Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Interest and Dividend Income, Operating	$ 91,829	$ 94,589	$ 92,226	$ 81,856	$ 82,167	$ 80,229	$ 74,691	$ 73,714	$ 360,500	$ 310,801	$ 286,424
Interest Expense	14,820	17,488	16,375	14,080	12,537	12,553	9,949	8,864	62,763	43,903	42,665
Interest Income (Expense), Net	77,009	77,101	75,851	67,776	69,630	67,676	64,742	64,850	297,737	266,898	243,759
Provision for loan losses	(213)	1,967	1,919	2,498	3,359	2,940	1,386	260	6,171	7,945	8,557
Income before income taxes	30,215	37,532	26,548	30,476	30,566	29,484	34,064	37,185	124,771	131,299	118,469
Net Income (Loss) Attributable to Parent	$ 23,936	$ 31,146	$ 22,163	$ 25,455	$ 26,261	$ 24,762	$ 28,241	$ 31,123	$ 102,700	$ 110,387	$ 84,242
Basic (in dollars per share)	$ 1.46	$ 1.90	$ 1.34	$ 1.63	$ 1.67	$ 1.58	$ 1.85	$ 2.04	$ 6.33	$ 7.13	$ 5.51
Diluted (in dollars per share)	$ 1.45	$ 1.89	$ 1.33	$ 1.62	$ 1.67	$ 1.56	$ 1.83	$ 2.02	$ 6.29	$ 7.07	$ 5.47
Weighted Average Number of Shares Outstanding, Basic	16,342,485,000	16,382,798,000	16,560,545,000	15,651,541,000	15,695,522,000	15,686,542,000	15,285,532,000	15,288,332,000	16,234,342	15,488,982	15,295,573
Weighted Average Number of Shares Outstanding, Diluted	16,454,553,000	16,475,741,000	16,642,571,000	15,744,777,000	15,764,548,000	15,832,734,000	15,417,607,000	15,431,625,000	16,329,456	15,611,489	15,390,352