CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Short-term Investments	$ 12,868	$ 24,965
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	560,000,000	560,000,000
Common stock, shares issued (in shares)	293,379,702	286,929,229
Common Stock, Shares, Outstanding	279,583,006	276,210,910
Treasury stock shares (in shares)	13,796,696	10,718,319
Tax effect of accumulated other comprehensive income	$ 0	$ 0

Face amount or stated value per share of common stock.

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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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Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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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.

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