Schedule of Share-Based Payment Award, Non-Qualified Stock Options, Valuation Assumptions (Detail) (Stock Options, USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
	Feb. 10, 2011 Grant Date February 10, 2011		Feb. 09, 2010 Grant Date February 9, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	2,142		1,703
Exercise price	$ 16.31		$ 16.67
Vesting date	Feb. 10, 2014		Feb. 09, 2013
Fair value per share	$ 3.47		$ 3.69
Dividend yield	3.00%	[1]	3.00%	[1]
Expected volatility	29.20%	[2]	30.60%	[2]
Risk-free interest rate	2.44%	[3]	2.35%	[3]
Expected option life (years)	5 years	[4]	5 years	[4]
Options, Outstanding at end of period	2,100		1,629

[1] Dividend yield - estimated yield based on the historical dividend payment for the four most recent dividend payments prior to the grant date.

[2] Expected volatility - based on historical volatility over the expected term using daily stock prices.

[3] Risk-free interest rate - United States Treasury Constant Maturity rates as of the grant date over the expected term.

[4] Expected option life - The 2010 and 2011 grant assumptions are based on the simplified formula determined in accordance with Staff Accounting Bulletin No. 110. The company does not have sufficient historical exercise behavior data to reasonably estimate the expected option life.