Investments (Amortized Cost And Fair Value Of Securities Available-For-Sale) (Details) (USD $)							9 Months Ended
	Jan. 31, 2014		Apr. 30, 2013		Jan. 31, 2013		Jan. 31, 2014 Mortgage-Backed Securities	Jan. 31, 2013 Short-Term Municipal Bonds		Jan. 31, 2013 Long-Term		Jan. 31, 2014 Long-Term Mortgage-Backed Securities		Apr. 30, 2013 Long-Term Mortgage-Backed Securities		Jan. 31, 2013 Long-Term Mortgage-Backed Securities		Jan. 31, 2014 Long-Term Municipal Bonds		Apr. 30, 2013 Long-Term Municipal Bonds		Jan. 31, 2013 Long-Term Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Investments in available-for-sale securities, Amortized Cost	$ 453,231,000		$ 480,628,000		$ 391,933,000			$ 1,000,000		$ 390,933,000		$ 449,097,000		$ 476,450,000		$ 386,741,000		$ 4,134,000		$ 4,178,000		$ 4,192,000
Gross Unrealized Gains	3,442,000		6,912,000		6,160,000			1,000		6,159,000		3,201,000		6,592,000		5,825,000		241,000		320,000		334,000
Available For Sale Securities, Gross Unrealized Loss, Accumulated In Investments	12,903,000	[1]	664,000	[1]	780,000	[1]		0	[1]	780,000	[1]	12,903,000	[1]	664,000	[1]	780,000	[1]	0	[1]	0	[1]	0	[1]
Investments in available-for-sale securities, Fair Value	443,770,000		486,876,000		397,313,000			1,001,000		396,312,000		439,395,000		482,378,000		391,786,000		4,375,000		4,498,000		4,526,000
Mortgage-backed securities, cost							25,800,000
Mortgage-backed securities, gross unrealized loss							$ 2,800,000

[1] As of January 31, 2014, mortgage-backed securities with a cost of $25.8 million and gross unrealized losses of $2.8 million had been in a continuous loss position for more than twelve months. As of January 31, 2013 and April 30, 2013, we had no securities that had been in a continuous loss position for more than twelve months.