Fair Value Measurements - Condensed Consolidated Balance Sheet (Details) - Fair value, Measurements, Recurring - USD ($) $ in Thousands	Apr. 30, 2018	Oct. 31, 2017
Assets:
Total assets measured at fair value	$ 879,947	$ 900,641
Liabilities:
Total liabilities measured at fair value	1,317	2,129
Cash equivalents
Assets:
Cash equivalents	546,038	571,280
Short-term investments
Assets:
Short-term investments	268,584	279,133
Prepaid expenses and other
Assets:
Prepaid expenses and other	97	227
Long-term investments
Assets:
Long-term investments	58,895	49,783
Other long-term assets
Assets:
Other long-term assets	6,333	218
Accrued liabilities
Liabilities:
Accrued liabilities	1,317	2,129
Level 1
Assets:
Total assets measured at fair value	476,187	511,355
Liabilities:
Total liabilities measured at fair value	0	0
Level 1 | Cash equivalents
Assets:
Cash equivalents	476,187	511,355
Level 1 | Short-term investments
Assets:
Short-term investments	0	0
Level 1 | Prepaid expenses and other
Assets:
Prepaid expenses and other	0	0
Level 1 | Long-term investments
Assets:
Long-term investments	0	0
Level 1 | Other long-term assets
Assets:
Other long-term assets	0	0
Level 1 | Accrued liabilities
Liabilities:
Accrued liabilities	0	0
Level 2
Assets:
Total assets measured at fair value	403,760	389,286
Liabilities:
Total liabilities measured at fair value	1,317	2,129
Level 2 | Cash equivalents
Assets:
Cash equivalents	69,851	59,925
Level 2 | Short-term investments
Assets:
Short-term investments	268,584	279,133
Level 2 | Prepaid expenses and other
Assets:
Prepaid expenses and other	97	227
Level 2 | Long-term investments
Assets:
Long-term investments	58,895	49,783
Level 2 | Other long-term assets
Assets:
Other long-term assets	6,333	218
Level 2 | Accrued liabilities
Liabilities:
Accrued liabilities	$ 1,317	$ 2,129