Quarterly Financial Data (unaudited) (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
Quarterly Financial Information Disclosure [Abstract]
Interest and Dividend Income, Operating	$ 91,800	$ 89,566	$ 87,445	$ 88,909	$ 91,829	$ 94,589	$ 92,226	$ 81,856	$ 357,720	$ 360,500	$ 310,801
Interest Expense	5,479	5,726	6,259	12,626	14,820	17,488	16,375	14,080	30,090	62,763	43,903
Interest Income (Expense), Net	86,321	83,840	81,186	76,283	77,009	77,101	75,851	67,776	327,630	297,737	266,898
Provision for loan losses	(19,159)	13,836	12,224	5,153	(213)	1,967	1,919	2,498	12,054	6,171	7,945
Income before income taxes	55,475	36,703	35,127	27,340	30,215	37,532	26,548	30,476	154,645	124,771	131,299
Net Income (Loss) Attributable to Parent	$ 45,200	$ 30,846	$ 29,505	$ 22,372	$ 23,936	$ 31,146	$ 22,163	$ 25,455	$ 127,923	$ 102,700	$ 110,387
Basic (in dollars per share)	$ 2.77	$ 1.89	$ 1.81	$ 1.37	$ 1.46	$ 1.90	$ 1.34	$ 1.63	$ 7.85	$ 6.33	$ 7.13
Diluted (in dollars per share)	$ 2.75	$ 1.88	$ 1.80	$ 1.36	$ 1.45	$ 1.89	$ 1.33	$ 1.62	$ 7.80	$ 6.29	$ 7.07
Weighted Average Number of Shares Outstanding, Basic	16,310,551,000	16,300,720,000	16,296,427,000	16,303,602,000	16,342,485,000	16,382,798,000	16,560,545,000	15,651,541,000	16,302,825	16,234,342	15,488,982
Weighted Average Number of Shares Outstanding, Diluted	16,434,812,000	16,393,792,000	16,375,434,000	16,425,881,000	16,454,553,000	16,475,741,000	16,642,571,000	15,744,777,000	16,407,502	16,329,456	15,611,489