CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015
ASSETS
SUPPLEMENTAL TYPE CERTIFICATES net of amortization	$ 3,549	$ 2,975
OTHER ASSETS:
Other assets, accumulated amortization	$ 5,579	$ 4,050
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	62,860,098
Common stock, shares outstanding (in shares)	64,066,873	62,860,098
Treasury stock (in shares)	600,000	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