
Preferred equity investment - face value	4,531,000	12,031,000
Level 3 | Carrying Amount
Financial assets:
Preferred equity investment	5,368,000	13,872,000
Level 3 | Fair Value
Financial assets:
Preferred equity investment	$ 5,241,000	$ 14,289,000