Earnings 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
Basic and Diluted Earnings per Share [Line Items]
Net income	$ (2,418)		$ 8,730		$ 14,716		$ 19,184		$ 16,891		$ (4,776)		$ (17,914)		$ 5,810		$ 40,212		$ 11		$ 47,513
Weighted-average common shares outstanding																	25,447,918		25,878,535		26,318,214
Weighted-average common shares, Diluted																	25,504,526		25,958,849		26,337,678
Basic earnings per common share	$ (0.10)	[1]	$ 0.34	[1]	$ 0.58	[1]	$ 0.75	[1]	$ 0.66	[1]	$ (0.19)	[1]	$ (0.69)	[1]	$ 0.22	[1]	$ 1.58		$ 0.00	[1]	$ 1.81
Diluted earnings per common share	$ (0.10)	[1]	$ 0.34	[1]	$ 0.58	[1]	$ 0.75	[1]	$ 0.66	[1]	$ (0.19)	[1]	$ (0.69)	[1]	$ 0.22	[1]	$ 1.58		$ 0.00	[1]	$ 1.80
Awards excluded from diluted calculation																	901,008	[2]	989,047	[2]	806,316	[2]
Restricted Stock Awards [Member]
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of share-based awards outstanding																	54,338		50,206		19,464
Stock Options [Member]
Basic and Diluted Earnings per Share [Line Items]
Add dilutive effect of share-based awards outstanding																	2,270		30,108		0

[1] The sum of the quarterly reported amounts may not equal the full year, as each is computed independently.

[2] Outstanding awards excluded from the diluted earnings per share calculation because the effect of including them would have been anti-dilutive.