Stockholders' Equity (Details 3) - May. 31, 2015 - 2009 Stock Option Plan - USD ($) $ / shares in Units, $ in Thousands	Total
Griffin Stock Option Plan
Outstanding at ending of the year (in shares)	227,149
Weighted Avg. Exercise Price (in dollars per share)	$ 30.45
Weighted Avg. Remaining Contractual Life	5 years
Total Intrinsic Value	$ 553
$23.00-$28.00
Griffin Stock Option Plan
Exercise prices, low end of range (in dollars per share)	$ 23.00
Exercise prices, high end of range (in dollars per share)	$ 28.00
Outstanding at ending of the year (in shares)	14,934
Weighted Avg. Exercise Price (in dollars per share)	$ 25.43
Weighted Avg. Remaining Contractual Life	6 years 8 months 12 days
Total Intrinsic Value	$ 106
$28.00-$32.00
Griffin Stock Option Plan
Exercise prices, low end of range (in dollars per share)	$ 28.00
Exercise prices, high end of range (in dollars per share)	$ 32.00
Outstanding at ending of the year (in shares)	129,140
Weighted Avg. Exercise Price (in dollars per share)	$ 29.06
Weighted Avg. Remaining Contractual Life	5 years 10 months 24 days
Total Intrinsic Value	$ 446
$32.00-$39.00
Griffin Stock Option Plan
Exercise prices, low end of range (in dollars per share)	$ 32.00
Exercise prices, high end of range (in dollars per share)	$ 39.00
Outstanding at ending of the year (in shares)	83,075
Weighted Avg. Exercise Price (in dollars per share)	$ 33.52
Weighted Avg. Remaining Contractual Life	3 years 4 months 24 days
Total Intrinsic Value	$ 1