CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Property and equipment, accumulated depreciation	$ 3,649,978	$ 3,524,098
Intangible assets, accumulated amortization	$ 75,283	$ 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)	166,532,889	166,387,307
Common stock, shares outstanding (in shares)	164,472,913	166,387,307

Face amount or stated value per share of common stock.

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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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