Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Statement of Financial Position [Abstract]
Common shares, par value (dollars per share)	$ 0us-gaap_CommonStockNoParValue	$ 0us-gaap_CommonStockNoParValue	$ 0us-gaap_CommonStockNoParValue
Common shares, shares authorized (shares)	42,000,000us-gaap_CommonStockSharesAuthorized	42,000,000us-gaap_CommonStockSharesAuthorized	42,000,000us-gaap_CommonStockSharesAuthorized
Common shares, shares issued (shares)	29,430,000us-gaap_CommonStockSharesIssued	29,353,000us-gaap_CommonStockSharesIssued	28,797,000us-gaap_CommonStockSharesIssued
Preferred shares, par value (dollars per share)	$ 0us-gaap_PreferredStockNoParValue	$ 0us-gaap_PreferredStockNoParValue	$ 0us-gaap_PreferredStockNoParValue
Preferred shares, shares authorized (shares)	1,000,000us-gaap_PreferredStockSharesAuthorized	1,000,000us-gaap_PreferredStockSharesAuthorized	1,000,000us-gaap_PreferredStockSharesAuthorized
Preferred shares, shares issued (shares)	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Treasury shares, at cost (shares)	859,000us-gaap_TreasuryStockShares	390,000us-gaap_TreasuryStockShares	378,000us-gaap_TreasuryStockShares

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

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)

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-Publisher SEC

-Name Regulation S-X (SX)

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- Definition

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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- Definition

Face amount per share of no-par value preferred stock nonredeemable or redeemable solely at the option of the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Paragraph 1

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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