Summary of Significant Accounting Policies - Additional Information (Detail) shares in Thousands		1 Months Ended		12 Months Ended
	Jan. 01, 2020 USD ($)	Aug. 31, 2017 shares	Jun. 30, 2015 shares	Dec. 31, 2019 USD ($) shareholder shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Jan. 01, 2019 USD ($)	Jan. 01, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of shareholders needed to qualify as a REIT | shareholder				100
Percentage of preferred stock issued by each REIT - less than				20.00%
Reserve balance in cash or deposits				$ 114,400,000	$ 120,700,000
Allowance for loan losses				161,759,000	151,859,000	$ 120,856,000
OREO and other repossessed assets total				9,400,000	9,500,000
Foreclosed residential real estate properties				2,100,000	852,000
Properties for which formal foreclosure proceedings are in process				$ 2,800,000	$ 1,800,000
Award vesting period				1 year
Anti-dilutive common stock options and warrants (in shares) | shares				288	2,100	3,100
Lease right of use assets				$ 285,129,000
Lease liabilities				309,849,000	$ 3,125,000
Loans				$ 29,699,208,000	25,035,469,000
Noncumulative Preferred Stock
Summary Of Significant Accounting Policies [Line Items]
Stock issued (in shares) | shares		4,000	4,600
Minimum
Summary Of Significant Accounting Policies [Line Items]
Premises and equipment, useful life				3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Premises and equipment, useful life				40 years
Commercial and industrial
Summary Of Significant Accounting Policies [Line Items]
Allowance for loan losses				$ 104,059,000	90,956,000	$ 57,232,000
Loans evaluated for impairment				250,000
Loans				4,825,997,000	4,331,032,000
PCI Loans
Summary Of Significant Accounting Policies [Line Items]
Allowance for loan losses				0	0
PCI Loans
Summary Of Significant Accounting Policies [Line Items]
Loans				6,629,599,000	4,190,086,000
PCI Loans | Commercial and industrial
Summary Of Significant Accounting Policies [Line Items]
Loans				$ 682,014,000	$ 740,657,000
ASU 2016-16
Summary Of Significant Accounting Policies [Line Items]
Reclassification due to the adoption of an ASU								$ (17,611,000)
ASU 2016-02
Summary Of Significant Accounting Policies [Line Items]
Lease right of use assets							$ 216,000,000
Lease liabilities							241,000,000
Reclassification due to the adoption of an ASU							4,414,000
ASU 2017-08
Summary Of Significant Accounting Policies [Line Items]
Reclassification due to the adoption of an ASU							(1,446,000)
ASU 2016-13 | Forecast | Minimum
Summary Of Significant Accounting Policies [Line Items]
Increase in allowance for credit losses	$ 30,000,000
ASU 2016-13 | Forecast | Maximum
Summary Of Significant Accounting Policies [Line Items]
Increase in allowance for credit losses	40,000,000
ASU 2016-13 | Forecast | PCI Loans | Minimum
Summary Of Significant Accounting Policies [Line Items]
Increase in allowance for credit losses	60,000,000
ASU 2016-13 | Forecast | PCI Loans | Maximum
Summary Of Significant Accounting Policies [Line Items]
Increase in allowance for credit losses	$ 65,000,000
Retained Earnings | ASU 2016-16
Summary Of Significant Accounting Policies [Line Items]
Reclassification due to the adoption of an ASU								$ (17,611,000)
Retained Earnings | ASU 2016-02
Summary Of Significant Accounting Policies [Line Items]
Reclassification due to the adoption of an ASU							4,414,000
Retained Earnings | ASU 2017-08
Summary Of Significant Accounting Policies [Line Items]
Reclassification due to the adoption of an ASU							$ (1,446,000)
Commitments under commercial loans and lines of credit | Minimum
Summary Of Significant Accounting Policies [Line Items]
Number of days past due of loans to be full or partial charged-off				90 days
Commitments under commercial loans and lines of credit | Maximum
Summary Of Significant Accounting Policies [Line Items]
Number of days past due of loans to be full or partial charged-off				120 days
Residential mortgage and home equity
Summary Of Significant Accounting Policies [Line Items]
Number of days past due of loans to be full or partial charged-off				120 days
Automobile
Summary Of Significant Accounting Policies [Line Items]
Number of days past due of loans to be fully charged-off				120 days
Unsecured loans at banks
Summary Of Significant Accounting Policies [Line Items]
Number of days past due of loans to be fully charged-off				150 days