CONDENSED CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Jan. 31, 2017	Apr. 30, 2016
ASSETS
SUPPLEMENTAL TYPE CERTIFICATES net of amortization	$ 4,145	$ 3,549
OTHER ASSETS
Other assets, accumulated amortization	$ 6,556	$ 5,579
STOCKHOLDERS' EQUITY:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	64,066,873	64,066,873
Common stock, shares outstanding (in shares)	63,416,953	63,466,873
Common stock, shares owed but not issued (in shares)	0	0
Treasury stock (in shares)	649,920	600,000
Class A [Member]
STOCKHOLDERS' EQUITY:
Preferred stock, par value (in dollars per share)	$ 5	$ 5
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, stated value (in dollars per share)	$ 100	$ 100
Preferred stock, dividend rate	9.80%	9.80%
Preferred stock, liquidation preference value	9.80%	9.80%
Preferred stock, redemption value	$ 100	$ 100
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Class B [Member]
STOCKHOLDERS' EQUITY:
Preferred stock, par value (in dollars per share)	$ 5	$ 5
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, stated value (in dollars per share)	$ 1,000	$ 1,000
Preferred stock, dividend rate	6.00%	6.00%
Preferred stock, liquidation preference value	6.00%	6.00%
Preferred stock, redemption value	$ 1,000	$ 1,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Class A and B [Member]
STOCKHOLDERS' EQUITY:
Preferred stock, designated classes (in shares)	200,000	200,000