SHORT-TERM AND LONG-TERM INVESTMENTS (Details) - USD ($) $ in Thousands	Apr. 30, 2017	Oct. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 364,999
Estimated Fair Value	364,631
U.S. government obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	345,029	$ 350,270
Gross Unrealized Gains	0	197
Gross Unrealized Losses	(368)	(36)
Estimated Fair Value	344,661	350,431
U.S. government obligations | Included in short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	255,042	260,125
Gross Unrealized Gains	0	140
Gross Unrealized Losses	(233)	(6)
Estimated Fair Value	254,809	260,259
U.S. government obligations | Included in long-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	89,987	90,145
Gross Unrealized Gains	0	57
Gross Unrealized Losses	(135)	(30)
Estimated Fair Value	89,852	90,172
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,970	14,989
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	19,970	14,989
Commercial paper | Included in short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,970	14,989
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 19,970	$ 14,989