Consolidated Statements Of Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance at May. 31, 2009		$ 27,718	$ 469,908	$ 319,199	$ (13,680)
Stock issued to employees and non-employee directors related to stock compensation plans		78	872
Stock-based compensation			4,584
Tax benefit from stock-based compensation			220
Net income (loss)	(38,853)			(38,853)
Common dividends paid-$.075 per share in 2012 and $.30 per share in 2011 and 2010				(8,328)
Postretirement benefit obligation adjustments-net of tax expense (benefit) of $1,367 in 2012, $799 in 2011 and $(270) in 2010					(470)
COMPREHENSIVE INCOME (LOSS)
Net other comprehensive income (loss)	(470)
Net comprehensive loss	(39,323)
Balance at May. 31, 2010	761,248	27,796	475,584	272,018	(14,150)
Stock issued to employees and non-employee directors related to stock compensation plans		91	1,393
Stock-based compensation			4,729
Net income (loss)	(64,913)			(64,913)
Common dividends paid-$.075 per share in 2012 and $.30 per share in 2011 and 2010				(8,354)
Postretirement benefit obligation adjustments-net of tax expense (benefit) of $1,367 in 2012, $799 in 2011 and $(270) in 2010					1,388
COMPREHENSIVE INCOME (LOSS)
Net other comprehensive income (loss)	1,388
Net comprehensive loss	(63,525)
Balance at May. 31, 2011	695,582	27,887	481,706	198,751	(12,762)
Stock issued to employees and non-employee directors related to stock compensation plans		109	1,928
Stock-based compensation			5,003
Net income (loss)	7,476			7,476
Common dividends paid-$.075 per share in 2012 and $.30 per share in 2011 and 2010				(2,091)
Postretirement benefit obligation adjustments-net of tax expense (benefit) of $1,367 in 2012, $799 in 2011 and $(270) in 2010					(11,736)
COMPREHENSIVE INCOME (LOSS)
Net other comprehensive income (loss)	(11,736)
Net comprehensive loss	(4,260)
Balance at May. 31, 2012	$ 696,271	$ 27,996	$ 488,637	$ 204,136	$ (24,498)