Western Alliance Bancorporation (WAL) 10-Q 30 Apr 21 2021 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 26, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-32550
Entity Registrant Name	WESTERN ALLIANCE BANCORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	88-0365922
Entity Address, Address Line One	One E. Washington Street, Suite 1400
Entity Address, City or Town	Phoenix
Entity Address, State or Province	AZ
Entity Address, Postal Zip Code	85004
City Area Code	602
Local Phone Number	389-3500
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		103,474,792
Entity Central Index Key	0001212545
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Common Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, $0.0001 Par Value
Trading Symbol	WAL
Security Exchange Name	NYSE
Subordinated Debt [Member]
Entity Information [Line Items]
Title of 12(b) Security	6.25% Subordinated Debentures due 2056
Trading Symbol	WALA
Security Exchange Name	NYSE

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021		Dec. 31, 2020
Assets:
Cash and due from banks	$ 215.3		$ 174.2
Interest-bearing deposits in other financial institutions	5,131.2		2,497.5
Cash, cash equivalents and restricted cash	5,346.5		2,671.7
Available-for-sale Securities	6,939.9	[1]	4,708.5	[2]
Debt Securities, Held-to-maturity	698		568.8
Debt Securities, Held-to-maturity, Allowance for Credit Loss	(9.2)		(6.8)
Investment securities - equity	192.9	[1]	167.3	[2]
Investments in restricted stock, at cost	67.2		67
Loans:
Loans and Leases Receivable, Net of Deferred Income	28,711		27,053
Less: Allowance for credit losses	(247.1)		(278.9)
Net loans held for investment	28,463.9		26,774.1
Premises and equipment, net	138.4		134.1
Operating Lease, Right-of-Use Asset	77		72.5
Bank owned life insurance	177.3		176.3
Goodwill and intangible assets, net	298		298.5
Deferred Income Tax Assets, Net	49.8		31.3
Investments in LIHTC and renewable energy	487.9		405.6
Other assets	469.4		392.1
Total assets	43,397		36,461
Deposits:
Non-interest-bearing demand	17,542.8		13,463.3
Interest-bearing	20,850.3		18,467.2
Total deposits	38,393.1		31,930.5
Customer repurchase agreements	15.9		16
Other borrowings	5		5
Qualifying debt	543.7		548.7
Operating Lease, Liability	84.6		79.9
Other liabilities	642		467.4
Total liabilities	39,684.3		33,047.5
Commitments and Contingencies
Common Stock, Shares, Issued	105,771,103		103,013,290
Common stock, shares authorized	200,000,000		200,000,000
Stockholders’ equity:
Common Stock, Value, Issued	$ 1,608.2		$ 1,390.9
Treasury Stock, Shares	2,323,560		2,169,397
Treasury Stock, Value	$ (84)		$ (71.1)
Accumulated other comprehensive income	19.9		92.3
Retained earnings	2,168.6		2,001.4
Total stockholders’ equity	3,712.7		3,413.5
Total liabilities and stockholders’ equity	43,397		$ 36,461
Dividends, Common Stock, Cash	$ (25.3)
[1]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.
[2]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Amortized Cost	$ 6,913.3	$ 4,586.4
Debt Securities, Held-to-maturity, Fair Value	$ 740.4	$ 611.8
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	105,771,103	103,013,290
Treasury Stock, Value	$ 84	$ 71.1

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest income:
Loans, including fees	$ 298.4	$ 276.9
Investment securities	32.8	26.3
Dividends and other	2.9	4
Total interest income	334.1	307.2
Interest expense:
Deposits	10.8	32.5
Qualifying debt	5.9	5.3
Other short-term borrowings	0.1	0.4
Total interest expense	16.8	38.2
Net interest income	317.3	269
(Recovery of) provision for credit losses	(32.4)	51.2
Net interest income after (recovery of) provision for credit losses	349.7	217.8
Non-interest income:
Service charges and fees	6.7	6.4
Card Income	1.6	1.7
Foreign currency income	2.2	1.3
Income from bank owned life insurance	1	1
Income from equity instruments	7.6	3.8
Lending related income and gains (losses) on sale of loans, net	(0.1)	0.6
Unrealized gains (losses) on assets measured at fair value, net	(1.5)	(11.3)
Other income	2.2	1.6
Total non-interest income	19.7	5.1
Non-interest expense:
Salaries and employee benefits	83.7	72.1
Legal, professional, and directors' fees	10.1	10.4
Occupancy	8.6	8.2
Data processing	9.9	8.6
Deposit costs	6.3	7.3
Insurance	4.2	3
Loan and repossessed asset expenses	2.2	1.5
Business development	0.8	2.3
Marketing	0.6	0.9
Card expense	0.6	0.7
Intangible amortization	0.5	0.4
Net gain on sales / valuations of repossessed and other assets	(0.3)	(1.4)
Business Combination, Acquisition Related Costs	0.4	0
Other expense	7.4	6.5
Total non-interest expense	135	120.5
Income before provision for income taxes	234.4	102.4
Income Tax Expense (Benefit)	41.9	18.5
Net income	$ 192.5	$ 83.9
Earnings per share:
Basic	$ 1.91	$ 0.83
Diluted	$ 1.90	$ 0.83
Weighted average number of common shares outstanding:
Basic	100,800	101,300
Diluted	101,400	101,700

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 192.5	$ 83.9
Other comprehensive (loss) income, net:
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	(72)	6.3
Unrealized (loss) gain on AFS securities, net of tax effect of $23.5 and $(2.0), respectively	23.5	(2)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0	(0.3)
Unrealized (loss) on SERP, net of tax effect of $0.0 and $0.1, respectively	0	0.1
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax	(0.3)	(6.6)
Unrealized (loss) gain on junior subordinated debt, net of tax effect of $0.1 and $(2.1), respectively	(0.1)	(2.1)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(0.1)	(0.1)
Realized (gain) on sale of AFS securities included in income, net of tax effect of $0.0 and $0.0, respectively	0	0
Net other comprehensive (loss) income	(72.4)	12.5
Comprehensive income	$ 120.1	$ 96.4

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions		Total	Common Stock [Member]	Additional Paid in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Beginning balance, shares at Dec. 31, 2019			102,500,000
Beginning balance at Dec. 31, 2019		$ 3,016.7	$ 0	$ 1,374.1	$ 62.7	$ 25	$ 1,680.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		83.9					83.9
Restricted stock grants, net, shares			(500,000)
Restricted stock grants, net		7		7
Treasury Stock, Shares, Acquired	[1]		100,000
Treasury Stock, Value, Acquired, Cost Method	[1]	$ 7.5			7.5
Stock Repurchased and Retired During Period, Shares		(1,769,479)	(1,800,000)
Stock Repurchased and Retired During Period, Value		$ (62.5)		(10.6)			(51.9)
Dividends, Common Stock, Cash		(25.6)					(25.6)
Other comprehensive (loss) income, net		12.5				12.5
Ending balance, shares at Mar. 31, 2020			101,100,000
Ending Balance at Mar. 31, 2020		2,999.6	$ 0	1,370.5	70.2	37.5	1,661.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings		2,001.4
Beginning balance, shares at Dec. 31, 2020			100,800,000
Beginning balance at Dec. 31, 2020		3,413.5	$ 0	1,390.9	71.1	92.3	2,001.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		192.5					192.5
Restricted stock grants, net, shares			500,000
Restricted stock grants, net		8.1		8.1
Treasury Stock, Shares, Acquired	[1]		200,000
Treasury Stock, Value, Acquired, Cost Method	[1]	12.9			12.9
Stock Issued During Period, Value, New Issues		$ (209.2)		209.2
Stock Issued During Period, Shares, New Issues		2,300,000	(2,300,000)
Dividends, Common Stock, Cash		$ (25.3)					(25.3)
Other comprehensive (loss) income, net		(72.4)				(72.4)
Ending balance, shares at Mar. 31, 2021			103,400,000
Ending Balance at Mar. 31, 2021		3,712.7	$ 0	$ 1,608.2	$ 84	$ 19.9	$ 2,168.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained earnings		$ 2,168.6
[1]	Share amounts represent Treasury Shares, see "Note 1. Summary of Significant Accounting Policies" for further discussion.

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income	$ 192.5	$ 83.9
Adjustments to reconcile net income to cash provided by operating activities:
(Recovery of) provision for credit losses	(32.4)	51.2
Depreciation and amortization	6	5.4
Stock-based compensation	8	6.9
Deferred income taxes	5.1	(4.8)
Amortization of net premiums for investment securities	10.7	5.6
Amortization of tax credit investments	15.5	7.4
Amortization of operating lease right of use asset	3	2.8
Amortization of net deferred loan fees and net purchase premiums	(19.2)	(4.1)
Income from bank owned life insurance	(1)	(1)
(Gain) Loss on Sale and Valuation of Investment Securities and Other Assets, Net	(1.1)	(9.7)
Net (gains) losses on:
Equity Securities, FV-NI, Unrealized Gain (Loss)	1.5	11.3
Sale of loans	(0.7)	0
Changes in other assets and liabilities, net	(89.9)	(39)
Net cash provided by operating activities	100.1	124
Investment securities - AFS
Purchases	(2,748.5)	(654.5)
Principal pay downs and maturities	493.6	264.6
Proceeds from sales	0	62.3
Debt Securities, Held-to-maturity [Abstract]
Purchases	131.6	24.2
Principal pay downs and maturities	0.7	1.3
Equity Securities, FV-NI, Gain (Loss) [Abstract]
Purchases	(28.3)	(7.5)
Redemptions	0.4	4.2
Purchase of investment tax credits	(22.6)	(37.4)
Purchase of other investments	1.7	2.1
Net increase in loans	(1,611.1)	(1,991.1)
Purchase of premises, equipment, and other assets, net	(10.4)	(11.5)
Net cash used in investing activities	(4,058.9)	(2,395.9)
Cash flows from financing activities:
Net increase in deposits	6,462.6	2,034.2
Net (decrease) increase in other borrowings	(0.1)	314.3
Cash paid for tax withholding on vested restricted stock and other	12.8	7.4
Common stock repurchases	0	62.5
Cash dividends paid on common stock	25.3	25.6
Proceeds from Issuance of Common Stock	209.2	0
Net cash provided by financing activities	6,633.6	2,253
Net increase (decrease) in cash, cash equivalents, and restricted cash	2,674.8	(18.9)
Cash, cash equivalents, and restricted cash at beginning of period	2,671.7	434.6
Cash, cash equivalents, and restricted cash at end of period	5,346.5	415.7
Cash paid during the period for:
Interest	15	46.3
Income Taxes Paid, Net	30.8	1.3
Proceeds from Sale of Equity securities, FV-NI	$ 0.6	$ 0

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Nature of operation WAL is a bank holding company headquartered in Phoenix, Arizona, incorporated under the laws of the state of Delaware. WAL provides a full spectrum of deposit, lending, treasury management, international banking, and online banking products and services through its wholly-owned banking subsidiary, WAB. WAB operates the following full-service banking divisions: ABA, BON, FIB, Bridge, and TPB. The Company also serves business customers through a national platform of specialized financial services. In addition, the Company has two non-bank subsidiaries, which are LVSP, which held and managed certain OREO properties, and CSI, a captive insurance company formed and licensed under the laws of the State of Arizona and established as part of the Company's overall enterprise risk management strategy. Basis of presentation The accounting and reporting policies of the Company are in accordance with GAAP and conform to practices within the financial services industry. The accounts of the Company and its consolidated subsidiaries are included in the Consolidated Financial Statements. Recent accounting pronouncements Convertible Debt and Derivatives and Hedging In August 2020, the FASB issued guidance within ASU 2020-06, Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity’s Own Equity (Subtopic 815-40) . The amendments in this update affect entities that issue convertible instruments and/or contracts indexed to and potentially settled in an entity’s own equity. The new ASU simplifies the convertible accounting framework through elimination of the beneficial conversion and cash conversion accounting models for convertible instruments. It also amends the accounting for certain contracts in an entity’s own equity that are currently accounted for as derivatives because of specific settlement provisions. In addition, the new guidance modifies how particular convertible instruments and certain contracts that may be settled in cash or shares impact the diluted EPS computation. The amendments to Subtopics 470 and 815 are effective for interim and annual reporting periods beginning after December 15, 2021 and are not expected to have a material impact on the Company’s Consolidated Financial Statements. Reference Rate Reform In March 2020, the FASB issued guidance within ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, in response to the scheduled discontinuation of LIBOR on December 31, 2021. Since the issuance of this guidance, the publication cessation of U.S. dollar LIBOR has been extended to June 30, 2023 . The amendments in this Update provide optional guidance designed to provide relief from the accounting analysis and impacts that may otherwise be required for modifications to agreements (e.g., loans, debt securities, derivatives, borrowings) necessitated by reference rate reform. The following optional expedients for applying the requirements of certain Topics or Industry Subtopics in the Codification are permitted for contracts that are modified because of reference rate reform and that meet certain scope guidance: 1) modifications of contracts within the scope of Topics 310, Receivables , and 470, Debt , should be accounted for by prospectively adjusting the effective interest rate; 2) modifications of contracts within the scope of Topic 842, Leases , should be accounted for as a continuation of the existing contracts with no reassessments of the lease classification and the discount rate or remeasurements of lease payments that otherwise would be required under this Topic for modifications not accounted for as separate contracts; 3) modifications of contracts do not require an entity to reassess its original conclusion about whether that contract contains an embedded derivative that is clearly and closely related to the economic characteristics and risks of the host contract under Subtopic 815-15, Derivatives and Hedging- Embedded Derivatives; and 4) for other Topics or Industry Subtopics in the Codification, the amendments in this Update also include a general principle that permits an entity to consider contract modifications due to reference rate reform to be an event that does not require contract remeasurement at the modification date or reassessment of a previous accounting determination. In January 2021, the FASB issued ASU 2021-01, Reference Rate Reform (Topic 848): Scope in order to clarify that certain optional expedients and exceptions in Topic 848 apply to derivatives that are affected by the discounting transition. Specifically, certain provisions in Topic 848, if elected by an entity, apply to derivative instruments that use an interest rate for margining, discount, or contract price alignment that is modified as a result of reference rate reform. The amendments in these Updates are effective immediately for all entities and apply to contract modifications through December 31, 2022. The adoption of this accounting guidance is not expected to have a material impact on the Company's Consolidated Financial Statements. Recently adopted accounting guidance Income Taxes In December 2019, the FASB issued guidance within ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in ASU 2019-12 are intended to reduce the cost and complexity of applying ASC 740. The amendments that are applicable to the Company address: 1) franchise and other taxes partially based on income; 2) step-up in basis of goodwill in a business combination; 3) allocation of tax expense in separate entity financial statements; and 4) interim recognition of enactment of tax laws or rate changes. The adoption of this guidance did not have a significant impact on the Company’s Consolidated Financial Statements. Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Management's estimates and judgments are ongoing and are based on experience, current and expected future conditions, third-party evaluations and various other assumptions that management believes are reasonable under the circumstances. The results of these estimates form the basis for making judgments about the carrying values of assets and liabilities, as well as identifying and assessing the accounting treatment with respect to commitments and contingencies. Actual results may differ from those estimates and assumptions used in the Consolidated Financial Statements and related notes. Material estimates that are susceptible to significant changes in the near term, particularly to the extent that economic conditions worsen or persist longer than expected in an adverse state, relate to: 1) the determination of the allowance for credit losses; 2) certain assets and liabilities carried at fair value; and 3) accounting for income taxes. Principles of consolidation As of March 31, 2021, WAL has the following significant wholly-owned subsidiaries: WAB and eight unconsolidated subsidiaries used as business trusts in connection with the issuance of trust-preferred securities. WAB has the following significant wholly-owned subsidiaries: WABT, which holds certain investment securities, municipal and nonprofit loans, and leases; 1) WA PWI, which holds interests in certain limited partnerships invested primarily in low income housing tax credits and small business investment corporations; 2) Helios Prime, which holds interests in certain limited partnerships invested in renewable energy projects; and 3) BW Real Estate, Inc., which operates as a real estate investment trust and holds certain of WAB's real estate loans and related securities. The Company does not have any other significant entities that should be consolidated. All significant intercompany balances and transactions have been eliminated in consolidation. Reclassifications Certain amounts reported in prior periods may have been reclassified in the Consolidated Financial Statements to conform to the current presentation. The reclassifications have no effect on net income or stockholders’ equity as previously reported. Interim financial information The accompanying Unaudited Consolidated Financial Statements as of and for the three months ended March 31, 2021 and 2020 have been prepared in condensed format and, therefore, do not include all of the information and footnotes required by GAAP for complete financial statements. These statements have been prepared on a basis that is substantially consistent with the accounting principles applied to the Company's audited Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2020. The information furnished in these interim statements reflects all adjustments that are, in the opinion of management, necessary for a fair statement of the results for each respective period presented. Such adjustments are of a normal, recurring nature. The results of operations in the interim statements are not necessarily indicative of the results that may be expected for any other quarter or for the full year. The interim financial information should be read in conjunction with the Company's audited Consolidated Financial Statements. Investment securities Investment securities include debt and equity securities. Debt securities may be classified as HTM, AFS, or trading. The appropriate classification is initially decided at the time of purchase. Securities classified as HTM are those debt securities that the Company has both the intent and ability to hold to maturity regardless of changes in market conditions, liquidity needs, or general economic conditions. The sale of an HTM security within three months of its maturity date or after the majority of the principal outstanding has been collected is considered a maturity for purposes of classification and disclosure. Securities classified as AFS are securities that the Company intends to hold for an indefinite period of time, but not necessarily to maturity. Any decision to sell a security classified as AFS would be based on various factors, including significant movements in interest rates, changes in the maturity mix of the Company’s assets and liabilities, liquidity needs, decline in credit quality, and regulatory capital considerations. HTM securities are carried at amortized cost. AFS securities are carried at their estimated fair value, with unrealized holding gains and losses reported in other comprehensive income, net of tax. When AFS debt securities are sold, the unrealized gains or losses are reclassified from OCI to non-interest income. Trading securities are carried at their estimated fair value, with changes in fair value reported in earnings as part of non-interest income. Equity securities are carried at their estimated fair value, with changes in fair value reported in earnings as part of non-interest income. Interest income is recognized based on the coupon rate and includes the amortization of purchase premiums and the accretion of purchase discounts. Premiums and discounts on investment securities are generally amortized or accreted over the contractual life of the security using the interest method. For the Company's mortgage-backed securities, amortization or accretion of premiums or discounts are adjusted for anticipated prepayments. Gains and losses on the sale of investment securities are recorded on the trade date and determined using the specific identification method. A debt security is placed on nonaccrual status at the time its principal or interest payments become 90 days past due. Interest accrued but not received for a security placed on nonaccrual is reversed against interest income. Allowance for credit losses on investment securities On January 1, 2020, the Company adopted the amendments within ASU 2016-13, which replaces the legacy US GAAP OTTI model with a credit loss model. The credit loss model under ASC 326-20, applicable to HTM debt securities, requires recognition of lifetime expected credit losses through an allowance account at the time the security is purchased. The Company measures expected credit losses on its HTM debt securities on a collective basis by major security type. The Company's HTM securities portfolio consists of low income housing tax-exempt bonds, which share similar risk characteristics with the Company's CRE, non-owner occupied or construction and land loan pools, given the similarity in underlying assets or collateral. Accordingly, expected credit losses on HTM securities are estimated using the same models and approaches as these loan pools, which utilize risk parameters (probability of default, loss given default, and exposure at default) in the measurement of expected credit losses. The historical data used to estimate probability of default and severity of loss in the event of default is derived or obtained from internal and external sources and adjusted for the expected effects of reasonable and supportable forecasts over the expected lives of the securities on those historical losses. Accrued interest receivable on the HTM securities, which is included in other assets on the Consolidated Balance Sheet, is excluded from the estimate of expected credit losses. The credit loss model under ASC 326-30, applicable to AFS debt securities, requires recognition of credit losses through an allowance account, but retains the concept from the OTTI model that credit losses are recognized once securities become impaired. For AFS debt securities, a decline in fair value due to credit loss results in recognition of an allowance for credit losses. Impairment may result from credit deterioration of the issuer or collateral underlying the security. The assessment of determining if a decline in fair value resulted from a credit loss is performed at the individual security level. Among other factors, the Company considers: 1) the extent to which the fair value is less than the amortized cost basis; 2) the financial condition and near term prospects of the issuer, including consideration of relevant financial metrics or ratios of the issuer; 3) any adverse conditions related to an industry or geographic area of an issuer; 4) any changes to the rating of the security by a rating agency; and 5) any past due principal or interest payments from the issuer. If an assessment of the above factors indicates that a credit loss exists, the Company records an allowance for credit losses for the excess of the amortized cost basis over the present value of cash flows expected to be collected, limited to the amount that the security's fair value is less than its amortized cost basis. Subsequent changes in the allowance for credit losses are recorded as a provision for (or reversal of) credit loss expense. Interest accruals and amortization and accretion of premiums and discounts are suspended when the credit loss is recognized in earnings. Any interest received after the security has been placed on nonaccrual status is recognized on a cash basis. Accrued interest receivable on AFS securities, which is included in other assets on the Consolidated Balance Sheet, is excluded from the estimate of expected credit losses. For each AFS security in an unrealized loss position, the Company also considers: 1) its intent to retain the security until anticipated recovery of the security's fair value; and 2) whether it is more-likely-than not that the Company would be required to sell the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the debt security is written down to its fair value and the write-down is charged against the allowance for credit losses with any incremental impairment recorded in earnings. Write-offs are made through reversal of the allowance for credit losses and direct write-off of the amortized cost basis of the AFS security. The Company considers the following events to be indicators that a write-off should be taken: 1) bankruptcy of the issuer; 2) significant adverse event(s) affecting the issuer in which it is improbable for the issuer to make its remaining payments on the security; and 3) significant loss of value of the underlying collateral behind a security. Recoveries on debt securities, if any, are recorded in the period received. Restricted stock WAB is a member of the Federal Reserve System and, as part of its membership, is required to maintain stock in the FRB in a specified ratio to its capital. In addition, WAB is a member of the FHLB system and, accordingly, maintains an investment in capital stock of the FHLB based on the borrowing capacity used. These investments are considered equity securities with no actively traded market. Therefore, the shares are considered restricted investment securities. These investments are carried at cost, which is equal to the value at which they may be redeemed. The dividend income received from the stock is reported in interest income. The Company conducts a periodic review and evaluation of its restricted stock to determine if any impairment exists. No impairment has been recorded to date. Loans held for investment Loans that management has the intent and ability to hold for the foreseeable future or until maturity or payoff are reported at amortized cost. Amortized cost is the amount of unpaid principal, adjusted for unamortized net deferred fees and costs, premiums and discounts, and write-offs. In addition, the amortized cost of loans subject to a fair value hedge are adjusted for changes in value attributable to the effective portion of the hedged benchmark interest rate risk. The Company may also purchase loans or acquire loans through a business combination. At the purchase or acquisition date, loans are evaluated to determine if there has been more than insignificant credit deterioration since origination. Loans that have experienced more than insignificant credit deterioration since origination are referred to as PCD loans. In its evaluation of whether a loan has experienced more than insignificant deterioration in credit quality since origination, the Company takes into consideration loan grades, loan-to-values greater than policy limits, past due and nonaccrual status, and TDR loans. The Company may also consider external credit rating agency ratings for borrowers and for non-commercial loans, FICO score or band, probability of default levels, number of times past due, and standard deviations corresponding to FICO score or band. The initial estimate of credit losses on PCD loans is added to the purchase price on the acquisition date to establish the initial amortized cost basis of the loan; accordingly, the initial recognition of expected credit losses has no impact on net income. When the initial measurement of expected credit losses on PCD loans are calculated on a pooled loan basis, the expected credit losses are allocated to each loan within the pool. Any difference between the initial amortized cost basis and the unpaid principal balance of the loan represents a noncredit discount or premium, which is accreted (or amortized) into interest income over the life of the loan. Subsequent changes to the allowance for credit losses on PCD loans are recorded through the provision for credit losses. For purchased loans that are not deemed to have experienced more than insignificant credit deterioration since origination, any discounts or premiums included in the purchase price are accreted (or amortized) over the contractual life of the individual loan. For additional information, see "Note 3. Loans, Leases and Allowance for Credit Losses" of these Notes to Unaudited Consolidated Financial Statements. In applying the effective yield method to loans, the Company generally applies the contractual method whereby loan fees collected for the origination of loans less direct loan origination costs (net of deferred loan fees), as well as premiums and discounts and certain purchase accounting adjustments, are amortized over the contractual life of the loan through interest income. If a loan has scheduled payments, the amortization of the net deferred loan fee is calculated using the interest method over the contractual life of the loan. If a loan does not have scheduled payments, such as a line of credit, the net deferred loan fee is recognized as interest income on a straight-line basis over the contractual life of the loan commitment. Commitment fees based on a percentage of a customer’s unused line of credit and fees related to standby letters of credit are recognized over the commitment period. When loans are repaid, any remaining unamortized balances of premiums, discounts, or net deferred fees are recognized as interest income. Conversely, with respect to loans originated under the PPP, the Company incorporates projected prepayments in calculating effective yield. As a result, net deferred fees are accreted into interest income faster than would be the case when applying the contractual method based upon the timing and amount of estimated forgiven loan balances. The Company expects that a majority of PPP loans will qualify for forgiveness under the SBA program, based on requested loan amounts largely representing qualifying expenses at the time of application. Nonaccrual loans When a borrower discontinues making payments as contractually required by the note, the Company must determine whether it is appropriate to continue to accrue interest. The Company ceases accruing interest income when the loan has become delinquent by more than 90 days or when management determines that the full repayment of principal and collection of interest according to contractual terms is no longer likely. Past due status is based on the contractual terms of the loan. The Company may decide to continue to accrue interest on certain loans more than 90 days delinquent if the loans are well secured by collateral and in the process of collection. For all loan types, when a loan is placed on nonaccrual status, all interest accrued but uncollected is reversed against interest income in the period in which the status is changed, and the Company makes a loan-level decision to apply either the cash basis or cost recovery method. The Company may recognize income on a cash basis when a payment is received and only for those nonaccrual loans for which the collection of the remaining principal balance is not in doubt. Under the cost recovery method, subsequent payments received from the customer are applied to principal and generally no further interest income is recognized until the principal has been paid in full or until circumstances have changed such that payments are again consistently received as contractually required. Loans are returned to accrual status when all of the principal and interest amounts contractually due are brought current and future payments are reasonably assured. Troubled Debt Restructured Loans A TDR loan is a loan on which the Company, for reasons related to a borrower’s financial difficulties, grants a concession to the borrower that the Company would not otherwise consider. In order to determine whether a borrower is experiencing financial difficulty, an evaluation is performed of the probability that the borrower will be in payment default on any of its debt in the foreseeable future without the modification. The evaluation is performed under the Company's internal underwriting policy. The loan terms that may be modified or restructured due to a borrower’s financial situation include, but are not limited to, a reduction in the stated interest rate, an extension of the maturity or renewal of the loan at an interest rate below current market, a reduction in the face amount of the debt, a reduction in the accrued interest, or deferral of interest payments. A TDR loan may be returned to accrual status when the loan is brought current, has performed in accordance with the contractual restructured terms for a reasonable period of time (generally six months), and the ultimate collectability of the total contractual restructured principal and interest is no longer in doubt. Consistent with regulatory guidance, a TDR loan that is subsequently modified in another restructuring agreement but has shown sustained performance and classification as a TDR, will be removed from TDR status provided that the modified terms were market-based at the time of modification. The CARES Act, signed into law on March 27, 2020, permitted financial institutions to suspend requirements under GAAP for loan modifications to borrowers affected by COVID-19 that would otherwise be characterized as TDRs and suspend any determination related thereto if (i) the loan modification was made between March 1, 2020 and December 31, 2020 and (ii) the applicable loan was not more than 30 days past due as of December 31, 2019. The Consolidated Appropriations Act, 2021, signed into law on December 27, 2020, extends these provisions through January 1, 2022. In addition, federal bank regulatory authorities issued guidance to encourage financial institutions to make loan modifications for borrowers affected by COVID-19 and assured financial institutions that they will neither receive supervisory criticism for such prudent loan modifications, nor be required by examiners to automatically categorize COVID-19-related loan modifications as TDRs. The Company is applying this guidance to qualifying loan modifications. Credit quality indicators Loans are regularly reviewed to assess credit quality indicators and to determine appropriate loan classification and grading in accordance with applicable bank regulations. The Company’s risk rating methodology assigns risk ratings ranging from 1 to 9, where a higher rating represents higher risk. The Company differentiates its loan segments based on shared risk characteristics for which expected credit loss is measured on a pool basis. The nine risk rating categories can be generally described by the following groupings for loans: "Pass" (grades 1 through 5): The Company has five pass risk ratings, which represent a level of credit quality that ranges from no well-defined deficiency or weakness to some noted weakness; however, the risk of default on any loan classified as pass is expected to be remote. The five pass risk ratings are described below: Minimal risk. These consist of loans that are fully secured either with cash held in a deposit account at the Bank or by readily marketable securities with an acceptable margin based on the type of security pledged. Low risk. These consist of loans with a high investment grade rating equivalent. Modest risk. These consist of loans where the credit facility greatly exceeds all policy requirements or with policy exceptions that are appropriately mitigated. A secondary source of repayment is verified and considered sustainable. Collateral coverage on these loans is sufficient to fully cover the debt as a tertiary source of repayment. Debt of the borrower is low relative to borrower’s financial strength and ability to pay. Average risk. These consist of loans where the credit facility meets or exceeds all policy requirements or with policy exceptions that are appropriately mitigated. A secondary source of repayment is available to service the debt. Collateral coverage is more than adequate to cover the debt. The borrower exhibits acceptable cash flow and moderate leverage. Acceptable risk. These consist of loans with an acceptable primary source of repayment, but a less than preferable secondary source of repayment. Cash flow is adequate to service debt, but there is minimal excess cash flow. Leverage is moderate or high. "Special mention" (grade 6): Generally these are assets that possess potential weaknesses that warrant management's close attention. These loans may involve borrowers with adverse financial trends, higher debt-to-equity ratios, or weaker liquidity positions, but not to the degree of being considered a “problem loan” where risk of loss may be apparent. Loans in this category are usually performing as agreed, although there may be non-compliance with financial covenants. "Substandard" (grade 7): These assets are characterized by well-defined credit weaknesses and carry the distinct possibility that the Company will sustain some loss if such weakness or deficiency is not corrected. All loans 90 days or more past due and all loans on nonaccrual status are considered at least "Substandard," unless extraordinary circumstances would suggest otherwise. "Doubtful" (grade 8): These assets have all the weaknesses inherent in those classified as "Substandard" with the added characteristic that the weaknesses present make collection or liquidation in full, on the basis of currently existing facts, conditions and values, highly questionable and improbable, but because of certain known factors that may work to the advantage and strengthening of the asset (for example, capital injection, perfecting liens on additional collateral and refinancing plans), classification as an estimated loss is deferred until a more precise status may be determined. Due to the high probability of loss, loans classified as "Doubtful" are placed on nonaccrual status. "Loss" (grade 9): These assets are considered uncollectible and having such little recoverable value that it is not practical to defer writing off the asset. This classification does not mean that the loan has absolutely no recovery or salvage value, but rather that it is not practicable or desirable to defer writing off the asset, even though partial recovery may be achieved in the future. Allowance for credit losses on loans On January 1, 2020, the Company adopted the amendments within ASU 2016-13, Measurement of Credit Losses on Financial Instruments , which changes the impairment model for most financial assets carried at amortized cost from an incurred loss model to an expected loss model. The discussion below reflects the current expected credit loss model methodology. Credit risk is inherent in the business of extending loans and leases to borrowers and is continuously monitored by management and reflected within the allowance for credit losses for loans. The allowance for credit losses is an estimate of life-of-loan losses for the Company's loans held for investment. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of a loan to present the net amount expected to be collected on the loan. Accrued interest receivable on loans, which is included in other assets on the Consolidated Balance Sheet, is excluded from the estimate of expected credit losses. Expected recoveries of amounts previously written off and expected to be written off are included in the valuation account and may not exceed the aggregate of amounts previously written off and expected to be written off. The Company formally re-evaluates and establishes the appropriate level of the allowance for credit losses on a quarterly basis. Determining the appropriateness of the allowance is complex and requires judgment by management about the effect of matters that are inherently uncertain. In future periods, evaluations of the overall loan portfolio or particular segments of the loan portfolio, in light of the factors and forecasts then prevailing, may result in significant changes in the allowance for credit losses and credit loss expense in those future periods. The allowance level is influenced by loan volumes, mix, loan performance metrics, asset quality characteristics, delinquency status, historical credit loss experience, and the inputs and assumptions in economic forecasts, such as macroeconomic inputs, length of reasonable and supportable forecast periods, and reversion methods. The methodology for estimating the amount of expected credit losses reported in the allowance for credit losses has two basic components: first, an asset-specific component involving individual loans that do not share risk characteristics with other loans and the measurement of expected credit losses for such individual loans and; second, a pooled component for estimated expected credit losses for pools of loans that share similar risk characteristics. Loans that do not share risk characteristics with other loans Loans that do not share risk characteristics with other loans are evalua

