Subsequent Events - Additional Information (Details) - USD ($)				12 Months Ended
	Jan. 23, 2019	Jan. 09, 2019	Jan. 04, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 11, 2019
Subsequent Event [Line Items]
Derivative, notional amount				$ 69,670,000
Proceeds from the disposition of properties				63,866,000	$ 260,711,000	$ 150,378,000
Fund III
Subsequent Event [Line Items]
Capital called				423,900,000
Capital called company share amount				551,900,000
Interest Rate Swaps
Subsequent Event [Line Items]
Derivative, notional amount				$ 50,000,000
Derivative fixed interest rate				2.80%
Interest Rate Swaps | Mortgages
Subsequent Event [Line Items]
Derivative, notional amount				$ 136,600,000
Derivative fixed interest rate				2.86%
Subsequent Event
Subsequent Event [Line Items]
Derivative remaining maturity periods			10 years
Subsequent Event | Fund III | 3104 M Street Property
Subsequent Event [Line Items]
Proceeds from the disposition of properties	$ 10,500,000
Subsequent Event | Renaissance Portfolio | Fund III | 3104 M Street Property
Subsequent Event [Line Items]
Equity method investment, ownership percentage	20.00%
Subsequent Event | Renaissance Portfolio | Fund III | 3104 M Street Property | Mortgages
Subsequent Event [Line Items]
Equity method investments	$ 4,700,000
Subsequent Event | Interest Rate Swaps
Subsequent Event [Line Items]
Derivative, notional amount			$ 100,000,000
Derivative fixed interest rate			2.60%
Subsequent Event | Interest Rate Swaps | Fund V | Elk Grove Commons - Elk Grove, CA
Subsequent Event [Line Items]
Borrowings, amount							$ 41,500,000
Subsequent Event | Fund V
Subsequent Event [Line Items]
Capital called		$ 33,200,000
Capital called company share amount		$ 6,700,000