Supplemental Condensed Consolidated Financial Information - Condensed Consolidated Cash Flow Statement (Detail) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2016	Jul. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Cash provided by (used in) operating activities	$ 47,744	$ 25,239
Financing activities:
Sold interest in accounts receivable, net of collections	(21,620)	10,602
Debt proceeds	0	150,000
Debt and capital lease repayments	(549)	(95,868)
Repurchases of senior unsecured notes	0	(18,818)
Increase in deferred financing costs	0	(2,179)
Cash provided by (used in) financing activities	(22,169)	43,737
Investing activities:
Property and equipment additions	(11,282)	(80,095)
Proceeds from disposal of property and equipment	1,844	27,723
Helicopter deposits net of lease inception refunds	0	(24,360)
Restricted cash	9,056	(16,638)
Cash used in investing activities	(382)	(93,370)
Cash provided by (used in) operations	25,193	(24,394)
Effect of exchange rate changes on cash and cash equivalents	(3,303)	(7,793)
Change in cash and cash equivalents during the period	21,890	(32,187)
Cash and cash equivalents, beginning of period	266,130	134,297
Cash and cash equivalents, end of period	288,020	102,110
Parent
Condensed Financial Statements, Captions [Line Items]
Cash provided by (used in) operating activities	494	(95)
Financing activities:
Sold interest in accounts receivable, net of collections	0	0
Debt proceeds		0
Debt and capital lease repayments	0	0
Repurchases of senior unsecured notes		0
Increase in deferred financing costs		0
Cash provided by (used in) financing activities	0	0
Investing activities:
Property and equipment additions	0	0
Proceeds from disposal of property and equipment	0	0
Helicopter deposits net of lease inception refunds		0
Restricted cash	0	0
Cash used in investing activities	0	0
Cash provided by (used in) operations	494	(95)
Effect of exchange rate changes on cash and cash equivalents	0	0
Change in cash and cash equivalents during the period	494	(95)
Cash and cash equivalents, beginning of period	87	112
Cash and cash equivalents, end of period	581	17
Issuer
Condensed Financial Statements, Captions [Line Items]
Cash provided by (used in) operating activities	(2,604)	(9,792)
Financing activities:
Sold interest in accounts receivable, net of collections	0	0
Debt proceeds		150,000
Debt and capital lease repayments	0	(95,000)
Repurchases of senior unsecured notes		(18,818)
Increase in deferred financing costs		0
Cash provided by (used in) financing activities	0	36,182
Investing activities:
Property and equipment additions	0	0
Proceeds from disposal of property and equipment	0	0
Helicopter deposits net of lease inception refunds		0
Restricted cash	0	0
Cash used in investing activities	0	0
Cash provided by (used in) operations	(2,604)	26,390
Effect of exchange rate changes on cash and cash equivalents	0	0
Change in cash and cash equivalents during the period	(2,604)	26,390
Cash and cash equivalents, beginning of period	3,138	82,458
Cash and cash equivalents, end of period	534	108,848
Guarantor
Condensed Financial Statements, Captions [Line Items]
Cash provided by (used in) operating activities	31,249	15,384
Financing activities:
Sold interest in accounts receivable, net of collections	0	0
Debt proceeds		150,000
Debt and capital lease repayments	(549)	(95,868)
Repurchases of senior unsecured notes		(18,818)
Increase in deferred financing costs		0
Cash provided by (used in) financing activities	(549)	35,314
Investing activities:
Property and equipment additions	(10,292)	(38,706)
Proceeds from disposal of property and equipment	1,819	27,723
Helicopter deposits net of lease inception refunds		(24,360)
Restricted cash	(141)	2,248
Cash used in investing activities	(8,614)	(33,095)
Cash provided by (used in) operations	22,086	17,603
Effect of exchange rate changes on cash and cash equivalents	(993)	(8,627)
Change in cash and cash equivalents during the period	21,093	8,976
Cash and cash equivalents, beginning of period	27,581	96,428
Cash and cash equivalents, end of period	48,674	105,404
Non-guarantor
Condensed Financial Statements, Captions [Line Items]
Cash provided by (used in) operating activities	16,001	9,950
Financing activities:
Sold interest in accounts receivable, net of collections	(21,620)	10,602
Debt proceeds		0
Debt and capital lease repayments	0	0
Repurchases of senior unsecured notes		0
Increase in deferred financing costs		(2,179)
Cash provided by (used in) financing activities	(21,620)	8,423
Investing activities:
Property and equipment additions	(990)	(41,389)
Proceeds from disposal of property and equipment	25	0
Helicopter deposits net of lease inception refunds		0
Restricted cash	9,197	(18,886)
Cash used in investing activities	8,232	(60,275)
Cash provided by (used in) operations	2,613	(41,902)
Effect of exchange rate changes on cash and cash equivalents	(2,310)	834
Change in cash and cash equivalents during the period	303	(41,068)
Cash and cash equivalents, beginning of period	238,462	37,757
Cash and cash equivalents, end of period	238,765	(3,311)
Eliminations
Condensed Financial Statements, Captions [Line Items]
Cash provided by (used in) operating activities	2,604	9,792
Financing activities:
Sold interest in accounts receivable, net of collections	0	0
Debt proceeds		(150,000)
Debt and capital lease repayments	0	95,000
Repurchases of senior unsecured notes		18,818
Increase in deferred financing costs		0
Cash provided by (used in) financing activities	0	(36,182)
Investing activities:
Property and equipment additions	0	0
Proceeds from disposal of property and equipment	0	0
Helicopter deposits net of lease inception refunds		0
Restricted cash	0	0
Cash used in investing activities	0	0
Cash provided by (used in) operations	2,604	(26,390)
Effect of exchange rate changes on cash and cash equivalents	0	0
Change in cash and cash equivalents during the period	2,604	(26,390)
Cash and cash equivalents, beginning of period	(3,138)	(82,458)
Cash and cash equivalents, end of period	$ (534)	$ (108,848)