Summary of Significant Accounting Policies Basic Earnings Per Share (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share, Basic, by Common Class [Line Items]
Net income	$ 17,549	$ 10,907	$ 67,223	$ 42,068
Net income available to common stockholders	17,190	10,679	65,833	41,171
Earnings Per Share, Basic [Member]
Earnings Per Share, Basic, by Common Class [Line Items]
Income attributable to participating securities	$ (359)	$ (228)	$ (1,390)	$ (897)