CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Property and equipment, accumulated depreciation	$ 3,792,683	$ 3,524,098
Intangible assets, accumulated amortization	$ 78,437	$ 80,566
Preferred stock, par value (usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, issued (in shares)	0	0
Common stock, par value (usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	450,000,000	450,000,000
Common stock, shares issued (in shares)	166,540,590	166,387,307
Common stock, shares outstanding (in shares)	133,888,864	166,387,307
Treasury Stock, Common, Shares	32,651,726	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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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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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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The cumulative amount of depreciation (related to long-lived, depreciable flight assets owned by the entity and used in the entity's principle business operations and capitalized assets classified as property, plant and equipment that are owned by the entity) that has been recognized in the income statement.

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Number of previously issued common shares repurchased by the issuing entity and held in treasury.

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