Industry Segment Information (Details) - USD ($) $ 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
Segment Reporting Information [Line Items]
Fee income from customers										$ 110,069	$ 104,076	$ 95,512
Interest income	[1]									54,694	50,348	47,667
Interest expense		$ 1,206	$ 1,392	$ 1,305	$ 1,290	$ 1,234	$ 1,029	$ 794	$ 679	5,193	3,736	2,187
Intersegment income (expense)
Depreciation and amortization										4,790	4,396	4,051
Tax-equivalized pre-tax income										39,550	38,768	40,589
Goodwill		14,262				12,569				14,262	12,569	12,569
Other intangible assets, net		4,281				1,554				4,281	1,554	1,996
Total Assets		1,764,243				1,695,176				1,764,243	1,695,176	1,603,209
Funding Sources		1,268,973				1,215,386				1,268,973	1,215,386	1,203,479
Information Services [Member]
Segment Reporting Information [Line Items]
Fee income from customers										108,882	102,839	93,484
Interest income	[1]									25,616	25,074	23,813
Interest expense
Intersegment income (expense)
Depreciation and amortization										4,659	4,254	3,902
Tax-equivalized pre-tax income										28,542	27,763	28,168
Goodwill		12,433				12,433				12,433	12,433	12,433
Other intangible assets, net		1,142				1,554				1,142	1,554	1,996
Total Assets		844,483				826,201				844,483	826,201	854,214
Funding Sources		676,068				642,733				676,068	642,733	604,493
Banking Services [Member]
Segment Reporting Information [Line Items]
Fee income from customers										1,660	1,307	1,547
Interest income	[1]									30,646	27,770	27,376
Interest expense										5,193	3,736	2,187
Intersegment income (expense)										2,107	1,880	1,362
Depreciation and amortization										131	142	149
Tax-equivalized pre-tax income										13,048	13,571	15,460
Goodwill		1,829				136				1,829	136	136
Other intangible assets, net		3,139								3,139
Total Assets		915,341				886,291				915,341	886,291	830,672
Funding Sources		592,905				572,653				592,905	572,653	598,986
Corporate Eliminations and Other [Member]
Segment Reporting Information [Line Items]
Fee income from customers										(473)	(70)	481
Interest income	[1]									(1,568)	(2,496)	(3,522)
Interest expense
Intersegment income (expense)										(2,107)	(1,880)	(1,362)
Depreciation and amortization
Tax-equivalized pre-tax income										(2,040)	(2,566)	(3,039)
Goodwill
Other intangible assets, net
Total Assets		4,419				(17,316)				4,419	(17,316)	(27,677)
Funding Sources

[1] Presented on a tax-equivalent basis assuming a tax rate of 21% for 2019 and 2018 and 35% for 2017. The tax-equivalent adjustment was approximately $2,084,000 for 2019, $2,422,000 for 2018, and $5,691,000 for 2017.