Allowance for Credit Losses - Aggregated analysis of the changes in allowance for loan losses Details (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Allowance for loan losses:
Balance at beginning of period	$ 434,608	$ 58,213	$ 56,927	$ 55,798
Charge-offs	(4,642)	(2,779)	(10,296)	(7,260)
Recoveries	4,048	884	8,287	2,833
Provision (benefit)	7,687	4,028	71,957	9,220
Balance at end of period	440,159	60,255	440,159	60,255
Loans individually evaluated for impairment	1,171		1,171
Loans collectively evaluated for impairment	$ 426,934		$ 426,934
Loans
Total loans		11,290,147		11,290,147	$ 11,375,104
Construction and land development
Loans
Total loans		1,025,387		1,025,387	1,017,261
Commercial non-owner occupied | Commercial loans
Loans
Total loans		2,357,730		2,357,730	2,323,967
Consumer Owner Occupied Loans
Loans
Total loans		2,760,126		2,760,126	2,706,960
Home equity loans | Consumer
Loans
Total loans		773,363		773,363	758,020
Commercial and industrial | Commercial loans
Loans
Total loans		1,261,527		1,261,527	1,386,327
Other income producing property
Loans
Total loans		361,879		361,879	346,554
Consumer | Consumer
Loans
Total loans		654,883		654,883	663,422
Other loans
Loans
Total loans		1,457		1,457	13,892
Non-acquired loans
Allowance for loan losses:
Balance at beginning of period		53,590		51,194
Charge-offs		(1,969)		(4,541)
Recoveries		834		2,461
Provision (benefit)		2,482		5,823
Balance at end of period		54,937		54,937
Loans individually evaluated for impairment		1,221		1,221
Loans collectively evaluated for impairment		53,716		53,716
Loans
Loans individually evaluated for impairment		54,867		54,867
Loans collectively evaluated for impairment		8,873,645		8,873,645
Total loans		8,928,512		8,928,512	9,252,831
Non-acquired loans | Commercial loans
Loans
Total loans		5,762,144		5,762,144	6,062,991
Non-acquired loans | Consumer
Loans
Total loans		3,166,368		3,166,368	3,189,840
Non-acquired loans | Real estate | Commercial loans
Loans
Total loans					968,360
Non-acquired loans | Real estate | Consumer
Loans
Total loans		2,639,871		2,639,871	2,637,467
Non-acquired loans | Construction and land development
Allowance for loan losses:
Balance at beginning of period		5,718		5,682
Charge-offs		(69)		(78)
Recoveries		208		833
Provision (benefit)		159		(421)
Balance at end of period		6,016		6,016
Loans individually evaluated for impairment		587		587
Loans collectively evaluated for impairment		5,429		5,429
Loans
Loans individually evaluated for impairment		32,673		32,673
Loans collectively evaluated for impairment		922,645		922,645
Total loans		955,318		955,318
Non-acquired loans | Construction and land development | Commercial loans
Loans
Total loans		955,318		955,318	968,360
Non-acquired loans | Commercial non-owner occupied
Allowance for loan losses:
Balance at beginning of period		10,311		8,754
Charge-offs				(3)
Recoveries		2		47
Provision (benefit)		238		1,753
Balance at end of period		10,551		10,551
Loans collectively evaluated for impairment		10,551		10,551
Loans
Loans individually evaluated for impairment		87		87
Loans collectively evaluated for impairment		1,777,240		1,777,240
Total loans		1,777,327		1,777,327
Non-acquired loans | Commercial non-owner occupied | Commercial loans
Loans
Total loans		1,777,327		1,777,327	1,811,138
Non-acquired loans | Commercial owner occupied real estate loan
Allowance for loan losses:
Balance at beginning of period		9,526		9,369
Charge-offs		(31)		(43)
Recoveries		18		84
Provision (benefit)		456		559
Balance at end of period		9,969		9,969
Loans individually evaluated for impairment		33		33
Loans collectively evaluated for impairment		9,936		9,936
Loans
Loans individually evaluated for impairment		7,135		7,135
Loans collectively evaluated for impairment		1,670,560		1,670,560
Total loans		1,677,695		1,677,695
Non-acquired loans | Commercial owner occupied real estate loan | Commercial loans
Loans
Total loans		1,677,695		1,677,695	1,784,017
Non-acquired loans | Consumer Owner Occupied Loans
Allowance for loan losses:
Balance at beginning of period		12,432		11,913
Charge-offs		(10)		(95)
Recoveries		149		181
Provision (benefit)		(24)		548
Balance at end of period		12,547		12,547
Loans individually evaluated for impairment		33		33
Loans collectively evaluated for impairment		12,514		12,514
Loans
Loans individually evaluated for impairment		5,127		5,127
Loans collectively evaluated for impairment		2,113,000		2,113,000