Investment Securities

Investment Securities	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Investment Securities	d fair values of investment securities at March 31, 2021 and December 31, 2020 are summarized as follows: March 31, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized (Losses) Fair Value (in millions) Held-to-maturity Tax-exempt $ 698.0 $ 43.8 $ (1.4) $ 740.4 Available-for-sale debt securities CLO $ 980.3 $ 0.8 $ (0.4) $ 980.7 Commercial MBS issued by GSEs 88.0 1.6 (1.8) 87.8 Corporate debt securities 286.0 5.0 (5.9) 285.1 Private label residential MBS 1,905.7 9.8 (14.9) 1,900.6 Residential MBS issued by GSEs 2,277.8 18.5 (46.7) 2,249.6 Tax-exempt 1,271.4 62.0 (3.7) 1,329.7 U.S. treasury securities 50.0 — — 50.0 Other 54.1 7.4 (5.1) 56.4 Total AFS debt securities $ 6,913.3 $ 105.1 $ (78.5) $ 6,939.9 Equity securities CRA investments $ 57.6 $ — $ (0.2) $ 57.4 Preferred stock 129.5 6.2 (0.2) 135.5 Total equity securities $ 187.1 $ 6.2 $ (0.4) $ 192.9 December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized (Losses) Fair Value (in millions) Held-to-maturity Tax-exempt $ 568.8 $ 43.0 $ — $ 611.8 Available-for-sale debt securities CLO $ 146.9 $ — $ — $ 146.9 Commercial MBS issued by GSEs 80.8 3.8 — 84.6 Corporate debt securities 271.1 4.8 (5.7) 270.2 Private label residential MBS 1,461.7 15.7 (0.5) 1,476.9 Residential MBS issued by GSEs 1,462.5 27.9 (3.8) 1,486.6 Tax-exempt 1,109.3 78.1 — 1,187.4 Other 54.1 7.3 (5.5) 55.9 Total AFS debt securities $ 4,586.4 $ 137.6 $ (15.5) $ 4,708.5 Equity securities CRA investments $ 53.1 $ 0.3 $ — $ 53.4 Preferred stock 107.0 7.3 (0.4) 113.9 Total equity securities $ 160.1 $ 7.6 $ (0.4) $ 167.3 Securities with carrying amounts of approximately $693.2 million and $778.0 million at March 31, 2021 and December 31, 2020, respectively, were pledged for various purposes as required or permitted by law. The following tables summarize the Company's AFS debt securities in an unrealized loss position at March 31, 2021 and December 31, 2020, aggregated by major security type and length of time in a continuous unrealized loss position: March 31, 2021 Less Than Twelve Months More Than Twelve Months Total Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (in millions) Held-to-maturity Tax-exempt $ 1.4 $ 48.0 $ — $ — $ 1.4 $ 48.0 Available-for-sale debt securities CLO $ 0.4 $ 638.6 $ — $ — $ 0.4 $ 638.6 Commercial MBS issued by GSEs 1.8 48.0 — — 1.8 48.0 Corporate debt securities 0.2 32.0 5.7 94.3 5.9 126.3 Private label residential MBS 14.5 810.2 0.4 9.6 14.9 819.8 Residential MBS issued by GSEs 46.7 1,225.7 — — 46.7 1,225.7 Tax-exempt 3.7 158.0 — — 3.7 158.0 Other 0.4 11.6 4.7 27.3 5.1 38.9 Total AFS securities $ 67.7 $ 2,924.1 $ 10.8 $ 131.2 $ 78.5 $ 3,055.3 December 31, 2020 Less Than Twelve Months More Than Twelve Months Total Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (in millions) Available-for-sale debt securities Corporate debt securities $ 0.1 $ 17.3 $ 5.6 $ 94.3 $ 5.7 $ 111.6 Private label residential MBS 0.5 149.7 — — 0.5 149.7 Residential MBS issued by GSEs 3.8 231.9 — — 3.8 231.9 Other — — 5.5 26.5 5.5 26.5 Total AFS securities $ 4.4 $ 398.9 $ 11.1 $ 120.8 $ 15.5 $ 519.7 The total number of AFS securities in an unrealized loss position at March 31, 2021 is 187, compared to 49 at December 31, 2020. On a quarterly basis, the Company performs an impairment analysis on its AFS debt securities that are in an unrealized loss position at the end of the period to determine whether credit losses should be recognized on these securities. Qualitative considerations made by the Company in its impairment analysis are further discussed below. Government Issued Securities Residential MBS issued by GSEs held by the Company are issued by U.S. government entities and agencies. These securities are either explicitly or implicitly guaranteed by the U.S. government, are highly rated by major rating agencies, and have a long history of no credit losses. Further, principal and interest payments on these securities continue to be made on a timely basis. Non-Government Issued Securities Qualitative factors used in the Company's credit loss assessment of its securities that are not issued and guaranteed by the U.S. government include consideration of any adverse conditions related to a specific security, industry, or geographic region of its securities, any credit ratings below investment grade, the payment structure of the security and the likelihood of the issuer to be able to make payments that increase in the future, and failure of the issuer to make any scheduled principal or interest payments. For the Company's corporate debt and tax-exempt securities, the Company also considers various metrics of the issuer including days of cash on hand, the ratio of long-term debt to total assets, the net change in cash between reporting periods, and consideration of any breach in covenant requirements. The Company's corporate debt securities continue to be highly rated, issuers continue to make timely principal and interest payments, and the unrealized losses on these security portfolios primarily relate to changes in interest rates and other market conditions that are not considered to be credit-related issues. The Company continues to receive timely principal and interest payments on its tax-exempt securities and the majority of these issuers have revenues pledged for payment of debt service prior to payment of other types of expenses. For the Company's private label residential MBS, which consist of non-agency collateralized mortgage obligations that are secured by pools of residential mortgage loans, the Company also considers metrics such as securitization risk weight factor, current credit support, whether there were any mortgage principal losses resulting from defaults in payments on the underlying mortgage collateral, and the credit default rate over the last twelve months. These securities primarily carry investment grade credit ratings, principal and interest payments on these securities continue to be made on a timely basis, and credit support for these securities is considered adequate. The Company's CLO portfolio consists of highly rated securitization tranches, containing pools of medium to large-sized corporate, high yield bank loans. These are floating rate securities that have an investment grade rating of Single-A or better. The Company has been increasing its investment in these securities over the past several months and unrealized losses on these securities is primarily a function of the differential from the offer price and the valuation mid-market price. Unrealized losses on the Company's Other securities portfolio relate to taxable municipal and trust preferred securities. The Company is continuing to receive timely principal and interest payments on its taxable municipal securities, these securities continue to be highly rated and the number of days of cash on hand is strong. The Company's trust preferred securities are investment grade and the issuers continue to make timely principal and interest payments. Based on the qualitative factors noted above and as the Company does not intend to sell these securities and it is more likely than not that the Company will not be required to sell the securities prior to their anticipated recovery, no credit losses have been recognized on these securities during the three months ended March 31, 2021 and 2020. In addition, as of March 31, 2021 and December 31, 2020, no allowance for credit losses on the Company's AFS securities has been recognized. The credit loss model under ASC 326-20, applicable to HTM debt securities, requires recognition of lifetime expected credit losses through an allowance account at the time the security is purchased. The following table presents a rollforward by major security type of the allowance for credit losses on the Company's HTM debt securities: Three Months Ended March 31, 2021 Balance, Provision for Credit Losses Write-offs Recoveries Balance, (in millions) Held-to-maturity debt securities Tax-exempt $ 6.8 $ 2.4 $ — $ — $ 9.2 Three Months Ended March 31, 2020: Balance, Provision for Credit Losses Write-offs Recoveries Balance (in millions) Held-to-maturity debt securities Tax-exempt $ 2.6 $ 0.3 $ — $ — $ 2.9 Accrued interest receivable on HTM securities totaled $2.4 million and $2.0 million at March 31, 2021 and December 31, 2020, respectively, and is excluded from the estimate of credit losses. The following tables summarize the carrying amount of the Company’s investment ratings position as of March 31, 2021 and December 31, 2020, which are updated quarterly and used to monitor the credit quality of the Company's securities: March 31, 2021 AAA Split-rated AAA/AA+ AA+ to AA- A+ to A- BBB+ to BBB- BB+ and below Unrated Totals (in millions) Held-to-maturity Tax-exempt $ — $ — $ — $ — $ — $ — $ 698.0 $ 698.0 Available-for-sale debt securities CLO $ 25.0 $ — $ 649.8 $ 305.9 $ — $ — $ — $ 980.7 Commercial MBS issued by GSEs — 87.8 — — — — — 87.8 Corporate debt securities — — 19.2 28.1 219.6 18.2 — 285.1 Private label residential MBS 1,812.8 — 86.5 0.1 0.3 0.9 — 1,900.6 Residential MBS issued by GSEs — 2,249.6 — — — — — 2,249.6 Tax-exempt 43.2 56.5 519.1 679.1 — — 31.8 1,329.7 U.S. treasury securities 50.0 — — — — — — 50.0 Other — — 11.6 — 29.8 6.9 8.1 56.4 Total AFS securities (1) $ 1,931.0 $ 2,393.9 $ 1,286.2 $ 1,013.2 $ 249.7 $ 26.0 $ 39.9 $ 6,939.9 Equity securities CRA investments $ — $ 27.4 $ — $ — $ — $ — $ 30.0 $ 57.4 Preferred stock — — — — 81.3 39.1 15.1 135.5 Total equity securities (1) $ — $ 27.4 $ — $ — $ 81.3 $ 39.1 $ 45.1 $ 192.9 (1) Where ratings differ, the Company uses an average of the available ratings by major credit agencies. December 31, 2020 AAA Split-rated AAA/AA+ AA+ to AA- A+ to A- BBB+ to BBB- BB+ and below Unrated Totals (in millions) Held-to-maturity Tax-exempt $ — $ — $ — $ — $ — $ — $ 568.8 $ 568.8 Available-for-sale debt securities CLO $ — $ — $ 139.6 $ 7.3 $ — $ — $ — $ 146.9 Commercial MBS issued by GSEs — 84.6 — — — — — 84.6 Corporate debt securities — — 19.2 28.1 194.5 28.4 — 270.2 Private label residential MBS 1,385.5 — 90.1 0.1 0.3 0.9 — 1,476.9 Residential MBS issued by GSEs — 1,486.6 — — — — — 1,486.6 Tax-exempt 44.3 57.3 454.7 599.3 — — 31.8 1,187.4 Other — — 12.3 — 29.1 6.9 7.6 55.9 Total AFS securities (1) $ 1,429.8 $ 1,628.5 $ 715.9 $ 634.8 $ 223.9 $ 36.2 $ 39.4 $ 4,708.5 Equity securities CRA investments $ — $ 27.8 $ — $ — $ — $ — $ 25.6 $ 53.4 Preferred stock — — — — 73.2 39.0 1.7 113.9 Total equity securities (1) $ — $ 27.8 $ — $ — $ 73.2 $ 39.0 $ 27.3 $ 167.3 (1) Where ratings differ, the Company uses an average of the available ratings by major credit agencies. A security is considered to be past due once it is 30 days contractually past due under the terms of the agreement. As of March 31, 2021, there were no investment securities that were past due. In addition, the Company does not have a significant amount of investment securities on nonaccrual status as of March 31, 2021. The amortized cost and fair value of the Company's debt securities as of March 31, 2021, by contractual maturities, are shown below. MBS are shown separately as individual MBS are comprised of pools of loans with varying maturities. Therefore, these securities are listed separately in the maturity summary. March 31, 2021 Amortized Cost Estimated Fair Value (in millions) Held-to-maturity Due in one year or less $ 10.7 $ 10.7 After one year through five years 31.3 31.8 After ten years 656.0 697.9 Total HTM securities $ 698.0 $ 740.4 Available-for-sale Due in one year or less $ 50.0 $ 50.0 After one year through five years 38.0 38.5 After five years through ten years 780.5 780.8 After ten years 1,773.3 1,832.6 Mortgage-backed securities 4,271.5 4,238.0 Total AFS securities $ 6,913.3 $ 6,939.9 During the three months ended March 31, 2021 and 2020, the Company did not have significant sales of investments securities.

Other Borrowings

Other Borrowings	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Other Borrowings	The following table summarizes the Company’s borrowings as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 (in millions) Short-Term: Federal funds purchased $ — $ — FHLB advances 5.0 5.0 Total short-term borrowings $ 5.0 $ 5.0 The Company maintains federal fund lines of credit totaling $2.5 billion as of March 31, 2021, which have rates comparable to the federal funds effective rate plus 0.10% to 0.20%. As of March 31, 2021 and December 31, 2020, there were no outstanding balances on the Company's federal fund lines of credit. The Company also maintains secured lines of credit with the FHLB and the FRB. The Company’s borrowing capacity is determined based on collateral pledged, generally consisting of investment securities and loans, at the time of the borrowing. The Company has a PPP lending facility with the FRB that allows the Company to pledge loans originated under the PPP in return for dollar for dollar funding from the FRB, which would provide up to $1.5 billion in additional credit. The amount of available credit under the PPP lending facility will decline each period as these loans are paid down. At March 31, 2021, the Company had no amounts outstanding under its line of credit or its PPP lending facility with the FRB and had $5.0 million in borrowings under its lines of credit with the FHLB. As of March 31, 2021 and December 31, 2020, the Company had additional available credit with the FHLB of approximately $4.2 billion and $4.0 billion, respectively, and with the FRB of approximately $2.7 billion.

Qualifying Debt

Qualifying Debt	3 Months Ended
	Mar. 31, 2021
Qualifying Debt Disclosure [Abstract]
Qualifying Debt	Subordinated Debt The Company's subordinated debt consists of three separate issuances. The Parent issued $175.0 million of subordinated debentures in June 2016, which were recorded net of issuance costs of $5.5 million, and mature July 1, 2056. Beginning on or after July 1, 2021, the Company may redeem the debentures, in whole or in part, at their principal amount plus any accrued and unpaid interest. The debentures have a fixed interest rate of 6.25% per annum. In June 2015, WAB issued $150.0 million of subordinated debt, which was recorded net of debt issuance costs of $1.8 million, and matures July 15, 2025. The subordinated debt is redeemable by WAB, in whole or in part, for a price equal to the principal amount plus accrued and unpaid interest. The subordinated debt had a fixed interest rate of 5.00% through June 30, 2020, which then converted to a variable rate of 3.20% plus three-month LIBOR through maturity. On October 15, 2020, WAB redeemed $75 million of this subordinated debt issuance. In May 2020, WAB issued $225.0 million of subordinated debt, which was recorded net of debt issuance costs of $3.1 million, and matures June 1, 2030. The subordinated debt is redeemable by WAB, in whole or in part, on or after June 1, 2025 and on every interest payment date thereafter, at a redemption price equal to the principal amount plus accrued and unpaid interest. The subordinated debt has a fixed interest rate of 5.25% through June 1, 2025 and then converts to a floating rate per annum equal to the three-month SOFR plus 512 basis points for each quarterly interest period during the floating rate period. To hedge the interest rate risk on the Company's 2015 and 2016 subordinated debt issuances, the Company entered into fair value interest rate hedges with receive fixed/pay variable swaps. The carrying value of all subordinated debt issuances, which includes the fair value of the related hedges, totals $464.4 million and $469.8 million at March 31, 2021 and December 31, 2020, respectively. Junior Subordinated Debt The Company has formed or acquired through acquisition eight statutory business trusts, which exist for the exclusive purpose of issuing Cumulative Trust Preferred Securities. With the exception of debt issued by Bridge Capital Trust I and Bridge Capital Trust II, junior subordinated debt is recorded at fair value at each reporting date due to the FVO election made by the Company under ASC 825. The Company did not make the FVO election for the junior subordinated debt acquired as part of the Bridge acquisition. Accordingly, the carrying value of these trusts does not reflect the current fair value of the debt and includes a fair market value adjustment established at acquisition that is being accreted over the remaining life of the trusts. The carrying value of junior subordinated debt was $79.3 million and $78.9 million as of March 31, 2021 and December 31, 2020, respectively. The weighted average interest rate of all junior subordinated debt as of March 31, 2021 was 2.53%, which is three-month LIBOR plus the contractual spread of 2.34%, compared to a weighted average interest rate of 2.58% at December 31, 2020. In the event of certain changes or amendments to regulatory requirements or federal tax rules, the debt is redeemable in whole. The obligations under these instruments are fully and unconditionally guaranteed by the Company and rank subordinate and junior in right of payment to all other liabilities of the Company. Based on guidance issued by the FRB, the Company's securities continue to qualify as Tier 1 Capital.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2021
Stockholders' Equity Note [Abstract]
Stockholder's Equity	Stock-Based Compensation Restricted Stock Awards Restricted stock awards granted to employees generally vest over a 3-year period. Stock grants made to non-employee WAL directors in 2021 will be fully vested on July 1, 2021. The Company estimates the compensation cost for stock grants based upon the grant date fair value. Stock compensation expense is recognized on a straight-line basis over the requisite service period for the entire award. The aggregate grant date fair value for the restricted stock awards granted during the three months ended March 31, 2021 and 2020 was $23.7 million and $21.7 million, respectively. Stock compensation expense related to restricted stock awards granted to employees are included in Salaries and employee benefits in the Consolidated Income Statement. For restricted stock awards granted to WAL directors, related stock compensation expense is included in Legal, professional, and directors' fees. For the three months ended March 31, 2021, the Company recognized $5.6 million in stock-based compensation expense related to these stock grants, compared to $4.9 million for the three months ended March 31, 2020. In addition, the Company previously granted shares of restricted stock to certain members of executive management that had both performance and service conditions that affect vesting. There were no such grants made during the three months ended March 31, 2021 and 2020, however expense is still being recognized for a grant made in 2017 with a four-year vesting period. For the three months ended March 31, 2021 and 2020, the Company recognized $0.3 million in stock-based compensation expense related to these performance-based restricted stock grant. Performance Stock Units The Company grants performance stock units to members of its executive management that do not vest unless the Company achieves a specified cumulative EPS target and a TSR performance measure over a three-year performance period. The number of shares issued will vary based on the cumulative EPS target and relative TSR performance factor that is achieved. The Company estimates the cost of performance stock units based upon the grant date fair value and expected vesting percentage over the three-year performance period. For the three months ended March 31, 2021, the Company recognized $2.1 million in stock-based compensation expense related to these performance stock units, compared to $1.7 million for the three months ended March 31, 2020. The three-year performance period for the 2018 grant ended on December 31, 2020, and the Company's cumulative EPS and TSR performance measure for the performance period exceeded the level required for a maximum award under the terms of the grant. As a result, 152,418 shares became fully vested and were distributed to executive management in the first quarter of 2021. Common Stock Sale The Company sold 2.3 million shares of its common stock in a registered direct offering during the three months ended March 31, 2021. The shares were sold for $91.00 per share for aggregate net proceeds of $209.2 million. Common Stock Repurchase The Company's common stock repurchase program, which expired on December 31, 2020, authorized the Company to repurchase up to $250.0 million of its outstanding common stock. During the three months ended March 31, 2020, the Company repurchased 1,769,479 shares of its common stock at a weighted average price of $35.30 for a total payment of $62.5 million. Cash Dividend During the three months ended March 31, 2021, the Company declared and paid a cash dividend of $0.25 per share, for a total dividend payment to shareholders of $25.3 million. During the three months ended March 31, 2020, the Company declared and paid a cash dividend of $0.25 per share, for a total payment to shareholders of $25.6 million. Treasury Shares

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Accumulated Other Comprehensive Income	The following table summarizes the changes in accumulated other comprehensive income by component, net of tax, for the periods indicated: Three Months Ended March 31, Unrealized holding gains (losses) on AFS Unrealized holding gains (losses) on SERP Unrealized holding gains (losses) on junior subordinated debt Total (in millions) Balance, December 31, 2020 $ 92.1 $ (0.3) $ 0.5 $ 92.3 Other comprehensive loss before reclassifications (72.0) — (0.3) (72.3) Amounts reclassified from AOCI (0.1) — — (0.1) Net current-period other comprehensive loss (72.1) — (0.3) (72.4) Balance, March 31, 2021 $ 20.0 $ (0.3) $ 0.2 $ 19.9 Balance, December 31, 2019 $ 21.4 $ 0.0 $ 3.6 $ 25.0 Other comprehensive income (loss) before reclassifications 6.3 (0.3) 6.6 12.6 Amounts reclassified from AOCI (0.1) — — (0.1) Net current-period other comprehensive income (loss) 6.2 (0.3) 6.6 12.5 Balance, March 31, 2020 $ 27.6 $ (0.3) $ 10.2 $ 37.5 The following table presents reclassifications out of accumulated other comprehensive income: Three Months Ended March 31, Income Statement Classification 2021 2020 (in millions) Gain on sales of investment securities, net $ 0.1 $ 0.1 Income tax expense 0.0 0.0 Net of tax $ 0.1 $ 0.1

Derivatives and Hedging

Derivatives and Hedging	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging Activities	8. DERIVATIVES AND HEDGING ACTIVITIES The Company is a party to various derivative instruments. Derivative instruments are contracts between two or more parties that have a notional amount and an underlying variable, require a small or no initial investment, and allow for the net settlement of positions. A derivative’s notional amount serves as the basis for the payment provision of the contract and takes the form of units, such as shares or dollars. A derivative’s underlying variable is a specified interest rate, security price, commodity price, foreign exchange rate, index, or other variable. The interaction between the notional amount and the underlying variable determines the number of units to be exchanged between the parties and influences the fair value of the derivative contract. The primary type of derivatives that the Company uses are interest rate swaps. Generally, these instruments are used to help manage the Company's exposure to interest rate risk and meet client financing and hedging needs. Derivatives are recorded at fair value on the Consolidated Balance Sheets, after taking into account the effects of bilateral collateral and master netting agreements. These agreements allow the Company to settle all derivative contracts held with the same counterparty on a net basis, and to offset net derivative positions with related cash collateral, where applicable. Derivatives Designated in Hedge Relationships The Company utilizes derivatives that have been designated as part of a hedge relationship in accordance with the applicable accounting guidance to minimize the exposure to changes in benchmark interest rates and volatility of net interest income and EVE to interest rate fluctuations. The primary derivative instruments used to manage interest rate risk are interest rate swaps, which convert the contractual interest rate index of agreed-upon amounts of assets and liabilities (i.e., notional amounts) from either a fixed rate to a floating rate, or from a floating rate to a fixed rate. The Company has entered into pay fixed/receive variable interest rate swaps designated as fair value hedges of certain fixed rate loans. As a result, the Company receives variable-rate interest payments in exchange for making fixed-rate payments over the lives of the contracts without exchanging the notional amounts. During the year ended December 31, 2020, the Company entered into interest rate swap contracts, designated as fair value hedges using the last-of-layer method to manage the exposure to changes in fair value associated with fixed rate loans, resulting from changes in the designated benchmark interest rate (Federal Funds rate). These last-of-layer hedges provide the Company the ability to execute a fair value hedge of the interest rate risk associated with a portfolio of similar prepayable assets whereby the last dollar amount estimated to remain in the portfolio of assets is identified as the hedged item. Under these interest rate swap contracts, the Company receives a floating rate and pays a fixed rate on the outstanding notional amount. The Company has also entered into receive fixed/pay variable interest rate swaps, designated as fair value hedges on its fixed rate 2015 and 2016 subordinated debt offerings. As a result, the Company is paying a floating rate of three-month LIBOR plus 3.16% and is receiving semi-annual fixed payments of 5.00% to match the payments on the $150.0 million subordinated debt. In July 2020, the interest payment on this subordinated debt issuance converted from a fixed rate to a floating rate, at which time the Company unwound this swap. For the fair value hedge on the Parent's $175.0 million subordinated debentures issued on June 16, 2016, the Company is paying a floating rate of three-month LIBOR plus 3.25% and is receiving quarterly fixed payments of 6.25% to match the payments on the debt. Derivatives Not Designated in Hedge Relationships Management also enters into certain foreign exchange derivative contracts and back-to-back interest rate swaps which are not designated as accounting hedges. Foreign exchange derivative contracts include spot, forward, forward window, and swap contracts. The purpose of these derivative contracts is to mitigate foreign currency risk on transactions entered into, or on behalf of customers. Contracts with customers, along with the related derivative trades that the Company places, are both remeasured at fair value, and are referred to as economic hedges since they economically offset the Company's exposure. The Company's back-to-back interest rate swaps are used to manage long-term interest rate risk. Fair Value Hedges As of March 31, 2021 and December 31, 2020, the following amounts are reflected on the Consolidated Balance Sheets related to cumulative basis adjustments for fair value hedges: March 31, 2021 December 31, 2020 Carrying Value of Hedged Assets/(Liabilities) Cumulative Fair Value Hedging Adjustment (1) Carrying Value of Hedged Assets/(Liabilities) Cumulative Fair Value Hedging Adjustment (1) (in millions) Loans - HFI, net of deferred loan fees and costs (2) $ 1,543.4 $ 46.8 $ 1,587.1 $ 85.5 Qualifying debt (242.0) 3.0 (247.6) (2.7) (1) Included in the carrying value of the hedged assets/(liabilities). (2) The Company designated $1.0 billion as the hedged amount (from a closed portfolio of prepayable fixed rate loans with a carrying value of $1.8 billion and $1.9 billion as of March 31, 2021 and December 31, 2020, respectively) in this last-of-layer hedging relationship, which commenced in the fourth quarter of 2020. The cumulative basis adjustment included in the carrying value of these hedged items totaled $7.9 million and $0.6 million as of March 31, 2021 and December 31, 2020, respectively. For the Company's derivative instruments that are designated and qualify as a fair value hedge, the gain or loss on the derivative instrument as well as the offsetting loss or gain on the hedged item attributable to the hedged risk are recognized in current earnings in the same line item as the offsetting loss or gain on the related interest rate swaps. For loans, the gain or loss on the hedged item is included in interest income and for subordinated debt, the gain or loss on the hedged items is included in interest expense, as shown in the table below. Three Months Ended March 31, 2021 2020 Income Statement Classification Gain/(Loss) on Swaps Gain/(Loss) on Hedged Item Gain/(Loss) on Swaps Gain/(Loss) on Hedged Item (in millions) Interest income $ 38.7 $ (38.7) $ (41.8) $ 41.8 Interest expense (5.7) 5.7 4.8 (4.8) Fair Values, Volume of Activity, and Gain/Loss Information Related to Derivative Instruments The following table summarizes the fair values of the Company's derivative instruments on a gross and net basis as of March 31, 2021, December 31, 2020, and March 31, 2020. The change in the notional amounts of these derivatives from March 31, 2020 to March 31, 2021 indicates the volume of the Company's derivative transaction activity during these periods. The derivative asset and liability balances are presented on a gross basis, prior to the application of bilateral collateral and master netting agreements. Total derivative assets and liabilities are adjusted to take into account the impact of legally enforceable master netting agreements that allow the Company to settle all derivative contracts with the same counterparty on a net basis and to offset the net derivative position with the related collateral. Where master netting agreements are not in effect or are not enforceable under bankruptcy laws, the Company does not adjust those derivative amounts with counterparties. The fair value of derivative contracts, after taking into account the effects of master netting agreements, is included in other assets or other liabilities on the Consolidated Balance Sheets, as indicated in the following table: March 31, 2021 December 31, 2020 March 31, 2020 Fair Value Fair Value Fair Value Notional Derivative Assets Derivative Liabilities Notional Derivative Assets Derivative Liabilities Notional Derivative Assets Derivative Liabilities (in millions) Derivatives designated as hedging instruments: Fair value hedges Interest rate swaps (1) $ 1,685.9 $ 7.9 $ 57.7 $ 1,689.9 $ 3.3 $ 86.1 $ 859.1 $ 4.4 $ 95.1 Total 1,685.9 7.9 57.7 1,689.9 3.3 86.1 859.1 4.4 95.1 Netting adjustments (2) — 5.4 5.4 — 0.6 0.6 — — — Net $ 1,685.9 $ 2.5 $ 52.3 $ 1,689.9 $ 2.7 $ 85.5 $ 859.1 $ 4.4 $ 95.1 Derivatives not designated as hedging instruments: Foreign currency contracts $ 119.3 $ 1.0 $ 0.7 $ 119.2 $ 0.7 $ 1.2 $ 9.3 $ 0.3 $ 0.2 Interest rate swaps 3.5 0.2 0.2 3.5 0.2 0.2 2.9 0.2 0.2 Total $ 122.8 $ 1.2 $ 0.9 $ 122.7 $ 0.9 $ 1.4 $ 12.2 $ 0.5 $ 0.4 (1) Interest rate swap amounts include a notional amount of $1.0 billion related to the last-of-layer hedges. (2) Netting adjustments represent the amounts recorded to convert the Company's derivative balances from a gross basis to a net basis in accordance with the applicable accounting guidance. Counterparty Credit Risk Like other financial instruments, derivatives contain an element of credit risk. This risk is measured as the expected replacement value of the contracts. Management enters into bilateral collateral and master netting agreements that provide for the net settlement of all contracts with the same counterparty. Additionally, management monitors counterparty credit risk exposure on each contract to determine appropriate limits on the Company's total credit exposure across all product types, which may require the Company to post collateral to counterparties when these contracts are in a net liability position and conversely, for counterparties to post collateral to the Company when these contracts are in a net asset position. Management reviews the Company's collateral positions on a daily basis and exchanges collateral with counterparties in accordance with standard ISDA documentation and other related agreements. The Company generally posts or holds collateral in the form of cash deposits or highly rated securities issued by the U.S. Treasury or government-sponsored enterprises, such as GNMA, FNMA, and FHLMC. The total collateral pledged by the Company to counterparties exceeded its net derivative liabilities as of March 31, 2021, December 31, 2020, and March 31, 2020, resulting in excess collateral postings of $36.4 million, $31.7 million and $22.4 million, respectively. The following table summarizes the Company's largest exposure to an individual counterparty at the dates indicated: March 31, 2021 December 31, 2020 March 31, 2020 (in millions) Largest gross exposure (derivative asset) to an individual counterparty $ 7.9 $ 2.7 $ 4.3 Collateral posted by this counterparty — — — Derivative liability with this counterparty 5.4 — — Collateral pledged to this counterparty 18.1 — — Net exposure after netting adjustments and collateral $ 7.9 $ 2.7 $ 4.3

Earnings per Share

Earnings per Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings Per Share	Diluted EPS is based on the weighted average outstanding common shares during each period, including common stock equivalents. Basic EPS is based on the weighted average outstanding common shares during the period. The following table presents the calculation of basic and diluted EPS: Three Months Ended March 31, 2021 2020 (in millions, except per share amounts) Weighted average shares - basic 100.8 101.3 Dilutive effect of stock awards 0.6 0.4 Weighted average shares - diluted 101.4 101.7 Net income $ 192.5 $ 83.9 Earnings per share - basic 1.91 0.83 Earnings per share - diluted 1.90 0.83 The Company had no anti-dilutive stock options outstanding at each of the periods ended March 31, 2021 and 2020.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	The Company's effective tax rate was 17.9% and 18.1% for the three months ended March 31, 2021 and 2020, respectively. There is not a significant difference in the effective tax rate. As of March 31, 2021, the net DTA balance totaled $49.8 million, an increase of $18.5 million from the year end 2020 DTA balance of $31.3 million. This overall increase in the net deferred tax asset was primarily the result of decreases in the fair market value of AFS securities and tax credit carryforwards. These items were not fully offset by decreases in deferred insurance premiums and increases to premises and equipment. Although realization is not assured, the Company believes that the realization of the recognized deferred tax asset of $49.8 million at March 31, 2021 is more-likely-than-not based on expectations as to future taxable income and based on available tax planning strategies that could be implemented if necessary to prevent a carryover from expiring. At March 31, 2021 and December 31, 2020, the Company had no deferred tax valuation allowance. As of March 31, 2021, the Company’s gross federal NOL carryovers after current year-to-date utilization, all of which are subject to limitations under Section 382 of the IRC, totaled approximately $42.4 million for which a deferred tax asset of $4.7 million has been recorded, reflecting the expected benefit of these remaining federal NOL carryovers. The Company does not have any significant state NOL carryovers. LIHTC and renewable energy projects The Company holds ownership interests in limited partnerships and limited liability companies that invest in affordable housing and renewable energy projects. These investments are designed to generate a return primarily through the realization of federal tax credits and deductions. The limited liability entities are considered to be VIEs; however, as a limited partner, the Company is not the primary beneficiary and is not required to consolidate these entities.

