Investments (Amortized Cost And Fair Value Of Securities Available-For-Sale) (Details) (USD $)	Apr. 30, 2013		Apr. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	$ 480,628,000		$ 366,428,000
Investments in available-for-sale securities, Gross Unrealized Gains	6,912,000		6,045,000
Gross Unrealized Losses	(664,000)	[1]	(121,000)	[1]
Investments in available-for-sale securities, Fair Value	486,876,000		372,352,000
Mortgage-Backed Securities
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 | Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	0		1,008,000
Investments in available-for-sale securities, Gross Unrealized Gains	0		29,000
Gross Unrealized Losses	0	[1]	0	[1]
Investments in available-for-sale securities, Fair Value	0		1,037,000
Long-Term
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	480,628,000		365,420,000
Investments in available-for-sale securities, Gross Unrealized Gains	6,912,000		6,016,000
Gross Unrealized Losses	(664,000)	[1]	(121,000)	[1]
Investments in available-for-sale securities, Fair Value	486,876,000		371,315,000
Long-Term | Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	476,450,000		361,184,000
Investments in available-for-sale securities, Gross Unrealized Gains	6,592,000		5,620,000
Gross Unrealized Losses	(664,000)	[1]	(121,000)	[1]
Investments in available-for-sale securities, Fair Value	482,378,000		366,683,000
Long-Term | Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	4,178,000		4,236,000
Investments in available-for-sale securities, Gross Unrealized Gains	320,000		396,000
Gross Unrealized Losses	0	[1]	0	[1]
Investments in available-for-sale securities, Fair Value	$ 4,498,000		$ 4,632,000

[1] As of April 30, 2013, we had no securities that had been in a continuous loss position for more than twelve months. As of 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.