Assets and liabilities measured at fair value on a recurring basis (Details) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014
Total:
Earn-Out Payments	$ 376	$ 0
Holdback Payment and Earn-Out Payments	0	895
Total assets at fair value	376	895
Quoted prices in active markets (Level 1)
Earn-Out Payments	0	0
Holdback Payment and Earn-Out Payments	0	0
Total assets at fair value	0	0
Significant other observable inputs (Level 2)
Earn-Out Payments	0	0
Holdback Payment and Earn-Out Payments	0	0
Total assets at fair value	0	0
Significant unobservable inputs (Level 3)
Earn-Out Payments	283	44
Holdback Payment and Earn-Out Payments	0	320
Total assets at fair value	$ 376	$ 895