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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
NET INCOME PER SHARE
Net Income	$ 49,705	$ 136	$ (37,060)	$ 55,863	$ 9,512	$ 18,806	$ 16,606	$ 18,160	$ 68,644	$ 63,084	$ 44,985
Weighted average number of common shares outstanding (basic)									19,614,000	16,168,000	15,848,000
Weighted Average Number Diluted Shares Outstanding Adjustment									1,244,000	1,086,000	648,000
Weighted Average common and common equivalent shares outstandding (diluted)									20,858,000	17,254,000	16,496,000
Basic	$ 2.47	$ 0.01	$ (1.87)	$ 3.03	$ 0.58	$ 1.16	$ 1.03	$ 1.13	$ 3.50	$ 3.90	$ 2.84
Diluted	$ 2.33	$ 0.01	$ (1.87)	$ 2.86	$ 0.54	$ 1.09	$ 0.98	$ 1.08	$ 3.29	$ 3.66	$ 2.73
Weighted Average Number Diluted Shares Outstanding Adjustment										413,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									337	0	0
Stock Issued During Period, Shares, Acquisitions									3,200,000