Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share [Abstract]
Net income (loss)	$ 5,508	$ 77,775	$ (5,634)	$ 101,977
Weighted average common shares outstanding (used to calculate basic EPS) (in shares)	45,945,000	45,422,000	45,892,000	45,376,000
Dilutive effect of stock awards (in shares)	279,000	858,000	0	872,000
Weighted average common shares outstanding (used to calculate diluted EPS) (in shares)	46,224,000	46,280,000	45,892,000	46,248,000
Earnings (loss) per common share - basic (in dollars per share)	$ 0.12	$ 1.71	$ (0.12)	$ 2.25
Earnings (loss) per common share - diluted (in dollars per share)	$ 0.12	$ 1.68	$ (0.12)	$ 2.21
Additional shares used to calculated diluted EPS, if income (in shares)			500,000
Stated interest rate on debt instrument	4.25%	4.25%	4.25%	4.25%
Conversion Price on Convertible Senior Notes due 2016 (in dollars per share)	$ 22.45	$ 22.45	$ 22.45	$ 22.45
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	2,600,000	800,000	2,000,000	800,000