Marketable Securities (Details 1) - USD ($) $ in Thousands	May 31, 2017	May 31, 2016
Amortized cost and fair value of marketable securities by contractual maturity
Amortized cost, Due in one year or less	$ 0
Amortized cost, Due after one through five years	0
Amortized cost, Due after five through twenty years	1,350
Amortized cost	1,350	$ 1,800
Fair Value, Due in one year or less	0
Fair Value, Due after one through five years	0
Fair Value, Due after five through twenty years	1,215
Fair Value, Total	$ 1,215