INCOME/(LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Aug. 31, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2017
Antidilutive securities
Net income/(loss)												$ 199,579	$ 221,542	$ 132,655
Net (income)/loss attributable to redeemable noncontrolling interests in the Operating Partnership and DownREIT Partnership												(14,426)	(18,215)	(10,933)
Net (income)/loss attributable to noncontrolling interests												(188)	(221)	(164)
Net income/(loss) attributable to UDR, Inc.												184,965	203,106	121,558
Distributions to preferred stockholders - Series E (Convertible)												(4,104)	(3,868)	(3,708)
Net income/(loss) attributable to common stockholders								$ 81,168	$ 17,639	$ 19,630	$ 80,801	$ 180,861	$ 199,238	$ 117,850
Denominator for earnings per share - basic and diluted:
Weighted average common shares outstanding												285,509,000	268,513,000	267,567,000
Non-vested restricted stock awards												(262,000)	(334,000)	(543,000)
Denominator for basic income/(loss) per share				293,107,000	288,706,000	281,960,000	277,002,000	270,107,000	267,727,000	267,311,000	267,546,000	285,247,000	268,179,000	267,024,000
Denominator for diluted income/(loss) per share				294,073,000	289,529,000	282,575,000	277,557,000	270,755,000	268,861,000	268,890,000	269,208,000	286,015,000	269,483,000	268,830,000
Income/(loss) per weighted average common share - basic				$ 0.33	$ 0.09	$ 0.12	$ 0.08	$ 0.30	$ 0.07	$ 0.07	$ 0.30	$ 0.63	$ 0.74	$ 0.44
Income/(loss) per weighted average common share - diluted				$ 0.33	$ 0.09	$ 0.12	$ 0.08	$ 0.30	$ 0.07	$ 0.07	$ 0.30	$ 0.63	$ 0.74	$ 0.44
Number of shares authorized	350,000,000			350,000,000				350,000,000				350,000,000	350,000,000
Number of shares sold			7,500,000
Aggregate gross proceeds			$ 349,900									$ 725,315	$ 299,825
Weighted average price per share			$ 46.65
Proceeds from the issuance of common shares through public offering, net			$ 349,900									725,315	299,825
Aggregate net proceeds from sales, after deducting related costs			$ 349,800									$ 725,315	$ 299,825
OP/DownREIT Units
Antidilutive securities
Antidilutive securities												22,773,000	24,548,000	24,821,000
Convertible preferred stock
Antidilutive securities
Antidilutive securities												3,011,000	3,011,000	3,021,000
stock options, unvested LTIP Units, and unvested restricted stock
Antidilutive securities
Antidilutive securities												768,000	1,304,000	1,806,000
Denominator for earnings per share - basic and diluted:
Incremental shares issuable from assumed conversion of stock options, unvested LTIP Units, unvested restricted stock, and shares issuable upon settlement of forward purchase agreements												768,000	1,304,000	1,806,000
ATM
Denominator for earnings per share - basic and diluted:
Number of shares authorized															20,000,000.0
Number of shares sold												7,000,000.0
Aggregate gross proceeds												$ 316,500
Weighted average price per share												$ 45.29
Proceeds from the issuance of common shares through public offering, net												$ 316,500
Commissions paid to sales agents												4,000
Aggregate net proceeds from sales, after deducting related costs												$ 312,300
Shares of common stock available for future issuance	11,700,000			11,700,000								11,700,000
Forward Sales Agreement
Denominator for earnings per share - basic and diluted:
Number of shares authorized		1,300,000			1,300,000
Number of shares sold	1,300,000
Aggregate gross proceeds	$ 63,500												$ 63,200
Weighted average price per share	$ 47.41	$ 47.68
Forward price													$ 47.41
Proceeds from the issuance of common shares through public offering, net	$ 63,500												$ 63,200
Commissions paid to sales agents	600
Aggregate net proceeds from sales, after deducting related costs	$ 63,200