Consolidated Statements Of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Deficit)	Treasury Stock
Beginning Balances, Shares at Apr. 30, 2018		246,199				36,945
Beginning Balances, Value at Apr. 30, 2018	$ 393,711	$ 2,462	$ 760,250	$ (14,303)	$ 362,980	$ (717,678)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(152,670)				(152,670)
Other comprehensive (loss) income	(1,731)			(1,731)
Stock-based compensation	4,307		4,307
Stock-based awards exercised or vested, shares						627
Stock-based awards exercised or vested	1,211		(9,945)		(1,029)	$ 12,185
Acquisition of treasury shares, shares						(200)
Acquisition of treasury shares	(4,560)					$ (4,560)
Repurchase and retirement of common shares, shares		(4,173)
Repurchase and retirement of common shares	(97,105)	$ (42)	(2,503)		(94,560)
Cash dividends declared	(52,104)				(52,104)
Ending Balances, Shares at Jul. 31, 2018		242,026				36,518
Ending Balances, Value at Jul. 31, 2018	192,009	$ 2,420	752,109	(16,034)	163,567	$ (710,053)
Beginning Balances, Shares at Apr. 30, 2018		246,199				36,945
Beginning Balances, Value at Apr. 30, 2018	393,711	$ 2,462	760,250	(14,303)	362,980	$ (717,678)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(328,946)
Ending Balances, Shares at Oct. 31, 2018		242,026				36,499
Ending Balances, Value at Oct. 31, 2018	(31,325)	$ 2,420	759,235	(18,880)	(64,291)	$ (709,809)
Beginning Balances, Shares at Jul. 31, 2018		242,026				36,518
Beginning Balances, Value at Jul. 31, 2018	192,009	$ 2,420	752,109	(16,034)	163,567	$ (710,053)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(176,276)				(176,276)
Other comprehensive (loss) income	(2,846)			(2,846)
Stock-based compensation	$ 7,352		7,352
Stock-based awards exercised or vested, shares	700					35
Stock-based awards exercised or vested	$ 247		(226)		(202)	$ 675
Acquisition of treasury shares, shares						(16)
Acquisition of treasury shares	(431)					$ (431)
Cash dividends declared	(51,380)				(51,380)
Ending Balances, Shares at Oct. 31, 2018		242,026				36,499
Ending Balances, Value at Oct. 31, 2018	(31,325)	$ 2,420	759,235	(18,880)	(64,291)	$ (709,809)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(126,454)				(126,454)
Other comprehensive (loss) income	1,238			1,238
Stock-based compensation	6,067		6,067
Stock-based awards exercised or vested, shares						41
Stock-based awards exercised or vested	622		(5)		(169)	$ 796
Acquisition of treasury shares, shares						(2)
Acquisition of treasury shares	(56)					$ (56)
Repurchase and retirement of common shares, shares		(525)
Repurchase and retirement of common shares	(12,301)	$ (5)	(315)		(11,981)
Cash dividends declared	(51,382)				(51,382)
Ending Balances, Shares at Jan. 31, 2019		241,501				36,460
Ending Balances, Value at Jan. 31, 2019	(213,591)	$ 2,415	764,982	(17,642)	(254,277)	$ (709,069)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	877,909				877,909
Other comprehensive (loss) income	(2,774)			(2,774)
Stock-based compensation	5,784		5,784
Stock-based awards exercised or vested, shares						84
Stock-based awards exercised or vested	253		(1,231)		(150)	$ 1,634
Acquisition of treasury shares, shares						(1)
Acquisition of treasury shares	(27)					$ (27)
Repurchase and retirement of common shares, shares		(3,164)
Repurchase and retirement of common shares	(75,432)	$ (32)	(1,899)		(73,501)
Cash dividends declared	(50,595)				(50,595)
Ending Balances, Shares at Apr. 30, 2019		238,337				36,377
Ending Balances, Value at Apr. 30, 2019	541,527	$ 2,383	767,636	(20,416)	499,386	$ (707,462)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(150,247)				(150,247)
Other comprehensive (loss) income	(2,320)			(2,320)
Stock-based compensation	6,557		6,557
Stock-based awards exercised or vested, shares						906
Stock-based awards exercised or vested	1,056		(13,789)		(2,786)	$ 17,631
Acquisition of treasury shares, shares						(314)
Acquisition of treasury shares	(9,185)					$ (9,185)
Repurchase and retirement of common shares, shares		(1,593)
Repurchase and retirement of common shares	(44,072)	$ (16)	(955)		(43,101)
Cash dividends declared	(52,512)				(52,512)
Ending Balances, Shares at Jul. 31, 2019		236,744				35,785
Ending Balances, Value at Jul. 31, 2019	290,804	$ 2,367	759,449	(22,736)	250,740	$ (699,016)
Beginning Balances, Shares at Apr. 30, 2019		238,337				36,377
Beginning Balances, Value at Apr. 30, 2019	541,527	$ 2,383	767,636	(20,416)	499,386	$ (707,462)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(338,246)
Ending Balances, Shares at Oct. 31, 2019		231,024				35,778
Ending Balances, Value at Oct. 31, 2019	(75,747)	$ 2,310	765,220	(21,817)	(122,535)	$ (698,925)
Beginning Balances, Shares at Jul. 31, 2019		236,744				35,785
Beginning Balances, Value at Jul. 31, 2019	290,804	$ 2,367	759,449	(22,736)	250,740	$ (699,016)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(187,999)				(187,999)
Other comprehensive (loss) income	919			919
Stock-based compensation	$ 9,331		9,331
Stock-based awards exercised or vested, shares	900					13
Stock-based awards exercised or vested	$ (139)		(127)		(276)	$ 264
Acquisition of treasury shares, shares						(6)
Acquisition of treasury shares	(173)					$ (173)
Repurchase and retirement of common shares, shares		(5,720)
Repurchase and retirement of common shares	(136,939)	$ (57)	(3,433)		(133,449)
Cash dividends declared	(51,551)				(51,551)
Ending Balances, Shares at Oct. 31, 2019		231,024				35,778
Ending Balances, Value at Oct. 31, 2019	$ (75,747)	$ 2,310	$ 765,220	$ (21,817)	$ (122,535)	$ (698,925)