Allowance for Credit Losses - Schedule of Allowance for Loan Losses and Carrying Amount of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	$ 77,057	$ 76,703
Charge-offs	(8,761)	(29,110)
Recoveries	2,073	8,151
Provision	27,112	21,313
Allowance for Loan Losses Ending balance	154,923	77,057
Allowance for Loan Losses, individually evaluated for impairment		16,499
Allowance for Loan Losses, collectively evaluated for impairment		60,558
Financing receivables		13,713,548
Financing receivables, individually evaluated for impairment		123,505
Financing receivables, collectively evaluated for impairment		13,494,039
Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	52,321
Allowance for Loan Losses Ending balance		52,321
Accounting Standards Update 2016-13 [Member] | PCD loans Member [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	5,121
Allowance for Loan Losses Ending balance		5,121
Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses		0
Financing receivables		96,004
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	3,353	7,992
Charge-offs	(1,744)	(1,303)
Recoveries	844	175
Provision	(523)	(3,511)
Allowance for Loan Losses Ending balance	18,792	3,353
Allowance for Loan Losses, individually evaluated for impairment		262
Allowance for Loan Losses, collectively evaluated for impairment		3,091
Financing receivables		1,408,205
Financing receivables, individually evaluated for impairment		14,047
Financing receivables, collectively evaluated for impairment		1,382,369
Construction & Land Development [Member] | Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	14,817
Allowance for Loan Losses Ending balance		14,817
Construction & Land Development [Member] | Accounting Standards Update 2016-13 [Member] | PCD loans Member [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	2,045
Allowance for Loan Losses Ending balance		2,045
Construction & Land Development [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses		0
Financing receivables		11,789
Bankcard [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	74
Charge-offs	(46)
Recoveries	6
Provision	164
Allowance for Loan Losses Ending balance	226	74
Financing receivables		10,074
Bankcard [Member] | Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	28
Allowance for Loan Losses Ending balance		28
Bankcard [Member] | Accounting Standards Update 2016-13 [Member] | PCD loans Member [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	0
Allowance for Loan Losses Ending balance		0
Allowance for Estimated Imprecision [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	297	245
Charge-offs	0	0
Recoveries	0	0
Provision	0	52
Allowance for Loan Losses Ending balance	0	297
Allowance for Loan Losses, individually evaluated for impairment		0
Allowance for Loan Losses, collectively evaluated for impairment		297
Financing receivables		0
Financing receivables, individually evaluated for impairment		0
Financing receivables, collectively evaluated for impairment		0
Allowance for Estimated Imprecision [Member] | Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	(297)
Allowance for Loan Losses Ending balance		(297)
Allowance for Estimated Imprecision [Member] | Accounting Standards Update 2016-13 [Member] | PCD loans Member [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	0
Allowance for Loan Losses Ending balance		0
Allowance for Estimated Imprecision [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses		0
Financing receivables		0
Commercial Real Estate [Member] | Owner-Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	5,554	5,063
Charge-offs	(179)	(7,905)
Recoveries	66	3,733
Provision	2,474	4,663
Allowance for Loan Losses Ending balance	19,495	5,554
Allowance for Loan Losses, individually evaluated for impairment		973
Allowance for Loan Losses, collectively evaluated for impairment		4,581
Financing receivables		1,201,652
Financing receivables, individually evaluated for impairment		16,703
Financing receivables, collectively evaluated for impairment		1,160,556
Commercial Real Estate [Member] | Owner-Occupied [Member] | Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	9,737
Allowance for Loan Losses Ending balance		9,737
Commercial Real Estate [Member] | Owner-Occupied [Member] | Accounting Standards Update 2016-13 [Member] | PCD loans Member [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	1,843
Allowance for Loan Losses Ending balance		1,843
Commercial Real Estate [Member] | Owner-Occupied [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses		0
Financing receivables		24,393
Commercial Real Estate [Member] | Nonowner-Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	8,524	6,919
Charge-offs	0	(1,093)
Recoveries	585	80
Provision	(684)	2,618
Allowance for Loan Losses Ending balance	17,569	8,524
Allowance for Loan Losses, individually evaluated for impairment		2,979
Allowance for Loan Losses, collectively evaluated for impairment		5,545
Financing receivables		3,965,960
Financing receivables, individually evaluated for impairment		27,121
Financing receivables, collectively evaluated for impairment		3,925,249
Commercial Real Estate [Member] | Nonowner-Occupied [Member] | Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	9,023
Allowance for Loan Losses Ending balance		9,023
Commercial Real Estate [Member] | Nonowner-Occupied [Member] | Accounting Standards Update 2016-13 [Member] | PCD loans Member [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	121
Allowance for Loan Losses Ending balance		121
Commercial Real Estate [Member] | Nonowner-Occupied [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses		0
Financing receivables		13,590
Other Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	47,325	41,341
Charge-offs	(5,688)	(12,975)
Recoveries	315	2,599
Provision	15,766	16,360
Allowance for Loan Losses Ending balance	53,827	47,325
Allowance for Loan Losses, individually evaluated for impairment		11,931
Allowance for Loan Losses, collectively evaluated for impairment		35,394
Financing receivables		2,285,037
Financing receivables, individually evaluated for impairment		54,108
Financing receivables, collectively evaluated for impairment		2,194,432
Other Commercial [Member] | Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	(4,829)
Allowance for Loan Losses Ending balance		(4,829)
Other Commercial [Member] | Accounting Standards Update 2016-13 [Member] | PCD loans Member [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	938
Allowance for Loan Losses Ending balance		938
Other Commercial [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses		0
Financing receivables		36,497
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	8,997	12,448
Charge-offs	(367)	(2,967)
Recoveries	142	858
Provision	8,581	(1,342)
Allowance for Loan Losses Ending balance	30,624	8,997
Allowance for Loan Losses, individually evaluated for impairment		354
Allowance for Loan Losses, collectively evaluated for impairment		8,643
Financing receivables		3,686,401
Financing receivables, individually evaluated for impairment		11,526
Financing receivables, collectively evaluated for impairment		3,665,140
Residential Real Estate [Member] | Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	13,097
Allowance for Loan Losses Ending balance		13,097
Residential Real Estate [Member] | Accounting Standards Update 2016-13 [Member] | PCD loans Member [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	174
Allowance for Loan Losses Ending balance		174
Residential Real Estate [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses		0
Financing receivables		9,735
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	3,007	2,695
Charge-offs		(2,867)
Recoveries		706
Provision		2,473
Allowance for Loan Losses Ending balance		3,007
Allowance for Loan Losses, individually evaluated for impairment		0
Allowance for Loan Losses, collectively evaluated for impairment		3,007
Financing receivables		1,166,293
Financing receivables, individually evaluated for impairment		0
Financing receivables, collectively evaluated for impairment		1,166,293
Consumer [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses		0
Financing receivables		0
Other Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	2,933
Charge-offs	(737)
Recoveries	115
Provision	1,334
Allowance for Loan Losses Ending balance	14,390	2,933
Other Consumer [Member] | Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	10,745
Allowance for Loan Losses Ending balance		10,745
Other Consumer [Member] | Accounting Standards Update 2016-13 [Member] | PCD loans Member [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	$ 0
Allowance for Loan Losses Ending balance		$ 0