Fair Value Accounting

Fair Value Accounting	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Accounting	The fair value of an asset or liability is the price that would be received to sell that asset or paid to transfer that liability in an orderly transaction occurring in the principal market (or most advantageous market in the absence of a principal market) for such asset or liability. In estimating fair value, the Company utilizes valuation techniques that are consistent with the market approach, the income approach, and/or the cost approach. Such valuation techniques are consistently applied. Inputs to valuation techniques include the assumptions that market participants would use in pricing an asset or liability. ASC 825 establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). The three levels of the fair value hierarchy under ASC 825 are described in "Note 1. Summary of Significant Accounting Policies" of these Notes to Unaudited Consolidated Financial Statements. In general, fair value is based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon internally-developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be made to ensure that financial instruments are recorded at fair value. These adjustments may include amounts to reflect counterparty credit quality and the Company’s creditworthiness, among other things, as well as unobservable parameters. Any such valuation adjustments are applied consistently over time. The Company’s valuation methodologies may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. While management believes the Company’s valuation methodologies are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. Furthermore, the reported fair value amounts have not been comprehensively revalued since the presentation dates, and therefore, estimates of fair value after the balance sheet date may differ significantly from the amounts presented herein. A more detailed description of the valuation methodologies used for assets and liabilities measured at fair value is set forth below. Under ASC 825, the Company elected the FVO treatment for junior subordinated debt issued by WAL. This election is irrevocable and results in the recognition of unrealized gains and losses on these items at each reporting date. These unrealized gains and losses are recognized as part of other comprehensive income rather than earnings. The Company did not elect FVO treatment for the junior subordinated debt assumed in the Bridge Capital Holdings acquisition. For the three months ended March 31, 2021 and 2020, unrealized gains and losses from fair value changes on junior subordinated debt were as follows: Three Months Ended March 31, 2021 2020 (in millions) Unrealized (losses) gains $ (0.4) $ 8.7 Changes included in OCI, net of tax (0.3) 6.6 Fair value on a recurring basis Financial assets and financial liabilities measured at fair value on a recurring basis include the following: AFS securities: Securities classified as AFS are reported at fair value utilizing Level 1 and Level 2 inputs. For these securities, the Company obtains fair value measurements from an independent pricing service. The fair value measurements consider observable data that may include quoted prices in active markets, dealer quotes, market spreads, cash flows, the U.S. Treasury yield curve, live trading levels, trade execution data, market consensus prepayment speeds, credit information, and the bond’s terms and conditions, among other things. Equity securities: Preferred stock and CRA investments are reported at fair value primarily utilizing Level 1 inputs. Independent pricing service: The Company's independent pricing service provides pricing information on the majority of the Company's Level 1 and Level 2 AFS securities. For a small subset of securities, other pricing sources are used, including observed prices on publicly traded securities and dealer quotes. Management independently evaluates the fair value measurements received from the Company's third-party pricing service through multiple review steps. First, management reviews what has transpired in the marketplace with respect to interest rates, credit spreads, volatility, and mortgage rates, among other things, and develops an expectation of changes to the securities' valuations from the previous quarter. Then, management selects a sample of investment securities and compares the values provided by its primary third-party pricing service to the market values obtained from secondary sources, including other pricing services and safekeeping statements, and evaluates those with notable variances. In instances where there are discrepancies in pricing from various sources and management expectations, management may manually price securities using currently observed market data to determine whether they can develop similar prices or may utilize bid information from broker dealers. Any remaining discrepancies between management’s review and the prices provided by the vendor are discussed with the vendor and/or the Company’s other valuation advisors. Interest rate swaps: Interest rate swaps are reported at fair value utilizing Level 2 inputs. The Company obtains dealer quotations to value its interest rate swaps. Junior subordinated debt: The Company estimates the fair value of its junior subordinated debt using a discounted cash flow model which incorporates the effect of the Company’s own credit risk in the fair value of the liabilities (Level 3). The Company’s cash flow assumptions are based on contractual cash flows as the Company anticipates that it will pay the debt according to its contractual terms. The fair value of assets and liabilities measured at fair value on a recurring basis was determined using the following inputs as of the periods presented: Fair Value Measurements at the End of the Reporting Period Using: Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Fair Value (in millions) March 31, 2021 Assets: Available-for-sale debt securities CLO $ — $ 980.7 $ — $ 980.7 Commercial MBS issued by GSEs — 87.8 — 87.8 Corporate debt securities — 285.1 — 285.1 Private label residential MBS — 1,900.6 — 1,900.6 Residential MBS issued by GSEs — 2,249.6 — 2,249.6 Tax-exempt — 1,329.7 — 1,329.7 U.S. treasury securities 50.0 — — 50.0 Other 27.3 29.1 — 56.4 Total AFS debt securities $ 77.3 $ 6,862.6 $ — $ 6,939.9 Equity securities CRA investments $ 27.4 $ 30.0 $ — $ 57.4 Preferred stock 135.5 — — 135.5 Total equity securities $ 162.9 $ 30.0 $ — $ 192.9 Derivative assets (1) $ — $ 9.1 $ — $ 9.1 Liabilities: Junior subordinated debt (2) $ — $ — $ 66.3 $ 66.3 Derivative liabilities (1) — 58.6 — 58.6 (1) Derivative assets and liabilities relate primarily to interest rate swaps, see "Note 8. Derivatives and Hedging Activities." In addition, the carrying value of loans is increased by $46.8 million and the net carrying value of subordinated debt is increased by $3.0 million as of March 31, 2021 for the effective portion of the hedge, which relates to the fair value of the hedges put in place to mitigate against fluctuations in interest rates. (2) Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment. Fair Value Measurements at the End of the Reporting Period Using: Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Fair Value (in millions) December 31, 2020 Assets: Available-for-sale debt securities CLO $ — $ 146.9 $ — $ 146.9 Commercial MBS issued by GSEs — 84.6 — 84.6 Corporate debt securities — 270.2 — 270.2 Private label residential MBS — 1,476.9 — 1,476.9 Residential MBS issued by GSEs — 1,486.6 — 1,486.6 Tax-exempt — 1,187.4 — 1,187.4 Other 26.5 29.4 — 55.9 Total AFS debt securities $ 26.5 $ 4,682.0 $ — $ 4,708.5 Equity securities CRA investments $ 27.8 $ 25.6 $ — $ 53.4 Preferred stock 113.9 — — 113.9 Total equity securities $ 141.7 $ 25.6 $ — $ 167.3 Derivative assets (1) $ — $ 4.2 $ — $ 4.2 Liabilities: Junior subordinated debt (2) $ — $ — $ 65.9 $ 65.9 Derivative liabilities (1) — 87.5 — 87.5 (1) Derivative assets and liabilities relate primarily to interest rate swaps, see "Note 8. Derivatives and Hedging Activities." In addition, the carrying value of loans is increased by $85.5 million and the net carrying value of subordinated debt is increased by $2.7 million as of December 31, 2020 for the effective portion of the hedge, which relates to the fair value of the hedges put in place to mitigate against fluctuations in interest rates. (2) Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment. For the three months ended March 31, 2021 and 2020, the change in Level 3 liabilities measured at fair value on a recurring basis was as follows: Junior Subordinated Debt Three Months Ended March 31, 2021 2020 (in millions) Beginning balance $ (65.9) $ (61.7) Change in fair value (1) (0.4) 8.7 Ending balance $ (66.3) $ (53.0) (1) Unrealized gains (losses) attributable to changes in the fair value of junior subordinated debt are recorded as part of OCI, net of tax, and totaled $(0.3) million and $6.6 million for three months ended March 31, 2021 and 2020, respectively. For Level 3 liabilities measured at fair value on a recurring basis as of March 31, 2021 and December 31, 2020, the significant unobservable inputs used in the fair value measurements were as follows: March 31, 2021 Valuation Technique Significant Unobservable Inputs Input Value (in millions) Junior subordinated debt $ 66.3 Discounted cash flow Implied credit rating of the Company 2.78 % December 31, 2020 Valuation Technique Significant Unobservable Inputs Input Value (in millions) Junior subordinated debt $ 65.9 Discounted cash flow Implied credit rating of the Company 2.87 % The significant unobservable inputs used in the fair value measurement of the Company’s junior subordinated debt as of March 31, 2021 and December 31, 2020 was the implied credit risk for the Company. As of March 31, 2021 and December 31, 2020, the implied credit risk spread was calculated as the difference between the average of the 15-year 'BB' and 'BBB' rated financial indexes over the corresponding swap index. As of March 31, 2021, the Company estimates the discount rate at 2.78%, which represents an implied credit spread of 2.59% plus three-month LIBOR (0.19%). As of December 31, 2020, the Company estimated the discount rate at 2.87%, which was a 2.64% credit spread plus three-month LIBOR (0.24%). Fair value on a nonrecurring basis Certain assets are measured at fair value on a nonrecurring basis. That is, the assets are not measured at fair value on an ongoing basis, but are subject to fair value adjustments in certain circumstances (for example, when there is evidence of credit deterioration). The following table presents such assets carried on the Consolidated Balance Sheet by caption and by level within the ASC 825 hierarchy: Fair Value Measurements at the End of the Reporting Period Using Total Quoted Prices in Active Markets for Identical Assets Active Markets for Similar Assets Unobservable Inputs (in millions) As of March 31, 2021: Loans $ 183.0 $ — $ — $ 183.0 Other assets acquired through foreclosure 4.2 — — 4.2 As of December 31, 2020: Loans $ 187.3 $ — $ — $ 187.3 Other assets acquired through foreclosure 1.4 — — 1.4 For Level 3 assets measured at fair value on a nonrecurring basis as of March 31, 2021 and December 31, 2020, the significant unobservable inputs used in the fair value measurements were as follows: March 31, 2021 Valuation Technique(s) Significant Unobservable Inputs Range (in millions) Loans $ 183.0 Collateral method Third party appraisal Costs to sell 4.0% to 10.0% Discounted cash flow method Discount rate Contractual loan rate 2.0% to 7.0% Other assets acquired through foreclosure 4.2 Collateral method Third party appraisal Costs to sell 4.0% to 10.0% December 31, 2020 Valuation Technique(s) Significant Unobservable Inputs Range (in millions) Loans $ 187.3 Collateral method Third party appraisal Costs to sell 4.0% to 10.0% Discounted cash flow method Discount rate Contractual loan rate 2.0% to 7.0% Other assets acquired through foreclosure 1.4 Collateral method Third party appraisal Costs to sell 4.0% to 10.0% Loans: Loans measured at fair value on a nonrecurring basis include collateral dependent loans held for investment. The specific reserves for these loans are based on collateral value, net of estimated disposition costs and other identified quantitative inputs. Collateral value is determined based on independent third-party appraisals or internally-developed discounted cash flow analyses. Appraisals may utilize a single valuation approach or a combination of approaches, including comparable sales and the income approach. Fair value is determined, where possible, using market prices derived from an appraisal or evaluation, which are considered to be Level 2. However, certain assumptions and unobservable inputs are often used by the appraiser, therefore qualifying the assets as Level 3 in the fair value hierarchy. In addition, when adjustments are made to an appraised value to reflect various factors such as the age of the appraisal or known changes in the market or the collateral, such valuation inputs are considered unobservable and the fair value measurement is categorized as a Level 3 measurement. Internal discounted cash flow analyses are also utilized to estimate the fair value of these loans, which considers internally-developed, unobservable inputs such as discount rates, default rates, and loss severity. Total Level 3 collateral dependent loans had an estimated fair value of $183.0 million and $187.3 million at March 31, 2021 and December 31, 2020, respectively, net of a specific valuation allowance of $9.5 million and $8.9 million at March 31, 2021 and December 31, 2020, respectively. Other assets acquired through foreclosure: Other assets acquired through foreclosure consist of properties acquired as a result of, or in-lieu-of, foreclosure. These assets are initially reported at the fair value determined by independent appraisals using appraised value less estimated cost to sell. Such properties are generally re-appraised every twelve months. There is risk for subsequent volatility. Costs relating to the development or improvement of the assets are capitalized and costs relating to holding the assets are charged to expense. Fair value is determined, where possible, using market prices derived from an appraisal or evaluation, which are considered to be Level 2. However, certain assumptions and unobservable inputs are often used by the appraiser, therefore qualifying the assets as Level 3 in the fair value hierarchy. When significant adjustments are based on unobservable inputs, such as when a current appraised value is not available or management determines the fair value of the collateral is further impaired below the appraised value and there is no observable market price, the resulting fair value measurement has been categorized as a Level 3 measurement. The Company had $4.2 million and $1.4 million of such assets at March 31, 2021 and December 31, 2020, respectively. Fair Value of Financial Instruments The estimated fair value of the Company’s financial instruments is as follows: March 31, 2021 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total (in millions) Financial assets: Investment securities: HTM $ 698.0 $ — $ 740.4 $ — $ 740.4 AFS 6,939.9 77.3 6,862.6 — 6,939.9 Equity 192.9 162.9 30.0 — 192.9 Derivative assets 9.1 — 9.1 — 9.1 Loans, net 28,463.9 — — 29,244.8 29,244.8 Accrued interest receivable 169.9 — 169.9 — 169.9 Financial liabilities: Deposits $ 38,393.1 $ — $ 38,397.4 $ — $ 38,397.4 Customer repurchase agreements 15.9 — 15.9 — 15.9 Other borrowings 5.0 — 5.0 — 5.0 Qualifying debt 543.7 — 492.6 79.8 572.4 Derivative liabilities 58.6 — 58.6 — 58.6 Accrued interest payable 12.7 — 12.7 — 12.7 December 31, 2020 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total (in millions) Financial assets: Investment securities: HTM $ 568.8 $ — $ 611.8 $ — $ 611.8 AFS 4,708.5 26.5 4,682.0 — 4,708.5 Equity securities 167.3 141.7 25.6 — 167.3 Derivative assets 4.2 — 4.2 — 4.2 Loans, net 26,774.1 — — 27,231.0 27,231.0 Accrued interest receivable 166.1 — 166.1 — 166.1 Financial liabilities: Deposits $ 31,930.5 $ — $ 31,935.9 $ — $ 31,935.9 Customer repurchase agreements 16.0 — 16.0 — 16.0 Other borrowings 5.0 — 5.0 — 5.0 Qualifying debt 548.7 — 488.1 79.3 567.4 Derivative liabilities 87.5 — 87.5 — 87.5 Accrued interest payable 11.0 — 11.0 — 11.0 Interest rate risk The Company assumes interest rate risk (the risk to the Company’s earnings and capital from changes in interest rate levels) as a result of its normal operations. As a result, the fair values of the Company’s financial instruments, as well as its future net interest income, will change when interest rate levels change and that change may be either favorable or unfavorable to the Company. Interest rate risk exposure is measured using interest rate sensitivity analysis to determine the Company's change in EVE and net interest income resulting from hypothetical changes in interest rates. If potential changes to EVE and net interest income resulting from hypothetical interest rate changes are not within the limits established by the BOD, the BOD may direct management to adjust the asset and liability mix to bring interest rate risk within BOD-approved limits. WAB has an ALCO charged with managing interest rate risk within the BOD-approved limits. Limits are structured to preclude an interest rate risk profile that does not conform to both management and BOD risk tolerances without ALCO approval. There is also ALCO reporting at the Parent level for reviewing interest rate risk for the Company, which gets reported to the BOD and its Finance and Investment Committee. Fair value of commitments The estimated fair value of standby letters of credit outstanding at March 31, 2021 and December 31, 2020 approximates zero as there have been no significant changes in borrower creditworthiness. Loan commitments on which the committed interest rates are less than the current market rate are insignificant at March 31, 2021 and December 31, 2020.

Segments

Segments	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Segments	The Company's reportable segments are aggregated with a focus on products and services offered and consist of three reportable segments: • Commercial segment: provides commercial banking and treasury management products and services to small and middle-market businesses, specialized banking services to sophisticated commercial institutions and investors within niche industries, as well as financial services to the real estate industry. • Consumer Related segment: offers both commercial banking services to enterprises in consumer-related sectors and consumer banking services, such as residential mortgage banking. • Corporate & Other segment: consists of the Company's investment portfolio, Corporate borrowings and other related items, income and expense items not allocated to our other reportable segments, and inter-segment eliminations. The Company's segment reporting process begins with the assignment of all loan and deposit accounts directly to the segments where these products are originated and/or serviced. Equity capital is assigned to each segment based on the risk profile of their assets and liabilities. With the exception of goodwill, which is assigned a 100% weighting, equity capital allocations ranged from 0% to 8% during the year. Any excess or deficient equity not allocated to segments based on risk is assigned to the Corporate & Other segment. Net interest income, provision for credit losses, and non-interest expense amounts are recorded in their respective segments to the extent that the amounts are directly attributable to those segments. Net interest income is recorded in each segment on a TEB with a corresponding increase in income tax expense, which is eliminated in the Corporate & Other segment. Further, net interest income of a reportable segment includes a funds transfer pricing process that matches assets and liabilities with similar interest rate sensitivity and maturity characteristics. Using this funds transfer pricing methodology, liquidity is transferred between users and providers. A net user of funds has lending/investing in excess of deposits/borrowings and a net provider of funds has deposits/borrowings in excess of lending/investing. A segment that is a user of funds is charged for the use of funds, while a provider of funds is credited through funds transfer pricing, which is determined based on the average life of the assets or liabilities in the portfolio. Residual funds transfer pricing mismatches are allocable to the Corporate & Other segment and presented as part of net interest income. The net income amount for each reportable segment is further derived by the use of expense allocations. Certain expenses not directly attributable to a specific segment are allocated across all segments based on key metrics, such as number of employees, number of transactions processed for loans and deposits, and average loan and deposit balances. These types of expenses include information technology, operations, human resources, finance, risk management, credit administration, legal, and marketing. Income taxes are applied to each segment based on the effective tax rate for the geographic location of the segment. Any difference in the corporate tax rate and the aggregate effective tax rates in the segments are adjusted in the Corporate & Other segment.

