General and Summary of Significant Accounting Policies Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
NET INCOME PER SHARE
Net Income	$ 26,142	$ 24,986	$ 18,908	$ 16,834	$ 20,641	$ 26,563	$ 22,833	$ 30,998	$ 86,870	$ 101,035	$ 28,793
Weighted average number of common shares outstanding (basic)									20,907,000	20,629,000	20,394,000
Weighted Average Number Diluted Shares Outstanding Adjustment									684,000	916,000	1,207,000
Weighted Average common and common equivalent shares outstandding (diluted)									21,591,000	21,545,000	21,601,000
Basic	$ 1.24	$ 1.19	$ 0.91	$ 0.81	$ 1.00	$ 1.29	$ 1.11	$ 1.51	$ 4.16	$ 4.90	$ 1.41
Diluted	$ 1.21	$ 1.16	$ 0.88	$ 0.78	$ 0.96	$ 1.24	$ 1.06	$ 1.44	$ 4.02	$ 4.69	$ 1.33
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									12,083	10,760	5,300