Significant Accounting Policies Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Significant Accounting Policies [Abstract]
Net Income Loss	$ 70,806	$ 72,967	$ 72,677
Weighted Average Number of Shares Outstanding, Basic	81,388	81,980	82,378
Basic EPS	$ 0.87	$ 0.89	$ 0.88
Dilutive Securities, Effect on Basic Earnings Per Share, Including Options and Restrictive Stock Units	$ 0	$ 0	$ 0
Incremental Common Shares Attributable to Share-based Payment Arrangements	56	44	32
Net Income (Loss) Available to Common Stockholders, Diluted	$ 70,806	$ 72,967	$ 72,677
Weighted Average Number of Shares Outstanding, Diluted	81,444	82,024	82,410
Diluted EPS	$ 0.87	$ 0.89	$ 0.88