Loans and Allowance for Credit Losses - Textual (Details)	3 Months Ended	12 Months Ended
	Sep. 30, 2020 credit	Dec. 31, 2021 USD ($) loan	Dec. 31, 2020 USD ($) loan credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans		$ 12,012,503,000	$ 12,900,897,000
Premiums and discounts associated with acquired loans		21,500,000	57,300,000
Financing receivable, accrued interest excluded from amortized costs		39,800,000	54,400,000
Nonaccrual loans with no allowance for credit loss		$ 14,500,000	$ 16,800,000
Number of loans | loan		4	5
Balance Prior to TDR		$ 1,058,000	$ 1,948,000
Number of previously restructured loans paid off | loan		9	6
Restructured loans paid off		$ 1,002,874	$ 837,265
Financial impact on date of restructure			51,300
OREO secured by residential estate properties		6,032,000	18,393,000
Financing receivable, collateral dependent, amount		47,089,000	69,998,000
Number of energy credits | credit	2
Unfunded commitments, allowance for credit loss		$ 22,400,000	22,400,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, term of loan		1 year
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, term of loan		3 years
COVID-19 Pandemic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans		$ 116,700,000	$ 904,700,000
Extended Maturity and Payment Deferral | COVID-19 Pandemic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan		51	3,729
Troubled debt, balance		$ 8,600,000	$ 2,990,000,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans which formal proceedings in process		1,806,000	7,182,000
Energy
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount		0	40,703,000
OREO Received in Full or Partial Satisfaction of Loans | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
OREO secured by residential estate properties		831,000	3,172,000
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans		$ 9,167,250,000	$ 9,223,791,000
Number of loans | loan		4	5
Balance Prior to TDR		$ 1,058,000	$ 1,948,000
Financial impact on date of restructure		0	0
Real Estate | OREO Received in Full or Partial Satisfaction of Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance Prior to TDR		0	0
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans		2,160,760,000	$ 2,750,291,000
Number of energy credits | credit			4
Single family residential | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans		$ 2,101,975,000	$ 1,880,673,000
Number of loans | loan		3	5
Balance Prior to TDR		$ 274,000	$ 1,948,000
Allowance for credit losses on loans		5,129
Financial impact on date of restructure		0	0
Financing receivable, collateral dependent, amount		1,838,000	6,950,000
Single family residential | Real Estate | Energy
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount		0	0
Other commercial | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans		$ 5,738,904,000	$ 5,746,863,000
Number of loans | loan		1
Balance Prior to TDR		$ 784,000
Financial impact on date of restructure		0
Number of loans for which payment default | loan			1
Charge-off of loans			$ 2,100,000
Financing receivable, collateral dependent, amount		32,849,000	46,444,000
Other commercial | Real Estate | Energy
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount		$ 0	40,703,000
Charge-offs			$ 32,600,000
Other commercial | Real Estate | Energy | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Moody's, S-2 Rating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Baseline economic forecast percentage		17.00%
Other commercial | Real Estate | Energy | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Moody's, S-3 Rating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Baseline economic forecast percentage		18.00%
Other commercial | Real Estate | Energy | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Internal Investment Grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Baseline economic forecast percentage		65.00%