Significant Transactions During the Second Quarter of 2017 and Subsequent Event (Details) - USD ($)	1 Months Ended				2 Months Ended	3 Months Ended	6 Months Ended
	Jul. 31, 2017	Jul. 27, 2017	May 31, 2017	Apr. 30, 2017	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016
Other Commitments [Line Items]
Proceeds from partial redemption of preferred equity investment in a joint venture							$ 67,674,000	$ 34,564,000
Gain on early redemption of preferred equity investment							0	13,046,000
Payments to acquire preferred equity investments							$ 12,750,000	$ 0
Common stock issued under equity distribution program (in shares)						311,873
Common stock issued under equity distribution program average price (in dollars per share)					$ 260.30	$ 260.30	$ 260.30
Sale of common stock, net						$ 80,600,000	$ 80,565,000
Subsequent Event [Member]
Other Commitments [Line Items]
Common stock issued under equity distribution program (in shares)		0
Repaid amount of private placement	$ 40,000,000
Private placement repurchase, coupon rate (as a percent)	4.50%
Senior Notes [Member] | Senior Unsecured Notes At 3.625% [Member]
Other Commitments [Line Items]
Debt, face amount				$ 350,000,000
Debt, term (in years)				10 years
Debt, stated interest rate (as a percent)				3.625%
Limited Liability Company With Development Projects In The Jefferson At Stadium Park Apartments [Member] | Notes and Other Receivables from Affiliates [Member]
Other Commitments [Line Items]
Co-investments			$ 13,200,000
Preferred equity investment, dividend rate, first 30 months (as a percent)			10.00%
Payments to acquire preferred equity investments					$ 4,000,000
Preferred Equity Investment in a Joint Venture that Holds a Property in Seattle, Washington [Member]
Other Commitments [Line Items]
Proceeds from partial redemption of preferred equity investment in a joint venture				$ 12,600,000
Reduction in preferred equity investment				12,400,000
Gain on early redemption of preferred equity investment				$ 200,000
Preferred Equity Investment In Multifamily Development Project In Seattle, Washington [Member] | Subsequent Event [Member]
Other Commitments [Line Items]
Preferred equity investment, dividend rate, first 30 months (as a percent)	11.00%
Commitment to fund preferred equity investment in a multifamily development project located in Seattle, WA	$ 11,900,000