Revenue from Contracts with Cus

Revenue from Contracts with Customers (Notes)	3 Months Ended
	Mar. 31, 2021
Revenue from Contracts with Customers [Abstract]
Revenue from Contract with Customer [Text Block]	14. REVENUE FROM CONTRACTS WITH CUSTOMERS ASC 606, Revenue from Contracts with Customers , requires revenue to be recognized at an amount that reflects the consideration to which the entity expects to be entitled in exchange for transferring goods or services to a customer. ASC 606 applies to all contracts with customers to provide goods or services in the ordinary course of business, except for contracts that are specifically excluded from its scope. The majority of the Company’s revenue streams including interest income, credit and debit card fees, income from equity investments including warrants and SBIC equity income, income from bank owned life insurance, foreign currency income, and lending related income are outside the scope of ASC 606. Revenue streams including service charges and fees, interchange fees on credit and debit cards, and success fees are within the scope of ASC 606. Disaggregation of Revenue The following table represents a disaggregation of revenue from contracts with customers for the periods indicated along with the reportable segment for each revenue category: Consolidated Company Commercial Consumer Related Corporate & Other Three Months Ended March 31, 2021 (in millions) Revenue from contracts with customers: Service charges and fees $ 6.7 $ 6.2 $ 0.5 $ — Debit and credit card interchange (1) 1.3 1.3 — — Success fees (2) 1.0 1.0 — — Other income 0.2 0.2 — — Total revenue from contracts with customers $ 9.2 $ 8.7 $ 0.5 $ — Revenues outside the scope of ASC 606 (3) 10.5 10.5 — — Total non-interest income $ 19.7 $ 19.2 $ 0.5 $ — Consolidated Company Commercial Consumer Related Corporate & Other Three Months Ended March 31, 2020 (in millions) Revenue from contracts with customers: Service charges and fees $ 6.4 $ 6.0 $ 0.4 $ — Debit and credit card interchange (1) 1.4 1.4 — — Success fees (2) 0.1 0.1 — — Other income 0.1 0.1 — — Total revenue from contracts with customers $ 8.0 $ 7.6 $ 0.4 $ — Revenues outside the scope of ASC 606 (3) (2.9) 3.8 — (6.7) Total non-interest income $ 5.1 $ 11.4 $ 0.4 $ (6.7) (1) Included as part of Card income in the Consolidated Income Statement. (2) Included as part of Income from equity investments in the Consolidated Income Statement. (3) Amounts are accounted for under separate guidance. Refer to discussion of revenue sources not subject to ASC 606 under the Non-interest income section in "Note 1. Summary of Significant Accounting Policies." Performance Obligations Many of the services the Company performs for its customers are ongoing, and either party may cancel at any time. The fees for these contracts are dependent upon various underlying factors, such as customer deposit balances, and as such may be considered variable. The Company’s performance obligations for these services are satisfied as the services are rendered and payment is collected on a monthly, quarterly, or semi-annual basis. Other contracts with customers are for services to be provided at a point in time, and fees are recognized at the time such services are rendered. The Company had no material unsatisfied performance obligations as of March 31, 2021. The revenue streams within the scope of ASC 606 are described in further detail below. Service Charges and Fees The Company performs deposit account services for its customers, which include analysis and treasury management services, use of safe deposit boxes, check upcharges, and other ancillary services. The depository arrangements the Company holds with its customers are considered day-to-day contracts with ongoing renewals and optional purchases, and as such, the contract duration does not extend beyond the services performed. Due to the short-term nature of such contracts, the Company generally recognizes revenue for deposit related fees as services are rendered. From time to time, the Company may waive certain fees for its customers. The Company considers historical experience when recognizing revenue from contracts with customers, and may reduce the transaction price to account for fee waivers or refunds. Debit and Credit Card Interchange When a credit or debit card issued by the Company is used to purchase goods or services from a merchant, the Company earns an interchange fee. The Company considers the merchant its customer in these transactions as the Company provides the merchant with the service of enabling the cardholder to purchase the merchant’s goods or services with increased convenience, and it enables the merchants to transact with a class of customer that may not have access to sufficient funds at the time of purchase. The Company acts as an agent to the payment network by providing nightly settlement services between the network and the merchant. This transmission of data and funds represents the Company’s performance obligation and is performed nightly. As the payment network is in direct control of setting the rates and the Company is acting as an agent, the interchange fee is recorded net of expenses as the services are provided. Success Fees Success fees are one-time fees detailed as part of certain loan agreements and are earned immediately upon occurrence of a triggering event. Examples of triggering events include: a borrower obtaining its next round of funding, an acquisition, or completion of a public offering. Success fees are variable consideration as the transaction price can vary and is contingent on the occurrence or non-occurrence of a future event. As the consideration is highly susceptible to factors outside of the Company’s influence and uncertainty about the amount of consideration is not expected to be resolved for an extended period of time, the variable consideration is constrained and is not recognized until the achievement of the triggering event. Principal versus Agent Considerations When more than one party is involved in providing goods or services to a customer, ASC 606 requires the Company to determine whether it is the principal or an agent in these transactions by evaluating the nature of its promise to the customer. An entity is a principal and therefore records revenue on a gross basis, if it controls a promised good or service before transferring that good or service to the customer. An entity is an agent and records as revenue the net amount it retains for its agency services if its role is to arrange for another entity to provide the goods or services. The Company most commonly acts as a principal and records revenue on a gross basis, except in certain circumstances. As an example, revenues earned from interchange fees, in which the Company acts as an agent, are recorded as non-interest income, net of the related expenses paid to the principal. Contract Balances The timing of revenue recognition may differ from the timing of cash settlements or invoicing to customers. The Company records contract liabilities, or deferred revenue, when payments from customers are received or due in advance of providing services to customers. The Company generally receives payments for its services during the period or at the time services are provided, therefore, does not have material contract liability balances at period-end. The Company records contract assets or receivables when revenue is recognized prior to receipt of cash from the customer. Accounts receivable totals $1.7 million and $1.6 million as of March 31, 2021 and December 31, 2020, respectively, and are presented in Other assets on the Consolidated Balance Sheets.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	15. SUBSEQUENT EVENTS On April 7, 2021, the Company completed its previously announced acquisition of Aris, the parent company of AHM, and certain other parties, pursuant to which, Aris merged with and into an indirect subsidiary of WAB. As a result of the Merger, AHM is now a wholly-owned indirect subsidiary of the Company and will continue to operate as AmeriHome Mortgage, a Western Alliance Bank company. AHM is a leading national business to business mortgage acquirer and servicer. The acquisition of AHM is expected to extend the Company’s national commercial businesses with a complementary national mortgage franchise that will allow the Company to expand mortgage offerings to existing clients. In addition, this acquisition positions the Company for continued growth, increased returns, and diversifies the Company’s revenue profile by expanding sources of fee revenue. Based on AHM's closing balance sheet and a $275 million cash premium, total consideration was approximately $1.22 billion. This transaction will be accounted for as a business combination under the acquisition method of accounting. The Company will record the assets acquired and liabilities assumed at their fair values as of the acquisition date. Due to the limited time since the closing of the acquisition, the valuation efforts and related acquisition accounting are incomplete at the time of filing of these consolidated financial statements. As a result, the Company is unable to provide amounts recognized as of the acquisition date for major classes of assets and liabilities acquired, including goodwill and other intangible assets. In addition, because the acquisition accounting is incomplete, the Company is also unable to provide the supplemental pro forma revenue and earnings for the combined entity. The Company expects to file all required financial statements of AHM and related pro forma financial information through an amendment to its Form 8-K filed with the SEC on April 7, 2021 no later than 71 days following the date that such 8-K was required to be filed.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Nature of Operation	Nature of operation WAL is a bank holding company headquartered in Phoenix, Arizona, incorporated under the laws of the state of Delaware. WAL provides a full spectrum of deposit, lending, treasury management, international banking, and online banking products and services through its wholly-owned banking subsidiary, WAB.
Basis of Presentation	Basis of presentation The accounting and reporting policies of the Company are in accordance with GAAP and conform to practices within the financial services industry. The accounts of the Company and its consolidated subsidiaries are included in the Consolidated Financial Statements.
Recent Accounting Pronouncements	Recent accounting pronouncements Convertible Debt and Derivatives and Hedging In August 2020, the FASB issued guidance within ASU 2020-06, Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity’s Own Equity (Subtopic 815-40) . The amendments in this update affect entities that issue convertible instruments and/or contracts indexed to and potentially settled in an entity’s own equity. The new ASU simplifies the convertible accounting framework through elimination of the beneficial conversion and cash conversion accounting models for convertible instruments. It also amends the accounting for certain contracts in an entity’s own equity that are currently accounted for as derivatives because of specific settlement provisions. In addition, the new guidance modifies how particular convertible instruments and certain contracts that may be settled in cash or shares impact the diluted EPS computation. The amendments to Subtopics 470 and 815 are effective for interim and annual reporting periods beginning after December 15, 2021 and are not expected to have a material impact on the Company’s Consolidated Financial Statements. Reference Rate Reform In March 2020, the FASB issued guidance within ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, in response to the scheduled discontinuation of LIBOR on December 31, 2021. Since the issuance of this guidance, the publication cessation of U.S. dollar LIBOR has been extended to June 30, 2023 . The amendments in this Update provide optional guidance designed to provide relief from the accounting analysis and impacts that may otherwise be required for modifications to agreements (e.g., loans, debt securities, derivatives, borrowings) necessitated by reference rate reform. The following optional expedients for applying the requirements of certain Topics or Industry Subtopics in the Codification are permitted for contracts that are modified because of reference rate reform and that meet certain scope guidance: 1) modifications of contracts within the scope of Topics 310, Receivables , and 470, Debt , should be accounted for by prospectively adjusting the effective interest rate; 2) modifications of contracts within the scope of Topic 842, Leases , should be accounted for as a continuation of the existing contracts with no reassessments of the lease classification and the discount rate or remeasurements of lease payments that otherwise would be required under this Topic for modifications not accounted for as separate contracts; 3) modifications of contracts do not require an entity to reassess its original conclusion about whether that contract contains an embedded derivative that is clearly and closely related to the economic characteristics and risks of the host contract under Subtopic 815-15, Derivatives and Hedging- Embedded Derivatives; and 4) for other Topics or Industry Subtopics in the Codification, the amendments in this Update also include a general principle that permits an entity to consider contract modifications due to reference rate reform to be an event that does not require contract remeasurement at the modification date or reassessment of a previous accounting determination. In January 2021, the FASB issued ASU 2021-01, Reference Rate Reform (Topic 848): Scope in order to clarify that certain optional expedients and exceptions in Topic 848 apply to derivatives that are affected by the discounting transition. Specifically, certain provisions in Topic 848, if elected by an entity, apply to derivative instruments that use an interest rate for margining, discount, or contract price alignment that is modified as a result of reference rate reform. The amendments in these Updates are effective immediately for all entities and apply to contract modifications through December 31, 2022. The adoption of this accounting guidance is not expected to have a material impact on the Company's Consolidated Financial Statements. Recently adopted accounting guidance Income Taxes In December 2019, the FASB issued guidance within ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes.
Use of Estimates	Use of estimatesThe preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Management's estimates and judgments are ongoing and are based on experience, current and expected future conditions, third-party evaluations and various other assumptions that management believes are reasonable under the circumstances. The results of these estimates form the basis for making judgments about the carrying values of assets and liabilities, as well as identifying and assessing the accounting treatment with respect to commitments and contingencies. Actual results may differ from those estimates and assumptions used in the Consolidated Financial Statements and related notes. Material estimates that are susceptible to significant changes in the near term, particularly to the extent that economic conditions worsen or persist longer than expected in an adverse state, relate to: 1) the determination of the allowance for credit losses; 2) certain assets and liabilities carried at fair value; and 3) accounting for income taxes.
Principles of Consolidation	Principles of consolidation As of March 31, 2021, WAL has the following significant wholly-owned subsidiaries: WAB and eight unconsolidated subsidiaries used as business trusts in connection with the issuance of trust-preferred securities. WAB has the following significant wholly-owned subsidiaries: WABT, which holds certain investment securities, municipal and nonprofit loans, and leases; 1) WA PWI, which holds interests in certain limited partnerships invested primarily in low income housing tax credits and small business investment corporations; 2) Helios Prime, which holds interests in certain limited partnerships invested in renewable energy projects; and 3) BW Real Estate, Inc., which operates as a real estate investment trust and holds certain of WAB's real estate loans and related securities. The Company does not have any other significant entities that should be consolidated. All significant intercompany balances and transactions have been eliminated in consolidation.
Reclassifications	Reclassifications Certain amounts reported in prior periods may have been reclassified in the Consolidated Financial Statements to conform to the current presentation. The reclassifications have no effect on net income or stockholders’ equity as previously reported.
Investment Securities	Investment securities Investment securities include debt and equity securities. Debt securities may be classified as HTM, AFS, or trading. The appropriate classification is initially decided at the time of purchase. Securities classified as HTM are those debt securities that the Company has both the intent and ability to hold to maturity regardless of changes in market conditions, liquidity needs, or general economic conditions. The sale of an HTM security within three months of its maturity date or after the majority of the principal outstanding has been collected is considered a maturity for purposes of classification and disclosure. Securities classified as AFS are securities that the Company intends to hold for an indefinite period of time, but not necessarily to maturity. Any decision to sell a security classified as AFS would be based on various factors, including significant movements in interest rates, changes in the maturity mix of the Company’s assets and liabilities, liquidity needs, decline in credit quality, and regulatory capital considerations. HTM securities are carried at amortized cost. AFS securities are carried at their estimated fair value, with unrealized holding gains and losses reported in other comprehensive income, net of tax. When AFS debt securities are sold, the unrealized gains or losses are reclassified from OCI to non-interest income. Trading securities are carried at their estimated fair value, with changes in fair value reported in earnings as part of non-interest income. Equity securities are carried at their estimated fair value, with changes in fair value reported in earnings as part of non-interest income. Interest income is recognized based on the coupon rate and includes the amortization of purchase premiums and the accretion of purchase discounts. Premiums and discounts on investment securities are generally amortized or accreted over the contractual life of the security using the interest method. For the Company's mortgage-backed securities, amortization or accretion of premiums or discounts are adjusted for anticipated prepayments. Gains and losses on the sale of investment securities are recorded on the trade date and determined using the specific identification method.
Credit Loss, Financial Instrument [Policy Text Block]	Allowance for credit losses on investment securities On January 1, 2020, the Company adopted the amendments within ASU 2016-13, which replaces the legacy US GAAP OTTI model with a credit loss model. The credit loss model under ASC 326-20, applicable to HTM debt securities, requires recognition of lifetime expected credit losses through an allowance account at the time the security is purchased. The Company measures expected credit losses on its HTM debt securities on a collective basis by major security type. The Company's HTM securities portfolio consists of low income housing tax-exempt bonds, which share similar risk characteristics with the Company's CRE, non-owner occupied or construction and land loan pools, given the similarity in underlying assets or collateral. Accordingly, expected credit losses on HTM securities are estimated using the same models and approaches as these loan pools, which utilize risk parameters (probability of default, loss given default, and exposure at default) in the measurement of expected credit losses. The historical data used to estimate probability of default and severity of loss in the event of default is derived or obtained from internal and external sources and adjusted for the expected effects of reasonable and supportable forecasts over the expected lives of the securities on those historical losses. Accrued interest receivable on the HTM securities, which is included in other assets on the Consolidated Balance Sheet, is excluded from the estimate of expected credit losses. The credit loss model under ASC 326-30, applicable to AFS debt securities, requires recognition of credit losses through an allowance account, but retains the concept from the OTTI model that credit losses are recognized once securities become impaired. For AFS debt securities, a decline in fair value due to credit loss results in recognition of an allowance for credit losses. Impairment may result from credit deterioration of the issuer or collateral underlying the security. The assessment of determining if a decline in fair value resulted from a credit loss is performed at the individual security level. Among other factors, the Company considers: 1) the extent to which the fair value is less than the amortized cost basis; 2) the financial condition and near term prospects of the issuer, including consideration of relevant financial metrics or ratios of the issuer; 3) any adverse conditions related to an industry or geographic area of an issuer; 4) any changes to the rating of the security by a rating agency; and 5) any past due principal or interest payments from the issuer. If an assessment of the above factors indicates that a credit loss exists, the Company records an allowance for credit losses for the excess of the amortized cost basis over the present value of cash flows expected to be collected, limited to the amount that the security's fair value is less than its amortized cost basis. Subsequent changes in the allowance for credit losses are recorded as a provision for (or reversal of) credit loss expense. Interest accruals and amortization and accretion of premiums and discounts are suspended when the credit loss is recognized in earnings. Any interest received after the security has been placed on nonaccrual status is recognized on a cash basis. Accrued interest receivable on AFS securities, which is included in other assets on the Consolidated Balance Sheet, is excluded from the estimate of expected credit losses. For each AFS security in an unrealized loss position, the Company also considers: 1) its intent to retain the security until anticipated recovery of the security's fair value; and 2) whether it is more-likely-than not that the Company would be required to sell the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the debt security is written down to its fair value and the write-down is charged against the allowance for credit losses with any incremental impairment recorded in earnings. Write-offs are made through reversal of the allowance for credit losses and direct write-off of the amortized cost basis of the AFS security. The Company considers the following events to be indicators that a write-off should be taken: 1) bankruptcy of the issuer; 2) significant adverse event(s) affecting the issuer in which it is improbable for the issuer to make its remaining payments on the security; and 3) significant loss of value of the underlying collateral behind a security. Recoveries on debt securities, if any, are recorded in the period received. Off-balance sheet credit exposures, including unfunded loan commitments The Company maintains a separate allowance for credit losses on off-balance-sheet credit exposures, including unfunded loan commitments, financial guarantees, and letters of credit, which is classified in other liabilities on the Consolidated Balance Sheet. The allowance for credit losses on off-balance sheet credit exposures is adjusted through increases or decreases to the provision for credit loss expense. The estimate includes consideration of the likelihood that funding will occur, an estimate of exposure at default that is derived from utilization rate assumptions using a non-modeled approach, and PD and LGD estimates that are derived from the same models and approaches for the Company's other loan portfolio segments described above as these unfunded commitments share similar risk characteristics with these loan portfolio segments. No credit loss estimate is reported for off-balance sheet credit exposures that are unconditionally cancellable by the Company or for undrawn amounts under such arrangements that may be drawn prior to the cancellation of the arrangement.
Restricted Stock	Restricted stockWAB is a member of the Federal Reserve System and, as part of its membership, is required to maintain stock in the FRB in a specified ratio to its capital. In addition, WAB is a member of the FHLB system and, accordingly, maintains an investment in capital stock of the FHLB based on the borrowing capacity used. These investments are considered equity securities with no actively traded market. Therefore, the shares are considered restricted investment securities. These investments are carried at cost, which is equal to the value at which they may be redeemed. The dividend income received from the stock is reported in interest income. The Company conducts a periodic review and evaluation of its restricted stock to determine if any impairment exists. No impairment has been recorded to date.
Loans, Interest and Fees from Loans	Loans held for investment Loans that management has the intent and ability to hold for the foreseeable future or until maturity or payoff are reported at amortized cost. Amortized cost is the amount of unpaid principal, adjusted for unamortized net deferred fees and costs, premiums and discounts, and write-offs. In addition, the amortized cost of loans subject to a fair value hedge are adjusted for changes in value attributable to the effective portion of the hedged benchmark interest rate risk. The Company may also purchase loans or acquire loans through a business combination. At the purchase or acquisition date, loans are evaluated to determine if there has been more than insignificant credit deterioration since origination. Loans that have experienced more than insignificant credit deterioration since origination are referred to as PCD loans. In its evaluation of whether a loan has experienced more than insignificant deterioration in credit quality since origination, the Company takes into consideration loan grades, loan-to-values greater than policy limits, past due and nonaccrual status, and TDR loans. The Company may also consider external credit rating agency ratings for borrowers and for non-commercial loans, FICO score or band, probability of default levels, number of times past due, and standard deviations corresponding to FICO score or band. The initial estimate of credit losses on PCD loans is added to the purchase price on the acquisition date to establish the initial amortized cost basis of the loan; accordingly, the initial recognition of expected credit losses has no impact on net income. When the initial measurement of expected credit losses on PCD loans are calculated on a pooled loan basis, the expected credit losses are allocated to each loan within the pool. Any difference between the initial amortized cost basis and the unpaid principal balance of the loan represents a noncredit discount or premium, which is accreted (or amortized) into interest income over the life of the loan. Subsequent changes to the allowance for credit losses on PCD loans are recorded through the provision for credit losses. For purchased loans that are not deemed to have experienced more than insignificant credit deterioration since origination, any discounts or premiums included in the purchase price are accreted (or amortized) over the contractual life of the individual loan. For additional information, see "Note 3. Loans, Leases and Allowance for Credit Losses" of these Notes to Unaudited Consolidated Financial Statements. In applying the effective yield method to loans, the Company generally applies the contractual method whereby loan fees collected for the origination of loans less direct loan origination costs (net of deferred loan fees), as well as premiums and discounts and certain purchase accounting adjustments, are amortized over the contractual life of the loan through interest income. If a loan has scheduled payments, the amortization of the net deferred loan fee is calculated using the interest method over the contractual life of the loan. If a loan does not have scheduled payments, such as a line of credit, the net deferred loan fee is recognized as interest income on a straight-line basis over the contractual life of the loan commitment. Commitment fees based on a percentage of a customer’s unused line of credit and fees related to standby letters of credit are recognized over the commitment period. When loans are repaid, any remaining unamortized balances of premiums, discounts, or net deferred fees are recognized as interest income. Conversely, with respect to loans originated under the PPP, the Company incorporates projected prepayments in calculating effective yield. As a result, net deferred fees are accreted into interest income faster than would be the case when applying the contractual method based upon the timing and amount of estimated forgiven loan balances. The Company expects that a majority of PPP loans will qualify for forgiveness under the SBA program, based on requested loan amounts largely representing qualifying expenses at the time of application. Nonaccrual loans When a borrower discontinues making payments as contractually required by the note, the Company must determine whether it is appropriate to continue to accrue interest. The Company ceases accruing interest income when the loan has become delinquent by more than 90 days or when management determines that the full repayment of principal and collection of interest according to contractual terms is no longer likely. Past due status is based on the contractual terms of the loan. The Company may decide to continue to accrue interest on certain loans more than 90 days delinquent if the loans are well secured by collateral and in the process of collection. For all loan types, when a loan is placed on nonaccrual status, all interest accrued but uncollected is reversed against interest income in the period in which the status is changed, and the Company makes a loan-level decision to apply either the cash basis or cost recovery method. The Company may recognize income on a cash basis when a payment is received and only for those nonaccrual loans for which the collection of the remaining principal balance is not in doubt. Under the cost recovery method, subsequent payments received from the customer are applied to principal and generally no further interest income is recognized until the principal has been paid in full or until circumstances have changed such that payments are again consistently received as contractually required. Loans are returned to accrual status when all of the principal and interest amounts contractually due are brought current and future payments are reasonably assured. Troubled Debt Restructured Loans A TDR loan is a loan on which the Company, for reasons related to a borrower’s financial difficulties, grants a concession to the borrower that the Company would not otherwise consider. In order to determine whether a borrower is experiencing financial difficulty, an evaluation is performed of the probability that the borrower will be in payment default on any of its debt in the foreseeable future without the modification. The evaluation is performed under the Company's internal underwriting policy. The loan terms that may be modified or restructured due to a borrower’s financial situation include, but are not limited to, a reduction in the stated interest rate, an extension of the maturity or renewal of the loan at an interest rate below current market, a reduction in the face amount of the debt, a reduction in the accrued interest, or deferral of interest payments. A TDR loan may be returned to accrual status when the loan is brought current, has performed in accordance with the contractual restructured terms for a reasonable period of time (generally six months), and the ultimate collectability of the total contractual restructured principal and interest is no longer in doubt. Consistent with regulatory guidance, a TDR loan that is subsequently modified in another restructuring agreement but has shown sustained performance and classification as a TDR, will be removed from TDR status provided that the modified terms were market-based at the time of modification. The CARES Act, signed into law on March 27, 2020, permitted financial institutions to suspend requirements under GAAP for loan modifications to borrowers affected by COVID-19 that would otherwise be characterized as TDRs and suspend any determination related thereto if (i) the loan modification was made between March 1, 2020 and December 31, 2020 and (ii) the applicable loan was not more than 30 days past due as of December 31, 2019. The Consolidated Appropriations Act, 2021, signed into law on December 27, 2020, extends these provisions through January 1, 2022. In addition, federal bank regulatory authorities issued guidance to encourage financial institutions to make loan modifications for borrowers affected by COVID-19 and assured financial institutions that they will neither receive supervisory criticism for such prudent loan modifications, nor be required by examiners to automatically categorize COVID-19-related loan modifications as TDRs. The Company is applying this guidance to qualifying loan modifications. Credit quality indicators Loans are regularly reviewed to assess credit quality indicators and to determine appropriate loan classification and grading in accordance with applicable bank regulations. The Company’s risk rating methodology assigns risk ratings ranging from 1 to 9, where a higher rating represents higher risk. The Company differentiates its loan segments based on shared risk characteristics for which expected credit loss is measured on a pool basis. The nine risk rating categories can be generally described by the following groupings for loans: "Pass" (grades 1 through 5): The Company has five pass risk ratings, which represent a level of credit quality that ranges from no well-defined deficiency or weakness to some noted weakness; however, the risk of default on any loan classified as pass is expected to be remote. The five pass risk ratings are described below: Minimal risk. These consist of loans that are fully secured either with cash held in a deposit account at the Bank or by readily marketable securities with an acceptable margin based on the type of security pledged. Low risk. These consist of loans with a high investment grade rating equivalent. Modest risk. These consist of loans where the credit facility greatly exceeds all policy requirements or with policy exceptions that are appropriately mitigated. A secondary source of repayment is verified and considered sustainable. Collateral coverage on these loans is sufficient to fully cover the debt as a tertiary source of repayment. Debt of the borrower is low relative to borrower’s financial strength and ability to pay. Average risk. These consist of loans where the credit facility meets or exceeds all policy requirements or with policy exceptions that are appropriately mitigated. A secondary source of repayment is available to service the debt. Collateral coverage is more than adequate to cover the debt. The borrower exhibits acceptable cash flow and moderate leverage. Acceptable risk. These consist of loans with an acceptable primary source of repayment, but a less than preferable secondary source of repayment. Cash flow is adequate to service debt, but there is minimal excess cash flow. Leverage is moderate or high. "Special mention" (grade 6): Generally these are assets that possess potential weaknesses that warrant management's close attention. These loans may involve borrowers with adverse financial trends, higher debt-to-equity ratios, or weaker liquidity positions, but not to the degree of being considered a “problem loan” where risk of loss may be apparent. Loans in this category are usually performing as agreed, although there may be non-compliance with financial covenants. "Substandard" (grade 7): These assets are characterized by well-defined credit weaknesses and carry the distinct possibility that the Company will sustain some loss if such weakness or deficiency is not corrected. All loans 90 days or more past due and all loans on nonaccrual status are considered at least "Substandard," unless extraordinary circumstances would suggest otherwise. "Doubtful" (grade 8): These assets have all the weaknesses inherent in those classified as "Substandard" with the added characteristic that the weaknesses present make collection or liquidation in full, on the basis of currently existing facts, conditions and values, highly questionable and improbable, but because of certain known factors that may work to the advantage and strengthening of the asset (for example, capital injection, perfecting liens on additional collateral and refinancing plans), classification as an estimated loss is deferred until a more precise status may be determined. Due to the high probability of loss, loans classified as "Doubtful" are placed on nonaccrual status. "Loss" (grade 9): These assets are considered uncollectible and having such little recoverable value that it is not practical to defer writing off the asset. This classification does not mean that the loan has absolutely no recovery or salvage value, but rather that it is not practicable or desirable to defer writing off the asset, even though partial recovery may be achieved in the future.
Allowance for Credit Losses	Allowance for credit losses on loans On January 1, 2020, the Company adopted the amendments within ASU 2016-13, Measurement of Credit Losses on Financial Instruments , which changes the impairment model for most financial assets carried at amortized cost from an incurred loss model to an expected loss model. The discussion below reflects the current expected credit loss model methodology. Credit risk is inherent in the business of extending loans and leases to borrowers and is continuously monitored by management and reflected within the allowance for credit losses for loans. The allowance for credit losses is an estimate of life-of-loan losses for the Company's loans held for investment. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of a loan to present the net amount expected to be collected on the loan. Accrued interest receivable on loans, which is included in other assets on the Consolidated Balance Sheet, is excluded from the estimate of expected credit losses. Expected recoveries of amounts previously written off and expected to be written off are included in the valuation account and may not exceed the aggregate of amounts previously written off and expected to be written off. The Company formally re-evaluates and establishes the appropriate level of the allowance for credit losses on a quarterly basis. Determining the appropriateness of the allowance is complex and requires judgment by management about the effect of matters that are inherently uncertain. In future periods, evaluations of the overall loan portfolio or particular segments of the loan portfolio, in light of the factors and forecasts then prevailing, may result in significant changes in the allowance for credit losses and credit loss expense in those future periods. The allowance level is influenced by loan volumes, mix, loan performance metrics, asset quality characteristics, delinquency status, historical credit loss experience, and the inputs and assumptions in economic forecasts, such as macroeconomic inputs, length of reasonable and supportable forecast periods, and reversion methods. The methodology for estimating the amount of expected credit losses reported in the allowance for credit losses has two basic components: first, an asset-specific component involving individual loans that do not share risk characteristics with other loans and the measurement of expected credit losses for such individual loans and; second, a pooled component for estimated expected credit losses for pools of loans that share similar risk characteristics. Loans that do not share risk characteristics with other loans Loans that do not share risk characteristics with other loans are evaluated on an individual basis. Loans evaluated individually are not included in the collective evaluation. These loans consist of loans with unique features or loans that no longer share risk characteristics with other pooled loans. The process for determining whether a loan should be evaluated on an individual basis begins with determination of credit rating. All loans graded substandard or worse and all PCD loans, irrespective of credit rating, are assigned a reserve based on an individual evaluation. For these loans, the allowance is based primarily on the fair value of the underlying collateral, utilizing independent third-party appraisals. Loans that share similar risk characteristics with other loans In estimating the component of the allowance for credit losses for loans that share similar risk characteristics with other loans, such loans are segregated into loan segments. The Company's primary portfolio segments have changed due to adoption of the amendments within ASU 2016-13 to align with the methodology applied in estimating the allowance for credit losses under CECL. Loans are designated into loan segments based on loans pooled by product types, business lines, and similar risk characteristics or areas of risk concentration. Accordingly, the loan portfolio segments discussed below are based upon CECL-defined shared risk characteristics and are not comparable to the segments reported prior to adoption of the new accounting guidance. In determining the allowance for credit losses, the Company derives an estimate of expected credit losses primarily using an expected loss methodology that incorporates risk parameters (probability of default, loss given default, and exposure at default), which are derived from various vendor models, internally-developed statistical models, or non-statistical estimation approaches. Probability of default is projected in these models or estimation approaches using multiple economic scenarios, whose outcomes are weighted based on the Company's economic outlook and were developed to incorporate relevant information about past events, current conditions, and reasonable and supportable forecasts. With the exception of the Company's residential loan segment, the Company's PD models share a common definition of default, which include loans that are 90 days past due, on nonaccrual status, have a charge-off, or obligor bankruptcy. Input reversion is used for all loan segment models, except for the commercial and industrial and CRE, owner-occupied loan segments. Output reversion is used for the commercial and industrial and CRE, owner-occupied segments by incorporating, after the forecast period, a one-year linear reversion to the long-term reversion rate in year three through the remaining life of the loans within the respective segments. LGDs are typically derived from the Company's historical loss experience. However, for the residential, warehouse lending, and municipal and nonprofit loan segments, where the Company has either zero (or near zero) losses, or has a limited loss history through the last economic downturn, certain non-modeled methodologies are employed. Factors utilized in calculating average LGD vary for each loan segment and are further described below. Exposure at default refers to the Company's exposure to loss at the time of borrower default. For revolving lines of credit, the Company incorporates an expectation of increased line utilization for a higher EAD on defaulted loans based on historical experience. For term loans, EAD is calculated using an amortization schedule based on contractual loan terms, adjusted for a prepayment rate assumption. Prepayment trends are sensitive to interest rates and the macroeconomic environment. Fixed rate loans are more influenced by interest rates, whereas variable rate loans are more influenced by the macroeconomic environment. After the quantitative expected loss estimates are calculated, management then adjusts these estimates to incorporate considerations of current trends and conditions that are not captured in the quantitative loss estimates, through the use of qualitative and/or environmental factors. The following provides credit quality indicators and risk elements most relevant in monitoring and measuring the allowance for credit losses on loans for each of the loan portfolio segments identified: Warehouse lending The warehouse lending portfolio segment consists of mortgage warehouse lines, mortgage servicing rights financing facilities, and note finance loans, which have a monitored borrowing base to mortgage companies and similar lenders and are primarily structured as commercial and industrial loans. These loans are collateralized by real estate notes and mortgages or mortgage servicing rights and the borrowing base of these loans is tightly monitored and controlled by the Company. The primary support for the loan takes the form of pledged collateral, with secondary support provided by the capacity of the financial institution. The collateral-driven nature of these loans distinguish them from traditional commercial and industrial loans. These loans are impacted by interest rate shocks, residential lending rates, prepayment assumptions, and general real estate stress. As a result of the unique loan characteristics, limited historical default and loss experience, and the collateral nature of this loan portfolio segment, the Company uses a non-modeled approach to estimate expected credit losses, leveraging grade information, grade migration history, and management judgment. Municipal and nonprofit The municipal and nonprofit portfolio segment consists of loans to local governments, government-operated utilities, special assessment districts, hospitals, schools and other nonprofits. These loans are generally, but not exclusively, entered into for the purpose of financing real estate investment or for refinancing existing debt and are primarily structured as commercial and industrial loans. Loans are supported by taxes or utility fees, and in some cases tax liens on real estate, operating revenue of the institution, or other collateral support the loans. Unemployment rates and the market valuation of residential properties have an effect on the tax revenues supporting these loans; however, these loans tend to be less cyclical in comparison to similar commercial loans as these loans rely on diversified tax bases. The Company uses a non-modeled approach to estimate expected credit losses, leveraging grade information and historical municipal default rates. Tech & innovation The Tech & innovation portfolio segment is comprised of commercial loans that are originated within this business line and not collateralized by real estate. The source of repayment of these loans is generally expected to be the income that is generated from the business. The models used to estimate expected credit losses for this loan segment include a combination of a vendor model and an internally-developed model. These models incorporate both market level and company-specific factors such as financial statement variables, adjusted for the current stage of the credit cycle and for the Company's loan performance data such as delinquency, utilization, maturity, and size of the loan commitment under specific macroeconomic scenarios to produce a probability of default. Macroeconomic variables include the Dow Jones Index, credit spread between the BBB Bond Yield and 10-Year Treasury Bond Yield, unemployment rate, and CBOE VIX Index quarterly high. LGD and the prepayment rate assumption for EAD for this loan segment are driven by unemployment levels. Other commercial and industrial The other commercial and industrial segment is comprised of commercial and industrial loans that are not originated within the Company's specialty business lines and are not collateralized by real estate. The models used to estimate expected credit losses for this loan segment is the same as those used for the Tech & Innovation portfolio segment. Commercial real estate, owner-occupied The CRE, owner-occupied portfolio segment is comprised of commercial loans that are collateralized by real estate, where the primary source of repayment is the business that occupies the property. These loans are typically entered into for the purpose of providing real estate finance or improvement. The primary source of repayment of these loans is the income generated by the business and where rental or sale of the property may provide secondary support for the loan. These loans are sensitive to general economic conditions as well as the market valuation of CRE properties. The probability of default estimate for this loan segment is modeled using the same model as the commercial and industrial loan segment. LGD for this loan segment is driven by property appreciation and the prepayment rate assumption for EAD is driven by unemployment levels. Hotel franchise finance The Hotel franchise finance segment is comprised of loans that are originated within this business line and are collateralized by real estate, where the owner is not the primary tenant. These loans are typically entered into for the purpose of financing or the improvement of commercial investment properties. The primary source of repayment of these loans are the rents paid by tenants and where the sale of the property may provide secondary support for the loan. These loans are sensitive to the market valuation of CRE properties, rental rates, and general economic conditions. The vendor model used to estimate expected credit losses for this loan segment projects probabilities of default and exposure at default based on multiple macroeconomic scenarios by modeling how macroeconomic conditions affect the commercial real estate market. Real estate market factors utilized in this model include vacancy rate, rental growth rate, net operating income growth rate, and commercial property price changes for each specific property type. The model then incorporates loan and property-level characteristics including debt coverage, leverage, collateral size, seasoning, and property type. LGD for this loan segment is derived from a non-modeled approach that is driven by property appreciation and the prepayment rate assumption for EAD is driven by the property appreciation for fixed rate loans and unemployment levels for variable rate loans. Other commercial real estate, non-owner occupied The other commercial real estate, non-owner occupied segment is comprised of loans that are not originated within the Company's specialty business lines and are collateralized by real estate, where the owner is not the primary tenant. The model used to estimate expected credit losses for this loan segment is the same as the model used for the Hotel Franchise Finance portfolio segment. Residential The residential loan portfolio segment is comprised of loans collateralized primarily by first liens on 1-4 residential family properties and home equity lines of credit that are collateralized by either first liens or junior liens on residential properties. The primary source of repayment of these loans is the value of the property and the capacity of the owner to make payments on the loan. Unemployment rates and the market valuation of residential properties will impact the ultimate repayment of these loans. The residential mortgage loan model is a vendor model that projects probability of default, loss given default severity, prepayment rate, and exposure at default to calculate expected losses. The model is intended to capture the borrower's payment behavior during the lifetime of the residential loan by incorporating loan level characteristics such as loan type, coupon, age, loan-to-value, and credit score and economic conditions such as Home Price Index, interest rate, and unemployment rate. A default event for residential loans is defined as 60 days or more past due, with property appreciation as the driver for LGD results. The prepayment rate assumption for exposure at default for residential loans is based on industry prepayment history. Probability of default for HELOCs is derived from an internally-developed model that projects PD by incorporating loan level information such as FICO score, lien position, balloon payments, and macroeconomic conditions such as property appreciation. LGD for this loan segment is driven by property appreciation and lien position. Exposure at default for HELOCs is calculated based on utilization rate assumptions using a non-modeled approach and incorporates management judgment. Construction and land development The construction and land portfolio segment is comprised of loans collateralized by land or real estate, which are entered into for the purpose of real estate development. The primary source of repayment of loans is the eventual sale or refinance of the completed project and where claims on the property provide secondary support for the loan. These loans are impacted by the market valuation of CRE and residential properties and general economic conditions that have a higher sensitivity to real estate markets compared to other real estate loans. Default risk of a property is driven by loan-specific drivers, including loan-to-value, maturity, origination date, and the MSA in which the property is located, among other items. The variables used in the internally-developed model include loan level drivers such as origination loan-to-value, loan maturity, and macroeconomic drivers such as property appreciation, MSA level unemployment rate, and national GDP growth. LGD for this loan segment is driven by property appreciation. The prepayment rate assumption for EAD is driven by the property appreciation for fixed rate loans and unemployment levels for variable rate loans. Other
Lessee, Leases [Policy Text Block]	Leases (lessee) At inception, contracts are evaluated to determine whether the contract constitutes a lease agreement. For contracts that are determined to be an operating lease, a corresponding ROU asset and operating lease liability are recorded in separate line items on the Consolidated Balance Sheet. A ROU asset represents the Company’s right to use an underlying asset during the lease term and a lease liability represents the Company’s commitment to make contractually obligated lease payments. Operating lease ROU assets and liabilities are recognized at the commencement date of the lease and are based on the present value of lease payments over the lease term. The measurement of the operating lease ROU asset includes any lease payments made and is reduced by lease incentives that are paid or are payable to the Company. Variable lease payments that depend on an index or rate such as the Consumer Price Index are included in lease payments based on the rate in effect at the commencement date of the lease. Lease payments are recognized on a straight-line basis as part of occupancy expense over the lease term. As the rate implicit in the lease is not readily determinable, the Company's incremental collateralized borrowing rate is used to determine the present value of lease payments. This rate gives consideration to the applicable FHLB collateralized borrowing rates and is based on the information available at the commencement date. The Company has elected to apply the short-term lease measurement and recognition exemption to leases with an initial term of 12 months or less; therefore, these leases are not recorded on the Company’s Consolidated Balance Sheet, but rather, lease expense is recognized over the lease term on a straight-line basis. The Company’s lease agreements may include options to extend or terminate the lease. These options are included in the lease term when it is reasonably certain that the options will be exercised.
Goodwill and Other Intangible Assets	Goodwill and other intangible assets The Company records as goodwill the excess of the purchase price in a business combination over the fair value of the identifiable net assets acquired in accordance with applicable guidance. The Company performs its annual goodwill and intangibles impairment tests as of October 1 each year, or more often if events or circumstances indicate that the carrying value may not be recoverable. The Company can first elect to assess, through qualitative factors, whether it is more likely than not that goodwill is impaired. If the qualitative assessment indicates potential impairment, a quantitative impairment test is necessary. If, based on the quantitative test, a reporting unit's carrying amount exceeds its fair value, a goodwill impairment charge for this difference is recorded to current period earnings as non-interest expense. The Company’s intangible assets consist primarily of core deposit intangible assets that are amortized over periods ranging from five to 10 years. The Company considers the remaining useful lives of its core deposit intangible assets each reporting period, as required by ASC 350, Intangibles—Goodwill and Other, to determine whether events and circumstances warrant a revision to the remaining period of amortization. If the estimate of an intangible asset’s remaining useful life has changed, the remaining carrying amount of the intangible asset is amortized prospectively over the revised remaining useful life. The Company has not revised its estimates of the useful lives of its core deposit intangibles during the three months ended March 31, 2021 or 2020.
Stockholders' Equity, Policy	Stock compensation plans The Company has the Incentive Plan, as amended, which is described more fully in "Note 6. Stockholders' Equity" of these Notes to Unaudited Consolidated Financial Statements. Compensation expense on non-vested restricted stock awards is based on the fair value of the award on the measurement date which, for the Company, is the date of the grant and is recognized ratably over the service period of the award. Forfeitures are estimated at the time of the award grant and revised in subsequent periods if actual forfeitures differ from those estimates. The fair value of non-vested restricted stock awards is the market price of the Company’s stock on the date of grant. The Company's performance stock units have a cumulative EPS target and a TSR performance measure component. The TSR component is a market-based performance condition that is separately valued as of the date of the grant. A Monte Carlo valuation model is used to determine the fair value of the TSR performance metric, which simulates potential TSR outcomes over the performance period and determines the payouts that would occur in each scenario. The resulting fair value of the TSR component is based on the average of these results. Compensation expense related to the TSR component is based on the fair value determination on the date of the grant and is not subsequently revised based on actual performance. Compensation expense on the EPS component for these awards is based on the fair value (market price of the Company's stock on the date of the grant) of the award. Compensation expense related to both the TSR and EPS components is recognized ratably over the service period of the award. See "Note 6. Stockholders' Equity" of these Notes to Unaudited Consolidated Financial Statements for further discussion of stock awards. Dividends WAL is a legal entity separate and distinct from its subsidiaries. As a holding company with limited significant assets other than the capital stock of its subsidiaries, WAL's ability to pay dividends depends primarily upon the receipt of dividends or other capital distributions from its subsidiaries. The Company's subsidiaries' ability to pay dividends to WAL is subject to, among other things, their individual earnings, financial condition, and need for funds, as well as federal and state governmental policies and regulations applicable to WAL and each of those subsidiaries, which limit the amount that may be paid as dividends without prior approval. In addition, the terms and conditions of other securities the Company issues may restrict its ability to pay dividends to holders of the Company's common stock. For example, if any required payments on outstanding trust preferred securities are not made, WAL would be prohibited from paying cash dividends on its common stock. Treasury shares The Company separately presents treasury shares, which represent shares surrendered to the Company equal in value to the statutory payroll tax withholding obligations arising from the vesting of employee restricted stock awards. Treasury shares are carried at cost. Common stock repurchases
Derivative Financial Instruments	Derivative financial instruments The Company uses interest rate swaps to mitigate interest-rate risk associated with changes to the fair value of certain fixed-rate financial instruments (fair value hedges). The Company recognizes derivatives as assets or liabilities on the Consolidated Balance Sheet at their fair value in accordance with ASC 815, Derivatives and Hedging . The accounting for changes in the fair value of a derivative instrument depends on whether it has been designated and qualifies as part of a hedging relationship and further, on the type of hedging relationship. Derivative instruments designated in a hedge relationship to mitigate exposure to changes in the fair value of an asset or liability attributable to a particular risk, such as interest rate risk, are considered fair value hedges. Changes in the fair value of a derivative that is designated and qualifies as a fair value hedge, along with changes in the fair value of the hedged asset or liability that are attributable to the hedged risk, are recorded in current period earnings. Changes in the fair value of derivatives not considered to be highly effective in hedging the change in fair value of the hedged item are recognized in earnings as non-interest income during the period of the change. The Company documents its hedge relationships, including identification of the hedging instruments and the hedged items, as well as its risk management objectives and strategies for undertaking the hedge transaction after the derivative contract is executed. At inception, the Company performs a quantitative assessment to determine whether the derivatives used in hedging transactions are highly effective (as defined in the guidance) in offsetting changes in the fair value of the hedged item. Retroactive effectiveness is assessed, as well as the continued expectation that the hedge will remain effective prospectively. After the initial quantitative assessment is performed, on a quarterly basis, the Company performs a qualitative hedge effectiveness assessment. This assessment takes into consideration any adverse developments related to the counterparty's risk of default and any negative events or circumstances that affect the factors that originally enabled the Company to assess that it could reasonably support, qualitatively, an expectation that the hedging relationship was and will continue to be highly effective. The Company discontinues hedge accounting prospectively when it is determined that a hedge is no longer highly effective. When hedge accounting is discontinued on a fair value hedge that no longer qualifies as an effective hedge, the derivative instrument continues to be reported at fair value on the Consolidated Balance Sheet, but the carrying amount of the hedged item is no longer adjusted for future changes in fair value. The adjustment to the carrying amount of the hedged item that existed at the date hedge accounting is discontinued is amortized over the remaining life of the hedged item into earnings. Derivative instruments that are not designated as hedges, so called free-standing derivatives, are reported on the Consolidated Balance Sheet at fair value and the changes in fair value are recognized in earnings as non-interest income during the period of change. The Company may in the normal course of business purchase a financial instrument or originate a loan that contains an embedded derivative instrument. Upon purchasing the instrument or originating the loan, the Company assesses whether the economic characteristics of the embedded derivative are clearly and closely related to the economic characteristics of the remaining component of the financial instrument (i.e., the host contract) and whether a separate instrument with the same terms as the embedded instrument would meet the definition of a derivative instrument. When it is determined that the embedded derivative possesses economic characteristics that are not clearly and closely related to the economic characteristics of the host contract and a separate instrument with the same terms would qualify as a derivative instrument, the embedded derivative is separated from the host contract and carried at fair value. However, in cases where the host contract is measured at fair value, with changes in fair value reported in current earnings, or the Company is unable to reliably identify and measure an embedded derivative for separation from its host contract, the entire contract is carried on the Consolidated Balance Sheet at fair value and is not designated as a hedging instrument.
Off-Balance Sheet Instruments	Off-balance sheet instruments In the ordinary course of business, the Company has entered into off-balance sheet financial instrument arrangements consisting of commitments to extend credit and standby letters of credit. Such financial instruments are recorded in the Consolidated Financial Statements when they are funded. They involve, to varying degrees, elements of credit risk in excess of amounts recognized on the Consolidated Balance Sheet. Losses could be experienced when the Company is contractually obligated to make a payment under these instruments and must seek repayment from the borrower, which may not be as financially sound in the current period as they were when the commitment was originally made. Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract and, in certain instances, may be unconditionally cancelable. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. The Company enters into credit arrangements that generally provide for the termination of advances in the event of a covenant violation or other event of default. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. The Company evaluates each customer’s creditworthiness on a case-by-case basis. The amount of collateral obtained, if deemed necessary by the Company upon extension of credit, is based on management’s credit evaluation of the party. The commitments are collateralized by the same types of assets used as loan collateral. The Company also has off-balance sheet arrangements related to its derivative instruments. Derivative instruments are recognized in the Consolidated Financial Statements at fair value and their notional values are carried off-balance sheet. See "Note 8. Derivatives and Hedging Activities" of these Notes to Unaudited Consolidated Financial Statements for further discussion.
Fair Values of Financial Instruments	Fair values of financial instruments The Company uses fair value measurements to record fair value adjustments to certain assets and liabilities. ASC 820, Fair Value Measurement , establishes a framework for measuring fair value and a three-level valuation hierarchy for disclosure of fair value measurement, and also sets forth disclosure requirements for fair value measurements. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability as of the measurement date. The Company uses various valuation approaches, including market, income, and/or cost approaches. ASC 820 establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the asset or liability developed based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the factors market participants would consider in pricing the asset or liability developed based on the best information available in the circumstances. The hierarchy is broken down into three levels based on the reliability of inputs, as follows: • Level 1 - Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities. • Level 2 - Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. These might include quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (such as interest rates, prepayment speeds, volatilities, etc.) or model-based valuation techniques where all significant assumptions are observable, either directly or indirectly, in the market. • Level 3 - Valuation is generated from model-based techniques where one or more significant inputs are not observable, either directly or indirectly, in the market. These unobservable assumptions reflect the Company’s own estimates of assumptions that market participants would use in pricing the asset or liability. Valuation techniques may include use of matrix pricing, discounted cash flow models, and similar techniques. The availability of observable inputs varies based on the nature of the specific financial instrument. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. In certain cases, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, for disclosure purposes, the level in the fair value hierarchy within which the fair value measurement in its entirety falls is determined based on the lowest level input that is significant to the fair value measurement in its entirety. Fair value is a market-based measure considered from the perspective of a market participant who may purchase the asset or assume the liability, rather than an entity-specific measure. When market assumptions are available, ASC 820 requires that the Company consider the assumptions that market participants would use to estimate the fair value of the financial instrument at the measurement date. ASC 825, Financial Instruments , requires disclosure of fair value information about financial instruments, whether or not recognized in the balance sheet, for which it is practicable to estimate that value. Management uses its best judgment in estimating the fair value of the Company’s financial instruments; however, there are inherent limitations in any estimation technique. Therefore, for substantially all financial instruments, the fair value estimates presented herein are not necessarily indicative of the amounts the Company could have realized in a sales transaction at March 31, 2021 and December 31, 2020. The estimated fair value amounts for March 31, 2021 and December 31, 2020 have been measured as of period-end, and have not been re-evaluated or updated for purposes of these Unaudited Consolidated Financial Statements subsequent to those dates. As such, the estimated fair values of these financial instruments subsequent to the reporting date may be different than the amounts reported at period-end. The information in "Note 12. Fair Value Accounting" of these Notes to Unaudited Consolidated Financial Statements should not be interpreted as an estimate of the fair value of the entire Company since a fair value calculation is only required for a limited portion of the Company’s assets and liabilities. Due to the wide range of valuation techniques and the degree of subjectivity used in making the estimate, comparisons between the Company’s disclosures and those of other companies or banks may not be meaningful. The following methods and assumptions were used by the Company in estimating the fair value of its financial instruments: Cash, cash equivalents, and restricted cash The carrying amounts reported on the Consolidated Balance Sheet for cash and due from banks approximate their fair value. Money market investments The carrying amounts reported on the Consolidated Balance Sheet for money market investments approximate their fair value. Investment securities The fair values of publicly-traded CRA investments, exchange-listed preferred stock, trust preferred securities, and certain corporate debt securities are based on quoted market prices and are categorized as Level 1 in the fair value hierarchy. The fair values of debt securities are primarily determined based on matrix pricing. Matrix pricing is a mathematical technique that utilizes observable market inputs including, for example, yield curves, credit ratings, and prepayment speeds. Fair values determined using matrix pricing are generally categorized as Level 2 in the fair value hierarchy. In addition to matrix pricing, the Company uses other pricing sources, including observed prices on publicly traded securities and dealer quotes, to estimate the fair value of debt securities, which are also categorized as Level 2 in the fair value hierarchy. Restricted stock WAB is a member of the Federal Reserve System and the FHLB and, accordingly, maintains investments in the capital stock of the FRB and the FHLB. These investments are carried at cost since no ready market exists for them, and they have no quoted market value. The Company conducts a periodic review and evaluation of its restricted stock to determine if any impairment exists. The fair values of these investments have been categorized as Level 2 in the fair value hierarchy. Loans The fair value of loans is estimated based on discounted cash flows using interest rates currently being offered for loans with similar terms to borrowers with similar credit quality and adjustments that the Company believes a market participant would consider in determining fair value based on a third-party independent valuation. As a result, the fair value for loans is categorized as Level 3 in the fair value hierarchy. Accrued interest receivable and payable The carrying amounts reported on the Consolidated Balance Sheet for accrued interest receivable and payable approximate their fair values. Derivative financial instruments All derivatives are recognized on the Consolidated Balance Sheets at their fair value. The fair value for derivatives is determined based on market prices, broker-dealer quotations on similar products, or other related input parameters. As a result, the fair values have been categorized as Level 2 in the fair value hierarchy. Deposits The fair value disclosed for demand and savings deposits is by definition equal to the amount payable on demand at their reporting date (that is, their carrying amount), as these deposits do not have a contractual term. The carrying amount for variable rate deposit accounts approximates their fair value. Fair values for fixed rate certificates of deposit are estimated using a discounted cash flow calculation that applies interest rates currently being offered on certificates to a schedule of aggregated expected monthly maturities on these deposits. The fair value measurement of the deposit liabilities is categorized as Level 2 in the fair value hierarchy. FHLB advances and customer repurchase agreements The fair values of the Company’s borrowings are estimated using discounted cash flow analyses, based on the market rates for similar types of borrowing arrangements. The FHLB advances and customer repurchase agreements have been categorized as Level 2 in the fair value hierarchy due to their short durations. Subordinated debt The fair value of subordinated debt is based on the market rate for the respective subordinated debt security. Subordinated debt has been categorized as Level 2 in the fair value hierarchy. Junior subordinated debt Junior subordinated debt is valued based on a discounted cash flow model which uses as inputs Treasury Bond rates and the 'BB' and 'BBB' rated financial indexes. Junior subordinated debt has been categorized as Level 3 in the fair value hierarchy. Off-balance sheet instruments The fair value of the Company’s off-balance sheet instruments (lending commitments and letters of credit) is based on quoted fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements, and the counterparties’ credit standing.
Income Taxes	Income taxes The Company is subject to income taxes in the United States and files a consolidated federal income tax return with all of its subsidiaries, with the exception of BW Real Estate, Inc. Deferred income taxes are recorded to reflect the effects of temporary differences between the financial reporting carrying amounts of assets and liabilities and their income tax bases using enacted tax rates that are expected to be in effect when the taxes are actually paid or recovered. As changes in tax laws or rates are enacted, deferred tax assets and liabilities are adjusted through the provision for income taxes. Net deferred tax assets are recorded to the extent that these assets will more-likely-than-not be realized. In making these determinations, all available positive and negative evidence is considered, including scheduled reversals of deferred tax liabilities, tax planning strategies, projected future taxable income, and recent operating results. If it is determined that deferred income tax assets to be realized in the future are in excess of their net recorded amount, an adjustment to the valuation allowance will be recorded, which will reduce the Company's provision for income taxes.
Revenue from Contract with Customer [Policy Text Block]	Non-interest income Non-interest income includes service charges and fees, income from equity investments, card income, foreign currency income, income from bank owned life insurance, lending related income, net gain or loss on sales of investment securities, net fair value gain or loss adjustments on assets measured at fair value, and other income. Service charges and fees consist of fees earned from performance of account analysis, general account services, and other deposit account services. These fees are recognized as the related services are provided in accordance with ASC 606, Revenue from Contracts with Customers . Income from equity investments includes gains on equity warrant assets, SBIC equity income, and success fees. Card income includes fees earned from customer use of debit and credit cards, interchange income from merchants, and international charges. Card income is generally within the scope of ASC 310, Receivables ; however, certain processing transactions for merchants, such as interchange fees, are within the scope of ASC 606. Foreign currency income represents fees earned on the differential between purchases and sales of foreign currency on behalf of the Company’s clients. Income from bank owned life insurance is accounted for in accordance with ASC 325, Investments - Other . Lending related income includes fees earned from gains or losses on the sale of loans, SBA income, and letter of credit fees. Gains and losses on the sale of loans and SBA income are recognized pursuant to ASC 860, Transfers and Servicing . Net unrealized gains or losses on assets measured at fair value represent fair value changes in equity securities and are accounted for in accordance with ASC 321, Investments - Equity Securities . Fees related to standby letters of credit are accounted for in accordance with ASC 440, Commitments . Other income includes operating lease income, which is recognized on a straight-line basis over the lease term in accordance with ASC 842, Leases . Net gain or loss on sales/valuations of repossessed and other assets is presented as a component of non-interest expense, but may also be presented as a component of non-interest income in the event that a net gain is recognized. Net gain or loss on sales of repossessed and other assets are accounted for in accordance with ASC 610, Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets

