Investments (Amortized Cost And Fair Value Of Securities Available-For-Sale) (Details) (USD $)	Oct. 31, 2013		Apr. 30, 2013		Oct. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	$ 470,010,000		$ 480,628,000		$ 383,265,000
Gross Unrealized Gains	4,682,000		6,912,000		6,498,000
Gross Unrealized Losses	(9,348,000)	[1]	(664,000)	[1]	(109,000)	[1]
Investments in available-for-sale securities, Fair Value	465,344,000		486,876,000		389,654,000
Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Mortgage-backed securities, cost					4,600,000
Mortgage-backed securities, gross unrealized loss					1,000
Short-Term | Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost					1,003,000
Gross Unrealized Gains					11,000
Gross Unrealized Losses					0	[1]
Investments in available-for-sale securities, Fair Value					1,014,000
Long-Term
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost					382,262,000
Gross Unrealized Gains					6,487,000
Gross Unrealized Losses					(109,000)	[1]
Investments in available-for-sale securities, Fair Value					388,640,000
Long-Term | Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	465,861,000		476,450,000		378,055,000
Gross Unrealized Gains	4,422,000		6,592,000		6,116,000
Gross Unrealized Losses	(9,348,000)	[1]	(664,000)	[1]	(109,000)	[1]
Investments in available-for-sale securities, Fair Value	460,935,000		482,378,000		384,062,000
Long-Term | Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	4,149,000		4,178,000		4,207,000
Gross Unrealized Gains	260,000		320,000		371,000
Gross Unrealized Losses	0	[1]	0	[1]	0	[1]
Investments in available-for-sale securities, Fair Value	$ 4,409,000		$ 4,498,000		$ 4,578,000

[1] As of October 31, 2013 and April 30, 2013, we had no securities that had been in a continuous loss position for more than twelve months. As of October 31, 2012, mortgage-backed securities with a cost of $4.6 million and gross unrealized losses of $1 thousand had been in a continuous loss position for more than twelve months.