Loans and Allowance for Credit Losses - Schedule of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	$ 54,619	[1]	$ 55,461		$ 50,381
Charge-offs	(15,553)				(12,969)
Recoveries	12,580				11,083
Provision for Credit Losses	38,395				6,966
Balance at End of Period	131,388	[1]	54,619	[1]	55,461
Previously Reported
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	54,619		55,461
Charge-offs			(14,789)
Recoveries			9,200
Provision for Credit Losses			4,747
Balance at End of Period			54,619		55,461
Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	41,347
Balance at End of Period			41,347
Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	95,966
Balance at End of Period	131,388		95,966
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	21,359		21,742		19,246
Charge-offs	(5,593)				(3,087)
Recoveries	3,629				1,519
Provision for Credit Losses	4,022				4,064
Balance at End of Period	30,567		21,359		21,742
Commercial | Previously Reported
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	22,585		21,742
Charge-offs			(3,819)
Recoveries			1,650
Provision for Credit Losses			3,012
Balance at End of Period			22,585		21,742
Commercial | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	7,150
Balance at End of Period			7,150
Commercial | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	28,509
Balance at End of Period			28,509
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	20,535		23,470		21,436
Charge-offs	(4,323)				(879)
Recoveries	4,515				2,740
Provision for Credit Losses	29,535				173
Balance at End of Period	75,810		20,535		23,470
Commercial real estate | Previously Reported
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	21,588		23,470
Charge-offs			(2,846)
Recoveries			3,774
Provision for Credit Losses			(2,810)
Balance at End of Period			21,588		23,470
Commercial real estate | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	25,548
Balance at End of Period			25,548
Commercial real estate | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	46,083
Balance at End of Period			46,083
BBCC
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	2,279
Charge-offs	(95)
Recoveries	140
Provision for Credit Losses	94
Balance at End of Period	6,120		2,279
BBCC | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	3,702
Balance at End of Period			3,702
BBCC | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	5,981
Balance at End of Period			5,981
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	2,299		2,277		1,763
Charge-offs	(824)				(1,100)
Recoveries	633				2,118
Provision for Credit Losses	3,514				(504)
Balance at End of Period	12,608		2,299		2,277
Residential real estate | Previously Reported
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	2,299		2,277
Charge-offs			(661)
Recoveries			146
Provision for Credit Losses			537
Balance at End of Period			2,299		2,277
Residential real estate | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	6,986
Balance at End of Period			6,986
Residential real estate | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	9,285
Balance at End of Period			9,285
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period			7,972		7,936
Charge-offs					(7,903)
Recoveries					4,706
Provision for Credit Losses					3,233
Balance at End of Period					7,972
Consumer | Previously Reported
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	8,147		7,972
Charge-offs			(7,463)
Recoveries			3,630
Provision for Credit Losses			4,008
Balance at End of Period			8,147		$ 7,972
Indirect
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	5,319
Charge-offs	(2,754)
Recoveries	1,922
Provision for Credit Losses	762
Balance at End of Period	3,580		5,319
Indirect | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	(1,669)
Balance at End of Period			(1,669)
Indirect | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	3,650
Balance at End of Period			3,650
Direct
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	1,863
Charge-offs	(1,763)
Recoveries	819
Provision for Credit Losses	995
Balance at End of Period	855		1,863
Direct | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	(1,059)
Balance at End of Period			(1,059)
Direct | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	804
Balance at End of Period			804
Home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	965
Charge-offs	(201)
Recoveries	922
Provision for Credit Losses	(527)
Balance at End of Period	1,848		965
Home equity | Adjustment
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	689
Balance at End of Period			689
Home equity | Adjusted Balance
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at Beginning of Period	$ 1,654
Balance at End of Period			$ 1,654

[1] Beginning January 1, 2020, calculation is based on current expected loss methodology. Prior to January 1, 2020, calculation was based on incurred loss methodology.