Long-Term Debt - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended			1 Months Ended	9 Months Ended	1 Months Ended											1 Months Ended	9 Months Ended
	Feb. 28, 2013	Feb. 29, 2012	Feb. 28, 2013 payment	Feb. 29, 2012	May 31, 2012	Feb. 28, 2013 Guarantee Of Joint Venture Debt	Feb. 28, 2013 Maximum Increase	Feb. 28, 2013 Minimum Increase	Aug. 25, 2011 Senior Secured Revolving Credit Facility	Feb. 28, 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	Feb. 28, 2013 Credit Agreement	Aug. 10, 2010 9.25% Senior Notes	Feb. 28, 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									$ 200,000,000				$ 50,000,000	$ 15,000,000
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	148,100,000		148,100,000				20,000,000	10,700,000
Unused portion of borrowing amount	25,000,000		25,000,000
Fixed charge coverage ratio, maximum allowed according to covenant			1.0
Fixed charge coverage ratio	0.48		0.48							1.0											1.0
Borrowing limited to an amount under credit facility	123,100,000		123,100,000
Borrowings outstanding										0
Borrowing base used to support letters of credit			30,100,000
Line of credit facility, remaining borrowing capacity	93,000,000		93,000,000
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	40,000,000		40,000,000
Cash dividend on common stock			2,500,000
Number of cash dividend payments allowed annually, maximum			4
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		60,000,000
Line of credit facility percentage of aggregate commitments to lenders			30.00%
Senior note aggregate principal amount																						650,000,000	650,000,000
Senior notes offering price in percentage																						100.00%
Senior notes, interest rate																						9.25%	9.25%	7.25%
Senior notes maturity date																						2020	2020
Redemption of aggregate principal amount of notes, percentage			35.00%
Percentage of principal amount redemption price			109.25%
Required purchase price of principal amount, percentage			101.00%
Principal payments due on long-term debt, year one	1,800,000		1,800,000
Principal payments due on long-term debt, year two	1,900,000		1,900,000
Principal payments due on long-term debt, year three	1,900,000		1,900,000
Principal payments due on long-term debt, year four	1,900,000		1,900,000
Principal payments due on long-term debt, year five	800,000		800,000
Interest incurred on long-term debt	17,400,000	17,000,000	51,900,000	51,400,000
Interest amount capitalized	10,200,000	8,500,000	29,400,000	24,600,000
Total amount of interest paid			66,000,000	66,000,000
Percentage of joint venture's debt guaranteed			50.00%
Debt guaranteed under joint venture's	$ 657,879,000		$ 657,879,000		$ 655,778,000	$ 10,500,000
Debt maturity date						Nov. 18, 2013