Investment Securities (Tables)

Investment Securities (Tables)	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Table Text Block]	Three Months Ended March 31, 2021 Balance, Provision for Credit Losses Write-offs Recoveries Balance, (in millions) Held-to-maturity debt securities Tax-exempt $ 6.8 $ 2.4 $ — $ — $ 9.2 Three Months Ended March 31, 2020: Balance, Provision for Credit Losses Write-offs Recoveries Balance (in millions) Held-to-maturity debt securities Tax-exempt $ 2.6 $ 0.3 $ — $ — $ 2.9
Carrying Amounts and Fair Values of Investment Securities	The carrying amounts and fair values of investment securities at March 31, 2021 and December 31, 2020 are summarized as follows: March 31, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized (Losses) Fair Value (in millions) Held-to-maturity Tax-exempt $ 698.0 $ 43.8 $ (1.4) $ 740.4 Available-for-sale debt securities CLO $ 980.3 $ 0.8 $ (0.4) $ 980.7 Commercial MBS issued by GSEs 88.0 1.6 (1.8) 87.8 Corporate debt securities 286.0 5.0 (5.9) 285.1 Private label residential MBS 1,905.7 9.8 (14.9) 1,900.6 Residential MBS issued by GSEs 2,277.8 18.5 (46.7) 2,249.6 Tax-exempt 1,271.4 62.0 (3.7) 1,329.7 U.S. treasury securities 50.0 — — 50.0 Other 54.1 7.4 (5.1) 56.4 Total AFS debt securities $ 6,913.3 $ 105.1 $ (78.5) $ 6,939.9 Equity securities CRA investments $ 57.6 $ — $ (0.2) $ 57.4 Preferred stock 129.5 6.2 (0.2) 135.5 Total equity securities $ 187.1 $ 6.2 $ (0.4) $ 192.9 December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized (Losses) Fair Value (in millions) Held-to-maturity Tax-exempt $ 568.8 $ 43.0 $ — $ 611.8 Available-for-sale debt securities CLO $ 146.9 $ — $ — $ 146.9 Commercial MBS issued by GSEs 80.8 3.8 — 84.6 Corporate debt securities 271.1 4.8 (5.7) 270.2 Private label residential MBS 1,461.7 15.7 (0.5) 1,476.9 Residential MBS issued by GSEs 1,462.5 27.9 (3.8) 1,486.6 Tax-exempt 1,109.3 78.1 — 1,187.4 Other 54.1 7.3 (5.5) 55.9 Total AFS debt securities $ 4,586.4 $ 137.6 $ (15.5) $ 4,708.5 Equity securities CRA investments $ 53.1 $ 0.3 $ — $ 53.4 Preferred stock 107.0 7.3 (0.4) 113.9 Total equity securities $ 160.1 $ 7.6 $ (0.4) $ 167.3 Securities with carrying amounts of approximately $693.2 million and $778.0 million at March 31, 2021 and December 31, 2020, respectively, were pledged for various purposes as required or permitted by law.
Unrealized Losses and Fair Value of Investment Securities in Continuous Unrealized Loss Position	unrealized loss position at March 31, 2021 and December 31, 2020, aggregated by major security type and length of time in a continuous unrealized loss position: March 31, 2021 Less Than Twelve Months More Than Twelve Months Total Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (in millions) Held-to-maturity Tax-exempt $ 1.4 $ 48.0 $ — $ — $ 1.4 $ 48.0 Available-for-sale debt securities CLO $ 0.4 $ 638.6 $ — $ — $ 0.4 $ 638.6 Commercial MBS issued by GSEs 1.8 48.0 — — 1.8 48.0 Corporate debt securities 0.2 32.0 5.7 94.3 5.9 126.3 Private label residential MBS 14.5 810.2 0.4 9.6 14.9 819.8 Residential MBS issued by GSEs 46.7 1,225.7 — — 46.7 1,225.7 Tax-exempt 3.7 158.0 — — 3.7 158.0 Other 0.4 11.6 4.7 27.3 5.1 38.9 Total AFS securities $ 67.7 $ 2,924.1 $ 10.8 $ 131.2 $ 78.5 $ 3,055.3 December 31, 2020 Less Than Twelve Months More Than Twelve Months Total Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (in millions) Available-for-sale debt securities Corporate debt securities $ 0.1 $ 17.3 $ 5.6 $ 94.3 $ 5.7 $ 111.6 Private label residential MBS 0.5 149.7 — — 0.5 149.7 Residential MBS issued by GSEs 3.8 231.9 — — 3.8 231.9 Other — — 5.5 26.5 5.5 26.5 Total AFS securities $ 4.4 $ 398.9 $ 11.1 $ 120.8 $ 15.5 $ 519.7
Amortized Cost and Fair Value of Investment Securities by Contractual Maturities	A security is considered to be past due once it is 30 days contractually past due under the terms of the agreement. As of March 31, 2021, there were no investment securities that were past due. In addition, the Company does not have a significant amount of investment securities on nonaccrual status as of March 31, 2021. The amortized cost and fair value of the Company's debt securities as of March 31, 2021, by contractual maturities, are shown below. MBS are shown separately as individual MBS are comprised of pools of loans with varying maturities. Therefore, these securities are listed separately in the maturity summary. March 31, 2021 Amortized Cost Estimated Fair Value (in millions) Held-to-maturity Due in one year or less $ 10.7 $ 10.7 After one year through five years 31.3 31.8 After ten years 656.0 697.9 Total HTM securities $ 698.0 $ 740.4 Available-for-sale Due in one year or less $ 50.0 $ 50.0 After one year through five years 38.0 38.5 After five years through ten years 780.5 780.8 After ten years 1,773.3 1,832.6 Mortgage-backed securities 4,271.5 4,238.0 Total AFS securities $ 6,913.3 $ 6,939.9
Investment Securities by Credit Rating Type	The following tables summarize the carrying amount of the Company’s investment ratings position as of March 31, 2021 and December 31, 2020, which are updated quarterly and used to monitor the credit quality of the Company's securities: March 31, 2021 AAA Split-rated AAA/AA+ AA+ to AA- A+ to A- BBB+ to BBB- BB+ and below Unrated Totals (in millions) Held-to-maturity Tax-exempt $ — $ — $ — $ — $ — $ — $ 698.0 $ 698.0 Available-for-sale debt securities CLO $ 25.0 $ — $ 649.8 $ 305.9 $ — $ — $ — $ 980.7 Commercial MBS issued by GSEs — 87.8 — — — — — 87.8 Corporate debt securities — — 19.2 28.1 219.6 18.2 — 285.1 Private label residential MBS 1,812.8 — 86.5 0.1 0.3 0.9 — 1,900.6 Residential MBS issued by GSEs — 2,249.6 — — — — — 2,249.6 Tax-exempt 43.2 56.5 519.1 679.1 — — 31.8 1,329.7 U.S. treasury securities 50.0 — — — — — — 50.0 Other — — 11.6 — 29.8 6.9 8.1 56.4 Total AFS securities (1) $ 1,931.0 $ 2,393.9 $ 1,286.2 $ 1,013.2 $ 249.7 $ 26.0 $ 39.9 $ 6,939.9 Equity securities CRA investments $ — $ 27.4 $ — $ — $ — $ — $ 30.0 $ 57.4 Preferred stock — — — — 81.3 39.1 15.1 135.5 Total equity securities (1) $ — $ 27.4 $ — $ — $ 81.3 $ 39.1 $ 45.1 $ 192.9 (1) Where ratings differ, the Company uses an average of the available ratings by major credit agencies. December 31, 2020 AAA Split-rated AAA/AA+ AA+ to AA- A+ to A- BBB+ to BBB- BB+ and below Unrated Totals (in millions) Held-to-maturity Tax-exempt $ — $ — $ — $ — $ — $ — $ 568.8 $ 568.8 Available-for-sale debt securities CLO $ — $ — $ 139.6 $ 7.3 $ — $ — $ — $ 146.9 Commercial MBS issued by GSEs — 84.6 — — — — — 84.6 Corporate debt securities — — 19.2 28.1 194.5 28.4 — 270.2 Private label residential MBS 1,385.5 — 90.1 0.1 0.3 0.9 — 1,476.9 Residential MBS issued by GSEs — 1,486.6 — — — — — 1,486.6 Tax-exempt 44.3 57.3 454.7 599.3 — — 31.8 1,187.4 Other — — 12.3 — 29.1 6.9 7.6 55.9 Total AFS securities (1) $ 1,429.8 $ 1,628.5 $ 715.9 $ 634.8 $ 223.9 $ 36.2 $ 39.4 $ 4,708.5 Equity securities CRA investments $ — $ 27.8 $ — $ — $ — $ — $ 25.6 $ 53.4 Preferred stock — — — — 73.2 39.0 1.7 113.9 Total equity securities (1) $ — $ 27.8 $ — $ — $ 73.2 $ 39.0 $ 27.3 $ 167.3 (1) Where ratings differ, the Company uses an average of the available ratings by major credit agencies.

Loans, Leases and Allowance for

Loans, Leases and Allowance for Credit Losses (Tables)	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Financing Receivable, Troubled Debt Restructuring [Table Text Block]	The following table presents TDR loans as of March 31, 2021: March 31, 2021 Number of Loans Recorded Investment (dollars in millions) Tech & innovation 4 $ 19.8 Other commercial and industrial 10 24.3 CRE - owner occupied 3 1.9 Hotel franchise finance 2 5.3 Other CRE - non-owned occupied 3 8.9 Total 22 $ 60.2
Schedule of Held for Investment Loan Portfolio Composition of Loans, Leases and Allowance for Credit Losses	The composition of the Company's held for investment loan portfolio is as follows: March 31, 2021 December 31, 2020 (in millions) Warehouse lending $ 4,901.8 $ 4,340.2 Municipal & nonprofit 1,676.9 1,728.8 Tech & innovation 2,514.2 2,548.3 Other commercial and industrial 6,174.3 5,911.2 CRE - owner occupied 1,814.5 1,909.3 Hotel franchise finance 2,038.8 1,983.9 Other CRE - non-owned occupied 3,613.0 3,640.2 Residential 3,055.8 2,378.5 Construction and land development 2,767.6 2,429.4 Other 154.1 183.2 Total loans HFI 28,711.0 27,053.0 Allowance for credit losses (247.1) (278.9) Total loans HFI, net of allowance $ 28,463.9 $ 26,774.1
Contractual Aging of Loan Portfolio by Class of Loans Including Loans Held for Sale and Excluding Deferred Fees/Costs	The following table presents an aging analysis of past due loans by loan portfolio segment: March 31, 2021 Current 30-59 Days 60-89 Days Over 90 days Total Total (in millions) Warehouse lending $ 4,901.8 $ — $ — $ — $ — $ 4,901.8 Municipal & nonprofit 1,676.9 — — — — 1,676.9 Tech & innovation 2,514.2 — — — — 2,514.2 Other commercial and industrial 6,174.2 0.1 — — 0.1 6,174.3 CRE - owner occupied 1,814.5 — — — — 1,814.5 Hotel franchise finance 2,038.8 — — — — 2,038.8 Other CRE - non-owned occupied 3,612.3 0.7 — — 0.7 3,613.0 Residential 3,049.4 6.4 — — 6.4 3,055.8 Construction and land development 2,767.6 — — — — 2,767.6 Other 154.0 — 0.1 — 0.1 154.1 Total loans $ 28,703.7 $ 7.2 $ 0.1 $ — $ 7.3 $ 28,711.0 December 31, 2020 Current 30-59 Days 60-89 Days Over 90 days Total Total (in millions) Warehouse lending $ 4,340.2 $ — $ — $ — $ — $ 4,340.2 Municipal & nonprofit 1,728.8 — — — — 1,728.8 Tech & innovation 2,548.3 — — — — 2,548.3 Other commercial and industrial 5,911.0 0.2 — — 0.2 5,911.2 CRE - owner occupied 1,909.3 — — — — 1,909.3 Hotel franchise finance 1,983.9 — — — — 1,983.9 Other CRE - non-owned occupied 3,640.2 — — — — 3,640.2 Residential 2,368.0 9.1 1.4 — 10.5 2,378.5 Construction and land development 2,429.4 — — — — 2,429.4 Other 182.7 0.4 0.1 — 0.5 183.2 Total loans $ 27,041.8 $ 9.7 $ 1.5 $ — $ 11.2 $ 27,053.0
Summary of Recorded Investment in Nonaccrual Loans and Loans Past Due 90 Days Still Accruing Interest by Loan Class	Loans are placed on nonaccrual status when management determines that the full repayment of principal and collection of interest according to contractual terms is no longer likely, generally when the loan becomes 90 days or more past due. The following tables present nonperforming loan balances by loan portfolio segment: March 31, 2021 Nonaccrual with No Allowance for Credit Loss Nonaccrual with an Allowance for Credit Loss Total Nonaccrual Loans Past Due 90 Days or More and Still Accruing (in millions) Warehouse lending $ — $ — $ — $ — Municipal & nonprofit — — — — Tech & innovation 9.3 3.4 12.7 — Other commercial and industrial 8.6 6.4 15.0 — CRE - owner occupied 32.1 — 32.1 — Hotel franchise finance — — — — Other CRE - non-owned occupied 41.5 — 41.5 — Residential 9.0 — 9.0 — Construction and land development — — — — Other 0.3 3.0 3.3 — Total $ 100.8 $ 12.8 $ 113.6 $ —
Loans by Risk Rating	Credit Quality Indicators The Company categorizes loans into risk categories based on relevant information about the ability of borrowers to service their debt such as current financial information, historical payment experience, credit documentation, public information, and current economic trends, among other factors. The Company analyzes loans individually to classify the loans as to credit risk. This analysis is performed on a quarterly basis. The risk rating categories are described in "Note 1. Summary of Significant Accounting Policies ." The following tables present risk ratings by loan portfolio segment and origination year. The origination year is the year of origination or renewal. Term Loan Amortized Cost Basis by Origination Year Revolving Loans Amortized Cost Basis Total March 31, 2021 2021 2020 2019 2018 2017 Prior (in millions) Warehouse lending Pass $ 91.6 $ 63.2 $ — $ 0.8 $ 1.5 $ — $ 4,744.7 $ 4,901.8 Special mention — — — — — — — — Classified — — — — — — — — Total $ 91.6 $ 63.2 $ — $ 0.8 $ 1.5 $ — $ 4,744.7 $ 4,901.8 Municipal & nonprofit Pass $ 10.7 $ 222.1 $ 133.6 $ 81.4 $ 227.7 $ 997.9 $ 3.5 $ 1,676.9 Special mention — — — — — — — — Classified — — — — — — — — Total $ 10.7 $ 222.1 $ 133.6 $ 81.4 $ 227.7 $ 997.9 $ 3.5 $ 1,676.9 Tech & innovation Pass $ 124.9 $ 549.2 $ 150.7 $ 45.1 $ 2.3 $ 0.4 $ 1,590.9 $ 2,463.5 Special mention 4.0 14.4 — — — — — 18.4 Classified 18.7 5.6 6.7 1.3 — — — 32.3 Total $ 147.6 $ 569.2 $ 157.4 $ 46.4 $ 2.3 $ 0.4 $ 1,590.9 $ 2,514.2 Other commercial and industrial Pass $ 1,025.9 $ 1,553.9 $ 736.5 $ 384.4 $ 204.8 $ 200.0 $ 1,907.1 $ 6,012.6 Special mention 0.2 2.8 43.1 17.8 29.9 4.8 5.2 103.8 Classified — 0.9 19.7 3.7 16.2 10.6 6.8 57.9 Total $ 1,026.1 $ 1,557.6 $ 799.3 $ 405.9 $ 250.9 $ 215.4 $ 1,919.1 $ 6,174.3 CRE - owner occupied Pass $ 88.3 $ 245.1 $ 291.8 $ 235.9 $ 370.8 $ 420.0 $ 32.6 $ 1,684.5 Special mention 2.3 0.9 11.5 9.2 22.5 13.8 24.4 84.6 Classified — 1.4 6.8 4.7 5.2 27.3 — 45.4 Total $ 90.6 $ 247.4 $ 310.1 $ 249.8 $ 398.5 $ 461.1 $ 57.0 $ 1,814.5 Hotel franchise finance Pass $ 102.8 $ 166.2 $ 684.7 $ 448.3 $ 139.0 $ 70.5 $ 158.8 $ 1,770.3 Special mention — 6.1 82.8 56.7 27.4 11.9 — 184.9 Classified — 11.0 56.8 — 12.5 3.3 — 83.6 Total $ 102.8 $ 183.3 $ 824.3 $ 505.0 $ 178.9 $ 85.7 $ 158.8 $ 2,038.8 Other CRE - non-owned occupied Pass $ 167.1 $ 1,069.3 $ 857.6 $ 527.1 $ 317.5 $ 337.4 $ 271.8 $ 3,547.8 Special mention — 1.4 — 8.3 1.4 11.2 — 22.3 Classified — 0.4 23.8 — 1.6 17.1 — 42.9 Total $ 167.1 $ 1,071.1 $ 881.4 $ 535.4 $ 320.5 $ 365.7 $ 271.8 $ 3,613.0 Residential Pass $ 599.9 $ 1,116.5 $ 715.6 $ 338.4 $ 92.8 $ 145.5 $ 38.3 $ 3,047.0 Special mention — — — — — — — — Classified — — 4.9 3.2 — 0.7 — 8.8 Total $ 599.9 $ 1,116.5 $ 720.5 $ 341.6 $ 92.8 $ 146.2 $ 38.3 $ 3,055.8 Term Loan Amortized Cost Basis by Origination Year Revolving Loans Amortized Cost Basis Total March 31, 2021 2021 2020 2019 2018 2017 Prior (in millions) Construction and land development Pass $ 219.6 $ 673.7 $ 668.9 $ 375.3 $ 8.9 $ 1.1 $ 758.0 $ 2,705.5 Special mention 1.0 8.2 6.3 44.5 — — — 60.0 Classified — 1.5 0.6 — — — — 2.1 Total $ 220.6 $ 683.4 $ 675.8 $ 419.8 $ 8.9 $ 1.1 $ 758.0 $ 2,767.6 Other Pass $ 8.5 $ 19.6 $ 13.5 $ 5.9 $ 4.8 $ 72.7 $ 25.2 $ 150.2 Special mention — — — 0.1 — 0.1 — 0.2 Classified 3.0 — 0.1 0.2 — 0.4 — 3.7 Total $ 11.5 $ 19.6 $ 13.6 $ 6.2 $ 4.8 $ 73.2 $ 25.2 $ 154.1 Total by Risk Category Pass $ 2,439.3 $ 5,678.8 $ 4,252.9 $ 2,442.6 $ 1,370.1 $ 2,245.5 $ 9,530.9 $ 27,960.1 Special mention 7.5 33.8 143.7 136.6 81.2 41.8 29.6 474.2 Classified 21.7 20.8 119.4 13.1 35.5 59.4 6.8 276.7 Total $ 2,468.5 $ 5,733.4 $ 4,516.0 $ 2,592.3 $ 1,486.8 $ 2,346.7 $ 9,567.3 $ 28,711.0 Term Loan Amortized Cost Basis by Origination Year Revolving Loans Amortized Cost Basis Total December 31, 2020 2020 2019 2018 2017 2016 Prior (in millions) Warehouse lending Pass $ 135.2 $ — $ 0.9 $ 1.6 $ 0.1 $ — $ 4,202.4 $ 4,340.2 Special mention — — — — — — — — Classified — — — — — — — — Total $ 135.2 $ — $ 0.9 $ 1.6 $ 0.1 $ — $ 4,202.4 $ 4,340.2 Municipal & nonprofit Pass $ 219.3 $ 156.6 $ 81.6 $ 231.2 $ 129.1 $ 905.6 $ 3.5 $ 1,726.9 Special mention — — — — — — — — Classified — — — 1.9 — — — 1.9 Total $ 219.3 $ 156.6 $ 81.6 $ 233.1 $ 129.1 $ 905.6 $ 3.5 $ 1,728.8 Tech & innovation Pass $ 609.7 $ 207.4 $ 76.9 $ 2.0 $ 0.9 $ — $ 1,608.8 $ 2,505.7 Special mention 10.7 4.6 — — — — — 15.3 Classified 25.2 2.0 — — — — 0.1 27.3 Total $ 645.6 $ 214.0 $ 76.9 $ 2.0 $ 0.9 $ — $ 1,608.9 $ 2,548.3 Other commercial and industrial Pass $ 2,069.5 $ 819.8 $ 447.7 $ 250.7 $ 99.7 $ 114.6 $ 1,935.7 $ 5,737.7 Special mention 2.2 52.1 32.1 22.1 1.7 0.2 34.3 144.7 Classified 0.9 8.4 3.2 1.6 9.7 0.8 4.2 28.8 Total $ 2,072.6 $ 880.3 $ 483.0 $ 274.4 $ 111.1 $ 115.6 $ 1,974.2 $ 5,911.2 CRE - owner occupied Pass $ 252.2 $ 307.1 $ 302.1 $ 402.4 $ 148.4 $ 323.5 $ 39.5 $ 1,775.2 Special mention 0.9 12.4 9.3 24.3 4.4 10.5 22.4 84.2 Classified 1.4 7.5 4.8 8.5 6.2 19.5 2.0 49.9 Total $ 254.5 $ 327.0 $ 316.2 $ 435.2 $ 159.0 $ 353.5 $ 63.9 $ 1,909.3 Term Loan Amortized Cost Basis by Origination Year Revolving Loans Amortized Cost Basis Total December 31, 2020 2020 2019 2018 2017 2016 Prior (in millions) Hotel franchise finance Pass $ 161.6 $ 792.0 $ 464.1 $ 139.9 $ — $ 101.5 $ 162.6 $ 1,821.7 Special mention — 32.7 56.9 27.3 — 18.2 — 135.1 Classified 8.9 — — 12.6 2.1 3.5 — 27.1 Total $ 170.5 $ 824.7 $ 521.0 $ 179.8 $ 2.1 $ 123.2 $ 162.6 $ 1,983.9 Other CRE - non-owned occupied Pass $ 1,032.6 $ 912.5 $ 560.8 $ 384.3 $ 164.7 $ 208.4 $ 281.0 $ 3,544.3 Special mention 1.4 — 7.0 5.4 1.0 7.4 — 22.2 Classified 7.4 26.4 — 20.3 6.5 13.1 — 73.7 Total $ 1,041.4 $ 938.9 $ 567.8 $ 410.0 $ 172.2 $ 228.9 $ 281.0 $ 3,640.2 Residential Pass $ 759.5 $ 869.3 $ 402.0 $ 108.9 $ 113.8 $ 74.1 $ 39.5 $ 2,367.1 Special mention — — — — — — — — Classified — 4.4 5.9 1.1 — — — 11.4 Total $ 759.5 $ 873.7 $ 407.9 $ 110.0 $ 113.8 $ 74.1 $ 39.5 $ 2,378.5 Construction and land development Pass $ 677.8 $ 704.2 $ 429.6 $ 15.4 $ 1.2 $ 15.0 $ 537.4 $ 2,380.6 Special mention 8.5 0.4 38.0 — — — 0.4 47.3 Classified — — 1.5 — — — — 1.5 Total $ 686.3 $ 704.6 $ 469.1 $ 15.4 $ 1.2 $ 15.0 $ 537.8 $ 2,429.4 Other Pass $ 21.1 $ 15.6 $ 14.5 $ 5.8 $ 1.8 $ 75.8 $ 45.7 $ 180.3 Special mention — — 0.1 1.7 — 0.5 — 2.3 Classified — 0.1 0.2 — 0.1 0.2 — 0.6 Total $ 21.1 $ 15.7 $ 14.8 $ 7.5 $ 1.9 $ 76.5 $ 45.7 $ 183.2 Total by Risk Category Pass $ 5,938.5 $ 4,784.5 $ 2,780.2 $ 1,542.2 $ 659.7 $ 1,818.5 $ 8,856.1 $ 26,379.7 Special mention 23.7 102.2 143.4 80.8 7.1 36.8 57.1 451.1 Classified 43.8 48.8 15.6 46.0 24.6 37.1 6.3 222.2 Total $ 6,006.0 $ 4,935.5 $ 2,939.2 $ 1,669.0 $ 691.4 $ 1,892.4 $ 8,919.5 $ 27,053.0
Allowances for Credit Losses	The below tables reflect the activity in the allowance for credit losses on loans held for investment by loan portfolio segment: Three Months Ended March 31, 2021 Balance, Provision for (Recovery of) Credit Losses Write-offs Recoveries Balance, (1) (1) (in millions) Warehouse lending $ 3.4 $ 0.2 $ — $ — $ 3.6 Municipal & nonprofit 15.9 (0.7) — — 15.2 Tech & innovation 35.3 (11.6) — (0.2) 23.9 Other commercial and industrial 94.7 (16.5) 0.1 (0.3) 78.4 CRE - owner occupied 18.6 (8.9) — — 9.7 Hotel franchise finance 43.3 6.1 — — 49.4 Other CRE - non-owned occupied 39.9 (5.4) 2.0 (0.2) 32.7 Residential 0.8 2.4 — — 3.2 Construction and land development 22.0 3.9 — — 25.9 Other 5.0 0.1 — — 5.1 Total $ 278.9 $ (30.4) $ 2.1 $ (0.7) $ 247.1 (1) Includes an estimate of future recoveries. Three Months Ended March 31, 2020 Balance, Provision for (Recovery of) Credit Losses Write-offs Recoveries Balance, (1) (1) (in millions) Warehouse lending $ 0.2 $ 0.2 $ — $ — $ 0.4 Municipal & nonprofit 17.4 (1.2) — — 16.2 Tech & innovation 22.4 17.4 — — 39.8 Other commercial and industrial 95.8 23.3 0.1 (1.3) 120.3 CRE - owner occupied 10.4 0.1 — — 10.5 Hotel franchise finance 14.1 4.7 — — 18.8 Other CRE - non-owned occupied 10.5 1.7 — (2.0) 14.2 Residential 3.8 (2.5) — — 1.3 Construction and land development 6.2 0.9 — — 7.1 Other 6.1 0.6 — — 6.7 Total $ 186.9 $ 45.2 $ 0.1 $ (3.3) $ 235.3 (1) Includes an estimate of future recoveries. Accrued interest receivable on loans totaled $138.1 million and $142.1 million at March 31, 2021 and December 31, 2020, respectively, and is excluded from the estimate of credit losses. In addition to the allowance for credit losses on loans held for investment, the Company maintains a separate allowance for credit losses related to off-balance sheet credit exposures, including unfunded loan commitments. This allowance is included in other liabilities on the consolidated balance sheets. The below tables reflect the activity in the allowance for credit losses on unfunded loan commitments: Three Months Ended March 31, 2021 2020 (in millions) Balance, beginning of period $ 37.0 $ 9.0 Beginning balance adjustment from adoption of CECL — 15.1 (Recovery of) provision for credit losses (4.4) 5.5 Balance, end of period $ 32.6 $ 29.6 The following tables disaggregate the Company's allowance for credit losses on loans held for investment and loan balances by measurement methodology: March 31, 2021 Loans Allowance Collectively Evaluated for Credit Loss Individually Evaluated for Credit Loss Total Collectively Evaluated for Credit Loss Individually Evaluated for Credit Loss Total (in millions) Warehouse lending $ 4,901.8 $ — $ 4,901.8 $ 3.6 $ — $ 3.6 Municipal & nonprofit 1,676.9 — 1,676.9 15.2 — 15.2 Tech & innovation 2,481.9 32.3 2,514.2 21.9 2.0 23.9 Other commercial and industrial 6,117.6 56.7 6,174.3 74.9 3.5 78.4 CRE - owner occupied 1,767.8 46.7 1,814.5 9.7 — 9.7 Hotel franchise finance 1,925.4 113.4 2,038.8 43.2 6.2 49.4 Other CRE - non-owned occupied 3,558.7 54.3 3,613.0 32.7 — 32.7 Residential 3,046.9 8.9 3,055.8 3.2 — 3.2 Construction and land development 2,765.6 2.0 2,767.6 25.9 — 25.9 Other 150.4 3.7 154.1 3.6 1.5 5.1 Total $ 28,393.0 $ 318.0 $ 28,711.0 $ 233.9 $ 13.2 $ 247.1 December 31, 2020 Loans Allowance Collectively Evaluated for Credit Loss Individually Evaluated for Credit Loss Total Collectively Evaluated for Credit Loss Individually Evaluated for Credit Loss Total (in millions) Warehouse lending $ 4,340.2 $ — $ 4,340.2 $ 3.4 $ — $ 3.4 Municipal & nonprofit 1,726.9 1.9 1,728.8 15.9 — 15.9 Tech & innovation 2,521.1 27.2 2,548.3 31.4 3.9 35.3 Other commercial and industrial 5,883.1 28.1 5,911.2 90.3 4.4 94.7 CRE - owner occupied 1,857.9 51.4 1,909.3 18.6 — 18.6 Hotel franchise finance 1,927.0 56.9 1,983.9 40.4 2.9 43.3 Other CRE - non-owned occupied 3,553.6 86.6 3,640.2 39.9 — 39.9 Residential 2,367.1 11.4 2,378.5 0.8 — 0.8 Construction and land development 2,427.9 1.5 2,429.4 22.0 — 22.0 Other 182.6 0.6 183.2 5.0 — 5.0 Total $ 26,787.4 $ 265.6 $ 27,053.0 $ 267.7 $ 11.2 $ 278.9

