CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Convertible Debt [Member]	Dec. 31, 2011 Convertible Debt [Member]
Other property and equipment, accumulated depreciation (in dollars)	$ 25,048	$ 23,985
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares	200,000,000	200,000,000
Common stock, issued shares	64,231,114	64,145,582
Common stock, outstanding, net of treasury shares	64,150,047	64,064,415
Treasury stock, shares	81,067	102,635
Interest rate on notes (as a percent)			3.50%	3.50%
Senior Convertible Notes, unamortized discount (in dollars)			$ 0	$ 2,431