Long-Term Debt (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended			6 Months Ended						6 Months Ended											6 Months Ended		0 Months Ended	6 Months Ended	0 Months Ended	1 Months Ended	2 Months Ended	3 Months Ended
	Aug. 10, 2010	Nov. 30, 2011	Nov. 30, 2010	Aug. 31, 2010	Nov. 30, 2011	Nov. 30, 2010	Nov. 30, 2011 Minimum [Member]	Nov. 30, 2011 Maximum [Member]	Nov. 30, 2011 Maximum Increase [Member]	Nov. 30, 2011 Minimum Increase [Member]	Nov. 30, 2011 Senior Secured Revolving Credit Facility [Member]	Nov. 30, 2011 Senior Secured Revolving Credit Facility [Member] Minimum [Member]	Nov. 30, 2011 Senior Secured Revolving Credit Facility [Member] Maximum [Member]	Nov. 30, 2011 Sub-Limit For Letters Of Credit [Member]	Nov. 30, 2011 Sub-Limit Swing Line Loans [Member]	Nov. 30, 2011 LIBOR Rate Plus [Member] Minimum [Member]	Nov. 30, 2011 LIBOR Rate Plus [Member] Maximum [Member]	Nov. 30, 2011 Base Rate Plus [Member] Minimum [Member]	Nov. 30, 2011 Base Rate Plus [Member] Maximum [Member]	Nov. 30, 2011 Federal Funds Rate Plus [Member]	Nov. 30, 2011 One-Month LIBOR Loans Plus [Member]	Nov. 30, 2011 Credit Agreement [Member] Minimum [Member]	Nov. 30, 2011 Credit Agreement [Member] Maximum [Member]	Aug. 10, 2010 9.25% Senior Notes [Member]	Nov. 30, 2011 9.25% Senior Notes [Member]	Sep. 09, 2010 7.25% Senior Notes Due 2013 [Member]	Jul. 27, 2010 7.25% Senior Notes Due 2013 [Member]	Jul. 27, 2010 7.25% Senior Notes Due 2013 [Member]	Aug. 31, 2010 7.25% Senior Notes Due 2013 [Member]
Maximum amount available to borrow under agreement											$ 200,000,000			$ 50,000,000	$ 15,000,000
Line of credit facility, interest rate description											Amounts drawn under the credit facility bear annual interest either at the LIBOR rate plus a margin of 2.0% to 2.75% or at a base rate plus a margin of 1.0% to 1.75%. The base rate is the higher of the federal funds rate plus 0.5%, the prime rate established by Bank of America, N.A. or the one-month LIBOR rate plus 1.0%. The interest rate margins are determined based on the Company's fixed charge coverage ratio. The commitment fee calculated on the unused portion of the credit facility ranges from 0.375% to 0.50% per year based on the Company's average daily loan balance.
Line of credit facility, commitment fee description											The commitment fee calculated on the unused portion of the credit facility ranges from 0.375% to 0.50% per year based on the Company's average daily loan balance
Debt maturity date																								2020	2020			2013
Credit facility expiration date											August 25, 2016
Variable interest rate																2.00%	2.75%	1.00%	1.75%	0.50%	1.00%
Commitment fee calculated on unused portion												0.375%	0.50%
Borrowing base agreement amount		137,000,000			137,000,000				20,000,000	10,700,000
Unused portion of borrowing amount					25,000,000
Fixed charge coverage ratio							(.57)	1.0				1.0	1.0									1.0	1.0
Borrowing limited to an amount under credit facility					112,000,000
Borrowing base used to support letter of credit					25,500,000
Future foreign subsidiaries equity interest available for credit facility guarantees		66.00%			66.00%
Borrowing availability under credit agreement					40,000,000
Cash dividend on common stock					2,500,000
Permitted to pay cash dividends on common stock aggregate during any calendar year					10,000,000
Minimum borrowing availability required to pay cash dividends					60,000,000
Line of credit facility percentage of aggregate commitments to lenders					30.00%
Line of credit facility, remaining borrowing capacity		86,500,000			86,500,000
Line of credit facility, covenant terms					The credit agreement contains a number of covenants restricting, among other things, prepayment or redemption of our senior notes, distributions and dividends on and repurchases of our capital stock, acquisitions and investments, indebtedness, liens and affiliate transactions. We are permitted to pay cash dividends on our common stock as long as the credit facility is not in default, the fixed charge coverage ratio is greater than 1.0 to 1.0 and borrowing availability under the borrowing base is more than $40 million. When our fixed charge coverage ratio is less than 1.0 to 1.0, we are permitted to pay cash dividends on our common stock not to exceed $2.5 million in any single instance (which shall not occur more than four times in any calendar year) or $10 million in the aggregate during any calendar year as long as the credit facility is not in default and borrowing availability is more than the greater of $60 million or 30% of the aggregate commitments of all lenders.
Senior note aggregate principal amount	650,000,000																								650,000,000
Senior notes offering price in percentage	100.00%
Redemption of aggregate principal amount of notes, percentage					35.00%
Percentage of principal amount redemption price					109.25%																					101.813%
Required purchase price of principal amount, percentage					101.00%
Cash tender offer for outstanding aggregate principal amount																											550,000,000
Principal amount of notes purchased pursuant to tender offer and consent solicitation																											536,600,000	536,600,000
Amount paid for purchase price and consent fees																											547,700,000
Remaining aggregate principal, amount redeemed																										13,400,000
Recognized loss on debt retirement			(613,000)			(29,619,000)																							29,600,000
Consent fees				11,400,000
Unamortized debt discount																													18,200,000
Principal payments due on long-term debt, year one		400,000			400,000
Principal payments due on long-term debt, year two		400,000			400,000
Principal payments due on long-term debt, year three		400,000			400,000
Principal payments due on long-term debt, year four		500,000			500,000
Principal payments due on long-term debt, year five		500,000			500,000
Interest incurred on long-term debt		17,100,000	17,300,000		34,400,000	31,700,000
Interest amount capitalized		8,300,000	3,400,000		16,100,000	3,400,000
Total amount of interest paid				$ 28,600,000	$ 35,400,000