Total loans		2,118,127		2,118,127
Non-acquired loans | Consumer Owner Occupied Loans | Consumer
Loans
Total loans		2,118,127		2,118,127	2,118,839
Non-acquired loans | Home equity loans
Allowance for loan losses:
Balance at beginning of period		3,177		3,434
Charge-offs		(100)		(115)
Recoveries		86		220
Provision (benefit)		28		(348)
Balance at end of period		3,191		3,191
Loans individually evaluated for impairment		121		121
Loans collectively evaluated for impairment		3,070		3,070
Loans
Loans individually evaluated for impairment		2,345		2,345
Loans collectively evaluated for impairment		519,399		519,399
Total loans		521,744		521,744
Non-acquired loans | Home equity loans | Consumer
Loans
Total loans		521,744		521,744	518,628
Non-acquired loans | Commercial and industrial
Allowance for loan losses:
Balance at beginning of period		7,495		7,454
Charge-offs		(32)		(141)
Recoveries		77		286
Provision (benefit)		21		(38)
Balance at end of period		7,561		7,561
Loans individually evaluated for impairment		387		387
Loans collectively evaluated for impairment		7,174		7,174
Loans
Loans individually evaluated for impairment		5,313		5,313
Loans collectively evaluated for impairment		1,125,534		1,125,534
Total loans		1,130,847		1,130,847
Non-acquired loans | Commercial and industrial | Commercial loans
Loans
Total loans		1,130,847		1,130,847	1,280,859
Non-acquired loans | Other income producing property
Allowance for loan losses:
Balance at beginning of period		1,359		1,446
Charge-offs				(31)
Recoveries		29		87
Provision (benefit)		(29)		(143)
Balance at end of period		1,359		1,359
Loans individually evaluated for impairment		58		58
Loans collectively evaluated for impairment		1,301		1,301
Loans
Loans individually evaluated for impairment		2,096		2,096
Loans collectively evaluated for impairment		218,861		218,861
Total loans		220,957		220,957	218,617
Non-acquired loans | Other income producing property | Commercial loans
Loans
Total loans		220,957		220,957	218,617
Non-acquired loans | Consumer
Allowance for loan losses:
Balance at beginning of period		3,572		3,101
Charge-offs		(1,727)		(4,035)
Recoveries		265		723
Provision (benefit)		1,633		3,954
Balance at end of period		3,743		3,743
Loans individually evaluated for impairment		2		2
Loans collectively evaluated for impairment		3,741		3,741
Loans
Loans individually evaluated for impairment		91		91
Loans collectively evaluated for impairment		524,949		524,949
Total loans		525,040		525,040
Non-acquired loans | Consumer | Consumer
Loans
Total loans		525,040		525,040	538,481
Non-acquired loans | Other loans
Allowance for loan losses:
Balance at beginning of period				41
Provision (benefit)				(41)
Loans
Loans collectively evaluated for impairment		1,457		1,457
Total loans		1,457		1,457	13,892
Non-acquired loans | Other loans | Consumer
Loans
Total loans		1,457		1,457	13,892
Acquired non-credit impaired loans
Allowance for loan losses:
Charge-offs		(810)		(2,719)
Recoveries		50		372
Provision (benefit)		760		2,347
Loans
Loans collectively evaluated for impairment		1,965,603		1,965,603
Total loans		1,965,603		1,965,603	1,760,427
Acquired non-credit impaired loans | Commercial loans
Loans
Total loans		1,130,970		1,130,970	985,780
Acquired non-credit impaired loans | Consumer
Loans
Total loans		834,633		834,633	774,647
Acquired non-credit impaired loans | Real estate | Consumer
Loans
Total loans		741,544		741,544	685,163
Acquired non-credit impaired loans | Construction and land development
Allowance for loan losses:
Charge-offs		(39)		(45)
Recoveries		1		3
Provision (benefit)		38		42
Loans
Loans collectively evaluated for impairment		53,302		53,302
Total loans		53,302		53,302
Acquired non-credit impaired loans | Construction and land development | Commercial loans
Loans
Total loans		53,302		53,302	33,569
Acquired non-credit impaired loans | Commercial non-owner occupied
Loans
Loans collectively evaluated for impairment		503,443		503,443
Total loans		503,443		503,443
Acquired non-credit impaired loans | Commercial non-owner occupied | Commercial loans
Loans
Total loans		503,443		503,443	447,441
Acquired non-credit impaired loans | Commercial owner occupied real estate loan
Allowance for loan losses:
Charge-offs				(786)
Provision (benefit)				786
Loans
Loans collectively evaluated for impairment		345,040		345,040
Total loans		345,040		345,040
Acquired non-credit impaired loans | Commercial owner occupied real estate loan | Commercial loans
