Cumulative Effect of the Changes to Consolidated Balance Sheet for the Adoption of Topic 606 (Detail) - USD ($) $ in Thousands	Oct. 31, 2018	Aug. 01, 2018	Jul. 31, 2018	Oct. 31, 2017	Jul. 31, 2017
ASSETS
Inventories, net	$ 29,969		$ 47,786
Prepaid expenses and other current assets	34,187		13,415
Total current assets	276,054		264,281
Total assets	827,727		827,050
Liabilities
Other current liabilities	38,408		42,125
Total current liabilities	280,197		276,356
Total liabilities	687,098		684,230
Stockholders' equity
Accumulated deficit	(7,365,332)		(7,363,569)
Total stockholders' equity	105,431		107,628	$ 58,314	$ 62,971
Total liabilities, contingently redeemable preferred stock and stockholders' equity	827,727		827,050
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
ASSETS
Inventories, net			47,786
Prepaid expenses and other current assets			13,415
Total current assets			264,281
Total assets			827,050
Liabilities
Other current liabilities			42,125
Total current liabilities			276,356
Total liabilities			684,230
Stockholders' equity
Accumulated deficit			(7,363,569)
Total stockholders' equity			107,628
Total liabilities, contingently redeemable preferred stock and stockholders' equity			$ 827,050
Accounting Standards Update 2014-09
ASSETS
Inventories, net		$ 26,553
Prepaid expenses and other current assets		37,456
Total current assets		267,089
Total assets		829,858
Liabilities
Other current liabilities		38,795
Total current liabilities		273,026
Total liabilities		680,900
Stockholders' equity
Accumulated deficit		(7,357,431)
Total stockholders' equity		113,766
Total liabilities, contingently redeemable preferred stock and stockholders' equity		829,858
Accounting Standards Update 2014-09 | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
ASSETS
Inventories, net	51,392
Prepaid expenses and other current assets	11,524
Total current assets	274,814
Total assets	826,487
Liabilities
Other current liabilities	44,041
Total current liabilities	285,830
Total liabilities	692,731
Stockholders' equity
Accumulated deficit	(7,372,205)
Total stockholders' equity	98,558
Total liabilities, contingently redeemable preferred stock and stockholders' equity	826,487
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
ASSETS
Inventories, net	(21,423)	(21,233)
Prepaid expenses and other current assets	22,663	24,041
Total current assets	1,240	2,808
Total assets	1,240	2,808
Liabilities
Other current liabilities	(5,633)	(3,330)
Total current liabilities	(5,633)	(3,330)
Total liabilities	(5,633)	(3,330)
Stockholders' equity
Accumulated deficit	6,873	6,138
Total stockholders' equity	6,873	6,138
Total liabilities, contingently redeemable preferred stock and stockholders' equity	$ 1,240	$ 2,808