Business Segments (Statement of Operations and Total Assets by Reportable Segment) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 33,878	$ 33,449	$ 33,111	$ 31,852	$ 30,889	$ 30,059	$ 29,904	$ 28,679	$ 132,290	$ 119,531	$ 110,478
Provision for loan losses	800	350	400	0	200	1,300	700	400	1,550	2,600	5,650
Net interest income (expense) after provision for loan losses	33,078	33,099	32,711	31,852	30,689	28,759	29,204	28,279	130,740	116,931	104,828
Noninterest income	15,163	15,215	15,993	15,743	16,210	17,283	16,806	14,510	62,114	64,809	65,129
Depreciation and amortization expense									4,261	4,489	4,935
Other noninterest expenses									101,901	99,611	96,168
Total noninterest expense	26,682	26,062	26,288	27,130	25,754	26,754	26,306	25,286	106,162	104,100	101,103
Income before income taxes	21,559	22,252	22,416	20,465	21,145	19,288	19,704	17,503	86,692	77,640	68,854
Income tax expense	4,523	4,741	4,742	4,254	13,163	6,326	6,505	5,721	18,260	31,715	22,373
Net income	17,036	$ 17,511	$ 17,674	$ 16,211	7,982	$ 12,962	$ 13,199	$ 11,782	68,432	45,925	46,481
Total assets at period end	5,010,766				4,529,850				5,010,766	4,529,850	4,381,115
Expenditures for long-lived assets									3,974	2,779	3,112
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)									106,668	98,736	91,221
Provision for loan losses									1,550	2,600	5,650
Net interest income (expense) after provision for loan losses									105,118	96,136	85,571
Noninterest income									21,509	23,244	24,783
Depreciation and amortization expense									2,589	2,604	2,771
Other noninterest expenses									62,673	60,828	58,452
Total noninterest expense									65,262	63,432	61,223
Income before income taxes									61,365	55,948	49,131
Income tax expense									13,149	23,876	16,790
Net income									48,216	32,072	32,341
Total assets at period end	3,804,021				3,491,845				3,804,021	3,491,845	3,354,633
Expenditures for long-lived assets									3,415	2,224	2,267
Wealth Management Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)									(334)	(167)	(66)
Provision for loan losses									0	0	0
Net interest income (expense) after provision for loan losses									(334)	(167)	(66)
Noninterest income									38,341	39,346	37,569
Depreciation and amortization expense									1,501	1,689	1,940
Other noninterest expenses									26,222	26,718	25,239
Total noninterest expense									27,723	28,407	27,179
Income before income taxes									10,284	10,772	10,324
Income tax expense									2,577	3,795	3,692
Net income									7,707	6,977	6,632
Total assets at period end	71,254				66,083				71,254	66,083	64,625
Expenditures for long-lived assets									407	360	464
Corporate [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)									25,956	20,962	19,323
Provision for loan losses									0	0	0
Net interest income (expense) after provision for loan losses									25,956	20,962	19,323
Noninterest income									2,264	2,219	2,777
Depreciation and amortization expense									171	196	224
Other noninterest expenses									13,006	12,065	12,477
Total noninterest expense									13,177	12,261	12,701
Income before income taxes									15,043	10,920	9,399
Income tax expense									2,534	4,044	1,891
Net income									12,509	6,876	7,508
Total assets at period end	$ 1,135,491				$ 971,922				1,135,491	971,922	961,857
Expenditures for long-lived assets									$ 152	$ 195	$ 381