Segment Information - Detail Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net interest income	$ 35,037	$ 35,032	$ 37,385	$ 36,333	$ 35,985	$ 37,398	$ 36,611	$ 37,647	$ 143,787	$ 147,641	$ 149,471
Provision for credit losses	(1,209)	4,101	3,435	35,350	2,404	966	1,610	3,615	41,677	8,595	7,089
Net interest income after provision for credit losses									102,110	139,046	142,382
Fees for wealth management services									44,532	44,400	42,326
Insurance commissions									5,911	6,877	6,808
Capital markets revenue									9,491	11,276	4,848
Service charges on deposit accounts									2,868	3,374	2,989
Loan servicing and other fees									1,646	2,206	2,259
Net gain on sale of loans									5,779	2,342	3,283
Net gain on sale of investment securities available for sale									0	0	7
Net gain on sale of long-lived assets									2,297	0	0
Net gain (loss) on sale of other real estate owned ("OREO")									148	(84)	295
Other operating income									9,299	11,793	13,167
Total noninterest income	22,006	21,099	20,566	18,300	23,255	19,455	20,221	19,253	81,971	82,184	75,982
Salaries and wages									68,846	74,371	66,671
Employee benefits									12,605	13,456	12,918
Occupancy and bank premises									12,727	12,591	11,599
Impairment of long-lived assets									1,605	0	0
Amortization of intangible assets									3,567	3,801	3,656
Professional fees									6,428	5,434	4,203
Other operating expenses									36,949	36,774	41,360
Total noninterest expenses	38,624	$ 35,197	$ 35,503	$ 33,403	36,251	$ 35,126	$ 35,205	$ 39,845	142,727	146,427	140,407
Segment profit									41,354	74,803	77,957
Intersegment (revenues) expenses									0	0	0
Pre-tax segment profit after eliminations									$ 41,354	$ 74,803	$ 77,957
% of segment pre-tax profit after eliminations									100.00%	100.00%	100.00%
Segment assets (dollars in millions)	5,432,022				5,263,259				$ 5,432,022	$ 5,263,259	$ 4,652,500
Wealth Management
Segment Reporting Information [Line Items]
Net interest income									3	6	7
Provision for credit losses									0	0	0
Net interest income after provision for credit losses									3	6	7
Fees for wealth management services									44,532	44,400	42,326
Insurance commissions									5,911	6,877	6,808
Capital markets revenue									0	0	0
Service charges on deposit accounts									0	0	0
Loan servicing and other fees									0	0	0
Net gain on sale of loans									0	0	0
Net gain on sale of investment securities available for sale									0	0	0
Net gain on sale of long-lived assets									0	0	0
Net gain (loss) on sale of other real estate owned ("OREO")									0	0	0
Other operating income									128	106	186
Total noninterest income									50,571	51,383	49,320
Salaries and wages									21,442	20,295	19,735
Employee benefits									3,500	3,884	3,872
Occupancy and bank premises									1,989	2,044	2,011
Impairment of long-lived assets									0	0	0
Amortization of intangible assets									2,458	2,492	2,101
Professional fees									881	594	456
Other operating expenses									5,240	6,263	5,328
Total noninterest expenses									35,510	35,572	33,503
Segment profit									15,064	15,817	15,824
Intersegment (revenues) expenses									622	613	715
Pre-tax segment profit after eliminations									$ 15,686	$ 16,430	$ 16,539
% of segment pre-tax profit after eliminations									37.90%	22.00%	21.20%
Segment assets (dollars in millions)	47,600				52,900				$ 47,600	$ 52,900	$ 50,800
Banking
Segment Reporting Information [Line Items]
Net interest income									143,784	147,635	149,464
Provision for credit losses									41,677	8,595	7,089
Net interest income after provision for credit losses									102,107	139,040	142,375
Fees for wealth management services									0	0	0
Insurance commissions									0	0	0
Capital markets revenue									9,491	11,276	4,848
Service charges on deposit accounts									2,868	3,374	2,989
Loan servicing and other fees									1,646	2,206	2,259
Net gain on sale of loans									5,779	2,342	3,283
Net gain on sale of investment securities available for sale									0	0	7
Net gain on sale of long-lived assets									2,297	0	0
Net gain (loss) on sale of other real estate owned ("OREO")									148	(84)	295
Other operating income									9,171	11,687	12,981
Total noninterest income									31,400	30,801	26,662
Salaries and wages									47,404	54,076	46,936
Employee benefits									9,105	9,572	9,046
Occupancy and bank premises									10,738	10,547	9,588
Impairment of long-lived assets									1,605	0	0
Amortization of intangible assets									1,109	1,309	1,555
Professional fees									5,547	4,840	3,747
Other operating expenses									31,709	30,511	36,032
Total noninterest expenses									107,217	110,855	106,904
Segment profit									26,290	58,986	62,133
Intersegment (revenues) expenses									(622)	(613)	(715)
Pre-tax segment profit after eliminations									$ 25,668	$ 58,373	$ 61,418
% of segment pre-tax profit after eliminations									62.10%	78.00%	78.80%
Segment assets (dollars in millions)	$ 5,384,400				$ 5,210,400				$ 5,384,400	$ 5,210,400	$ 4,601,700