Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Feb. 28, 2014	Feb. 28, 2013
OPERATING ACTIVITIES
Net loss	$ (38,979)	$ (19,594)
Adjustments to reconcile net loss to cash provided (used) by operating activities
Depreciation, depletion and amortization	58,556	42,968
Gain on asset disposals	(6,133)	(4,822)
Deferred income tax expense (benefit)	1,755	1,025
Stock-based compensation expense	5,349	7,015
Other – net	(9,942)	(7,555)
Changes in operating assets and liabilities
Receivables – net	(1,381)	830
Inventories	(3,072)	(710)
Prepaid expenses	2,632	(2,158)
Accounts payable and accrued liabilities	(9,450)	(7,228)
Net cash provided (used) by operating activities	(665)	9,771
INVESTING ACTIVITIES
Capital expenditures – expansions	(7,125)	(61,344)
Capital expenditures – other	(26,152)	(17,752)
Proceeds from asset disposals	8,390	5,783
Proceeds from insurance contracts, net of premiums paid	4,386	2,366
Other – net	0	(67)
Net cash used by investing activities	(20,501)	(71,014)
FINANCING ACTIVITIES
Debt payments	(1,373)	(2,236)
Stock option exercises	9,076	7,116
Net cash provided by financing activities	7,703	4,880
Decrease in cash and cash equivalents	(13,463)	(56,363)
Cash and cash equivalents at beginning of period	61,296	88,027
Cash and cash equivalents at end of period	$ 47,833	$ 31,664