Industry Segment Information (Details) - USD ($) $ 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
Fee revenue and other income:
Income from customers										$ 95,512		$ 86,136	$ 83,368
Intersegment income (expense)
Net interest income (expense) after provision for loan losses:
Income from customers										39,790		39,401	37,449
Intersegment income (expense)
Depreciation and amortization										4,052		3,653	3,416
Income taxes	$ 3,576	[1]	$ 2,396	$ 2,248	$ 1,665	$ 1,806	$ 1,855	$ 2,035	$ 2,020	9,885	[1]	7,716	7,978
Net income	5,331		$ 6,863	$ 6,513	$ 6,307	6,424	$ 6,222	$ 5,869	$ 5,833	25,014		24,348	23,056
Goodwill	12,569					11,590				12,569		11,590	11,590
Other intangible assets, net	1,996					1,997				1,996		1,997	2,405
Total assets	1,603,209					1,504,839				1,603,209		1,504,839	1,455,506
Information Services [Member]
Fee revenue and other income:
Income from customers										93,804		84,612	82,144
Intersegment income (expense)										13,317		12,164	10,078
Net interest income (expense) after provision for loan losses:
Income from customers										13,400		13,820	14,598
Intersegment income (expense)												2	12
Depreciation and amortization										3,784		3,368	3,164
Income taxes										4,326		1,478	2,818
Net income										13,597		14,049	14,635
Goodwill	12,433					11,454				12,433		11,454	11,454
Other intangible assets, net	1,996					1,997				1,996		1,997	2,405
Total assets	800,214					763,999				800,214		763,999	702,491
Banking Services [Member]
Fee revenue and other income:
Income from customers										1,708		1,524	1,224
Intersegment income (expense)										1,545		1,575	1,648
Net interest income (expense) after provision for loan losses:
Income from customers										26,390		25,581	22,851
Intersegment income (expense)												(2)	(12)
Depreciation and amortization										150		165	151
Income taxes										5,559		6,238	5,160
Net income										11,417		10,299	8,421
Goodwill	136					136				136		136	136
Other intangible assets, net
Total assets	830,672					756,164				830,672		756,164	761,739
Corporate Eliminations and Other [Member]
Fee revenue and other income:
Income from customers
Intersegment income (expense)										(14,862)		(13,739)	(11,726)
Net interest income (expense) after provision for loan losses:
Income from customers
Intersegment income (expense)
Depreciation and amortization										118		120	101
Income taxes
Net income
Goodwill
Other intangible assets, net
Total assets	$ (27,677)					$ (15,324)				$ (27,677)		$ (15,324)	$ (8,724)

[1] Includes one-time, non-cash TCJA charge of $1,824,000