Convertible Senior Notes, Net - Note Hedges and Warrants (Details) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended		9 Months Ended
	Jun. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($) shares	Oct. 31, 2020 USD ($) day $ / shares shares	Oct. 31, 2019 USD ($) shares
Debt Instrument [Line Items]
Payments for repurchase of Warrants | $			$ 175,399	$ 358,622
Antidilutive securities excluded from computation of earnings per share (in shares) | shares			26,524	29,525
Purchase of capped call on convertible debt | $			$ 133,975	$ 74,094
Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Shares issuable under warrants granted (in shares) | shares	1,400	4,600
Number of shares available for purchase (in shares) | shares			800
Number of warrants issued subject to anti-dilution adjustments (in shares) | shares			1,000
Limitation on sale of common stock due to sale price threshold (in days) | day			80
Value of shares issuable under warrants granted (in dollars per share) | $ / shares			$ 68.06
Proceeds from issuance of warrants related to 2023 convertible senior notes | $			$ 52,400
Payments for repurchase of Warrants | $	$ 175,400	$ 358,600
Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Initial cap price of capped calls (in dollars per share) | $ / shares			$ 255.88
Purchase of capped call on convertible debt | $			$ 74,100
Convertible Senior Notes Due 2026
Debt Instrument [Line Items]
Initial cap price of capped calls (in dollars per share) | $ / shares			$ 360.14
Purchase of capped call on convertible debt | $			$ 134,000
Senior Notes | Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Shares issuable under warrants granted (in shares) | shares	1,400	4,600	7,100
Conversion price (in dollars per share) | $ / shares			$ 48.36
Purchases of hedges related to 2023 convertible senior notes | $			$ 80,000
Proceeds from hedges related to convertible senior notes | $	$ 195,000	$ 405,900
Debt repurchased, face amount | $			$ 10,400
Number of warrants issued subject to anti-dilution adjustments (in shares) | shares			7,100
Limitation on sale of common stock due to sale price threshold (in days) | day			30
Limit within threshold of consecutive trading days | day			20
Senior Notes | Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Conversion price (in dollars per share) | $ / shares			$ 188.71
Limitation on sale of common stock due to sale price threshold (in days) | day			30
Limit within threshold of consecutive trading days | day			20
Senior Notes | Convertible Senior Notes Due 2026
Debt Instrument [Line Items]
Conversion price (in dollars per share) | $ / shares			$ 238.60
Limitation on sale of common stock due to sale price threshold (in days) | day			30
Limit within threshold of consecutive trading days | day			20
Shares related to convertible senior notes | Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares) | shares			832	2,494
Shares related to convertible senior notes | Convertible Senior Notes Due 2025
Debt Instrument [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares) | shares			5,617	5,617
Shares related to convertible senior notes | Convertible Senior Notes Due 2026
Debt Instrument [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares) | shares			4,820	0