Consolidated Balance Sheets (Parenthetical) - $ / shares	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Common stock, No par value
Common stock, Shares authorized	Unlimited	Unlimited
Common stock, Shares issued	197,053,583	196,346,736
Common stock, Shares outstanding	197,053,583	196,346,736

Face amount per share of no-par value common stock.

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- Definition

Indicates that the number of common shares permitted to be issued by an entity's charter and bylaws is unlimited. The acceptable value is "Unlimited".

+ References

+ Details

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- Definition

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.

+ References

+ Details

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

+ Details

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Period Type:	instant

- References

No definition available.

+ Details

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