Significant Accounting Policies (Details)	3 Months Ended
	Jul. 31, 2012 Y segments
Significant Accounting Policies [Line Items]
Number Of Operating Segments (in operating segments)	4
Expected economic lives of finite-lived intangible assets, maximum (in years)	7
Expected number of years Spares useage cost is expensed (in years)	4 years
4.0% Convertible Senior Notes due March 15, 2015 [Member]
Significant Accounting Policies [Line Items]
Interest rate on convertible notes	4.00%
Equipment, Furniture and Fixtures [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives capitalized and amortized straight-line, minimum (in years)	2
Estimated useful lives capitalized and amortized straight-line, maximum (in years)	5
Software and Website Development [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives capitalized and amortized straight-line, minimum (in years)	2
Estimated useful lives capitalized and amortized straight-line, maximum (in years)	5
Maximum [Member]
Significant Accounting Policies [Line Items]
Measurement period for cash and cash equivalents (in months)	3 months
Measurement period for marketable debt securities (in years)	1 year
Minimum [Member]
Significant Accounting Policies [Line Items]
One-time employee termination benefits related to service period (in days)	60 days