Summary of Significant Accounting Policies - Additional Information (Details) shares in Thousands, $ in Thousands	1 Months Ended		12 Months Ended
	Aug. 31, 2017 shares	Jun. 30, 2015 shares	Dec. 31, 2020 USD ($) shareholder shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares
Summary Of Significant Accounting Policies [Line Items]
Reserve balance in cash or deposits			$ 896,100	$ 114,400
Forecast period			2 years
Historical loss experience period			1 year
OREO and other repossessed assets total			$ 5,100	9,400
Foreclosed residential real estate properties			1,000	2,100
Properties for which formal foreclosure proceedings are in process			$ 1,900	$ 2,800
Award vesting period			1 year
Vesting percentage			8.33%
Anti-dilutive common stock options and warrants (in shares) | shares			1,700	288	2,100
Allowance for loan losses			$ 340,243	$ 161,759	$ 151,859
Allowance for unfunded credit commitments			11,111	2,845
Held-to-maturity, allowance for credit loss			$ 1,428
Cumulative Effect, Period of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses				100,400
Allowance for loan losses				92,531
Allowance for unfunded credit commitments				7,100
Held-to-maturity, allowance for credit loss				793
PCD loan related reserves				61,600
Non-credit discount				97,700
Cumulative Effect, Period of Adoption, Adjustment | Non Purchased Credit Impaired Loans
Summary Of Significant Accounting Policies [Line Items]
Allowance for loan losses				$ 38,800
Noncumulative Preferred Stock
Summary Of Significant Accounting Policies [Line Items]
Common stock issued (in shares) | shares	4,000	4,600
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 Loan
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
Minimum
Summary Of Significant Accounting Policies [Line Items]
Number of shareholders needed to qualify as a REIT | shareholder			100
Premises and equipment, useful life			3 years
Minimum | Commitments under commercial loans and lines of credit
Summary Of Significant Accounting Policies [Line Items]
Number of days past due of loans to be full or partial charged-off			90 days
Maximum
Summary Of Significant Accounting Policies [Line Items]
Percentage of preferred stock issued by each REIT - less than			20.00%
Premises and equipment, useful life			40 years
Maximum | Commitments under commercial loans and lines of credit
Summary Of Significant Accounting Policies [Line Items]
Number of days past due of loans to be full or partial charged-off			120 days