Fair Value of Financial Instruments Fair Value of Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013 investments
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Alternative [Abstract]
Less than Twelve Months, Fair Value	$ 11,959
Less than 12 Months, Aggregate Losses	(13)
Twelve Months or Longer, Fair Value	0
12 Months or Longer, Aggregate Losses	0
Fair Value	11,959
Aggregate Losses	(13)
Number of Positions (in number of investments)	12
Corporate Bond Securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Alternative [Abstract]
Less than Twelve Months, Fair Value	10,074
Less than 12 Months, Aggregate Losses	(8)
Twelve Months or Longer, Fair Value	0
12 Months or Longer, Aggregate Losses	0
Fair Value	10,074
Aggregate Losses	(8)
Foreign Government Debt Securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Alternative [Abstract]
Less than Twelve Months, Fair Value	787
Less than 12 Months, Aggregate Losses	(3)
Twelve Months or Longer, Fair Value	0
12 Months or Longer, Aggregate Losses	0
Fair Value	787
Aggregate Losses	(3)
Municipal debt securities
Fair Value, Assets Measured on Recurring and Nonrecurring Basis, Alternative [Abstract]
Less than Twelve Months, Fair Value	1,098
Less than 12 Months, Aggregate Losses	(2)
Twelve Months or Longer, Fair Value	0
12 Months or Longer, Aggregate Losses	0
Fair Value	1,098
Aggregate Losses	$ (2)