QUARTERLY RESULTS OF CONSOLIDATED OPERATIONS (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	2 Months Ended	3 Months Ended										8 Months Ended		12 Months Ended
	Dec. 31, 2018	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Selected Quarterly Financial Information [Abstract]
Revenues	$ 30,287	$ 45,638	$ 45,946	$ 44,185	$ 42,716	$ 41,866	$ 40,978	$ 42,811	$ 39,797	$ 39,195	$ 38,301	$ 121,871	$ 111,249	$ 169,745	$ 160,104	$ 145,500
Net income (loss) attributable to controlling interests	(2,756)	(4,558)	2,916	(20,874)	136,105	12,821	(11,264)	30,280	23,110	11,600	(21,643)	(4,398)	127,414	116,788	43,347	72,006
Net income (loss) available to common shareholders	$ (3,892)	$ (6,264)	$ 1,211	$ (22,579)	$ 134,331	$ 6,360	$ (13,550)	$ 27,994	$ 19,172	$ 8,722	$ (24,522)	$ (8,945)	$ 117,461	$ 104,562	$ 31,366	$ 60,492
Net income (loss) per common share - basic & diluted (in dollars per share)	$ (0.33)	$ (0.52)	$ 0.10	$ (1.89)	$ 11.22	$ 0.53	$ (1.12)	$ 2.33	$ 1.58	$ 0.72	$ (2.02)	$ (0.75)	$ 9.78	$ 8.71	$ 2.58	$ 4.91