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Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Allowance for doubtful accounts $ 5,981 $ 4,883
Property assets, accumulated depreciation $ 564,062 $ 551,750
Common stock - par value $ 0.01 $ 0.01
Common stock - shares authorized 250,000,000 250,000,000
Common stock - shares issued 111,105,930 109,909,504
Treasury stock - shares at cost 56,369,752 56,369,752