Allowance for Credit Losses - Aggregated analysis of the changes in allowance for loan losses Details (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019
Allowance for loan losses:
Balance at beginning of period	$ 144,785,000	$ 56,522,000	$ 56,927,000	$ 55,798,000
Charge-offs	(2,431,000)	(2,862,000)	(5,654,000)	(4,481,000)
Recoveries	2,330,000	991,000	4,239,000	1,949,000
Provision (benefit)	29,536,000	3,704,000	64,270,000	5,192,000
Balance at end of period	434,608,000	58,213,000	434,608,000	58,213,000
Loans individually evaluated for impairment	10,904,000		10,904,000
Loans collectively evaluated for impairment	356,187,000		356,187,000
Loans
Loans individually evaluated for impairment	$ 1,000,000.0		$ 1,000,000.0		$ 500,000
Total loans		11,226,192,000		11,226,192,000		$ 11,375,104,000
Real estate | Consumer
Loans
Total loans		3,540,500,000		3,540,500,000		3,464,980,000
Construction and land development
Loans
Total loans		957,346,000		957,346,000		1,017,261,000
Commercial non-owner occupied | Commercial loans
Loans
Total loans		2,398,249,000		2,398,249,000		2,323,967,000
Commercial owner occupied real estate loan | Commercial loans
Loans
Total loans		2,047,933,000		2,047,933,000		2,158,701,000
Consumer Owner Occupied Loans
Loans
Total loans		2,762,266,000		2,762,266,000		2,706,960,000
Home equity loans | Consumer
Loans
Total loans		778,234,000		778,234,000		758,020,000
Commercial and industrial | Commercial loans
Loans
Total loans		1,271,464,000		1,271,464,000		1,386,327,000
Other income producing property
Loans
Total loans		367,353,000		367,353,000		346,554,000
Consumer | Consumer
Loans
Total loans		641,746,000		641,746,000		663,422,000
Other loans | Commercial loans
Loans
Total loans		1,601,000		1,601,000		13,892,000
Non-acquired loans
Allowance for loan losses:
Balance at beginning of period		52,008,000		51,194,000
Charge-offs		(1,327,000)		(2,572,000)
Recoveries		875,000		1,627,000
Provision (benefit)		2,034,000		3,341,000
Balance at end of period		53,590,000		53,590,000
Loans individually evaluated for impairment		1,384,000		1,384,000
Loans collectively evaluated for impairment		52,206,000		52,206,000
Loans
Loans individually evaluated for impairment		54,509,000		54,509,000
Loans collectively evaluated for impairment		8,566,818,000		8,566,818,000
Total loans		8,621,327,000		8,621,327,000		9,252,831,000
Non-acquired loans | Commercial loans
Loans
Total loans		5,522,067,000		5,522,067,000		6,062,991,000
Non-acquired loans | Consumer
Loans
Total loans		3,099,260,000		3,099,260,000		3,189,840,000
Non-acquired loans | Real estate | Consumer
Loans
Total loans		2,594,191,000		2,594,191,000		2,637,467,000
Non-acquired loans | Construction and land development | Commercial loans
Allowance for loan losses:
Balance at beginning of period		5,371,000		5,682,000
Charge-offs		(9,000)		(9,000)
Recoveries		326,000		625,000
Provision (benefit)		30,000		(580,000)
Balance at end of period		5,718,000		5,718,000
Loans individually evaluated for impairment		715,000		715,000
Loans collectively evaluated for impairment		5,003,000		5,003,000
Loans
Loans individually evaluated for impairment		36,130,000		36,130,000
Loans collectively evaluated for impairment		843,594,000		843,594,000
Total loans		879,724,000		879,724,000		968,360,000
Non-acquired loans | Commercial non-owner occupied | Commercial loans
Allowance for loan losses:
Balance at beginning of period		9,740,000		8,754,000
Charge-offs		(3,000)		(3,000)
Recoveries		23,000		45,000
Provision (benefit)		551,000		1,515,000
Balance at end of period		10,311,000		10,311,000
Loans individually evaluated for impairment		1,000		1,000
Loans collectively evaluated for impairment		10,310,000		10,310,000
Loans
Loans individually evaluated for impairment		101,000		101,000
Loans collectively evaluated for impairment		1,723,539,000		1,723,539,000
Total loans		1,723,640,000		1,723,640,000		1,811,138,000
Non-acquired loans | Commercial owner occupied real estate loan | Commercial loans
Allowance for loan losses:
Balance at beginning of period		9,629,000		9,369,000
Charge-offs				(12,000)
Recoveries		41,000		66,000
Provision (benefit)		(144,000)		103,000
Balance at end of period		9,526,000		9,526,000
Loans individually evaluated for impairment		33,000		33,000
Loans collectively evaluated for impairment		9,493,000		9,493,000
Loans
Loans individually evaluated for impairment		5,440,000		5,440,000
Loans collectively evaluated for impairment		1,584,547,000		1,584,547,000
Total loans		1,589,987,000		1,589,987,000		1,784,017,000
Non-acquired loans | Consumer Owner Occupied Loans | Consumer
Allowance for loan losses:
Balance at beginning of period		12,058,000		11,913,000
Charge-offs		(48,000)		(85,000)
