UNAUDITED SUMMARIZED CONSOLIDATED QUARTERLY FINANCIAL DATA (Details) - 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
Quarterly financial data
Rental income	$ 264,732	$ 263,256	$ 256,634	$ 250,483	$ 250,116	$ 248,264	$ 244,658	$ 241,271	$ 1,035,105	$ 984,309	$ 948,461
Net income/(loss)	89,615	20,258	22,444	89,225	75,627	17,570	11,062	28,396	221,542	132,655	320,380
Net (loss)/income attributable to stakeholders	$ 81,168	$ 17,639	$ 19,630	$ 80,801	$ 68,356	$ 15,264	$ 9,228	$ 25,038	$ 199,238	$ 117,850	$ 289,001
Income/(loss) per weighted average common share - basic	$ 0.30	$ 0.07	$ 0.07	$ 0.30	$ 0.26	$ 0.06	$ 0.03	$ 0.09	$ 0.74	$ 0.44	$ 1.09
Income/(loss) per weighted average common share - diluted	$ 0.30	$ 0.07	$ 0.07	$ 0.30	$ 0.25	$ 0.06	$ 0.03	$ 0.09	$ 0.74	$ 0.44	$ 1.08
Weighted average number of common shares outstanding — Basic	270,107	267,727	267,311	267,546	267,270	267,056	266,972	266,790	268,179	267,024	265,386
Weighted average number of common shares outstanding — diluted	270,755	268,861	268,890	269,208	269,221	269,062	268,859	268,688	269,483	268,830	267,311