Significant Transactions During the Six Months Ended 2018 and Subsequent Events (Details)	1 Months Ended				2 Months Ended
	Jun. 30, 2018 USD ($) unit	May 31, 2018 USD ($) apartment	Mar. 31, 2018 USD ($)	Jan. 31, 2018 USD ($) shares	Jun. 30, 2018 USD ($)
Other Commitments [Line Items]
Proceeds from full redemption of a preferred equity investment in a joint venture	$ 26,500,000			$ 2,400,000
Gain on early redemption of preferred equity investment	$ 1,600,000
Promote income			$ 20,500,000
Stock repurchased and retired during the period (in shares) | shares				16,834
Stock repurchased and retired during the period				$ 3,800,000
Purchase authority remaining under stock repurchase plan			245,200,000
Senior Notes [Member] | Senior Unsecured Notes At 4.500% [Member]
Other Commitments [Line Items]
Debt, face amount			$ 300,000,000
Debt, term (in years)			30 years
Debt, stated interest rate			4.50%
Domain [Member]
Other Commitments [Line Items]
Number of units sold | unit	379
Proceeds from sale of real estate	$ 132,000,000
Gain (loss) on sale of properties	$ 22,200,000
Apartment Home Community In Ventura, California [Member]
Other Commitments [Line Items]
Commitment to fund preferred equity investment		$ 26,500,000
Number of units acquired | apartment		400
Preferred returns rate		10.25%
Commitment funded amount					$ 20,400,000
BEX III [Member]
Other Commitments [Line Items]
Repayments of related party debt				$ 29,500,000