CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Other property and equipment, accumulated depreciation (in dollars)	$ 20,799	$ 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	65,155,340	64,145,582
Common stock, outstanding, net of treasury shares	65,100,773	64,064,415
Treasury stock, shares	54,567	102,635
Convertible Debt [Member]
Interest rate on notes (as a percent)	3.50%	3.50%
Senior Convertible Notes, unamortized discount (in dollars)	$ 0	$ 2,431
6.625% Senior Notes [Member]
Interest rate on notes (as a percent)	6.625%	6.625%
6.50% Senior Notes [Member]
Interest rate on notes (as a percent)	6.50%	6.50%
6.50% Senior Notes due 2023 [Member]
Interest rate on notes (as a percent)	6.50%