Other Borrowings (Tables)

Other Borrowings (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Company's Borrowings	The following table summarizes the Company’s borrowings as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 (in millions) Short-Term: Federal funds purchased $ — $ — FHLB advances 5.0 5.0 Total short-term borrowings $ 5.0 $ 5.0

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive Income	The following table summarizes the changes in accumulated other comprehensive income by component, net of tax, for the periods indicated: Three Months Ended March 31, Unrealized holding gains (losses) on AFS Unrealized holding gains (losses) on SERP Unrealized holding gains (losses) on junior subordinated debt Total (in millions) Balance, December 31, 2020 $ 92.1 $ (0.3) $ 0.5 $ 92.3 Other comprehensive loss before reclassifications (72.0) — (0.3) (72.3) Amounts reclassified from AOCI (0.1) — — (0.1) Net current-period other comprehensive loss (72.1) — (0.3) (72.4) Balance, March 31, 2021 $ 20.0 $ (0.3) $ 0.2 $ 19.9 Balance, December 31, 2019 $ 21.4 $ 0.0 $ 3.6 $ 25.0 Other comprehensive income (loss) before reclassifications 6.3 (0.3) 6.6 12.6 Amounts reclassified from AOCI (0.1) — — (0.1) Net current-period other comprehensive income (loss) 6.2 (0.3) 6.6 12.5 Balance, March 31, 2020 $ 27.6 $ (0.3) $ 10.2 $ 37.5

Derivatives and Hedging (Tables

Derivatives and Hedging (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position	The fair value of derivative contracts, after taking into account the effects of master netting agreements, is included in other assets or other liabilities on the Consolidated Balance Sheets, as indicated in the following table: March 31, 2021 December 31, 2020 March 31, 2020 Fair Value Fair Value Fair Value Notional Derivative Assets Derivative Liabilities Notional Derivative Assets Derivative Liabilities Notional Derivative Assets Derivative Liabilities (in millions) Derivatives designated as hedging instruments: Fair value hedges Interest rate swaps (1) $ 1,685.9 $ 7.9 $ 57.7 $ 1,689.9 $ 3.3 $ 86.1 $ 859.1 $ 4.4 $ 95.1 Total 1,685.9 7.9 57.7 1,689.9 3.3 86.1 859.1 4.4 95.1 Netting adjustments (2) — 5.4 5.4 — 0.6 0.6 — — — Net $ 1,685.9 $ 2.5 $ 52.3 $ 1,689.9 $ 2.7 $ 85.5 $ 859.1 $ 4.4 $ 95.1 Derivatives not designated as hedging instruments: Foreign currency contracts $ 119.3 $ 1.0 $ 0.7 $ 119.2 $ 0.7 $ 1.2 $ 9.3 $ 0.3 $ 0.2 Interest rate swaps 3.5 0.2 0.2 3.5 0.2 0.2 2.9 0.2 0.2 Total $ 122.8 $ 1.2 $ 0.9 $ 122.7 $ 0.9 $ 1.4 $ 12.2 $ 0.5 $ 0.4 (1) Interest rate swap amounts include a notional amount of $1.0 billion related to the last-of-layer hedges. (2) Netting adjustments represent the amounts recorded to convert the Company's derivative balances from a gross basis to a net basis in accordance with the applicable accounting guidance.
Largest Exposure To Individual Counterparty	The following table summarizes the Company's largest exposure to an individual counterparty at the dates indicated: March 31, 2021 December 31, 2020 March 31, 2020 (in millions) Largest gross exposure (derivative asset) to an individual counterparty $ 7.9 $ 2.7 $ 4.3 Collateral posted by this counterparty — — — Derivative liability with this counterparty 5.4 — — Collateral pledged to this counterparty 18.1 — — Net exposure after netting adjustments and collateral $ 7.9 $ 2.7 $ 4.3
Schedule of Derivative Assets at Fair Value	As of March 31, 2021 and December 31, 2020, the following amounts are reflected on the Consolidated Balance Sheets related to cumulative basis adjustments for fair value hedges: March 31, 2021 December 31, 2020 Carrying Value of Hedged Assets/(Liabilities) Cumulative Fair Value Hedging Adjustment (1) Carrying Value of Hedged Assets/(Liabilities) Cumulative Fair Value Hedging Adjustment (1) (in millions) Loans - HFI, net of deferred loan fees and costs (2) $ 1,543.4 $ 46.8 $ 1,587.1 $ 85.5 Qualifying debt (242.0) 3.0 (247.6) (2.7) (1) Included in the carrying value of the hedged assets/(liabilities). (2) The Company designated $1.0 billion as the hedged amount (from a closed portfolio of prepayable fixed rate loans with a carrying value of $1.8 billion and $1.9 billion as of March 31, 2021 and December 31, 2020, respectively) in this last-of-layer hedging relationship, which commenced in the fourth quarter of 2020. The cumulative basis adjustment included in the carrying value of these hedged items totaled $7.9 million and $0.6 million as of March 31, 2021 and December 31, 2020, respectively.
Derivative Instruments, Gain (Loss)	For the Company's derivative instruments that are designated and qualify as a fair value hedge, the gain or loss on the derivative instrument as well as the offsetting loss or gain on the hedged item attributable to the hedged risk are recognized in current earnings in the same line item as the offsetting loss or gain on the related interest rate swaps. For loans, the gain or loss on the hedged item is included in interest income and for subordinated debt, the gain or loss on the hedged items is included in interest expense, as shown in the table below. Three Months Ended March 31, 2021 2020 Income Statement Classification Gain/(Loss) on Swaps Gain/(Loss) on Hedged Item Gain/(Loss) on Swaps Gain/(Loss) on Hedged Item (in millions) Interest income $ 38.7 $ (38.7) $ (41.8) $ 41.8 Interest expense (5.7) 5.7 4.8 (4.8)

Earnings per Share (Tables)

Earnings per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table presents the calculation of basic and diluted EPS: Three Months Ended March 31, 2021 2020 (in millions, except per share amounts) Weighted average shares - basic 100.8 101.3 Dilutive effect of stock awards 0.6 0.4 Weighted average shares - diluted 101.4 101.7 Net income $ 192.5 $ 83.9 Earnings per share - basic 1.91 0.83 Earnings per share - diluted 1.90 0.83

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Summary of Contractual Amounts for Unfunded Commitments and Letters of Credit	A summary of the contractual amounts for unfunded commitments and letters of credit are as follows: March 31, 2021 December 31, 2020 (in millions) Commitments to extend credit, including unsecured loan commitments of $1,134.0 at March 31, 2021 and $1,077.2 at December 31, 2020 $ 9,577.3 $ 9,425.2 Credit card commitments and financial guarantees 289.9 291.5 Letters of credit, including unsecured letters of credit of $7.4 at March 31, 2021 and $9.9 at December 31, 2020 158.8 186.9 Total $ 10,026.0 $ 9,903.6

Fair Value Accounting (Tables)

Fair Value Accounting (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Gains and Losses from Fair Value Changes Included in Consolidated Statement of Operations	For the three months ended March 31, 2021 and 2020, unrealized gains and losses from fair value changes on junior subordinated debt were as follows:
Fair Value of Assets and Liabilities	The fair value of assets and liabilities measured at fair value on a recurring basis was determined using the following inputs as of the periods presented: Fair Value Measurements at the End of the Reporting Period Using: Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Fair Value (in millions) March 31, 2021 Assets: Available-for-sale debt securities CLO $ — $ 980.7 $ — $ 980.7 Commercial MBS issued by GSEs — 87.8 — 87.8 Corporate debt securities — 285.1 — 285.1 Private label residential MBS — 1,900.6 — 1,900.6 Residential MBS issued by GSEs — 2,249.6 — 2,249.6 Tax-exempt — 1,329.7 — 1,329.7 U.S. treasury securities 50.0 — — 50.0 Other 27.3 29.1 — 56.4 Total AFS debt securities $ 77.3 $ 6,862.6 $ — $ 6,939.9 Equity securities CRA investments $ 27.4 $ 30.0 $ — $ 57.4 Preferred stock 135.5 — — 135.5 Total equity securities $ 162.9 $ 30.0 $ — $ 192.9 Derivative assets (1) $ — $ 9.1 $ — $ 9.1 Liabilities: Junior subordinated debt (2) $ — $ — $ 66.3 $ 66.3 Derivative liabilities (1) — 58.6 — 58.6 (1) Derivative assets and liabilities relate primarily to interest rate swaps, see "Note 8. Derivatives and Hedging Activities." In addition, the carrying value of loans is increased by $46.8 million and the net carrying value of subordinated debt is increased by $3.0 million as of March 31, 2021 for the effective portion of the hedge, which relates to the fair value of the hedges put in place to mitigate against fluctuations in interest rates. (2) Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment. Fair Value Measurements at the End of the Reporting Period Using: Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Fair Value (in millions) December 31, 2020 Assets: Available-for-sale debt securities CLO $ — $ 146.9 $ — $ 146.9 Commercial MBS issued by GSEs — 84.6 — 84.6 Corporate debt securities — 270.2 — 270.2 Private label residential MBS — 1,476.9 — 1,476.9 Residential MBS issued by GSEs — 1,486.6 — 1,486.6 Tax-exempt — 1,187.4 — 1,187.4 Other 26.5 29.4 — 55.9 Total AFS debt securities $ 26.5 $ 4,682.0 $ — $ 4,708.5 Equity securities CRA investments $ 27.8 $ 25.6 $ — $ 53.4 Preferred stock 113.9 — — 113.9 Total equity securities $ 141.7 $ 25.6 $ — $ 167.3 Derivative assets (1) $ — $ 4.2 $ — $ 4.2 Liabilities: Junior subordinated debt (2) $ — $ — $ 65.9 $ 65.9 Derivative liabilities (1) — 87.5 — 87.5 (1) Derivative assets and liabilities relate primarily to interest rate swaps, see "Note 8. Derivatives and Hedging Activities." In addition, the carrying value of loans is increased by $85.5 million and the net carrying value of subordinated debt is increased by $2.7 million as of December 31, 2020 for the effective portion of the hedge, which relates to the fair value of the hedges put in place to mitigate against fluctuations in interest rates. (2) Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.
Change in Level 3 Liabilities Measured at Fair Value on Recurring Basis	For the three months ended March 31, 2021 and 2020, the change in Level 3 liabilities measured at fair value on a recurring basis was as follows: Junior Subordinated Debt Three Months Ended March 31, 2021 2020 (in millions) Beginning balance $ (65.9) $ (61.7) Change in fair value (1) (0.4) 8.7 Ending balance $ (66.3) $ (53.0)
Assets Measured at Fair Value on Nonrecurring Basis	The following table presents such assets carried on the Consolidated Balance Sheet by caption and by level within the ASC 825 hierarchy: Fair Value Measurements at the End of the Reporting Period Using Total Quoted Prices in Active Markets for Identical Assets Active Markets for Similar Assets Unobservable Inputs (in millions) As of March 31, 2021: Loans $ 183.0 $ — $ — $ 183.0 Other assets acquired through foreclosure 4.2 — — 4.2 As of December 31, 2020: Loans $ 187.3 $ — $ — $ 187.3 Other assets acquired through foreclosure 1.4 — — 1.4
Estimated Fair Value of Financial Instruments	The estimated fair value of the Company’s financial instruments is as follows: March 31, 2021 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total (in millions) Financial assets: Investment securities: HTM $ 698.0 $ — $ 740.4 $ — $ 740.4 AFS 6,939.9 77.3 6,862.6 — 6,939.9 Equity 192.9 162.9 30.0 — 192.9 Derivative assets 9.1 — 9.1 — 9.1 Loans, net 28,463.9 — — 29,244.8 29,244.8 Accrued interest receivable 169.9 — 169.9 — 169.9 Financial liabilities: Deposits $ 38,393.1 $ — $ 38,397.4 $ — $ 38,397.4 Customer repurchase agreements 15.9 — 15.9 — 15.9 Other borrowings 5.0 — 5.0 — 5.0 Qualifying debt 543.7 — 492.6 79.8 572.4 Derivative liabilities 58.6 — 58.6 — 58.6 Accrued interest payable 12.7 — 12.7 — 12.7 December 31, 2020 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total (in millions) Financial assets: Investment securities: HTM $ 568.8 $ — $ 611.8 $ — $ 611.8 AFS 4,708.5 26.5 4,682.0 — 4,708.5 Equity securities 167.3 141.7 25.6 — 167.3 Derivative assets 4.2 — 4.2 — 4.2 Loans, net 26,774.1 — — 27,231.0 27,231.0 Accrued interest receivable 166.1 — 166.1 — 166.1 Financial liabilities: Deposits $ 31,930.5 $ — $ 31,935.9 $ — $ 31,935.9 Customer repurchase agreements 16.0 — 16.0 — 16.0 Other borrowings 5.0 — 5.0 — 5.0 Qualifying debt 548.7 — 488.1 79.3 567.4 Derivative liabilities 87.5 — 87.5 — 87.5 Accrued interest payable 11.0 — 11.0 — 11.0

Segments (Tables)

Segments (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Operating Segment Information	The following is a summary of operating segment information for the periods indicated: Balance Sheet: Consolidated Company Commercial Consumer Related Corporate & Other At March 31, 2021: (in millions) Assets: Cash, cash equivalents, and investment securities $ 13,235.3 $ 13.4 $ 33.1 $ 13,188.8 Loans, net of deferred loan fees and costs 28,711.0 20,660.4 8,048.9 1.7 Less: allowance for credit losses (247.1) (229.8) (17.3) — Total loans 28,463.9 20,430.6 8,031.6 1.7 Other assets acquired through foreclosure, net 4.2 4.2 — — Goodwill and other intangible assets, net 298.0 295.7 2.3 — Other assets 1,395.6 251.5 113.1 1,031.0 Total assets $ 43,397.0 $ 20,995.4 $ 8,180.1 $ 14,221.5 Liabilities: Deposits $ 38,393.1 $ 24,126.0 $ 13,286.5 $ 980.6 Borrowings and qualifying debt 548.7 — — 548.7 Other liabilities 742.5 226.4 6.0 510.1 Total liabilities 39,684.3 24,352.4 13,292.5 2,039.4 Allocated equity: 3,712.7 2,100.3 702.9 909.5 Total liabilities and stockholders' equity $ 43,397.0 $ 26,452.7 $ 13,995.4 $ 2,948.9 Excess funds provided (used) — 5,457.3 5,815.3 (11,272.6) Income Statement: Three Months Ended March 31, 2021: (in millions) Net interest income $ 317.3 $ 263.7 $ 107.9 $ (54.3) (Recovery of) provision for credit losses (32.4) (36.3) 1.7 2.2 Net interest income (expense) after provision for credit losses 349.7 300.0 106.2 (56.5) Non-interest income 19.7 19.2 0.5 — Non-interest expense 135.0 98.3 35.2 1.5 Income (loss) before income taxes 234.4 220.9 71.5 (58.0) Income tax expense (benefit) 41.9 52.7 17.5 (28.3) Net income $ 192.5 $ 168.2 $ 54.0 $ (29.7) Balance Sheet: Consolidated Company Commercial Consumer Related Corporate At December 31, 2020: (in millions) Assets: Cash, cash equivalents, and investment securities $ 8,176.5 $ 12.0 $ 45.6 $ 8,118.9 Loans, net of deferred loan fees and costs 27,053.0 20,245.8 6,798.2 9.0 Less: allowance for loan losses (278.9) (263.4) (15.4) (0.1) Total loans 26,774.1 19,982.4 6,782.8 8.9 Other assets acquired through foreclosure, net 1.4 1.4 — — Goodwill and other intangible assets, net 298.5 296.1 2.4 — Other assets 1,210.5 257.0 96.6 856.9 Total assets $ 36,461.0 $ 20,548.9 $ 6,927.4 $ 8,984.7 Liabilities: Deposits $ 31,930.5 $ 21,448.0 $ 9,936.8 $ 545.7 Borrowings and qualifying debt 553.7 — — 553.7 Other liabilities 563.3 170.4 3.3 389.6 Total liabilities 33,047.5 21,618.4 9,940.1 1,489.0 Allocated equity: 3,413.5 1,992.2 579.1 842.2 Total liabilities and stockholders' equity $ 36,461.0 $ 23,610.6 $ 10,519.2 $ 2,331.2 Excess funds provided (used) — 3,061.7 3,591.8 (6,653.5) Three Months Ended March 31, 2020: (in millions) Net interest income $ 269.0 $ 228.5 $ 55.7 $ (15.2) Provision for credit losses 51.2 47.9 3.0 0.3 Net interest income (expense) after provision for credit losses 217.8 180.6 52.7 (15.5) Non-interest income 5.1 11.4 0.4 (6.7) Non-interest expense 120.5 82.4 25.8 12.3 Income (loss) before income taxes 102.4 109.6 27.3 (34.5) Income tax expense (benefit) 18.5 26.0 6.4 (13.9) Net income $ 83.9 $ 83.6 $ 20.9 $ (20.6)

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue from Contracts with Customers [Abstract]
Disaggregation of Revenue [Table Text Block]	Consolidated Company Commercial Consumer Related Corporate & Other Three Months Ended March 31, 2021 (in millions) Revenue from contracts with customers: Service charges and fees $ 6.7 $ 6.2 $ 0.5 $ — Debit and credit card interchange (1) 1.3 1.3 — — Success fees (2) 1.0 1.0 — — Other income 0.2 0.2 — — Total revenue from contracts with customers $ 9.2 $ 8.7 $ 0.5 $ — Revenues outside the scope of ASC 606 (3) 10.5 10.5 — — Total non-interest income $ 19.7 $ 19.2 $ 0.5 $ — Consolidated Company Commercial Consumer Related Corporate & Other Three Months Ended March 31, 2020 (in millions) Revenue from contracts with customers: Service charges and fees $ 6.4 $ 6.0 $ 0.4 $ — Debit and credit card interchange (1) 1.4 1.4 — — Success fees (2) 0.1 0.1 — — Other income 0.1 0.1 — — Total revenue from contracts with customers $ 8.0 $ 7.6 $ 0.4 $ — Revenues outside the scope of ASC 606 (3) (2.9) 3.8 — (6.7) Total non-interest income $ 5.1 $ 11.4 $ 0.4 $ (6.7) (1) Included as part of Card income in the Consolidated Income Statement. (2) Included as part of Income from equity investments in the Consolidated Income Statement. (3) Amounts are accounted for under separate guidance. Refer to discussion of revenue sources not subject to ASC 606 under the Non-interest income section in "Note 1. Summary of Significant Accounting Policies."

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)Subsidiary	Dec. 31, 2020USD ($)	Mar. 31, 2020USD ($)	Jan. 01, 2020USD ($)	Dec. 31, 2019USD ($)
Significant Of Accounting Policies [Line Items]
Number Of Wholly Owned Subsidiaries Non Bank Subsidiaries | Subsidiary	2
Number Of Unconsolidated Subsidiaries | Subsidiary	8
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 9.2	$ 6.8	$ 2.9		$ 2.6
Loans and Leases Receivable, Allowance	247.1	278.9
Deferred Income Tax Assets, Net	49.8	31.3
Off-Balance Sheet, Credit Loss, Liability	32.6	37	$ 29.6		$ 9
Retained earnings	$ (2,168.6)	$ (2,001.4)
Cumulative Effect, Period of Adoption, Adjustment [Member]
Significant Of Accounting Policies [Line Items]
Off-Balance Sheet, Credit Loss, Liability				$ 15.1
Retained earnings				$ (24.9)

Investment Securities - Carryin

Investment Securities - Carrying Amounts and Fair Values of Investment Securities (Detail) - USD ($) $ in Millions	Mar. 31, 2021		Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	$ 192.9	[1]	$ 167.3	[2]
Debt Securities, Held-to-maturity	698		568.8
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	43.8		43
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	(1.4)		0
Debt Securities, Held-to-maturity, Fair Value	740.4		611.8
Securities available for sale Total, Amortized Cost	6,913.3		4,586.4
Securities available-for-sale, Gross Unrealized Gains	105.1		137.6
Securities available-for-sale, Gross Unrealized (Losses)	(78.5)		(15.5)
Securities available for sale Total, Estimated Fair Value	6,939.9	[1]	4,708.5	[2]
Equity Securities, FV-NI, Cost	187.1		160.1
Equity Securities, FV-NI, Unrealized Gain	6.2		7.6
Equity Securities, FV-NI, Unrealized Loss	0.4		0.4
Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Amortized Cost	88		80.8
Securities available-for-sale, Gross Unrealized Gains	1.6		3.8
Securities available-for-sale, Gross Unrealized (Losses)	(1.8)		0
Securities available for sale Total, Estimated Fair Value	87.8		84.6
Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Amortized Cost	286		271.1
Securities available-for-sale, Gross Unrealized Gains	5		4.8
Securities available-for-sale, Gross Unrealized (Losses)	(5.9)		(5.7)
Securities available for sale Total, Estimated Fair Value	285.1		270.2
Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Amortized Cost	1,905.7		1,461.7
Securities available-for-sale, Gross Unrealized Gains	9.8		15.7
Securities available-for-sale, Gross Unrealized (Losses)	(14.9)		(0.5)
Securities available for sale Total, Estimated Fair Value	1,900.6		1,476.9
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Amortized Cost	2,277.8		1,462.5
Securities available-for-sale, Gross Unrealized Gains	18.5		27.9
Securities available-for-sale, Gross Unrealized (Losses)	(46.7)		(3.8)
Securities available for sale Total, Estimated Fair Value	2,249.6		1,486.6
Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	698		568.8
Securities available for sale Total, Amortized Cost	1,271.4		1,109.3
Securities available-for-sale, Gross Unrealized Gains	62		78.1
Securities available-for-sale, Gross Unrealized (Losses)	(3.7)		0
Securities available for sale Total, Estimated Fair Value	1,329.7		1,187.4
US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Amortized Cost	50
Securities available-for-sale, Gross Unrealized Gains	0
Securities available-for-sale, Gross Unrealized (Losses)	0
Securities available for sale Total, Estimated Fair Value	50
CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	57.4		53.4
Equity Securities, FV-NI, Cost	57.6		53.1
Equity Securities, FV-NI, Unrealized Gain	0		0.3
Equity Securities, FV-NI, Unrealized Loss	0.2		0
Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	135.5		113.9
Equity Securities, FV-NI, Cost	129.5		107
Equity Securities, FV-NI, Unrealized Gain	6.2		7.3
Equity Securities, FV-NI, Unrealized Loss	0.2		0.4
Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Amortized Cost	980.3		146.9
Securities available-for-sale, Gross Unrealized Gains	0.8		0
Securities available-for-sale, Gross Unrealized (Losses)	(0.4)		0
Securities available for sale Total, Estimated Fair Value	980.7		146.9
Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Amortized Cost	54.1		54.1
Securities available-for-sale, Gross Unrealized Gains	7.4		7.3
Securities available-for-sale, Gross Unrealized (Losses)	(5.1)		(5.5)
Securities available for sale Total, Estimated Fair Value	56.4		55.9
AAA [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	[1]	0	[2]
Securities available for sale Total, Estimated Fair Value	1,931	[1]	1,429.8	[2]
AAA [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
AAA [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
AAA [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	1,812.8		1,385.5
AAA [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
AAA [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Securities available for sale Total, Estimated Fair Value	43.2		44.3
AAA [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	50
AAA [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
AAA [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
AAA [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	25		0
AAA [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
Split-rated AAA/AA Plus [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	27.4	[1]	27.8	[2]
Securities available for sale Total, Estimated Fair Value	2,393.9	[1]	1,628.5	[2]
Split-rated AAA/AA Plus [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	87.8		84.6
Split-rated AAA/AA Plus [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
Split-rated AAA/AA Plus [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
Split-rated AAA/AA Plus [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	2,249.6		1,486.6
Split-rated AAA/AA Plus [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Securities available for sale Total, Estimated Fair Value	56.5		57.3
Split-rated AAA/AA Plus [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0
Split-rated AAA/AA Plus [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	27.4		27.8
Split-rated AAA/AA Plus [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
Split-rated AAA/AA Plus [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
Split-rated AAA/AA Plus [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
AA Plus to AA- [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	[1]	0	[2]
Securities available for sale Total, Estimated Fair Value	1,286.2	[1]	715.9	[2]
AA Plus to AA- [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
AA Plus to AA- [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	19.2		19.2
AA Plus to AA- [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	86.5		90.1
AA Plus to AA- [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
AA Plus to AA- [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Securities available for sale Total, Estimated Fair Value	519.1		454.7
AA Plus to AA- [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0
AA Plus to AA- [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
AA Plus to AA- [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
AA Plus to AA- [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	649.8		139.6
AA Plus to AA- [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	11.6		12.3
A Plus to A- [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	[1]	0	[2]
Securities available for sale Total, Estimated Fair Value	1,013.2	[1]	634.8	[2]
A Plus to A- [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
A Plus to A- [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	28.1		28.1
A Plus to A- [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0.1		0.1
A Plus to A- [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
A Plus to A- [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Securities available for sale Total, Estimated Fair Value	679.1		599.3
A Plus to A- [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0
A Plus to A- [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
A Plus to A- [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
A Plus to A- [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	305.9		7.3
A Plus to A- [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
BBB Plus to BBB- [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	81.3	[1]	73.2	[2]
Securities available for sale Total, Estimated Fair Value	249.7	[1]	223.9	[2]
BBB Plus to BBB- [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
BBB Plus to BBB- [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	219.6		194.5
BBB Plus to BBB- [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0.3		0.3
BBB Plus to BBB- [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
BBB Plus to BBB- [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Securities available for sale Total, Estimated Fair Value	0		0
BBB Plus to BBB- [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0
BBB Plus to BBB- [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
BBB Plus to BBB- [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	81.3		73.2
BBB Plus to BBB- [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
BBB Plus to BBB- [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	29.8		29.1
BB Plus and below [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	39.1	[1]	39	[2]
Securities available for sale Total, Estimated Fair Value	26	[1]	36.2	[2]
BB Plus and below [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
BB Plus and below [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	18.2		28.4
BB Plus and below [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0.9		0.9
BB Plus and below [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
BB Plus and below [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Securities available for sale Total, Estimated Fair Value	0		0
BB Plus and below [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0
BB Plus and below [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
BB Plus and below [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	39.1		39
BB Plus and below [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
BB Plus and below [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	6.9		6.9
Corporate Credit Quality Indicator Unrated [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	45.1	[1]	27.3	[2]
Securities available for sale Total, Estimated Fair Value	39.9	[1]	39.4	[2]
Corporate Credit Quality Indicator Unrated [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
Corporate Credit Quality Indicator Unrated [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
Corporate Credit Quality Indicator Unrated [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
Corporate Credit Quality Indicator Unrated [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
Corporate Credit Quality Indicator Unrated [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	698		568.8
Securities available for sale Total, Estimated Fair Value	31.8		31.8
Corporate Credit Quality Indicator Unrated [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0
Corporate Credit Quality Indicator Unrated [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	30		25.6
Corporate Credit Quality Indicator Unrated [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	15.1		1.7
Corporate Credit Quality Indicator Unrated [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	0		0
Corporate Credit Quality Indicator Unrated [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Securities available for sale Total, Estimated Fair Value	$ 8.1		$ 7.6
[1]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.
[2]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.

