CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) shares	Sep. 30, 2016 USD ($) shares
Supplemental disclosures of non-cash investing and financing activities
Common stock issued through the dividend reinvestment plan (in shares) | shares		2,466	1,689
Common stock issued through the dividend reinvestment plan		$ 452	$ 304
Number of shares withheld to satisfy employees' tax withholding and other liabilities (in shares) | shares		60,165	53,214
Shares withheld to satisfy employees' tax withholding and other liabilities, value		$ 10,514	$ 8,316
Stock issued during period, shares, share-based compensation, forfeited (in shares) | shares		3,045
Stock issued during period, value, share-based compensation, forfeited		$ 528	627
Dividends declared but not paid	$ 185,384	196,079	185,384
Change in redemption value of redeemable noncontrolling interest		(458)
Increase (decrease) in prepaid expense and other assets		1,422	(2,689)
Income (loss) on cash flow hedges	719	(15,654)	(73,826)
Increase in accrued expenses, other liabilities and accrued interest payable		1,998	53,591
Other comprehensive income (loss), unrealized gain (loss) on derivatives arising during period, net of tax			56,280
Cash flow hedge losses reclassified to earnings	1,748	5,301	4,682
Net operating real estate		15,767,760
Prepaid expenses and other assets		277,122
Avalon Maplewood
Supplemental disclosures of non-cash investing and financing activities
Net operating real estate		16,361
Prepaid expenses and other assets		$ 2,965
Mortgage notes payable | Notes Payable Maturities 2020 | Avalon Hoboken [Member]
Supplemental disclosures of non-cash investing and financing activities
Business combination, recognized identifiable assets acquired and liabilities assumed, noncurrent liabilities, long-term debt	67,904		67,904
Mortgage notes payable | Notes Payable Maturities 2020 | Avalon Columbia Pike
Supplemental disclosures of non-cash investing and financing activities
Business combination, recognized identifiable assets acquired and liabilities assumed, noncurrent liabilities, long-term debt	$ 70,507		$ 70,507
Restricted Stock and Restricted Stock Converted From Performance Shares
Supplemental disclosures of non-cash investing and financing activities
Equity instruments granted (in shares) | shares		201,314	196,491
Restricted Stock Converted From Performance Shares
Supplemental disclosures of non-cash investing and financing activities
Equity instruments granted (in shares) | shares		128,482	115,618
Restricted stock
Supplemental disclosures of non-cash investing and financing activities
Equity instruments granted (in shares) | shares		72,832	80,873
Fair value of shares issued		$ 13,079	$ 13,129
Stock issued during period, shares, share-based compensation, forfeited (in shares) | shares		3,045	3,848
Accumulated earnings less dividends
Supplemental disclosures of non-cash investing and financing activities
Change in redemption value of redeemable noncontrolling interest		$ (458)	$ 529
Restricted stock and deferred stock awards | Non Employee Director
Supplemental disclosures of non-cash investing and financing activities
Equity instruments granted (in shares) | shares			44,327
Non Employee Director | Restricted stock and deferred stock awards
Supplemental disclosures of non-cash investing and financing activities
Fair value of shares issued			$ 3,894