Loans
Total loans		345,040		345,040	307,193
Acquired non-credit impaired loans | Consumer Owner Occupied Loans
Allowance for loan losses:
Charge-offs				(6)
Recoveries		21		26
Provision (benefit)		(21)		(20)
Loans
Loans collectively evaluated for impairment		543,432		543,432
Total loans		543,432		543,432
Acquired non-credit impaired loans | Consumer Owner Occupied Loans | Consumer
Loans
Total loans		543,432		543,432	496,431
Acquired non-credit impaired loans | Home equity loans
Allowance for loan losses:
Charge-offs		(23)		(263)
Recoveries		9		55
Provision (benefit)		14		208
Loans
Loans collectively evaluated for impairment		198,112		198,112
Total loans		198,112		198,112
Acquired non-credit impaired loans | Home equity loans | Consumer
Loans
Total loans		198,112		198,112	188,732
Acquired non-credit impaired loans | Commercial and industrial
Allowance for loan losses:
Charge-offs		(648)		(1,288)
Recoveries		10		181
Provision (benefit)		638		1,107
Loans
Loans collectively evaluated for impairment		126,092		126,092
Total loans		126,092		126,092
Acquired non-credit impaired loans | Commercial and industrial | Commercial loans
Loans
Total loans		126,092		126,092	101,880
Acquired non-credit impaired loans | Other income producing property
Allowance for loan losses:
Charge-offs				(26)
Recoveries				71
Provision (benefit)				(45)
Loans
Loans collectively evaluated for impairment		103,093		103,093
Total loans		103,093		103,093	95,697
Acquired non-credit impaired loans | Other income producing property | Commercial loans
Loans
Total loans		103,093		103,093	95,697
Acquired non-credit impaired loans | Consumer
Allowance for loan losses:
Charge-offs		(100)		(305)
Recoveries		9		36
Provision (benefit)		91		269
Loans
Loans collectively evaluated for impairment		93,089		93,089
Total loans		93,089		93,089
Acquired non-credit impaired loans | Consumer | Consumer
Loans
Total loans		93,089		93,089	89,484
Acquired credit impaired loans
Allowance for loan losses:
Balance at beginning of period		4,623		4,604
Provision (benefit)		786		1,050
Reduction due to loan removals		(91)		(336)
Balance at end of period		5,318		5,318
Loans collectively evaluated for impairment		5,318		5,318
Loans
Loans collectively evaluated for impairment		396,032		396,032
Total loans		396,032		396,032	361,846
Acquired credit impaired loans | Real estate | Commercial loans
Allowance for loan losses:
Balance at beginning of period		1,009		801
Provision (benefit)		386		599
Reduction due to loan removals				(5)
Balance at end of period		1,395		1,395
Loans collectively evaluated for impairment		1,395		1,395
Loans
Loans collectively evaluated for impairment		149,134		149,134
Total loans		149,134		149,134	130,938
Acquired credit impaired loans | Real estate | Consumer
Allowance for loan losses:
Balance at beginning of period		2,346		2,246
Provision (benefit)		447		742
Reduction due to loan removals		(91)		(286)
Balance at end of period		2,702		2,702
Loans collectively evaluated for impairment		2,702		2,702
Loans
Loans collectively evaluated for impairment		175,044		175,044
Total loans		175,044		175,044	163,359
Acquired credit impaired loans | Construction and land development
Allowance for loan losses:
Balance at beginning of period		798		717
Provision (benefit)		(38)		43
Balance at end of period		760		760
Loans collectively evaluated for impairment		760		760
Loans
Loans collectively evaluated for impairment		26,930		26,930
Total loans		26,930		26,930
Acquired credit impaired loans | Construction and land development | Commercial loans
Loans
Total loans		26,930		26,930	25,032
Acquired credit impaired loans | Commercial and industrial
Allowance for loan losses:
Balance at beginning of period				79
Provision (benefit)				(34)
Reduction due to loan removals				(45)
Loans
Loans collectively evaluated for impairment		8,112		8,112
Total loans		8,112		8,112
Acquired credit impaired loans | Commercial and industrial | Commercial loans
Loans
Total loans		8,112		8,112	7,029
Acquired credit impaired loans | Consumer
Allowance for loan losses:
Balance at beginning of period		470		761
Provision (benefit)		(9)		(300)
Balance at end of period		461		461
Loans collectively evaluated for impairment		461		461
Loans
Loans collectively evaluated for impairment		36,812		36,812
Total loans		36,812		36,812
Acquired credit impaired loans | Consumer | Consumer
Loans
Total loans		$ 36,812		$ 36,812	$ 35,488