Consolidated and Condensed Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Statement of Financial Position [Abstract]
Allowance for doubtful accounts (in dollars)	$ 0	$ 0	$ 0
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000	5,000,000
Preferred stock, shares issued	0	0	0
Preferred stock, shares outstanding	0	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000	200,000,000
Common stock, shares issued	146,335,002	144,484,051	143,966,276
Common stock, shares outstanding	141,899,492	140,368,351	139,813,241
Treasury stock, shares	4,435,510	4,125,700	4,153,035