Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Stockholders' equity
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized (actual number)	25,000,000us-gaap_PreferredStockSharesAuthorized	25,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, shares issued (actual number)	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred stock, shares outstanding (actual number)	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized (actual number)	600,000,000us-gaap_CommonStockSharesAuthorized	600,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued (actual number)	415,665,644us-gaap_CommonStockSharesIssued	411,779,911us-gaap_CommonStockSharesIssued
Treasury stock, shares (actual number)	58,651,623us-gaap_TreasuryStockShares	58,415,507us-gaap_TreasuryStockShares

Face amount or stated value per share of common stock.

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

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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.

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