Investments (Amortized Cost And Fair Value Of Securities Available-For-Sale) (Details) (USD $)	Apr. 30, 2012		Apr. 30, 2011
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	$ 366,428,000		$ 166,305,000
Investments in available-for-sale securities, Gross Unrealized Gains	6,045,000		806,000
Gross Unrealized Losses	(121,000)	[1]	(194,000)	[1]
Investments in available-for-sale securities, Fair Value	372,352,000		166,917,000
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage-backed securities, cost	8,100,000
Mortgage-backed securities, gross unrealized loss	21,000
Short-Term [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	1,008,000		3,023,000
Investments in available-for-sale securities, Gross Unrealized Gains	29,000		58,000
Investments in available-for-sale securities, Fair Value	1,037,000		3,081,000
Long-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	365,420,000		163,282,000
Investments in available-for-sale securities, Gross Unrealized Gains	6,016,000		748,000
Gross Unrealized Losses	(121,000)	[1]	(194,000)	[1]
Investments in available-for-sale securities, Fair Value	371,315,000		163,836,000
Long-Term [Member] | Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	361,184,000		157,970,000
Investments in available-for-sale securities, Gross Unrealized Gains	5,620,000		401,000
Gross Unrealized Losses	(121,000)	[1]	(194,000)	[1]
Investments in available-for-sale securities, Fair Value	366,683,000		158,177,000
Long-Term [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	4,236,000		5,312,000
Investments in available-for-sale securities, Gross Unrealized Gains	396,000		347,000
Investments in available-for-sale securities, Fair Value	$ 4,632,000		$ 5,659,000

[1] At April 30, 2012, mortgage-backed securities with a cost of $8.1 million and gross unrealized losses of $21 thousand had been in a continuous loss position for more than twelve months. At April 30, 2011, we had no investments that had been in a continuous loss position for more than twelve months.