Operating Segment and Geographic Information - Additional Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2017 USD ($)	Jan. 31, 2017 USD ($)	Oct. 31, 2016 USD ($)	Jul. 31, 2016 USD ($)	Apr. 30, 2016 USD ($)	Jan. 31, 2016 USD ($)	Oct. 31, 2015 USD ($)	Jul. 31, 2015 USD ($)	Apr. 30, 2017 USD ($)	Apr. 30, 2016 USD ($)	Apr. 30, 2015 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of Operating Segments									1
Number of Reportable Segments									1
Revenue	$ 50,209	$ 50,525	$ 50,408	$ 50,093	$ 50,709	$ 50,255	$ 49,926	$ 48,876	$ 201,235	$ 199,766	$ 191,181
UNITED KINGDOM
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									25,800	26,000	22,900
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 142,200	$ 140,800	$ 133,700