Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012
Income Statement [Abstract]
Revenues	$ 132,296	$ 116,836	$ 260,854	$ 234,474
Operating expenses:
Cost of operations	90,545	82,087	178,962	163,432
General and administration	16,425	13,883	31,503	29,073
Depreciation and amortization	15,669	14,570	30,866	29,279
Environmental remediation charge	150		150
Severance and reorganization costs	53	1,793	161	1,827
Expense from divestiture, acquisition and financing costs	4	77	24	631
Total operating expenses	122,846	112,410	241,666	224,242
Operating income	9,450	4,426	19,188	10,232
Other expense (income):
Interest income	(101)	(10)	(113)	(18)
Interest expense	9,635	11,516	18,994	23,207
(Income) loss from equity method investments	(91)	109	887	1,875
Loss (gain) on derivative instruments	629	3,896	(25)	3,896
Loss on debt extinguishment		9,670		9,670
Other income	(392)	(311)	(530)	(441)
Other expense, net	9,680	24,870	19,213	38,189
Loss from continuing operations before income taxes and discontinued operations	(230)	(20,444)	(25)	(27,957)
Provision for income taxes	300	413	619	1,063
Loss from continuing operations before discontinued operations	(530)	(20,857)	(644)	(29,020)
Discontinued operations:
(Loss) income from discontinued operations (net of income tax provision of $0, $0, $0 and $0)	(45)	(235)	284	(451)
Loss on disposal of discontinued operations (net of income tax provision of $0, $0, $0 and $0)			(378)
Net loss	(575)	(21,092)	(738)	(29,471)
Less: Net loss attributable to noncontrolling interests	(236)	(125)	(207)	(133)
Net loss attributable to common stockholders	(339)	(20,967)	(531)	(29,338)
Amounts attributable to common stockholders:
Loss from continuing operations before discontinued operations	(294)	(20,732)	(437)	(28,887)
(Loss) income from discontinued operations, net of tax	(45)	(235)	284	(451)
Loss on disposal of discontinued operations, net of tax			(378)
Net loss attributable to common stockholders	$ (339)	$ (20,967)	$ (531)	$ (29,338)
Basic and diluted earnings per share:
Loss from continuing operations before discontinued operations	$ (0.01)	$ (0.67)	$ (0.01)	$ (1.00)
(Loss) income from discontinued operations, net of tax	$ 0.00	$ (0.01)	$ 0.01	$ (0.01)
Loss on disposal of discontinued operations, net of tax			$ (0.01)
Net loss per common share	$ (0.01)	$ (0.68)	$ (0.01)	$ (1.01)
Weighted average common shares outstanding	39,821	30,872	39,742	28,932