Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current Assets
Allowance on trade accounts receivable	$ 6,896	$ 6,591
Allowance on other receivables	5,365	5,384
Accumulated depreciation and amortization on operating property	$ 149,465	$ 145,804
Shareholders' Equity
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized shares	160,000,000	160,000,000
Common stock, issued shares	66,833,233	66,602,486
Treasury stock, shares	19,882,431	19,882,289