SUMMARY OF QUARTERLY RESULTS (UNAUDITED) (Detail) - USD ($) $ / shares in Units, $ 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
Summary Of Quarterly Results [Line Items]
Revenues	$ 219,750	$ 221,852	$ 219,881	$ 220,199	$ 221,206	$ 219,638	$ 235,797	$ 231,744	$ 881,682	$ 908,385	$ 900,827
Net income (loss)	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	$ 62,216	$ 56,606	$ 78,536	$ 84,220	$ 62,400	$ (131,678)	$ 65,257	$ 104,440	$ 281,578	$ 100,419	$ 366,415
Net income (loss) available to common per share:
Basic (in dollars per share)	$ 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
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
Omega OP
Summary Of Quarterly Results [Line Items]
Revenues	$ 219,750	$ 221,852	$ 219,881	$ 220,199	$ 221,206	$ 219,638	$ 235,797	$ 231,744	$ 881,682	$ 908,385	$ 900,827
Net income (loss)	$ 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
Net income (loss) available to common per share:
Basic (in dollars per share)									$ 1.41	$ 0.51	$ 1.91
Net income (loss) per share
Diluted (in dollars per share)									1.40	0.51	1.90
Net income (loss) available to Omega OP Unit holders:
Basic (in dollars per share)	$ 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