CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2011	Dec. 31, 2010
Other property and equipment, accumulated depreciation (in dollars)	$ 18,312	$ 15,480
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	64,079,885	63,412,800
Common stock, outstanding, net of treasury shares	63,998,818	63,310,165
Treasury stock, shares	81,067	102,635
3.50% Senior Convertible Notes due 2027
Interest rate on notes (as a percent)	3.50%	3.50%
Senior Convertible Notes, unamortized discount (in dollars)	$ 4,861	$ 11,827
6.625% Senior Notes due 2019
Interest rate on notes (as a percent)	6.625%	6.625%