Income Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Per Common Share
Net income	$ (9,055)	$ 11,753	$ 11,818	$ 16,412	$ 20,276	$ 35,863	$ 19,206	$ 52,642	$ 30,928	$ 127,987	$ 361,760
Income from continuing operations per common share:
Basic (in dollars per share)	$ (0.23)	$ 0.30	$ 0.31	$ 0.43	$ 0.53	$ 0.91	$ 0.47	$ 1.32	$ 0.80	$ 3.23	$ 9.16
Diluted (in dollars per share)	$ (0.23)	$ 0.30	$ 0.30	$ 0.42	$ 0.52	$ 0.90	$ 0.45	$ 1.24	$ 0.79	$ 3.11	$ 8.51
Basic weighted average shares outstanding	38,698,000	38,577,000	38,370,000	38,261,000	38,212,000	39,335,000	40,998,000	39,842,000	38,477,000	39,658,000	39,499,000
Dilutive effect of stock options, restricted stock awards and units and convertible debt (in shares)									574,000	1,497,000	3,015,000
Diluted weighted average shares outstanding	38,698,000	39,169,000	38,988,000	38,863,000	38,771,000	40,069,000	43,002,000	42,531,000	39,051,000	41,155,000	42,514,000
Dilutive effect of assumed conversion of convertible debt (in shares)										600,000	1,200,000