SHORT-TERM AND LONG-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	Jul. 31, 2017	Oct. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 294,991
Estimated Fair Value	294,617
U.S. government obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	285,008	$ 350,270
Gross Unrealized Gains	0	197
Gross Unrealized Losses	(374)	(36)
Estimated Fair Value	284,634	350,431
U.S. government obligations | Included in short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	225,032	260,125
Gross Unrealized Gains	0	140
Gross Unrealized Losses	(272)	(6)
Estimated Fair Value	224,760	260,259
U.S. government obligations | Included in long-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	59,976	90,145
Gross Unrealized Gains	0	57
Gross Unrealized Losses	(102)	(30)
Estimated Fair Value	59,874	90,172
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,983	14,989
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	9,983	14,989
Commercial paper | Included in short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,983	14,989
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 9,983	$ 14,989