Investments (Amortized Cost And Fair Value Of Securities Available-For-Sale) (Details) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2014	Apr. 30, 2014	Oct. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	$ 380,488	$ 424,817	$ 470,010
Gross Unrealized Gains	10,466	3,007	4,682
Available For Sale Securities, Gross Unrealized Loss, Accumulated In Investments	0	0	(9,348)
Investments in available-for-sale securities, Fair Value	390,954	427,824	465,344
Long-Term | Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	371,297	420,697	465,861
Gross Unrealized Gains	9,783	2,798	4,422
Available For Sale Securities, Gross Unrealized Loss, Accumulated In Investments	0	0	(9,348)
Investments in available-for-sale securities, Fair Value	381,080	423,495	460,935
Long-Term | Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	4,091	4,120	4,149
Gross Unrealized Gains	151	209	260
Available For Sale Securities, Gross Unrealized Loss, Accumulated In Investments	0	0	0
Investments in available-for-sale securities, Fair Value	4,242	4,329	4,409
Long-Term | Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	5,000
Gross Unrealized Gains	532
Available For Sale Securities, Gross Unrealized Loss, Accumulated In Investments	0
Investments in available-for-sale securities, Fair Value	5,532
Long-Term | US Treasury Bill Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	100
Gross Unrealized Gains	0
Available For Sale Securities, Gross Unrealized Loss, Accumulated In Investments	0
Investments in available-for-sale securities, Fair Value	$ 100