Debt - Summary of Outstanding Debt (Parenthetical) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
1633 Broadway [Member]
Debt Instrument [Line Items]
Ownership interest rate of property	90.00%	90.00%
One Market Plaza [Member]
Debt Instrument [Line Items]
Ownership interest rate of property	49.00%	49.00%
300 Mission Street [Member]
Debt Instrument [Line Items]
Ownership interest rate of property	31.10%	31.10%