Earnings Per Share Basic Earnings Per Share (Details) (USD $) In Thousands, 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
Earnings Per Share, Basic, by Common Class [Line Items]
Net income	$ 16,485	$ 17,932	$ 3,895	$ (7,690)	$ 7,797	$ 17,549	$ 30,301	$ 19,373	$ 30,622	$ 75,020	$ 54,084
Net income available to common stockholders									30,014	73,468	52,938
Earnings Per Share, Basic [Member]
Earnings Per Share, Basic, by Common Class [Line Items]
Income attributable to participating securities									$ (608)	$ (1,552)	$ (1,146)