Share-Based Payments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013
Stock-based compensation expense	$ 941	$ 570	$ 1,968	$ 1,934
General and Administrative Expense [Member]
Stock-based compensation expense	866	500	1,686	1,619
Selling and Marketing Expense [Member]
Stock-based compensation expense	63	56	189	199
Research and Development Expense [Member]
Stock-based compensation expense	4	4	19	33
Translational Oncology Solutions Cost of Sales [Member]
Stock-based compensation expense	2	4	12	16
Personalized Oncology Solutions Cost of Sales [Member]
Stock-based compensation expense	$ 6	$ 6	$ 62	$ 67

General and Administrative Expense [Member]

Selling and Marketing Expense [Member]

Research and Development Expense [Member]

Translational Oncology Solutions Cost of Sales [Member]

Personalized Oncology Solutions Cost of Sales [Member]