Significant Accounting Policies Earnings per Share (Details) (USD $) In Thousands, except Per 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
Earnings Per Share, Diluted, by Common Class, Including Two Class Method
Net income	$ 14,292	$ 12,434	$ 18,227	$ 16,588	$ 17,122	$ 15,399	$ 22,532	$ 14,879	$ 61,541	$ 69,932	$ 62,216
Weighted Average Number of Shares Outstanding, Basic									85,892	89,656	90,689
Basic EPS	$ 0.17	$ 0.15	$ 0.21	$ 0.19	$ 0.20	$ 0.17	$ 0.25	$ 0.16	$ 0.72	$ 0.78	$ 0.69
Dilutive Securities, Effect on Basic Earnings Per Share, Including Options and Restrictive Stock Units									0	0
Incremental Common Shares Attributable to Share-based Payment Arrangements									309	17
Net Income (Loss) Available to Common Stockholders, Diluted									$ 61,541	$ 69,932
Weighted Average Number of Shares Outstanding, Diluted									86,201	89,673	90,689
Diluted EPS	$ 0.17	$ 0.14	$ 0.21	$ 0.19	$ 0.20	$ 0.17	$ 0.25	$ 0.16	$ 0.71	$ 0.78	$ 0.69