Consolidated Balance Sheets Consolidated Balance Sheets (Parethetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 5,601	$ 4,883
Accumulated depreciation of property assets	$ 522,826	$ 551,750
Common stock - par value	$ 0.01	$ 0.01
Common stock - shares authorized	250,000,000	250,000,000
Common stock - shares issued	111,166,229	109,909,504
Treasury stock - shares at cost	56,428,482	56,369,752