Long-Term Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended				1 Months Ended	6 Months Ended	1 Months Ended											0 Months Ended	1 Months Ended	6 Months Ended
	Nov. 30, 2013	Nov. 30, 2012	Nov. 30, 2013 payment	Nov. 30, 2012	Nov. 30, 2013 Maximum Increase	Nov. 30, 2013 Minimum Increase	Aug. 25, 2011 Senior Secured Revolving Credit Facility	Nov. 30, 2013 Senior Secured Revolving Credit Facility	Aug. 25, 2011 Senior Secured Revolving Credit Facility Minimum	Aug. 25, 2011 Senior Secured Revolving Credit Facility Maximum	Aug. 25, 2011 Sub-Limit For Letters Of Credit	Aug. 25, 2011 Sub-Limit Swing Line Loans	Aug. 25, 2011 Libor Rate Plus Minimum	Aug. 25, 2011 Libor Rate Plus Maximum	Aug. 25, 2011 Base Rate Plus Minimum	Aug. 25, 2011 Base Rate Plus Maximum	Aug. 25, 2011 Federal Funds Rate Plus	Aug. 25, 2011 One-Month Libor Rate Plus	Nov. 30, 2013 Credit Agreement	Aug. 10, 2010 9.25% Senior Notes	Aug. 10, 2010 9.25% Senior Notes	Nov. 30, 2013 9.25% Senior Notes	Aug. 10, 2010 7.25% Senior Notes Due 2013
Debt Instrument [Line Items]
Maximum amount available to borrow under agreement							$ 200				$ 50	$ 15
Credit facility expiration date							August 25, 2016	August 25, 2016
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
Variable interest rate													2.00%	2.75%	1.00%	1.75%	0.50%	1.00%
Commitment fee calculated on unused portion per year									0.375%	0.50%
Borrowing base agreement amount	131.2		131.2		20.0	10.7
Unused portion of borrowing amount	25		25
Fixed charge coverage ratio, maximum allowed according to covenant			1.0
Fixed charge coverage ratio	0.91		0.91					1.0											1.0
Borrowing limited to an amount under credit facility	106.2		106.2
Borrowings outstanding								0
Borrowing base used to support letters of credit			30.5
Line of credit facility, remaining borrowing capacity	75.7		75.7
Future foreign subsidiaries equity interest available for credit facility guarantees	66.00%		66.00%
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.
Borrowing availability under credit agreement	40		40
Cash dividend on common stock			2.5
Number of cash dividend payments allowed annually, maximum			4
Permitted to pay cash dividends on common stock aggregate during any calendar year			10
Minimum borrowing availability required to pay cash dividends	60		60
Line of credit facility percentage of aggregate commitments to lenders			30.00%
Senior note aggregate principal amount																				650	650	650
Senior notes offering price in percentage																					100.00%
Senior notes, interest rate																				9.25%	9.25%	9.25%	7.25%
Senior notes maturity date																				2020	2020	2020
Required purchase price of principal amount, percentage			101.00%
Principal payments due on long-term debt, year one	2.2		2.2
Principal payments due on long-term debt, year two	2.0		2.0
Principal payments due on long-term debt, year three	1.9		1.9
Principal payments due on long-term debt, year four	1.1		1.1
Principal payments due on long-term debt, year five	0.3		0.3
Interest incurred on long-term debt	17.4	17.4	34.8	34.4
Interest amount capitalized	9.9			19.2
Total amount of interest paid			$ 36.6	$ 35.5
Percentage of joint venture's debt guaranteed			50.00%