Investment Securities - Additio

Investment Securities - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Pledged Securities [Abstract]
Accrued Investment Income Receivable	$ 2.4	$ 2
Pledged Financial Instruments, Not Separately Reported, Other Debt Securities Available-for-sale or Held-for-investment	$ 693.2	$ 778

Investment Securities - Unreali

Investment Securities - Unrealized Losses and Fair Value of Investment Securities in Continuous Unrealized Loss Position (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)positions	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)positions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | positions	187		49
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 1.4
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	48
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	0
Held-to-maturity Securities, Fair Value	48
Available-for-sale securities, Less Than Twelve Months, Aggregate Losses	67.7		$ 4.4
Available-for-sale securities, Less Than Twelve Months, Fair Value	2,924.1		398.9
Available-for-sale securities, Twelve Months or Longer, Aggregate Losses	10.8		11.1
Available-for-sale securities, Twelve Months or Longer, Fair Value	131.2		120.8
Available-for-sale securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	78.5		15.5
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Total	3,055.3		519.7
Unrealized gains (losses) on assets measured at fair value, net	(1.5)	$ (11.3)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	1.4
Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, Less Than Twelve Months, Aggregate Losses	0.2		0.1
Available-for-sale securities, Less Than Twelve Months, Fair Value	32		17.3
Available-for-sale securities, Twelve Months or Longer, Aggregate Losses	5.7		5.6
Available-for-sale securities, Twelve Months or Longer, Fair Value	94.3		94.3
Available-for-sale securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	5.9		5.7
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Total	126.3		111.6
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, Less Than Twelve Months, Aggregate Losses	46.7		3.8
Available-for-sale securities, Less Than Twelve Months, Fair Value	1,225.7		231.9
Available-for-sale securities, Twelve Months or Longer, Aggregate Losses	0		0
Available-for-sale securities, Twelve Months or Longer, Fair Value	0		0
Available-for-sale securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	46.7		3.8
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Total	1,225.7		231.9
Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, Less Than Twelve Months, Aggregate Losses	3.7
Available-for-sale securities, Less Than Twelve Months, Fair Value	158
Available-for-sale securities, Twelve Months or Longer, Aggregate Losses	0
Available-for-sale securities, Twelve Months or Longer, Fair Value	0
Available-for-sale securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	3.7
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Total	158
Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, Less Than Twelve Months, Aggregate Losses	14.5		0.5
Available-for-sale securities, Less Than Twelve Months, Fair Value	810.2		149.7
Available-for-sale securities, Twelve Months or Longer, Aggregate Losses	0.4		0
Available-for-sale securities, Twelve Months or Longer, Fair Value	9.6		0
Available-for-sale securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	14.9		0.5
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Total	819.8		149.7
Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, Less Than Twelve Months, Aggregate Losses	1.8
Available-for-sale securities, Less Than Twelve Months, Fair Value	48
Available-for-sale securities, Twelve Months or Longer, Aggregate Losses	0
Available-for-sale securities, Twelve Months or Longer, Fair Value	0
Available-for-sale securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	1.8
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Total	48
Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, Less Than Twelve Months, Aggregate Losses	0.4		0
Available-for-sale securities, Less Than Twelve Months, Fair Value	11.6		0
Available-for-sale securities, Twelve Months or Longer, Aggregate Losses	4.7		5.5
Available-for-sale securities, Twelve Months or Longer, Fair Value	27.3		26.5
Available-for-sale securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	5.1		5.5
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Total	38.9		$ 26.5
Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, Less Than Twelve Months, Aggregate Losses	0.4
Available-for-sale securities, Less Than Twelve Months, Fair Value	638.6
Available-for-sale securities, Twelve Months or Longer, Aggregate Losses	0
Available-for-sale securities, Twelve Months or Longer, Fair Value	0
Available-for-sale securities, Continuous Unrealized Loss Position, Aggregate Losses, Total	0.4
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Total	$ 638.6

Investment Securities - Amortiz

Investment Securities - Amortized Cost and Fair Value of Investment Securities by Contractual Maturities (Detail) - USD ($) $ in Millions	Mar. 31, 2021		Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	$ 10.7
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost	31.3
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after 10 Years, Amortized Cost	656
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value	10.7
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value	31.8
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value	697.9
Debt Securities, Held-to-maturity	698		$ 568.8
Debt Securities, Held-to-maturity, Fair Value	740.4		611.8
Securities available for sale, Due in one year or less, Amortized Cost	50
Securities available for sale, After one year through five years, Amortized Cost	38
Securities available for sale, After five years through ten years, Amortized Cost	780.5
Securities available for sale, After ten years, Amortized Cost	1,773.3
Securities available for sale, Mortgage backed securities, Amortized Cost	4,271.5
Securities available for sale Total, Amortized Cost	6,913.3		4,586.4
Securities available for sale, Due in one year or less, Estimated Fair Value	50
Securities available for sale, After one year through five years, Estimated Fair Value	38.5
Securities available for sale, After five years through ten years, Estimated Fair Value	780.8
Securities available for sale, After ten years, Estimated Fair Value	1,832.6
Securities available for sale, Mortgage backed securities, Estimated Fair Value	4,238
Securities available for sale Total, Estimated Fair Value	$ 6,939.9	[1]	$ 4,708.5	[2]
[1]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.
[2]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.

Investment Securities - Investm

Investment Securities - Investment Securities by Credit Rating Type (Detail) - USD ($) $ in Millions	Mar. 31, 2021		Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	$ 698		$ 568.8
Available-for-sale Securities	6,939.9	[1]	4,708.5	[2]
Investment securities - equity	192.9	[1]	167.3	[2]
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	2,249.6		1,486.6
Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	698		568.8
Available-for-sale Securities	1,329.7		1,187.4
Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	87.8		84.6
Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	1,900.6		1,476.9
US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	50
Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	135.5		113.9
Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	285.1		270.2
CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	57.4		53.4
Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	56.4		55.9
Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	980.7		146.9
AAA [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	1,931	[1]	1,429.8	[2]
Investment securities - equity	0	[1]	0	[2]
AAA [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
AAA [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Available-for-sale Securities	43.2		44.3
AAA [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
AAA [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	1,812.8		1,385.5
AAA [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	50
AAA [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
AAA [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
AAA [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
AAA [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
AAA [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	25		0
Split-rated AAA/AA Plus [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	2,393.9	[1]	1,628.5	[2]
Investment securities - equity	27.4	[1]	27.8	[2]
Split-rated AAA/AA Plus [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	2,249.6		1,486.6
Split-rated AAA/AA Plus [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Available-for-sale Securities	56.5		57.3
Split-rated AAA/AA Plus [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	87.8		84.6
Split-rated AAA/AA Plus [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
Split-rated AAA/AA Plus [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0
Split-rated AAA/AA Plus [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
Split-rated AAA/AA Plus [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
Split-rated AAA/AA Plus [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	27.4		27.8
Split-rated AAA/AA Plus [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
Split-rated AAA/AA Plus [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
AA Plus to AA- [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	1,286.2	[1]	715.9	[2]
Investment securities - equity	0	[1]	0	[2]
AA Plus to AA- [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
AA Plus to AA- [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Available-for-sale Securities	519.1		454.7
AA Plus to AA- [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
AA Plus to AA- [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	86.5		90.1
AA Plus to AA- [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0
AA Plus to AA- [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
AA Plus to AA- [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	19.2		19.2
AA Plus to AA- [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
AA Plus to AA- [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	11.6		12.3
AA Plus to AA- [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	649.8		139.6
A Plus to A- [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	1,013.2	[1]	634.8	[2]
Investment securities - equity	0	[1]	0	[2]
A Plus to A- [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
A Plus to A- [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Available-for-sale Securities	679.1		599.3
A Plus to A- [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
A Plus to A- [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0.1		0.1
A Plus to A- [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0
A Plus to A- [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
A Plus to A- [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	28.1		28.1
A Plus to A- [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
A Plus to A- [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
A Plus to A- [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	305.9		7.3
BBB Plus to BBB- [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	249.7	[1]	223.9	[2]
Investment securities - equity	81.3	[1]	73.2	[2]
BBB Plus to BBB- [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
BBB Plus to BBB- [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Available-for-sale Securities	0		0
BBB Plus to BBB- [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
BBB Plus to BBB- [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0.3		0.3
BBB Plus to BBB- [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0
BBB Plus to BBB- [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	81.3		73.2
BBB Plus to BBB- [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	219.6		194.5
BBB Plus to BBB- [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
BBB Plus to BBB- [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	29.8		29.1
BBB Plus to BBB- [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
BB Plus and below [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	26	[1]	36.2	[2]
Investment securities - equity	39.1	[1]	39	[2]
BB Plus and below [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
BB Plus and below [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	0		0
Available-for-sale Securities	0		0
BB Plus and below [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
BB Plus and below [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0.9		0.9
BB Plus and below [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0
BB Plus and below [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	39.1		39
BB Plus and below [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	18.2		28.4
BB Plus and below [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0		0
BB Plus and below [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	6.9		6.9
BB Plus and below [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
Corporate Credit Quality Indicator Unrated [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	39.9	[1]	39.4	[2]
Investment securities - equity	45.1	[1]	27.3	[2]
Corporate Credit Quality Indicator Unrated [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
Corporate Credit Quality Indicator Unrated [Member] | Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity	698		568.8
Available-for-sale Securities	31.8		31.8
Corporate Credit Quality Indicator Unrated [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
Corporate Credit Quality Indicator Unrated [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
Corporate Credit Quality Indicator Unrated [Member] | US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0
Corporate Credit Quality Indicator Unrated [Member] | Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	15.1		1.7
Corporate Credit Quality Indicator Unrated [Member] | Corporate Bond Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0		0
Corporate Credit Quality Indicator Unrated [Member] | CRA investments [Member]
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	30		25.6
Corporate Credit Quality Indicator Unrated [Member] | Other Security Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	8.1		7.6
Corporate Credit Quality Indicator Unrated [Member] | Collateralized Loan Obligations
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	$ 0		$ 0
[1]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.
[2]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.

Investment Securities Investmen

Investment Securities Investment Securities - Allowance for Credit Losses - HTM (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 9.2	$ 2.9	$ 6.8	$ 2.6
Debt Securities, Held-to-maturity, Allowance for Credit Loss, Period Increase (Decrease)	2.4	0.3
Debt Securities, Held-to-maturity, Allowance for Credit Loss, Writeoff	0	0
Debt Securities, Held-to-maturity, Allowance for Credit Loss, Recovery	$ 0	$ 0

Loans, Leases and Allowance f_2

Loans, Leases and Allowance for Credit Losses - Schedule of Held for Investment Loan Portfolio Composition of Loans, Leases and Allowance for Credit Losses (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 28,711	$ 27,053
Loans and Leases Receivable, Allowance	(247.1)	(278.9)
Loans, net	28,463.9	26,774.1
Net deferred loan fees and costs	(88.6)	(75.4)
Receivable with Imputed Interest, Premium	45	26
Tech & Innovation [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,514.2	2,548.3
Other commercial and industrial [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,174.3	5,911.2
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,814.5	1,909.3
Hotel franchise finance [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,038.8	1,983.9
Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,613	3,640.2
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,055.8	2,378.5
Construction And Land Development Land [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,767.6	2,429.4
Warehouse lending [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,901.8	4,340.2
Municipal and nonprofit [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,676.9	1,728.8
Other, loan segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 154.1	$ 183.2

Loans, Leases and Allowance f_3

Loans, Leases and Allowance for Credit Losses - Summary of Recorded Investment in Nonaccrual Loans and Loans Past Due 90 Days Still Accruing Interest by Loan Class (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	$ 100.8		$ 104.9
Nonaccrual with an Allowance for Credit Loss	12.8		10.3
Total Non-accrual	113.6		115.2
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	28,703.7		27,041.8
Financing Receivable, Past Due	7.3		11.2
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	1.5	$ 0.7
Loans and Leases Receivable, Net of Deferred Income	28,711		27,053
Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	9.3		9.6
Nonaccrual with an Allowance for Credit Loss	3.4		3.9
Total Non-accrual	12.7		13.5
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	2,514.2		2,548.3
Financing Receivable, Past Due	0		0
Loans and Leases Receivable, Net of Deferred Income	2,514.2		2,548.3
Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	8.6		10.9
Nonaccrual with an Allowance for Credit Loss	6.4		6.3
Total Non-accrual	15		17.2
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	6,174.2		5,911
Financing Receivable, Past Due	0.1		0.2
Loans and Leases Receivable, Net of Deferred Income	6,174.3		5,911.2
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	32.1		34.5
Nonaccrual with an Allowance for Credit Loss	0		0
Total Non-accrual	32.1		34.5
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	1,814.5		1,909.3
Financing Receivable, Past Due	0		0
Loans and Leases Receivable, Net of Deferred Income	1,814.5		1,909.3
Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	0		0
Nonaccrual with an Allowance for Credit Loss	0		0
Total Non-accrual	0		0
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	2,038.8		1,983.9
Financing Receivable, Past Due	0		0
Loans and Leases Receivable, Net of Deferred Income	2,038.8		1,983.9
Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	41.5		36.5
Nonaccrual with an Allowance for Credit Loss	0		0
Total Non-accrual	41.5		36.5
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	3,612.3		3,640.2
Financing Receivable, Past Due	0.7		0
Loans and Leases Receivable, Net of Deferred Income	3,613		3,640.2
Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	9		11.4
Nonaccrual with an Allowance for Credit Loss	0		0
Total Non-accrual	9		11.4
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	3,049.4		2,368
Financing Receivable, Past Due	6.4		10.5
Loans and Leases Receivable, Net of Deferred Income	3,055.8		2,378.5
Construction And Land Development [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	0		0
Nonaccrual with an Allowance for Credit Loss	0		0
Total Non-accrual	0		0
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	2,767.6		2,429.4
Financing Receivable, Past Due	0		0
Loans and Leases Receivable, Net of Deferred Income	2,767.6		2,429.4
Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	0		0
Nonaccrual with an Allowance for Credit Loss	0		0
Total Non-accrual	0		0
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	4,901.8		4,340.2
Financing Receivable, Past Due	0		0
Loans and Leases Receivable, Net of Deferred Income	4,901.8		4,340.2
Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	0		1.9
Nonaccrual with an Allowance for Credit Loss	0		0
Total Non-accrual	0		1.9
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	1,676.9		1,728.8
Financing Receivable, Past Due	0		0
Loans and Leases Receivable, Net of Deferred Income	1,676.9		1,728.8
Other, loan segment
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual with No Allowance for Credit Loss	0.3		0.1
Nonaccrual with an Allowance for Credit Loss	3		0.1
Total Non-accrual	3.3		0.2
Financing Receivable, 90 Days or More Past Due, Still Accruing	0		0
Financing Receivable, Not Past Due	154		182.7
Financing Receivable, Past Due	0.1		0.5
Loans and Leases Receivable, Net of Deferred Income	154.1		183.2
Construction And Land Development Land [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 2,767.6		$ 2,429.4

Contractual Aging of Loan Portf

Contractual Aging of Loan Portfolio by Segment - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	$ 28,703.7	$ 27,041.8
Financing Receivable, Past Due	7.3	11.2
Loans and Leases Receivable, Net of Deferred Income	28,711	27,053
Financing Receivable, Originated in Current Fiscal Year	2,468.5	6,006
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,733.4	4,935.5
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,516	2,939.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,592.3	1,669
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,486.8	691.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	2,346.7	1,892.4
Financing Receivable, Revolving	9,567.3	8,919.5
Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	27,960.1	26,379.7
Financing Receivable, Originated in Current Fiscal Year	2,439.3	5,938.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,678.8	4,784.5
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,252.9	2,780.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,442.6	1,542.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,370.1	659.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	2,245.5	1,818.5
Financing Receivable, Revolving	9,530.9	8,856.1
Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	474.2	451.1
Financing Receivable, Originated in Current Fiscal Year	7.5	23.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	33.8	102.2
Financing Receivable, Originated Two Years before Latest Fiscal Year	143.7	143.4
Financing Receivable, Originated Three Years before Latest Fiscal Year	136.6	80.8
Financing Receivable, Originated Four Years before Latest Fiscal Year	81.2	7.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	41.8	36.8
Financing Receivable, Revolving	29.6	57.1
Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	276.7	222.2
Financing Receivable, Originated in Current Fiscal Year	21.7	43.8
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	20.8	48.8
Financing Receivable, Originated Two Years before Latest Fiscal Year	119.4	15.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	13.1	46
Financing Receivable, Originated Four Years before Latest Fiscal Year	35.5	24.6
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	59.4	37.1
Financing Receivable, Revolving	6.8	6.3
Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	2,514.2	2,548.3
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Net of Deferred Income	2,514.2	2,548.3
Financing Receivable, Originated in Current Fiscal Year	147.6	645.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	569.2	214
Financing Receivable, Originated Two Years before Latest Fiscal Year	157.4	76.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	46.4	2
Financing Receivable, Originated Four Years before Latest Fiscal Year	2.3	0.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.4	0
Financing Receivable, Revolving	1,590.9	1,608.9
Tech & Innovation [Member] | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,463.5	2,505.7
Financing Receivable, Originated in Current Fiscal Year	124.9	609.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	549.2	207.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	150.7	76.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	45.1	2
Financing Receivable, Originated Four Years before Latest Fiscal Year	2.3	0.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.4	0
Financing Receivable, Revolving	1,590.9	1,608.8
Tech & Innovation [Member] | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	18.4	15.3
Financing Receivable, Originated in Current Fiscal Year	4	10.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	14.4	4.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Tech & Innovation [Member] | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	32.3	27.3
Financing Receivable, Originated in Current Fiscal Year	18.7	25.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5.6	2
Financing Receivable, Originated Two Years before Latest Fiscal Year	6.7	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	1.3	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0.1
Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	6,174.2	5,911
Financing Receivable, Past Due	0.1	0.2
Loans and Leases Receivable, Net of Deferred Income	6,174.3	5,911.2
Financing Receivable, Originated in Current Fiscal Year	1,026.1	2,072.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,557.6	880.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	799.3	483
Financing Receivable, Originated Three Years before Latest Fiscal Year	405.9	274.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	250.9	111.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	215.4	115.6
Financing Receivable, Revolving	1,919.1	1,974.2
Other commercial and industrial [Member] | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,012.6	5,737.7
Financing Receivable, Originated in Current Fiscal Year	1,025.9	2,069.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,553.9	819.8
Financing Receivable, Originated Two Years before Latest Fiscal Year	736.5	447.7
Financing Receivable, Originated Three Years before Latest Fiscal Year	384.4	250.7
Financing Receivable, Originated Four Years before Latest Fiscal Year	204.8	99.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	200	114.6
Financing Receivable, Revolving	1,907.1	1,935.7
Other commercial and industrial [Member] | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	103.8	144.7
Financing Receivable, Originated in Current Fiscal Year	0.2	2.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2.8	52.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	43.1	32.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	17.8	22.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	29.9	1.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	4.8	0.2
Financing Receivable, Revolving	5.2	34.3
Other commercial and industrial [Member] | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	57.9	28.8
Financing Receivable, Originated in Current Fiscal Year	0	0.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.9	8.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	19.7	3.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	3.7	1.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	16.2	9.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	10.6	0.8
Financing Receivable, Revolving	6.8	4.2
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	1,814.5	1,909.3
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Net of Deferred Income	1,814.5	1,909.3
Financing Receivable, Originated in Current Fiscal Year	90.6	254.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	247.4	327
Financing Receivable, Originated Two Years before Latest Fiscal Year	310.1	316.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	249.8	435.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	398.5	159
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	461.1	353.5
Financing Receivable, Revolving	57	63.9
Commercial Real Estate Owner Occupied [Member] | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,684.5	1,775.2
Financing Receivable, Originated in Current Fiscal Year	88.3	252.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	245.1	307.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	291.8	302.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	235.9	402.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	370.8	148.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	420	323.5
Financing Receivable, Revolving	32.6	39.5
Commercial Real Estate Owner Occupied [Member] | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	84.6	84.2
Financing Receivable, Originated in Current Fiscal Year	2.3	0.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.9	12.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	11.5	9.3
Financing Receivable, Originated Three Years before Latest Fiscal Year	9.2	24.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	22.5	4.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	13.8	10.5
Financing Receivable, Revolving	24.4	22.4
Commercial Real Estate Owner Occupied [Member] | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	45.4	49.9
Financing Receivable, Originated in Current Fiscal Year	0	1.4
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1.4	7.5
Financing Receivable, Originated Two Years before Latest Fiscal Year	6.8	4.8
Financing Receivable, Originated Three Years before Latest Fiscal Year	4.7	8.5
Financing Receivable, Originated Four Years before Latest Fiscal Year	5.2	6.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	27.3	19.5
Financing Receivable, Revolving	0	2
Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	2,038.8	1,983.9
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Net of Deferred Income	2,038.8	1,983.9
Financing Receivable, Originated in Current Fiscal Year	102.8	170.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	183.3	824.7
Financing Receivable, Originated Two Years before Latest Fiscal Year	824.3	521
Financing Receivable, Originated Three Years before Latest Fiscal Year	505	179.8
Financing Receivable, Originated Four Years before Latest Fiscal Year	178.9	2.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	85.7	123.2
Financing Receivable, Revolving	158.8	162.6
Hotel franchise finance [Member] | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,770.3	1,821.7
Financing Receivable, Originated in Current Fiscal Year	102.8	161.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	166.2	792
Financing Receivable, Originated Two Years before Latest Fiscal Year	684.7	464.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	448.3	139.9
Financing Receivable, Originated Four Years before Latest Fiscal Year	139	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	70.5	101.5
Financing Receivable, Revolving	158.8	162.6
Hotel franchise finance [Member] | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	184.9	135.1
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	6.1	32.7
Financing Receivable, Originated Two Years before Latest Fiscal Year	82.8	56.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	56.7	27.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	27.4	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	11.9	18.2
Financing Receivable, Revolving	0	0
Hotel franchise finance [Member] | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	83.6	27.1
Financing Receivable, Originated in Current Fiscal Year	0	8.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	11	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	56.8	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	12.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	12.5	2.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	3.3	3.5
Financing Receivable, Revolving	0	0
Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	3,612.3	3,640.2
Financing Receivable, Past Due	0.7	0
Loans and Leases Receivable, Net of Deferred Income	3,613	3,640.2
Financing Receivable, Originated in Current Fiscal Year	167.1	1,041.4
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,071.1	938.9
Financing Receivable, Originated Two Years before Latest Fiscal Year	881.4	567.8
Financing Receivable, Originated Three Years before Latest Fiscal Year	535.4	410
Financing Receivable, Originated Four Years before Latest Fiscal Year	320.5	172.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	365.7	228.9
Financing Receivable, Revolving	271.8	281
Other Commercial Real Estate Non owner Occupied [Member] | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,547.8	3,544.3
Financing Receivable, Originated in Current Fiscal Year	167.1	1,032.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,069.3	912.5
Financing Receivable, Originated Two Years before Latest Fiscal Year	857.6	560.8
Financing Receivable, Originated Three Years before Latest Fiscal Year	527.1	384.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	317.5	164.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	337.4	208.4
Financing Receivable, Revolving	271.8	281
Other Commercial Real Estate Non owner Occupied [Member] | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	22.3	22.2
Financing Receivable, Originated in Current Fiscal Year	0	1.4
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1.4	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	7
Financing Receivable, Originated Three Years before Latest Fiscal Year	8.3	5.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	1.4	1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	11.2	7.4
Financing Receivable, Revolving	0	0
Other Commercial Real Estate Non owner Occupied [Member] | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	42.9	73.7
Financing Receivable, Originated in Current Fiscal Year	0	7.4
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.4	26.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	23.8	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	20.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	1.6	6.5
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	17.1	13.1
Financing Receivable, Revolving	0	0
Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	3,049.4	2,368
Financing Receivable, Past Due	6.4	10.5
Loans and Leases Receivable, Net of Deferred Income	3,055.8	2,378.5
Financing Receivable, Originated in Current Fiscal Year	599.9	759.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,116.5	873.7
Financing Receivable, Originated Two Years before Latest Fiscal Year	720.5	407.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	341.6	110
Financing Receivable, Originated Four Years before Latest Fiscal Year	92.8	113.8
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	146.2	74.1
Financing Receivable, Revolving	38.3	39.5
Residential Real Estate [Member] | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,047	2,367.1
Financing Receivable, Originated in Current Fiscal Year	599.9	759.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,116.5	869.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	715.6	402
Financing Receivable, Originated Three Years before Latest Fiscal Year	338.4	108.9
Financing Receivable, Originated Four Years before Latest Fiscal Year	92.8	113.8
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	145.5	74.1
Financing Receivable, Revolving	38.3	39.5
Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	0
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8.8	11.4
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	4.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	4.9	5.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	3.2	1.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.7	0
Financing Receivable, Revolving	0	0
Construction And Land Development [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	2,767.6	2,429.4
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Net of Deferred Income	2,767.6	2,429.4
Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	4,901.8	4,340.2
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Net of Deferred Income	4,901.8	4,340.2
Financing Receivable, Originated in Current Fiscal Year	91.6	135.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	63.2	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.8	1.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	1.5	0.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	4,744.7	4,202.4
Warehouse lending [Member] | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,901.8	4,340.2
Financing Receivable, Originated in Current Fiscal Year	91.6	135.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	63.2	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.8	1.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	1.5	0.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	4,744.7	4,202.4
Warehouse lending [Member] | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	0
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Warehouse lending [Member] | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	0
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	1,676.9	1,728.8
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Net of Deferred Income	1,676.9	1,728.8
Financing Receivable, Originated in Current Fiscal Year	10.7	219.3
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	222.1	156.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	133.6	81.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	81.4	233.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	227.7	129.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	997.9	905.6
Financing Receivable, Revolving	3.5	3.5
Municipal and nonprofit [Member] | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,676.9	1,726.9
Financing Receivable, Originated in Current Fiscal Year	10.7	219.3
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	222.1	156.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	133.6	81.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	81.4	231.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	227.7	129.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	997.9	905.6
Financing Receivable, Revolving	3.5	3.5
Municipal and nonprofit [Member] | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	0
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Municipal and nonprofit [Member] | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	1.9
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	1.9
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Other, loan segment
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Not Past Due	154	182.7
Financing Receivable, Past Due	0.1	0.5
Loans and Leases Receivable, Net of Deferred Income	154.1	183.2
Financing Receivable, Originated in Current Fiscal Year	11.5	21.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	19.6	15.7
Financing Receivable, Originated Two Years before Latest Fiscal Year	13.6	14.8
Financing Receivable, Originated Three Years before Latest Fiscal Year	6.2	7.5
Financing Receivable, Originated Four Years before Latest Fiscal Year	4.8	1.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	73.2	76.5
Financing Receivable, Revolving	25.2	45.7
Other, loan segment | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	150.2	180.3
Financing Receivable, Originated in Current Fiscal Year	8.5	21.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	19.6	15.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	13.5	14.5
Financing Receivable, Originated Three Years before Latest Fiscal Year	5.9	5.8
Financing Receivable, Originated Four Years before Latest Fiscal Year	4.8	1.8
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	72.7	75.8
Financing Receivable, Revolving	25.2	45.7
Other, loan segment | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0.2	2.3
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.1	1.7
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.1	0.5
Financing Receivable, Revolving	0	0
Other, loan segment | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3.7	0.6
Financing Receivable, Originated in Current Fiscal Year	3	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.1	0.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.2	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.4	0.2
Financing Receivable, Revolving	0	0
Construction And Land Development Land [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,767.6	2,429.4
Financing Receivable, Originated in Current Fiscal Year	220.6	686.3
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	683.4	704.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	675.8	469.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	419.8	15.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	8.9	1.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1.1	15
Financing Receivable, Revolving	758	537.8
Construction And Land Development Land [Member] | Pass [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2,705.5	2,380.6
Financing Receivable, Originated in Current Fiscal Year	219.6	677.8
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	673.7	704.2
Financing Receivable, Originated Two Years before Latest Fiscal Year	668.9	429.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	375.3	15.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	8.9	1.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1.1	15
Financing Receivable, Revolving	758	537.4
Construction And Land Development Land [Member] | Special Mention [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	60	47.3
Financing Receivable, Originated in Current Fiscal Year	1	8.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	8.2	0.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	6.3	38
Financing Receivable, Originated Three Years before Latest Fiscal Year	44.5	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0.4
Construction And Land Development Land [Member] | Substandard [Member]
Financing Receivable, Nonaccrual [Line Items]
Loans and Leases Receivable, Net of Deferred Income	2.1	1.5
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1.5	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.6	1.5
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	7.2	9.7
Financial Asset, 30 to 59 Days Past Due [Member] | Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 30 to 59 Days Past Due [Member] | Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0.1	0.2
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 30 to 59 Days Past Due [Member] | Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 30 to 59 Days Past Due [Member] | Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0.7	0
Financial Asset, 30 to 59 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	6.4	9.1
Financial Asset, 30 to 59 Days Past Due [Member] | Construction And Land Development [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 30 to 59 Days Past Due [Member] | Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 30 to 59 Days Past Due [Member] | Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 30 to 59 Days Past Due [Member] | Other, loan segment
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0.4
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0.1	1.5
Financial Asset, 60 to 89 Days Past Due [Member] | Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	1.4
Financial Asset, 60 to 89 Days Past Due [Member] | Construction And Land Development [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | Other, loan segment
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0.1	0.1
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Tech & Innovation [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Other commercial and industrial [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Hotel franchise finance [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Construction And Land Development [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Warehouse lending [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Municipal and nonprofit [Member]
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Other, loan segment
Financing Receivable, Nonaccrual [Line Items]
Financing Receivable, Past Due	$ 0	$ 0

