Business Segments (Statement of Operations and Total Assets by Reportable Segment) (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
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 30,889	$ 30,059	$ 29,904	$ 28,679	$ 28,588	$ 27,379	$ 26,776	$ 27,735	$ 119,531	$ 110,478	$ 103,982
Provision for loan losses	200	1,300	700	400	2,900	1,800	450	500	2,600	5,650	1,050
Net interest income after provision for loan losses	30,689	28,759	29,204	28,279	25,688	25,579	26,326	27,235	116,931	104,828	102,932
Noninterest income	16,210	17,283	16,806	14,510	17,320	17,261	15,914	14,634	64,809	65,129	58,340
Depreciation and amortization expense									4,489	4,935	4,285
Other noninterest expenses									99,611	96,168	92,644
Total noninterest expense	25,754	26,754	26,306	25,286	24,973	24,650	26,030	25,450	104,100	101,103	96,929
Income before income taxes	21,145	19,288	19,704	17,503	18,035	18,190	16,210	16,419	77,640	68,854	64,343
Income tax expense	13,163	6,326	6,505	5,721	5,873	5,863	5,153	5,484	31,715	22,373	20,878
Net income	7,982	$ 12,962	$ 13,199	$ 11,782	12,162	$ 12,327	$ 11,057	$ 10,935	45,925	46,481	43,465
Total assets at period end	4,529,850				4,381,115				4,529,850	4,381,115	3,771,604
Expenditures for long-lived assets									2,779	3,112	5,479
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)									98,736	91,221	84,757
Provision for loan losses									2,600	5,650	1,050
Net interest income after provision for loan losses									96,136	85,571	83,707
Noninterest income									23,244	24,783	20,618
Depreciation and amortization expense									2,604	2,771	2,584
Other noninterest expenses									60,828	58,452	55,203
Total noninterest expense									63,432	61,223	57,787
Income before income taxes									55,948	49,131	46,538
Income tax expense									23,876	16,790	15,330
Net income									32,072	32,341	31,208
Total assets at period end	3,491,845				3,354,633				3,491,845	3,354,633	3,152,231
Expenditures for long-lived assets									2,224	2,267	4,714
Wealth Management Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)									(167)	(66)	(47)
Provision for loan losses									0	0	0
Net interest income after provision for loan losses									(167)	(66)	(47)
Noninterest income									39,346	37,569	35,416
Depreciation and amortization expense									1,689	1,940	1,488
Other noninterest expenses									26,718	25,239	25,632
Total noninterest expense									28,407	27,179	27,120
Income before income taxes									10,772	10,324	8,249
Income tax expense									3,795	3,692	3,475
Net income									6,977	6,632	4,774
Total assets at period end	66,083				64,625				66,083	64,625	63,801
Expenditures for long-lived assets									360	464	411
Corporate [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)									20,962	19,323	19,272
Provision for loan losses									0	0	0
Net interest income after provision for loan losses									20,962	19,323	19,272
Noninterest income									2,219	2,777	2,306
Depreciation and amortization expense									196	224	213
Other noninterest expenses									12,065	12,477	11,809
Total noninterest expense									12,261	12,701	12,022
Income before income taxes									10,920	9,399	9,556
Income tax expense									4,044	1,891	2,073
Net income									6,876	7,508	7,483
Total assets at period end	$ 971,922				$ 961,857				971,922	961,857	555,572
Expenditures for long-lived assets									$ 195	$ 381	$ 354