EARNINGS PER SHARE/UNIT - Computation of basic and diluted earnings per share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income	$ 64,903	$ 59,062	$ 81,986	$ 87,933	$ 65,156	$ (137,515)	$ 68,157	$ 109,112	$ 293,884	$ 104,910	$ 383,367
Less: net income attributable to noncontrolling interests									(12,306)	(4,491)	(16,952)
Net income available to common stockholders	$ 62,216	$ 56,606	$ 78,536	$ 84,220	$ 62,400	$ (131,678)	$ 65,257	$ 104,440	$ 281,578	$ 100,419	$ 366,415
Denominator:
Denominator for basic earnings per share									200,279	197,738	191,781
Effect of dilutive securities:
Common stock equivalents									691	269	956
Noncontrolling interest - Omega OP Units									8,741	8,783	8,898
Denominator for diluted earnings per share									209,711	206,790	201,635
Earnings per share - basic:
Net income available to common stockholders	$ 0.31	$ 0.28	$ 0.39	$ 0.42	$ 0.31	$ (0.67)	$ 0.33	$ 0.53	$ 1.41	$ 0.51	$ 1.91
Net income (loss) per share
Net income	$ 0.31	$ 0.28	$ 0.39	$ 0.42	$ 0.31	$ (0.67)	$ 0.33	$ 0.53	$ 1.40	$ 0.51	$ 1.90
Omega OP
Numerator:
Net income	$ 64,903	$ 59,062	$ 81,986	$ 87,933	$ 65,156	$ (137,515)	$ 68,157	$ 109,112	$ 293,884	$ 104,910	$ 383,367
Net income available to common stockholders									$ 293,884	$ 104,910	$ 383,367
Denominator:
Denominator for basic earnings per share									209,020	206,521	200,679
Denominator for basic earnings per unit									209,020	206,521	200,679
Effect of dilutive securities:
Common stock equivalents									691	269	956
Denominator for diluted earnings per share									209,711	206,790	201,635
Denominator for diluted earnings per unit									209,711	206,790	201,635
Earnings per share - basic:
Net income available to common stockholders									$ 1.41	$ 0.51	$ 1.91
Net income (loss) per share
Net income									1.40	0.51	1.90
Earnings per unit - basic:
Net income available to Omega OP Unit holders	$ 0.31	$ 0.28	$ 0.39	$ 0.42	$ 0.31	$ (0.67)	$ 0.33	$ 0.53	1.41	0.51	1.91
Net income (loss) per unit
Diluted (in dollars per share)	$ 0.31	$ 0.28	$ 0.39	$ 0.42	$ 0.31	$ (0.67)	$ 0.33	$ 0.53	$ 1.40	$ 0.51	$ 1.90