Segment Information - Detail Segment Information (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	$ 37,987	$ 36,729	$ 37,316	$ 37,439	$ 30,321	$ 29,438	$ 27,965	$ 27,403	$ 149,471	$ 115,127	$ 106,236
Provision for loan and lease losses	2,362	664	3,137	1,030	1,077	1,333	(83)	291	7,193	2,618	4,326
Net interest income after provision for loan and lease losses									142,278	112,509	101,910
Fees for wealth management services									42,326	38,735	36,690
Insurance commissions									6,808	4,589	3,722
Capital markets revenue									4,848	2,396	0
Service charges on deposit accounts									2,989	2,608	2,791
Loan servicing and other fees									2,259	2,106	1,939
Net gain on sale of loans									3,283	2,441	3,048
Net gain on sale of investment securities available for sale									7	101	(77)
Net gain (loss) on sale of other real estate owned (OREO)									295	(104)	(76)
Other operating income									13,167	6,260	5,931
Total noninterest income	18,097	18,274	20,075	19,536	15,536	15,584	14,785	13,227	75,982	59,132	53,968
Salaries and wages									66,671	53,251	47,411
Employee benefits									12,918	10,170	9,249
Occupancy and bank premises									11,599	9,906	9,611
Amortization of intangible assets									3,656	2,734	3,498
Professional fees									4,203	3,268	3,659
Other operating expenses									41,256	35,066	28,246
Total noninterest expenses	34,845	$ 33,592	$ 35,836	$ 36,030	31,056	$ 28,184	$ 28,495	$ 26,660	140,303	114,395	101,674
Segment profit									77,957	57,246	54,204
Intersegment (revenues) expenses									0	0	0
Pre-tax segment profit after eliminations									$ 77,957	$ 57,246	$ 54,204
% of segment pre-tax profit after eliminations									100.00%	100.00%	100.00%
Segment assets (dollars in millions)	4,652,485				4,449,720				$ 4,652,485	$ 4,449,720	$ 3,421,500
Goodwill – Wealth
Segment Reporting Information [Line Items]
Net interest income									7	3	3
Provision for loan and lease losses									0	0	0
Net interest income after provision for loan and lease losses									7	3	3
Fees for wealth management services									42,326	38,735	36,690
Insurance commissions									6,808	4,589	3,722
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 (loss) on sale of other real estate owned (OREO)									0	0	0
Other operating income									186	197	158
Total noninterest income									49,320	43,521	40,570
Salaries and wages									19,735	16,692	15,090
Employee benefits									3,872	3,820	3,291
Occupancy and bank premises									2,011	1,698	1,606
Amortization of intangible assets									2,101	1,951	2,626
Professional fees									456	270	143
Other operating expenses									5,328	4,461	3,835
Total noninterest expenses									33,503	28,892	26,591
Segment profit									15,824	14,632	13,982
Intersegment (revenues) expenses									715	448	396
Pre-tax segment profit after eliminations									$ 16,539	$ 15,080	$ 14,378
% of segment pre-tax profit after eliminations									21.20%	26.30%	26.50%
Segment assets (dollars in millions)	50,800				51,200				$ 50,800	$ 51,200	$ 44,400
Banking
Segment Reporting Information [Line Items]
Net interest income									149,464	115,124	106,233
Provision for loan and lease losses									7,193	2,618	4,326
Net interest income after provision for loan and lease losses									142,271	112,506	101,907
Fees for wealth management services									0	0	0
Insurance commissions									0	0	0
Capital markets revenue									4,848	2,396	0
Service charges on deposit accounts									2,989	2,608	2,791
Loan servicing and other fees									2,259	2,106	1,939
Net gain on sale of loans									3,283	2,441	3,048
Net gain on sale of investment securities available for sale									7	101	(77)
Net gain (loss) on sale of other real estate owned (OREO)									295	(104)	(76)
Other operating income									12,981	6,063	5,773
Total noninterest income									26,662	15,611	13,398
Salaries and wages									46,936	36,559	32,321
Employee benefits									9,046	6,350	5,958
Occupancy and bank premises									9,588	8,208	8,005
Amortization of intangible assets									1,555	783	872
Professional fees									3,747	2,998	3,516
Other operating expenses									35,928	30,605	24,411
Total noninterest expenses									106,800	85,503	75,083
Segment profit									62,133	42,614	40,222
Intersegment (revenues) expenses									(715)	(448)	(396)
Pre-tax segment profit after eliminations									$ 61,418	$ 42,166	$ 39,826
% of segment pre-tax profit after eliminations									78.80%	73.70%	73.50%
Segment assets (dollars in millions)	$ 4,601,700				$ 4,398,500				$ 4,601,700	$ 4,398,500	$ 3,377,100