Basic and Diluted Net Income (Loss) Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Basic and Diluted Net Income (Loss) Per Common Share
Net income (loss) available to common shareholders	$ 11,885	$ (4,453)	$ 34,669	$ 14,169
Weighted Average Shares Outstanding
Basic (in shares)	53,900,119	56,682,153	53,774,268	56,611,496
Effect of Dilutive Securities (in shares)	863,677	515,266	732,110	559,346
Diluted (in shares)	54,763,796	57,197,419	54,506,378	57,170,842
Net income (loss) per common share Basic (in dollars per share)	$ 0.22	$ (0.08)	$ 0.64	$ 0.25
Net income (loss) per common share Diluted (in dollars per share)	$ 0.22	$ (0.08)	$ 0.64	$ 0.25
Antidilutive options excluded from calculation of net income per common share (in shares)	0	390,930	25,625	383,028