Copyright Data Fees (Detail Textuals) $ in Thousands	12 Months Ended
	Apr. 30, 2015 USD ($) Contract Fund	Apr. 30, 2014 USD ($) Contract	Apr. 30, 2013 USD ($)
Copyright Data Fees [Abstract]
Copyright data fees received	$ 2,847	$ 2,733	$ 3,900
Percentage of copyright data fees	4.20%
Number of contracts for copyright data | Contract	5	4
Third party sponsored assets for copyright data	$ 2,250,000	$ 2,280,000
Number of new ETFs subject to contract began trading in March 2015 | Fund	3