Earnings (Loss) Per Share (Earnings (Loss) Per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings (Loss) Per Share [Abstract]
Net income (loss)	$ 51,661		$ 53,360	$ 49,819	$ 41,027	$ 43,665	$ 34,491	$ 32,175	$ 36,153	$ 195,867	$ 146,484	$ (55,500)
Income/(loss) of effect of dilutive stock options, restricted stock and stock appreciation rights SARs										0	0	0
Income/(loss) of diluted earnings per common share										$ 195,867	$ 146,484	$ (55,500)
Weighted shares of basic earnings per common share										47,658,000	47,278,000	46,990,000
Weighted shares of effect of dilutive stock options, restricted stock and stock appreciation rights SARs										293,000	176,000	0
Weighted shares of diluted earnings per common share										47,951,000	47,454,000	46,990,000
Per-share amount of basic earnings (loss) per common share	$ 1.08		$ 1.12	$ 1.05	$ 0.86	$ 0.92	$ 0.73	$ 0.68	$ 0.77	$ 4.11	$ 3.10	$ (1.18)
Per-share amount of effect of dilutive stock options, restricted stock and stock appreciation rights SARs										$ (0.03)	$ (0.01)	$ 0.00
Per-share amount of diluted earnings (loss) per common share	$ 1.08	[1]	$ 1.11	$ 1.04	$ 0.86	$ 0.92	$ 0.73	$ 0.68	$ 0.76	$ 4.08	$ 3.09	$ (1.18)
Weighted average shares related to stock options, restricted stock and SARs												373,000

[1] Due to the effect of rounding the basic earnings or diluted per share for the year's four quarters does not equal annual earnings per share.