Recoveries		30,000		32,000
Provision (benefit)		392,000		572,000
Balance at end of period		12,432,000		12,432,000
Loans individually evaluated for impairment		35,000		35,000
Loans collectively evaluated for impairment		12,397,000		12,397,000
Loans
Loans individually evaluated for impairment		5,566,000		5,566,000
Loans collectively evaluated for impairment		2,074,383,000		2,074,383,000
Total loans		2,079,949,000		2,079,949,000		2,118,839,000
Non-acquired loans | Home equity loans | Consumer
Allowance for loan losses:
Balance at beginning of period		3,273,000		3,434,000
Charge-offs				(15,000)
Recoveries		98,000		134,000
Provision (benefit)		(194,000)		(376,000)
Balance at end of period		3,177,000		3,177,000
Loans individually evaluated for impairment		125,000		125,000
Loans collectively evaluated for impairment		3,052,000		3,052,000
Loans
Loans individually evaluated for impairment		2,436,000		2,436,000
Loans collectively evaluated for impairment		511,806,000		511,806,000
Total loans		514,242,000		514,242,000		518,628,000
Non-acquired loans | Commercial and industrial | Commercial loans
Allowance for loan losses:
Balance at beginning of period		7,249,000		7,454,000
Charge-offs		(90,000)		(109,000)
Recoveries		138,000		209,000
Provision (benefit)		198,000		(59,000)
Balance at end of period		7,495,000		7,495,000
Loans individually evaluated for impairment		394,000		394,000
Loans collectively evaluated for impairment		7,101,000		7,101,000
Loans
Loans individually evaluated for impairment		2,674,000		2,674,000
Loans collectively evaluated for impairment		1,111,839,000		1,111,839,000
Total loans		1,114,513,000		1,114,513,000		1,280,859,000
Non-acquired loans | Other income producing property
Allowance for loan losses:
Balance at beginning of period		1,387,000		1,446,000
Charge-offs		(31,000)		(31,000)
Recoveries		13,000		58,000
Provision (benefit)		(10,000)		(114,000)
Balance at end of period		1,359,000		1,359,000
Loans individually evaluated for impairment		78,000		78,000
Loans collectively evaluated for impairment		1,281,000		1,281,000
Loans
Loans individually evaluated for impairment		2,064,000		2,064,000
Loans collectively evaluated for impairment		212,139,000		212,139,000
Total loans		214,203,000		214,203,000		218,617,000
Non-acquired loans | Consumer
Allowance for loan losses:
Balance at beginning of period				3,101,000
Charge-offs				(2,308,000)
Recoveries				458,000
Provision (benefit)				2,321,000
Balance at end of period		3,572,000		3,572,000
Non-acquired loans | Consumer | Consumer
Allowance for loan losses:
Balance at beginning of period		3,195,000
Charge-offs		(1,146,000)
Recoveries		206,000
Provision (benefit)		1,317,000
Balance at end of period		3,572,000		3,572,000
Loans individually evaluated for impairment		3,000		3,000
Loans collectively evaluated for impairment		3,569,000		3,569,000
Loans
Loans individually evaluated for impairment		98,000		98,000
Loans collectively evaluated for impairment		503,370,000		503,370,000
Total loans		503,468,000		503,468,000		538,481,000
Non-acquired loans | Other loans
Allowance for loan losses:
Balance at beginning of period				41,000
Provision (benefit)				(41,000)
Non-acquired loans | Other loans | Commercial loans
Allowance for loan losses:
Balance at beginning of period		106,000
Provision (benefit)		(106,000)
Loans
Loans collectively evaluated for impairment		1,601,000		1,601,000
Total loans		1,601,000		1,601,000		13,892,000
Non-acquired loans | Other loans | Consumer
Loans
Total loans		1,601,000		1,601,000		13,892,000
Acquired non-credit impaired loans
Allowance for loan losses:
Charge-offs		(1,535,000)		(1,909,000)
Recoveries		116,000		322,000
Provision (benefit)		1,419,000		1,587,000
Loans
Loans collectively evaluated for impairment		2,180,281,000		2,180,281,000
Total loans		2,180,281,000		2,180,281,000		1,760,427,000
Acquired non-credit impaired loans | Commercial loans
Loans
Total loans		1,294,530,000		1,294,530,000		985,780,000
Acquired non-credit impaired loans | Consumer
Loans
Total loans		885,751,000		885,751,000		774,647,000
Acquired non-credit impaired loans | Real estate | Consumer
Loans
Total loans		786,061,000		786,061,000		685,163,000
Acquired non-credit impaired loans | Construction and land development | Commercial loans
Allowance for loan losses:
Charge-offs				(6,000)
Recoveries		1,000		2,000
Provision (benefit)		(1,000)		4,000
Loans
Loans collectively evaluated for impairment		60,391,000		60,391,000
Total loans		60,391,000		60,391,000		33,569,000
Acquired non-credit impaired loans | Commercial non-owner occupied | Commercial loans
Loans
Loans collectively evaluated for impairment		595,367,000		595,367,000
Total loans		595,367,000		595,367,000		447,441,000
