SHAREHOLDERS’ EQUITY (Details) - USD ($)				8 Months Ended	12 Months Ended
	Dec. 05, 2018	Dec. 05, 2017	Dec. 07, 2016	Dec. 31, 2018	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Class of Stock [Line Items]
Noncontrolling interests - Operating Partnership (in shares)				1,367,502	1,409,943	1,561,722
Conversion of Units to Common Shares. [Abstract]
Units converted to common stock (in shares)				9,000	149,000	17,000
Units converted to common stock, aggregate cost				$ 499,000	$ 8,775,000	$ 966,000
Units converted to common stock, unit price (in dollars per share)				$ 53.12	$ 58.90	$ 58.40
Units converted to common stock				$ 0	$ 0	$ 0	$ 0
Equity Awards
Common shares outstanding (in shares)				11,942,372	11,952,598	12,119,930
Share Repurchase Program
Repurchase period	1 year		1 year
Share Repurchase Program
Share Repurchase Program
Authorized share repurchase amount			$ 50,000,000
Repurchase period		1 year
Shares repurchased and retired (in shares)				42,000	178,000	78,000
Shares repurchased and retired				$ 2,200,000	$ 9,900,000	$ 4,500,000
Shares repurchased and retired (in dollars per share)				$ 51.36	$ 55.82	$ 57.69
2015 Incentive Plan
Equity Awards
Forfeited (in shares)				200	3,200	27,400
2015 Incentive Plan | Performance Shares
Equity Awards
Shares issued (in shares)				5,600	9,300	60,400
Shares issued				$ 347,000	$ 536,000	$ 2,600,000
2008 Incentive Award Plan
Equity Awards
Shares issued (in shares)						5,900
Shares issued						$ 352,000
Series C Preferred Stock
Cumulative Redeemable Preferred Shares of Beneficial Interest [Abstract]
Preferred shares issued (in shares)				4,118,460	4,118,460	0
Distribution rate percentage					6.625%
Liquidation preference per share (in dollars per share)						$ 25.00
Distribution accrual rate					$ 1.65625
Preferred shares liquidation preference						$ 102,971,475
Series B Preferred Stock
Cumulative Redeemable Preferred Shares of Beneficial Interest [Abstract]
Preferred shares issued (in shares)				0	0	4,600,000
Distribution rate percentage					7.95%
Preferred shares liquidation preference						$ 115,000,000
Shares redeemed (in shares)					4,600,000
Series A Preferred Stock
Cumulative Redeemable Preferred Shares of Beneficial Interest [Abstract]
Distribution rate percentage						8.25%
Aggregate redemption price						$ 29,200,000
Exercise of Exchange Rights
Conversion of Units to Common Shares. [Abstract]
Units converted to common stock (in shares)				33,000	3,000	50,000
Units converted to common stock				$ 649,000	$ 34,000	$ 875,000