Fair Value Measurements - Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2018	Apr. 30, 2019
Liabilities:
Debt conversion liability	$ 164,212	$ 0
Fair value, Measurements, Recurring
Assets:
Total assets measured at fair value	859,472	704,950
Liabilities:
Debt conversion liability	164,212
Total liabilities measured at fair value	178,343	25,457
Fair value, Measurements, Recurring | Cash equivalents
Assets:
Cash equivalents	650,609	584,859
Fair value, Measurements, Recurring | Short-term investments
Assets:
Short-term investments	148,981	119,327
Fair value, Measurements, Recurring | Prepaid expenses and other
Assets:
Prepaid expenses and other	133	764
Fair value, Measurements, Recurring | Long-term investments
Assets:
Long-term investments	58,970
Fair value, Measurements, Recurring | Other long-term assets
Assets:
Other long-term assets	779
Fair value, Measurements, Recurring | Accrued liabilities
Liabilities:
Accrued liabilities	3,231	11,121
Fair value, Measurements, Recurring | Debt conversion liability
Liabilities:
Debt conversion liability	164,212
Fair value, Measurements, Recurring | Other long-term obligations
Liabilities:
Other long-term obligations	10,900	14,336
Fair value, Measurements, Recurring | Level 1
Assets:
Total assets measured at fair value	590,684	584,859
Liabilities:
Debt conversion liability	0
Total liabilities measured at fair value	0	0
Fair value, Measurements, Recurring | Level 1 | Cash equivalents
Assets:
Cash equivalents	590,684	584,859
Fair value, Measurements, Recurring | Level 1 | Short-term investments
Assets:
Short-term investments	0	0
Fair value, Measurements, Recurring | Level 1 | Prepaid expenses and other
Assets:
Prepaid expenses and other	0	0
Fair value, Measurements, Recurring | Level 1 | Long-term investments
Assets:
Long-term investments	0
Fair value, Measurements, Recurring | Level 1 | Other long-term assets
Assets:
Other long-term assets	0
Fair value, Measurements, Recurring | Level 1 | Accrued liabilities
Liabilities:
Accrued liabilities	0	0
Fair value, Measurements, Recurring | Level 1 | Debt conversion liability
Liabilities:
Debt conversion liability	0
Fair value, Measurements, Recurring | Level 1 | Other long-term obligations
Liabilities:
Other long-term obligations	0	0
Fair value, Measurements, Recurring | Level 2
Assets:
Total assets measured at fair value	268,788	120,091
Liabilities:
Debt conversion liability	164,212
Total liabilities measured at fair value	167,443	14,557
Fair value, Measurements, Recurring | Level 2 | Cash equivalents
Assets:
Cash equivalents	59,925	0
Fair value, Measurements, Recurring | Level 2 | Short-term investments
Assets:
Short-term investments	148,981	119,327
Fair value, Measurements, Recurring | Level 2 | Prepaid expenses and other
Assets:
Prepaid expenses and other	133	764
Fair value, Measurements, Recurring | Level 2 | Long-term investments
Assets:
Long-term investments	58,970
Fair value, Measurements, Recurring | Level 2 | Other long-term assets
Assets:
Other long-term assets	779
Fair value, Measurements, Recurring | Level 2 | Accrued liabilities
Liabilities:
Accrued liabilities	3,231	3,630
Fair value, Measurements, Recurring | Level 2 | Debt conversion liability
Liabilities:
Debt conversion liability	164,212
Fair value, Measurements, Recurring | Level 2 | Other long-term obligations
Liabilities:
Other long-term obligations	0	10,927
Fair value, Measurements, Recurring | Level 3
Assets:
Total assets measured at fair value	0	0
Liabilities:
Debt conversion liability	0
Total liabilities measured at fair value	10,900	10,900
Fair value, Measurements, Recurring | Level 3 | Cash equivalents
Assets:
Cash equivalents	0	0
Fair value, Measurements, Recurring | Level 3 | Short-term investments
Assets:
Short-term investments	0	0
Fair value, Measurements, Recurring | Level 3 | Prepaid expenses and other
Assets:
Prepaid expenses and other	0	0
Fair value, Measurements, Recurring | Level 3 | Long-term investments
Assets:
Long-term investments	0
Fair value, Measurements, Recurring | Level 3 | Other long-term assets
Assets:
Other long-term assets	0
Fair value, Measurements, Recurring | Level 3 | Accrued liabilities
Liabilities:
Accrued liabilities	0	7,491
Fair value, Measurements, Recurring | Level 3 | Debt conversion liability
Liabilities:
Debt conversion liability	0
Fair value, Measurements, Recurring | Level 3 | Other long-term obligations
Liabilities:
Other long-term obligations	$ 10,900	$ 3,409
DonRiver
Liabilities:
Contingent consideration term	3 years