Fair Value Measurements (Details 3) (Significant unobservable inputs (Level 3), SEK)	12 Months Ended
	Apr. 30, 2014
Discounted cash flow | Auction rate securities | Minimum
Fair Value Inputs
Coupon rates (as a percent)	0.10%
Estimated redemption periods	5 years
Discount rates (as a percent)	7.20%
Discounted cash flow | Auction rate securities | Maximum
Fair Value Inputs
Coupon rates (as a percent)	0.30%
Estimated redemption periods	20 years
Discount rates (as a percent)	19.30%
Discounted cash flow | Convertible bonds | Bond component
Fair Value Inputs
Coupon rates (as a percent)	5.00%
Estimated redemption periods	3 years 7 months 6 days
Discount rates (as a percent)	5.20%
Binomial option pricing model | Convertible bonds | Embedded conversion feature
Fair Value Inputs
Contractual term	3 years 7 months 6 days
Conversion price (in SEK per share)	9.41
Volatility (as a percent)	45.00%
Risk-free interest rate (as a percent)	0.94%
Binomial option pricing model | Convertible bonds | Embedded conversion feature | CybAero
Fair Value Inputs
Stock price (in SEK per share)	33.90