Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 4,468	$ 4,883
Property assets, accumulated depreciation	$ 548,549	$ 551,750
Common stock - par value	$ 0.01	$ 0.01
Common stock - shares authorized	250,000,000	250,000,000
Common stock - shares issued	110,412,469	109,909,504
Treasury stock - shares at cost	56,369,752	56,369,752