Short-Term and Long-Term Investments (Details) - USD ($) $ in Thousands	Jan. 31, 2018	Oct. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 338,585
Estimated Fair Value	337,894
U.S. government obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	298,717	$ 299,408
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(692)	(432)
Estimated Fair Value	298,025	298,976
U.S. government obligations | Included in short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	239,404	249,498
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(530)	(305)
Estimated Fair Value	238,874	249,193
U.S. government obligations | Included in long-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	59,313	49,910
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(162)	(127)
Estimated Fair Value	59,151	49,783
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	39,868	29,939
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Estimated Fair Value	39,869	29,940
Commercial paper | Included in short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	39,868	29,939
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 39,869	$ 29,940