Acquired non-credit impaired loans | Commercial owner occupied real estate loan | Commercial loans
Allowance for loan losses:
Charge-offs		(786,000)		(786,000)
Provision (benefit)		786,000		786,000
Loans
Loans collectively evaluated for impairment		376,187,000		376,187,000
Total loans		376,187,000		376,187,000		307,193,000
Acquired non-credit impaired loans | Consumer Owner Occupied Loans | Consumer
Allowance for loan losses:
Charge-offs		(6,000)		(6,000)
Recoveries		3,000		5,000
Provision (benefit)		3,000		1,000
Loans
Loans collectively evaluated for impairment		577,284,000		577,284,000
Total loans		577,284,000		577,284,000		496,431,000
Acquired non-credit impaired loans | Home equity loans | Consumer
Allowance for loan losses:
Charge-offs		(168,000)		(240,000)
Recoveries		24,000		46,000
Provision (benefit)		144,000		194,000
Loans
Loans collectively evaluated for impairment		208,777,000		208,777,000
Total loans		208,777,000		208,777,000		188,732,000
Acquired non-credit impaired loans | Commercial and industrial | Commercial loans
Allowance for loan losses:
Charge-offs		(506,000)		(640,000)
Recoveries		6,000		171,000
Provision (benefit)		500,000		469,000
Loans
Loans collectively evaluated for impairment		151,579,000		151,579,000
Total loans		151,579,000		151,579,000		101,880,000
Acquired non-credit impaired loans | Other income producing property
Allowance for loan losses:
Charge-offs				(26,000)
Recoveries		71,000		71,000
Provision (benefit)		(71,000)		(45,000)
Loans
Loans collectively evaluated for impairment		111,006,000		111,006,000
Total loans		111,006,000		111,006,000		95,697,000
Acquired non-credit impaired loans | Other income producing property | Commercial loans
Loans
Total loans		111,006,000		111,006,000		95,697,000
Acquired non-credit impaired loans | Consumer
Allowance for loan losses:
Charge-offs		(69,000)		(205,000)
Recoveries		11,000		27,000
Provision (benefit)		58,000		178,000
Loans
Loans collectively evaluated for impairment		99,690,000		99,690,000
Total loans		99,690,000		99,690,000
Acquired non-credit impaired loans | Consumer | Consumer
Loans
Total loans		99,690,000		99,690,000		89,484,000
Acquired credit impaired loans
Allowance for loan losses:
Balance at beginning of period		4,514,000		4,604,000
Provision (benefit)		251,000		264,000
Reduction due to loan removals		(142,000)		(245,000)
Balance at end of period		4,623,000		4,623,000
Loans collectively evaluated for impairment		4,623,000		4,623,000
Loans
Loans collectively evaluated for impairment		424,584,000		424,584,000
Total loans		424,584,000		424,584,000		361,846,000
Acquired credit impaired loans | Real estate | Commercial loans
Allowance for loan losses:
Balance at beginning of period		847,000		801,000
Provision (benefit)		162,000		213,000
Reduction due to loan removals				(5,000)
Balance at end of period		1,009,000		1,009,000
Loans collectively evaluated for impairment		1,009,000		1,009,000
Loans
Loans collectively evaluated for impairment		164,540,000		164,540,000
Total loans		164,540,000		164,540,000		130,938,000
Acquired credit impaired loans | Real estate | Consumer
Allowance for loan losses:
Balance at beginning of period		2,164,000		2,246,000
Provision (benefit)		279,000		295,000
Reduction due to loan removals		(97,000)		(195,000)
Balance at end of period		2,346,000		2,346,000
Loans collectively evaluated for impairment		2,346,000		2,346,000
Loans
Loans collectively evaluated for impairment		184,208,000		184,208,000
Total loans		184,208,000		184,208,000		163,359,000
Acquired credit impaired loans | Construction and land development | Commercial loans
Allowance for loan losses:
Balance at beginning of period		717,000		717,000
Provision (benefit)		81,000		81,000
Balance at end of period		798,000		798,000
Loans collectively evaluated for impairment		798,000		798,000
Loans
Loans collectively evaluated for impairment		27,014,000		27,014,000
Total loans		27,014,000		27,014,000		25,032,000
Acquired credit impaired loans | Commercial and industrial | Commercial loans
Allowance for loan losses:
Balance at beginning of period		79,000		79,000
Provision (benefit)		(34,000)		(34,000)
Reduction due to loan removals		(45,000)		(45,000)
Loans
Loans collectively evaluated for impairment		10,198,000		10,198,000
Total loans		10,198,000		10,198,000		7,029,000
Acquired credit impaired loans | Consumer | Consumer
Allowance for loan losses:
Balance at beginning of period		707,000		761,000
Provision (benefit)		(237,000)		(291,000)
Balance at end of period		470,000		470,000
Loans collectively evaluated for impairment		470,000		470,000
Loans
Loans collectively evaluated for impairment		38,624,000		38,624,000
Total loans		$ 38,624,000		$ 38,624,000		$ 35,488,000