Business Segments (Statement of Operations and Total Assets by Reportable Segment) (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]
Net interest income (expense)	$ 31,994	$ 32,978	$ 33,858	$ 34,584	$ 33,878	$ 33,449	$ 33,111	$ 31,852	$ 133,414	[1]	$ 132,290	[1]	$ 119,531	[1]
Provision for loan losses	0	400	525	650	800	350	400	0	1,575		1,550		2,600
Net interest income (expense) after provision for loan losses	31,994	32,578	33,333	33,934	33,078	33,099	32,711	31,852	131,839		130,740		116,931
Noninterest income	16,618	18,342	16,753	15,367	15,163	15,215	15,993	15,743	67,080	[1]	62,114	[1]	64,809	[1]
Depreciation and amortization expense									4,234		4,261		4,489
Other noninterest expenses									106,506		101,901		99,611
Total noninterest expense	28,755	26,870	28,151	26,964	26,682	26,062	26,288	27,130	110,740		106,162		104,100
Income before income taxes	19,857	24,050	21,935	22,337	21,559	22,252	22,416	20,465	88,179		86,692		77,640
Income tax expense	4,321	5,236	4,662	4,842	4,523	4,741	4,742	4,254	19,061		18,260		31,715
Net income	15,536	$ 18,814	$ 17,273	$ 17,495	17,036	$ 17,511	$ 17,674	$ 16,211	69,118		68,432		45,925
Total assets at period end	5,292,659				5,010,766				5,292,659		5,010,766		4,529,850
Expenditures for long-lived assets									3,132		3,974		2,779
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)									112,414		106,668		98,736
Provision for loan losses									1,575		1,550		2,600
Net interest income (expense) after provision for loan losses									110,839		105,118		96,136
Noninterest income									27,857		21,509		23,244
Depreciation and amortization expense									2,630		2,589		2,604
Other noninterest expenses									66,517		62,673		60,828
Total noninterest expense									69,147		65,262		63,432
Income before income taxes									69,549		61,365		55,948
Income tax expense									15,189		13,149		23,876
Net income									54,360		48,216		32,072
Total assets at period end	4,070,594				3,804,021				4,070,594		3,804,021		3,491,845
Expenditures for long-lived assets									2,521		3,415		2,224
Wealth Management Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)									(438)		(334)		(167)
Provision for loan losses									0		0		0
Net interest income (expense) after provision for loan losses									(438)		(334)		(167)
Noninterest income									36,856		38,341		39,346
Depreciation and amortization expense									1,445		1,501		1,689
Other noninterest expenses									26,057		26,222		26,718
Total noninterest expense									27,502		27,723		28,407
Income before income taxes									8,916		10,284		10,772
Income tax expense									2,308		2,577		3,795
Net income									6,608		7,707		6,977
Total assets at period end	74,990				71,254				74,990		71,254		66,083
Expenditures for long-lived assets									445		407		360
Corporate [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)									21,438		25,956		20,962
Provision for loan losses									0		0		0
Net interest income (expense) after provision for loan losses									21,438		25,956		20,962
Noninterest income									2,367		2,264		2,219
Depreciation and amortization expense									159		171		196
Other noninterest expenses									13,932		13,006		12,065
Total noninterest expense									14,091		13,177		12,261
Income before income taxes									9,714		15,043		10,920
Income tax expense									1,564		2,534		4,044
Net income									8,150		12,509		6,876
Total assets at period end	$ 1,147,075				$ 1,135,491				1,147,075		1,135,491		971,922
Expenditures for long-lived assets									$ 166		$ 152		$ 195

[1] As reported in the Consolidated Statements of Income.