Actual Defined Benefit Plan Asset Allocation and Target Allocation (Detail) (Riverside Defined Benefit Plans)	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2012 Equity Securities	May 31, 2011 Equity Securities	May 31, 2012 Debt Securities	May 31, 2011 Debt Securities	May 31, 2013 Future Period	May 31, 2013 Future Period Equity Securities	May 31, 2013 Future Period Debt Securities
Defined Contribution Benefit Plans [Line Items]
Target allocations	100.00%	100.00%	59.00%	61.00%	41.00%	39.00%	100.00%	60.00%	40.00%