Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 6,849	$ 6,917
Accumulated depreciation, property assets	$ 414,188	$ 398,039
Common stock - par value	$ 0.01	$ 0.01
Common stock - shares authorized	250,000,000	250,000,000
Common stock - shares issued	108,875,165	108,530,911
Treasury stock - shares at cost	55,552,836	50,495,378