CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - $ / shares	Apr. 30, 2019	Jan. 31, 2019	Apr. 30, 2018
Statement of Financial Position [Abstract]
Preferred stock par value per share (usd per share)	$ 0.01	$ 0.01	$ 0.01
Preferred stock authorized (shares)	2,000,000	2,000,000	2,000,000.0
Preferred stock issued (shares)	0	0	0
Preferred stock outstanding (shares)	0	0	0
Common stock par value per share (usd per share)	$ 0.01	$ 0.01	$ 0.01
Common stock authorized (shares)	240,000,000	240,000,000	240,000,000
Common stock issued (shares)	121,400,000	121,500,000	124,200,000
Common stock outstanding (shares)	121,400,000	121,500,000	124,200,000

Face amount or stated value per share of common stock.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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-Topic 505
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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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