Convertible Senior Notes, Net - Schedule of Senior Notes (Detail) - USD ($)	3 Months Ended	9 Months Ended
Oct. 31, 2017	Oct. 31, 2018	Jan. 31, 2018	Jun. 30, 2013
Convertible Debt [Abstract]
Net carrying amount, current		$ 229,684,000	$ 341,509,000
Net carrying amount, non-current		961,139,000	1,149,845,000
2018 Notes
Convertible Debt [Abstract]
Principal		0	350,000,000	$ 350,000,000
Unamortized debt discount		0	(7,850,000)
Unamortized debt issuance costs		0	(641,000)
Net carrying amount, current		0	341,509,000
Carrying amount of the equity component		74,887,000	74,892,000
Equity issuance costs	$ 2,000,000	2,000,000
2020 Notes
Convertible Debt [Abstract]
Principal		249,997,000	250,000,000	$ 250,000,000
Unamortized debt discount		(19,163,000)	(26,968,000)
Unamortized debt issuance costs		(1,150,000)	(1,654,000)
Net carrying amount, current		229,684,000
Net carrying amount, non-current			221,378,000
Carrying amount of the equity component		66,007,000	66,007,000
Equity issuance costs		2,000,000
2022 Notes
Convertible Debt [Abstract]
Principal		1,150,000,000	1,150,000,000
Unamortized debt discount		(177,659,000)	(208,188,000)
Unamortized debt issuance costs		(11,202,000)	(13,345,000)
Net carrying amount, non-current		961,139,000	928,467,000
Carrying amount of the equity component		$ 219,702,000	$ 219,702,000

Carrying value as of the balance sheet date of the portion of long-term debt due within one year or the operating cycle if longer identified as Convertible Notes Payable. Convertible Notes Payable is a written promise to pay a note which can be exchanged for a specified amount of another, related security, at the option of the issuer and the holder.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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Face (par) amount of debt instrument at time of issuance.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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Debt Instrument, Convertible, After Unamortized Debt Issuance Costs

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