Loans, Leases and Allowance f_4

Loans, Leases and Allowance for Credit Losses - Loans by Risk Rating (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	$ 2,468.5	$ 6,006
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,733.4	4,935.5
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,516	2,939.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,592.3	1,669
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,486.8	691.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	2,346.7	1,892.4
Financing Receivable, Revolving	9,567.3	8,919.5
Loans and Leases Receivable, Net of Deferred Income	28,711	27,053
Financing Receivable, Not Past Due	28,703.7	27,041.8
Financing Receivable, Past Due	7.3	11.2
Loans and Leases Receivable, Collateral for Secured Borrowings	192.5
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	7.2	9.7
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0.1	1.5
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	2,439.3	5,938.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5,678.8	4,784.5
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,252.9	2,780.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	2,442.6	1,542.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	1,370.1	659.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	2,245.5	1,818.5
Financing Receivable, Revolving	9,530.9	8,856.1
Loans and Leases Receivable, Net of Deferred Income	27,960.1	26,379.7
Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	7.5	23.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	33.8	102.2
Financing Receivable, Originated Two Years before Latest Fiscal Year	143.7	143.4
Financing Receivable, Originated Three Years before Latest Fiscal Year	136.6	80.8
Financing Receivable, Originated Four Years before Latest Fiscal Year	81.2	7.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	41.8	36.8
Financing Receivable, Revolving	29.6	57.1
Loans and Leases Receivable, Net of Deferred Income	474.2	451.1
Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	21.7	43.8
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	20.8	48.8
Financing Receivable, Originated Two Years before Latest Fiscal Year	119.4	15.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	13.1	46
Financing Receivable, Originated Four Years before Latest Fiscal Year	35.5	24.6
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	59.4	37.1
Financing Receivable, Revolving	6.8	6.3
Loans and Leases Receivable, Net of Deferred Income	276.7	222.2
Tech & Innovation [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	147.6	645.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	569.2	214
Financing Receivable, Originated Two Years before Latest Fiscal Year	157.4	76.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	46.4	2
Financing Receivable, Originated Four Years before Latest Fiscal Year	2.3	0.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.4	0
Financing Receivable, Revolving	1,590.9	1,608.9
Loans and Leases Receivable, Net of Deferred Income	2,514.2	2,548.3
Financing Receivable, Not Past Due	2,514.2	2,548.3
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Collateral for Secured Borrowings	32.3
Tech & Innovation [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Tech & Innovation [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Tech & Innovation [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Tech & Innovation [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	124.9	609.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	549.2	207.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	150.7	76.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	45.1	2
Financing Receivable, Originated Four Years before Latest Fiscal Year	2.3	0.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.4	0
Financing Receivable, Revolving	1,590.9	1,608.8
Loans and Leases Receivable, Net of Deferred Income	2,463.5	2,505.7
Tech & Innovation [Member] | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	4	10.7
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	14.4	4.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	18.4	15.3
Tech & Innovation [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	18.7	25.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	5.6	2
Financing Receivable, Originated Two Years before Latest Fiscal Year	6.7	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	1.3	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0.1
Loans and Leases Receivable, Net of Deferred Income	32.3	27.3
Other commercial and industrial [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1,026.1	2,072.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,557.6	880.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	799.3	483
Financing Receivable, Originated Three Years before Latest Fiscal Year	405.9	274.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	250.9	111.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	215.4	115.6
Financing Receivable, Revolving	1,919.1	1,974.2
Loans and Leases Receivable, Net of Deferred Income	6,174.3	5,911.2
Financing Receivable, Not Past Due	6,174.2	5,911
Financing Receivable, Past Due	0.1	0.2
Loans and Leases Receivable, Collateral for Secured Borrowings	13.1
Other commercial and industrial [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0.1	0.2
Other commercial and industrial [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Other commercial and industrial [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Other commercial and industrial [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1,025.9	2,069.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,553.9	819.8
Financing Receivable, Originated Two Years before Latest Fiscal Year	736.5	447.7
Financing Receivable, Originated Three Years before Latest Fiscal Year	384.4	250.7
Financing Receivable, Originated Four Years before Latest Fiscal Year	204.8	99.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	200	114.6
Financing Receivable, Revolving	1,907.1	1,935.7
Loans and Leases Receivable, Net of Deferred Income	6,012.6	5,737.7
Other commercial and industrial [Member] | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0.2	2.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	2.8	52.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	43.1	32.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	17.8	22.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	29.9	1.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	4.8	0.2
Financing Receivable, Revolving	5.2	34.3
Loans and Leases Receivable, Net of Deferred Income	103.8	144.7
Other commercial and industrial [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.9	8.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	19.7	3.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	3.7	1.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	16.2	9.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	10.6	0.8
Financing Receivable, Revolving	6.8	4.2
Loans and Leases Receivable, Net of Deferred Income	57.9	28.8
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	90.6	254.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	247.4	327
Financing Receivable, Originated Two Years before Latest Fiscal Year	310.1	316.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	249.8	435.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	398.5	159
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	461.1	353.5
Financing Receivable, Revolving	57	63.9
Loans and Leases Receivable, Net of Deferred Income	1,814.5	1,909.3
Financing Receivable, Not Past Due	1,814.5	1,909.3
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Collateral for Secured Borrowings	37.6
Commercial Real Estate Owner Occupied [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Commercial Real Estate Owner Occupied [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Commercial Real Estate Owner Occupied [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Commercial Real Estate Owner Occupied [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	88.3	252.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	245.1	307.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	291.8	302.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	235.9	402.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	370.8	148.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	420	323.5
Financing Receivable, Revolving	32.6	39.5
Loans and Leases Receivable, Net of Deferred Income	1,684.5	1,775.2
Commercial Real Estate Owner Occupied [Member] | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	2.3	0.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.9	12.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	11.5	9.3
Financing Receivable, Originated Three Years before Latest Fiscal Year	9.2	24.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	22.5	4.4
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	13.8	10.5
Financing Receivable, Revolving	24.4	22.4
Loans and Leases Receivable, Net of Deferred Income	84.6	84.2
Commercial Real Estate Owner Occupied [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	1.4
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1.4	7.5
Financing Receivable, Originated Two Years before Latest Fiscal Year	6.8	4.8
Financing Receivable, Originated Three Years before Latest Fiscal Year	4.7	8.5
Financing Receivable, Originated Four Years before Latest Fiscal Year	5.2	6.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	27.3	19.5
Financing Receivable, Revolving	0	2
Loans and Leases Receivable, Net of Deferred Income	45.4	49.9
Hotel franchise finance [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	102.8	170.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	183.3	824.7
Financing Receivable, Originated Two Years before Latest Fiscal Year	824.3	521
Financing Receivable, Originated Three Years before Latest Fiscal Year	505	179.8
Financing Receivable, Originated Four Years before Latest Fiscal Year	178.9	2.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	85.7	123.2
Financing Receivable, Revolving	158.8	162.6
Loans and Leases Receivable, Net of Deferred Income	2,038.8	1,983.9
Financing Receivable, Not Past Due	2,038.8	1,983.9
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Collateral for Secured Borrowings	83.5
Hotel franchise finance [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Hotel franchise finance [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Hotel franchise finance [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Hotel franchise finance [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	102.8	161.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	166.2	792
Financing Receivable, Originated Two Years before Latest Fiscal Year	684.7	464.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	448.3	139.9
Financing Receivable, Originated Four Years before Latest Fiscal Year	139	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	70.5	101.5
Financing Receivable, Revolving	158.8	162.6
Loans and Leases Receivable, Net of Deferred Income	1,770.3	1,821.7
Hotel franchise finance [Member] | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	6.1	32.7
Financing Receivable, Originated Two Years before Latest Fiscal Year	82.8	56.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	56.7	27.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	27.4	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	11.9	18.2
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	184.9	135.1
Hotel franchise finance [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	8.9
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	11	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	56.8	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	12.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	12.5	2.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	3.3	3.5
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	83.6	27.1
Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	167.1	1,041.4
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,071.1	938.9
Financing Receivable, Originated Two Years before Latest Fiscal Year	881.4	567.8
Financing Receivable, Originated Three Years before Latest Fiscal Year	535.4	410
Financing Receivable, Originated Four Years before Latest Fiscal Year	320.5	172.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	365.7	228.9
Financing Receivable, Revolving	271.8	281
Loans and Leases Receivable, Net of Deferred Income	3,613	3,640.2
Financing Receivable, Not Past Due	3,612.3	3,640.2
Financing Receivable, Past Due	0.7	0
Loans and Leases Receivable, Collateral for Secured Borrowings	23.6
Other Commercial Real Estate Non owner Occupied [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0.7	0
Other Commercial Real Estate Non owner Occupied [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Other Commercial Real Estate Non owner Occupied [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Other Commercial Real Estate Non owner Occupied [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	167.1	1,032.6
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,069.3	912.5
Financing Receivable, Originated Two Years before Latest Fiscal Year	857.6	560.8
Financing Receivable, Originated Three Years before Latest Fiscal Year	527.1	384.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	317.5	164.7
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	337.4	208.4
Financing Receivable, Revolving	271.8	281
Loans and Leases Receivable, Net of Deferred Income	3,547.8	3,544.3
Other Commercial Real Estate Non owner Occupied [Member] | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	1.4
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1.4	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	7
Financing Receivable, Originated Three Years before Latest Fiscal Year	8.3	5.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	1.4	1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	11.2	7.4
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	22.3	22.2
Other Commercial Real Estate Non owner Occupied [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	7.4
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0.4	26.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	23.8	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	20.3
Financing Receivable, Originated Four Years before Latest Fiscal Year	1.6	6.5
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	17.1	13.1
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	42.9	73.7
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	599.9	759.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,116.5	873.7
Financing Receivable, Originated Two Years before Latest Fiscal Year	720.5	407.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	341.6	110
Financing Receivable, Originated Four Years before Latest Fiscal Year	92.8	113.8
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	146.2	74.1
Financing Receivable, Revolving	38.3	39.5
Loans and Leases Receivable, Net of Deferred Income	3,055.8	2,378.5
Financing Receivable, Not Past Due	3,049.4	2,368
Financing Receivable, Past Due	6.4	10.5
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Residential Real Estate [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	6.4	9.1
Residential Real Estate [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	1.4
Residential Real Estate [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Residential Real Estate [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	599.9	759.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1,116.5	869.3
Financing Receivable, Originated Two Years before Latest Fiscal Year	715.6	402
Financing Receivable, Originated Three Years before Latest Fiscal Year	338.4	108.9
Financing Receivable, Originated Four Years before Latest Fiscal Year	92.8	113.8
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	145.5	74.1
Financing Receivable, Revolving	38.3	39.5
Loans and Leases Receivable, Net of Deferred Income	3,047	2,367.1
Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	0	0
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	4.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	4.9	5.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	3.2	1.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.7	0
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	8.8	11.4
Construction And Land Development Land [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	220.6	686.3
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	683.4	704.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	675.8	469.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	419.8	15.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	8.9	1.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1.1	15
Financing Receivable, Revolving	758	537.8
Loans and Leases Receivable, Net of Deferred Income	2,767.6	2,429.4
Construction And Land Development Land [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	219.6	677.8
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	673.7	704.2
Financing Receivable, Originated Two Years before Latest Fiscal Year	668.9	429.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	375.3	15.4
Financing Receivable, Originated Four Years before Latest Fiscal Year	8.9	1.2
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	1.1	15
Financing Receivable, Revolving	758	537.4
Loans and Leases Receivable, Net of Deferred Income	2,705.5	2,380.6
Construction And Land Development Land [Member] | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	1	8.5
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	8.2	0.4
Financing Receivable, Originated Two Years before Latest Fiscal Year	6.3	38
Financing Receivable, Originated Three Years before Latest Fiscal Year	44.5	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0.4
Loans and Leases Receivable, Net of Deferred Income	60	47.3
Construction And Land Development Land [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	1.5	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.6	1.5
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	2.1	1.5
Warehouse lending [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	91.6	135.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	63.2	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.8	1.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	1.5	0.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	4,744.7	4,202.4
Loans and Leases Receivable, Net of Deferred Income	4,901.8	4,340.2
Financing Receivable, Not Past Due	4,901.8	4,340.2
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Warehouse lending [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Warehouse lending [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Warehouse lending [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Warehouse lending [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	91.6	135.2
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	63.2	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0.9
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.8	1.6
Financing Receivable, Originated Four Years before Latest Fiscal Year	1.5	0.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	4,744.7	4,202.4
Loans and Leases Receivable, Net of Deferred Income	4,901.8	4,340.2
Warehouse lending [Member] | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	0	0
Warehouse lending [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	0	0
Municipal and nonprofit [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	10.7	219.3
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	222.1	156.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	133.6	81.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	81.4	233.1
Financing Receivable, Originated Four Years before Latest Fiscal Year	227.7	129.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	997.9	905.6
Financing Receivable, Revolving	3.5	3.5
Loans and Leases Receivable, Net of Deferred Income	1,676.9	1,728.8
Financing Receivable, Not Past Due	1,676.9	1,728.8
Financing Receivable, Past Due	0	0
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Municipal and nonprofit [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Municipal and nonprofit [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Municipal and nonprofit [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Municipal and nonprofit [Member] | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	10.7	219.3
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	222.1	156.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	133.6	81.6
Financing Receivable, Originated Three Years before Latest Fiscal Year	81.4	231.2
Financing Receivable, Originated Four Years before Latest Fiscal Year	227.7	129.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	997.9	905.6
Financing Receivable, Revolving	3.5	3.5
Loans and Leases Receivable, Net of Deferred Income	1,676.9	1,726.9
Municipal and nonprofit [Member] | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	0	0
Municipal and nonprofit [Member] | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	1.9
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	0	1.9
Other, loan segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	11.5	21.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	19.6	15.7
Financing Receivable, Originated Two Years before Latest Fiscal Year	13.6	14.8
Financing Receivable, Originated Three Years before Latest Fiscal Year	6.2	7.5
Financing Receivable, Originated Four Years before Latest Fiscal Year	4.8	1.9
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	73.2	76.5
Financing Receivable, Revolving	25.2	45.7
Loans and Leases Receivable, Net of Deferred Income	154.1	183.2
Financing Receivable, Not Past Due	154	182.7
Financing Receivable, Past Due	0.1	0.5
Loans and Leases Receivable, Collateral for Secured Borrowings	0.4
Other, loan segment | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0.4
Other, loan segment | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0.1	0.1
Other, loan segment | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Past Due	0	0
Other, loan segment | Pass [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	8.5	21.1
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	19.6	15.6
Financing Receivable, Originated Two Years before Latest Fiscal Year	13.5	14.5
Financing Receivable, Originated Three Years before Latest Fiscal Year	5.9	5.8
Financing Receivable, Originated Four Years before Latest Fiscal Year	4.8	1.8
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	72.7	75.8
Financing Receivable, Revolving	25.2	45.7
Loans and Leases Receivable, Net of Deferred Income	150.2	180.3
Other, loan segment | Special Mention [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	0	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	0.1
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.1	1.7
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.1	0.5
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	0.2	2.3
Other, loan segment | Substandard [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Originated in Current Fiscal Year	3	0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0.1
Financing Receivable, Originated Two Years before Latest Fiscal Year	0.1	0.2
Financing Receivable, Originated Three Years before Latest Fiscal Year	0.2	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0.1
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0.4	0.2
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Net of Deferred Income	$ 3.7	$ 0.6

Loans, Leases and Allowance f_5

Loans, Leases and Allowance for Credit Losses Loans, Leases and Allowance for Credit Losses - Troubled Debt Restructurings (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)SecurityLoan	Mar. 31, 2020USD ($)SecurityLoan	Dec. 31, 2020USD ($)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 192.5
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts | SecurityLoan	0	1
Financing Receivable, Troubled Debt Restructuring, Commitment to Lend	$ 0.3		$ 0.6
Financing Receivable, Troubled Debt Restructuring, Subsequent Default		$ 0.7
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 4.7
Financing Receivable, Modifications, Number of Contracts | SecurityLoan	3
Financing Receivable, Troubled Debt Restructuring	$ 60.2	$ 26.5	61.6
Reserves allocated to customers whose loan terms modified in troubled debt restructurings	$ 3.1		$ 2.7
Financing Receivable, Troubled Debt Restructured Loans, Number of Outstanding Contracts | SecurityLoan	22
Tech & Innovation [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 32.3
Financing Receivable, Troubled Debt Restructuring	$ 19.8
Financing Receivable, Troubled Debt Restructured Loans, Number of Outstanding Contracts | SecurityLoan	4
Other commercial and industrial [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 13.1
Financing Receivable, Troubled Debt Restructuring	$ 24.3
Financing Receivable, Troubled Debt Restructured Loans, Number of Outstanding Contracts | SecurityLoan	10
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 37.6
Financing Receivable, Troubled Debt Restructuring	$ 1.9
Financing Receivable, Troubled Debt Restructured Loans, Number of Outstanding Contracts | SecurityLoan	3
Hotel franchise finance [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 83.5
Financing Receivable, Troubled Debt Restructuring	$ 5.3
Financing Receivable, Troubled Debt Restructured Loans, Number of Outstanding Contracts | SecurityLoan	2
Other Commercial Real Estate Non owner Occupied [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 23.6
Financing Receivable, Troubled Debt Restructuring	$ 8.9
Financing Receivable, Troubled Debt Restructured Loans, Number of Outstanding Contracts | SecurityLoan	3
Residential Real Estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 0
Construction And Land Development [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	2
Warehouse lending [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Municipal and nonprofit [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 0

Loans, Leases and Allowance f_6

Loans, Leases and Allowance for Credit Losses Loans, Leases and Allowance for Credit Losses - Collateral Dependent Loans (Details) $ in Millions	Mar. 31, 2021USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 192.5
Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	146.7
Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	45.8
Tech & Innovation [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	32.3
Tech & Innovation [Member] | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Tech & Innovation [Member] | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	32.3
Other commercial and industrial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	13.1
Other commercial and industrial [Member] | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Other commercial and industrial [Member] | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	13.1
Commercial Real Estate Owner Occupied [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	37.6
Commercial Real Estate Owner Occupied [Member] | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	37.6
Commercial Real Estate Owner Occupied [Member] | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Hotel franchise finance [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	83.5
Hotel franchise finance [Member] | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	83.5
Hotel franchise finance [Member] | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Other Commercial Real Estate Non owner Occupied [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	23.6
Other Commercial Real Estate Non owner Occupied [Member] | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	23.6
Other Commercial Real Estate Non owner Occupied [Member] | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Residential Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Residential Real Estate [Member] | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Residential Real Estate [Member] | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Construction And Land Development [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	2
Construction And Land Development [Member] | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	2
Construction And Land Development [Member] | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Warehouse lending [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Warehouse lending [Member] | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Warehouse lending [Member] | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Municipal and nonprofit [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Municipal and nonprofit [Member] | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Municipal and nonprofit [Member] | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Other, loan segment
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0.4
Other, loan segment | Real Estate Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	0
Other, loan segment | Other Collateral [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Collateral for Secured Borrowings	$ 0.4

Loans, Leases and Allowance f_7

Loans, Leases and Allowance for Credit Losses - Allowances for Credit Losses (Detail) Valuation - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	$ 247.1	$ 235.3	$ 278.9	$ 186.9
Provision for Loan and Lease Losses	30.4	(45.2)
Financing Receivable, Allowance for Credit Loss, Writeoff	2.1	0.1
Financing Receivable, Allowance for Credit Loss, Recovery	(0.7)	(3.3)
Financing Receivable, Collectively Evaluated for Impairment	28,393		26,787.4
Financing Receivable, Individually Evaluated for Impairment	318		265.6
Loans and Leases Receivable, Net of Deferred Income	28,711		27,053
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	233.9		267.7
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	13.2		11.2
Off-Balance Sheet, Credit Loss, Liability	32.6	29.6	37		$ 9
Loans and Leases Receivable, Allowance	247.1		278.9
Interest Receivable	138.1		142.1
Off-Balance Sheet, Credit Loss, Liability, Change in Method, Credit Loss Expense (Reversal)	(4.4)	5.5
Cumulative Effect, Period of Adoption, Adjustment [Member]
Valuation Allowance [Line Items]
Off-Balance Sheet, Credit Loss, Liability				15.1
Tech & Innovation [Member]
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	23.9	39.8	35.3	22.4
Provision for Loan and Lease Losses	(11.6)	17.4
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0.2	0
Financing Receivable, Collectively Evaluated for Impairment	2,481.9		2,521.1
Financing Receivable, Individually Evaluated for Impairment	32.3		27.2
Loans and Leases Receivable, Net of Deferred Income	2,514.2		2,548.3
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	21.9		31.4
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2		3.9
Other commercial and industrial [Member]
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	78.4	120.3	94.7	95.8
Provision for Loan and Lease Losses	(16.5)	23.3
Financing Receivable, Allowance for Credit Loss, Writeoff	0.1	0.1
Financing Receivable, Allowance for Credit Loss, Recovery	(0.3)	(1.3)
Financing Receivable, Collectively Evaluated for Impairment	6,117.6		5,883.1
Financing Receivable, Individually Evaluated for Impairment	56.7		28.1
Loans and Leases Receivable, Net of Deferred Income	6,174.3		5,911.2
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	74.9		90.3
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	3.5		4.4
Commercial Real Estate Owner Occupied [Member]
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	9.7	10.5	18.6	10.4
Provision for Loan and Lease Losses	8.9	(0.1)
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Collectively Evaluated for Impairment	1,767.8		1,857.9
Financing Receivable, Individually Evaluated for Impairment	46.7		51.4
Loans and Leases Receivable, Net of Deferred Income	1,814.5		1,909.3
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	9.7		18.6
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Hotel franchise finance [Member]
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	49.4	18.8	43.3	14.1
Provision for Loan and Lease Losses	(6.1)	(4.7)
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Collectively Evaluated for Impairment	1,925.4		1,927
Financing Receivable, Individually Evaluated for Impairment	113.4		56.9
Loans and Leases Receivable, Net of Deferred Income	2,038.8		1,983.9
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	43.2		40.4
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	6.2		2.9
Other Commercial Real Estate Non owner Occupied [Member]
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	32.7	14.2	39.9	10.5
Provision for Loan and Lease Losses	5.4	(1.7)
Financing Receivable, Allowance for Credit Loss, Writeoff	2	0
Financing Receivable, Allowance for Credit Loss, Recovery	0.2	2
Financing Receivable, Collectively Evaluated for Impairment	3,558.7		3,553.6
Financing Receivable, Individually Evaluated for Impairment	54.3		86.6
Loans and Leases Receivable, Net of Deferred Income	3,613		3,640.2
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	32.7		39.9
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Residential Real Estate [Member]
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	3.2	1.3	0.8	3.8
Provision for Loan and Lease Losses	(2.4)	2.5
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Collectively Evaluated for Impairment	3,046.9		2,367.1
Financing Receivable, Individually Evaluated for Impairment	8.9		11.4
Loans and Leases Receivable, Net of Deferred Income	3,055.8		2,378.5
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3.2		0.8
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Construction And Land Development [Member]
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	25.9	7.1	22	6.2
Provision for Loan and Lease Losses	(3.9)	(0.9)
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Collectively Evaluated for Impairment	2,765.6		2,427.9
Financing Receivable, Individually Evaluated for Impairment	2		1.5
Loans and Leases Receivable, Net of Deferred Income	2,767.6		2,429.4
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	25.9		22
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Warehouse lending [Member]
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	3.6	0.4	3.4	0.2
Provision for Loan and Lease Losses	(0.2)	(0.2)
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Collectively Evaluated for Impairment	4,901.8		4,340.2
Financing Receivable, Individually Evaluated for Impairment	0		0
Loans and Leases Receivable, Net of Deferred Income	4,901.8		4,340.2
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3.6		3.4
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Municipal and nonprofit [Member]
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	15.2	16.2	15.9	17.4
Provision for Loan and Lease Losses	0.7	1.2
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	0
Financing Receivable, Collectively Evaluated for Impairment	1,676.9		1,726.9
Financing Receivable, Individually Evaluated for Impairment	0		1.9
Loans and Leases Receivable, Net of Deferred Income	1,676.9		1,728.8
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	15.2		15.9
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Other, loan segment
Valuation Allowance [Line Items]
Financing Receivable, Allowance for Credit Loss	5.1	6.7	5	$ 6.1
Provision for Loan and Lease Losses	0.1	0.6
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	$ 0
Financing Receivable, Collectively Evaluated for Impairment	150.4		182.6
Financing Receivable, Individually Evaluated for Impairment	3.7		0.6
Loans and Leases Receivable, Net of Deferred Income	154.1		183.2
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	3.6		5
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	$ 1.5		$ 0

Loans, Leases and Allowance f_8

Loans, Leases and Allowance for Credit Losses Loans, Leases and Allowance for Credit Losses - Loan Purchases and Sales (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Purchase	$ 1,301.1	$ 667.6
Loans and Leases Receivable, Gain (Loss) on Sales, Net	0.7	0
Financing Receivable, Sale	100.1	0
Residential Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Purchase	1,016.6	279.5
Warehouse lending [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Purchase	0	99.4
Tech & Innovation [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Purchase	34.9	177.2
Other commercial and industrial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Purchase	217.6	91.5
Other, loan segment
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Purchase	$ 32	$ 0

Other Borrowings - Additional I

Other Borrowings - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt [Line Items]
FHLB advances	$ 5	$ 5
Short-term Debt	5	5
Customer repurchase agreements	15.9	16
Federal Funds Purchased	0	0
Federal Home Loan Bank Advances [Member]
Debt [Line Items]
Additional available credit with the entity	4,200	$ 4,000
FRB [Member]
Debt [Line Items]
Additional available credit with the entity	2,700
Unsecured Credit Facility [Member]
Debt [Line Items]
Secured borrowing credit line	$ 2,500

Qualifying Debt (Details)

Qualifying Debt (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2021USD ($)Trust$ / shares	Mar. 31, 2020$ / shares	Dec. 31, 2020USD ($)	Jun. 30, 2020	May 22, 2020USD ($)	Jun. 16, 2016USD ($)	Jun. 29, 2015USD ($)
Debt Instrument [Line Items]
Common Stock, Dividends, Per Share, Cash Paid | $ / shares	$ 0.25	$ 0.25
Subordinated Debt	$ 464,400,000		$ 469,800,000
Number of Statutory Business Trusts Formed or Acquired | Trust	8
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	$ 79,300,000		78,900,000
Subordinated Debt [Member] | Subordinated Debentures Maturing July 2056 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 175,000,000					$ 175,000,000
Debt Issuance Cost						$ 5,500,000
Debt Instrument, Interest Rate, Stated Percentage	6.25%
Subordinated Debt [Member] | Subordinated Debentures Maturing July 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 150,000,000
Debt Issuance Cost							$ 1,800,000
Debt Instrument, Interest Rate, Stated Percentage				5.00%
Early Repayment of Subordinated Debt			$ 75,000,000
Subordinated Debt [Member] | Subordinated Debentures Maturing June 2030 [Member] [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 225,000,000
Debt Issuance Cost					$ 3,100,000
Debt Instrument, Interest Rate, Stated Percentage	5.25%
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Weighted Average Interest Rate, at Point in Time	2.53%		2.58%

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchased and Retired During Period, Shares		1,769,479
Weighted Average Selling Price Per Share		$ 35.30
Stock Repurchased and Retired During Period, Value		$ 62.5
Dividends, Common Stock, Cash	$ 25.3	$ 25.6
Common Stock, Dividends, Per Share, Cash Paid	$ 0.25	$ 0.25
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation	154,163	139,111
Treasury Stock Acquired, Average Cost Per Share	$ 83.56	$ 53.61
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	152,418
Stock Issued During Period, Shares, New Issues	2,300,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	$ 2.1	$ 1.7
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Granted, Value, Share-based Payment Arrangement, before Forfeiture	23.7	21.7
Share-based Payment Arrangement, Expense	5.6	4.9
Executive Officer [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	0.3	0.3
Retained Earnings [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchased and Retired During Period, Value		51.9
Dividends, Common Stock, Cash	$ 25.3	$ 25.6

Stockholders' Equity Common Sto

Stockholders' Equity Common Stock Repurchase (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchase Program, Authorized Amount		$ 250
Stock Repurchased and Retired During Period, Shares	1,769,479
Weighted Average Selling Price Per Share	$ 35.30
Stock Repurchased and Retired During Period, Value	$ (62.5)
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchased and Retired During Period, Shares	1,800,000

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income - Summary of Changes in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 92.3	$ 25
Other comprehensive income before reclassifications	72.3	(12.6)
Amounts reclassified from accumulated other comprehensive income	(0.1)	(0.1)
Net other comprehensive (loss) income	72.4	(12.5)
Ending balance	19.9	37.5
Unrealized holding gains (losses) on AFS
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	92.1	21.4
Other comprehensive income before reclassifications	72	(6.3)
Amounts reclassified from accumulated other comprehensive income	(0.1)	(0.1)
Net other comprehensive (loss) income	72.1	(6.2)
Ending balance	20	27.6
Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	0.5	3.6
Other comprehensive income before reclassifications	(0.3)	(6.6)
Amounts reclassified from accumulated other comprehensive income	0	0
Net other comprehensive (loss) income	(0.3)	(6.6)
Ending balance	0.2	10.2
Supplemental Employee Retirement Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	0.3	0
Other comprehensive income before reclassifications	0	(0.3)
Amounts reclassified from accumulated other comprehensive income	0	0
Net other comprehensive (loss) income	0	(0.3)
Ending balance	$ 0.3	$ (0.3)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Realized gains on sales of investment securities	$ 0.1	$ 0.1
Amount reclassified from accumulated other comprehensive income	0	0
Amount reclassified from accumulated other comprehensive income	$ 0.1	$ 0.1

Derivatives and Hedging Fair Va

Derivatives and Hedging Fair Value of Derivative Contracts (Detail) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Derivatives, Fair Value [Line Items]
Hedged Asset, Fair Value Hedge, Last-of-Layer, Amount		$ 1,000
Prepayable Financial Asset Closed Portfolio, Last-of-Layer, Amortized Cost		1,800	$ 1,900
Hedged Asset, Fair Value Hedge, Last-of-Layer, Cumulative Increase (Decrease)		7.9	0.6
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value		1.2	0.9	$ 0.5
Derivative Liability, Fair Value		0.9	1.4	0.4
Derivative, Notional Amount		122.8	122.7	12.2
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value		0.2	0.2	0.2
Derivative Liability, Fair Value		0.2	0.2	0.2
Derivative, Notional Amount		3.5	3.5	2.9
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value		1	0.7	0.3
Derivative Liability, Fair Value		0.7	1.2	0.2
Derivative, Notional Amount		119.3	119.2	9.3
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value		7.9	3.3	4.4
Derivative Liability, Fair Value		57.7	86.1	95.1
Notional Amount, Netting Adjustments	[1]	0	0	0
Derivative Netting Adjustments	[1]	5.4	0.6	0
Derivative, Notional Amount		1,685.9	1,689.9	859.1
Positive NPVs		2.5	2.7	4.4
Negative NPVs		52.3	85.5	95.1
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value		7.9	3.3	4.4
Derivative Liability, Fair Value		57.7	86.1	95.1
Derivative, Notional Amount		$ 1,685.9	$ 1,689.9	$ 859.1
[1]	Netting adjustments represent the amounts recorded to convert the Company's derivative balances from a gross basis to a net basis in accordance with the applicable accounting guidance.

Derivatives and Hedging Pre-Tax

Derivatives and Hedging Pre-Tax Net Gains (Losses) on Fair Value Hedges (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	$ 38.7	$ (41.8)
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	(38.7)	41.8
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	(5.7)	4.8
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	$ 5.7	$ (4.8)

Derivatives and Hedging Largest

Derivatives and Hedging Largest Exposure to Individual Counterparty (Detail) - Individual Counterparty - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Largest gross exposure (positive derivative NPV) to an individual counterparty	$ 7.9	$ 2.7	$ 4.3
Collateral posted by this counterparty	0	0	0
Negative derivative NPV with this counterparty	5.4	0	0
Collateral pledged to this counterparty	18.1	0	0
Net exposure after netting adjustments and collateral	$ 7.9	$ 2.7	$ 4.3

Derivatives and Hedging Additio

Derivatives and Hedging Additional Information (Detail) - USD ($)		Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Jun. 16, 2016	Jun. 29, 2015
Derivative [Line Items]
Hedged Asset, Fair Value Hedge		$ 1,543,400,000	$ 1,587,100,000
Fair Value Hedge Assets, Loans	[1]	46,800,000	85,500,000
Hedged Liability, Fair Value Hedge		(242,000,000)	(247,600,000)
Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease)	[1]	3,000,000	(2,700,000)
Derivative, Collateral, Right to Reclaim Securities		36,400,000	31,700,000	$ 22,400,000
Subordinated Debentures Maturing July 2025 [Member] | Subordinated Debt [Member]
Derivative [Line Items]
Debt Instrument, Face Amount						$ 150,000,000
Subordinated Debentures Maturing July 2056 [Member] | Subordinated Debt [Member]
Derivative [Line Items]
Debt Instrument, Face Amount		175,000,000			$ 175,000,000
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative Liability, Fair Value		57,700,000	86,100,000	95,100,000
Negative NPVs		$ 52,300,000	$ 85,500,000	$ 95,100,000
[1]	Included in the carrying value of the hedged assets/(liabilities). (2) The Company designated $1.0 billion as the hedged amount (from a closed portfolio of prepayable fixed rate loans with a carrying value of $1.8 billion and $1.9 billion as of March 31, 2021 and December 31, 2020, respectively) in this last-of-layer hedging relationship, which commenced in the fourth quarter of 2020. The cumulative basis adjustment included in the carrying value of these hedged items totaled $7.9 million and $0.6 million as of March 31, 2021 and December 31, 2020, respectively.

Earnings per Share (Details)

Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Basic	100,800	101,300
Weighted Average Number Diluted Shares Outstanding Adjustment	600	400
Diluted	101,400	101,700
Net income available to common shareholders	$ 192,500	$ 83,900
Earnings (loss) per share - basic	$ 1.91	$ 0.83
Earnings (loss) per share - diluted	$ 1.90	$ 0.83
Anti-dilutive stock options outstanding that were not included in computation of diluted earnings per common share	0	0

Income Taxes Additional Informa

Income Taxes Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation, Percent	17.90%	18.10%
Deferred Income Tax Assets, Net	$ 49,800		$ 31,300
Increase (Decrease) in Deferred Income Taxes	18,500
Operating Loss Carryforwards, Valuation Allowance	0
Investments in LIHTC and renewable energy	487,900		405,600
Investment-related Liabilities	228,900		$ 151,700
Amortization of tax credit investments	15,500	$ 7,400
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	42,400
Deferred Tax Assets, Operating Loss Carryforwards	$ 4,700

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Letters of credit expiration period	1 year
Off-Balance Sheet, Credit Loss, Liability	$ 32.6	$ 37	$ 29.6		$ 9
Percentage of first liens initial loan to value ratio	75.00%
Percentage Of Commercial Real Estate Loans Occupied By Owners	27.00%	28.00%
Commercial Real Estate Portfolio Segment [Member] | Loans Receivable [Member] | Credit Concentration Risk [Member]
Loss Contingencies [Line Items]
Percent of commercial real estate related loans	37.00%	38.00%
Unfunded Loan Commitment [Member]
Loss Contingencies [Line Items]
Loss Contingency Accrual	$ 32.6	$ 37
Cumulative Effect, Period of Adoption, Adjustment [Member]
Loss Contingencies [Line Items]
Off-Balance Sheet, Credit Loss, Liability				$ 15.1

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Contractual Amounts for Unfunded Commitments and Letters of Credit (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Other Commitments [Line Items]
Total amount	$ 10,026	$ 9,903.6
Percentage Of Commercial Real Estate Loans Occupied By Owners	27.00%	28.00%
Commitments to extend credit [Member]
Other Commitments [Line Items]
Unsecured Loan Commitments	$ 1,134	$ 1,077.2
Total amount	9,577.3	9,425.2
Credit card guarantees [Member]
Other Commitments [Line Items]
Total amount	289.9	291.5
Standby letters of credit [Member]
Other Commitments [Line Items]
Total amount	158.8	186.9
Unsecured Letters Of Credit	$ 7.4	$ 9.9
Commercial Real Estate Portfolio Segment [Member] | Credit Concentration Risk [Member] | Loans Receivable [Member]
Other Commitments [Line Items]
Concentration Risk, Percentage	37.00%	38.00%

Commitments and Contingencies L

Commitments and Contingencies Lease Commitments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Lease, Cost	$ 3.7	$ 3.4
Lessee, operating lease, other cost	1	1.1
Other Commitments [Line Items]
Lease, Cost	3.7	3.4
Lessee, operating lease, other cost	$ 1	$ 1.1

Fair Value Accounting - Gains a

Fair Value Accounting - Gains and Losses from Fair Value Changes Included in Consolidated Statement of Operations (Detail) $ in Millions		3 Months Ended
		Mar. 31, 2021USD ($)		Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Subordinated Debt Obligations, Fair Value Disclosure		$ 66.3	[1]		$ 65.9	[2]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax		$ (0.3)		$ (6.6)
Junior Subordinated Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Measurement Input		0.0278			0.0287
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss)		$ (0.4)		8.7
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	[3]	$ (0.4)		$ 8.7
Period of basis point spread		2.59%		2.64%
Percentage of LIBOR		0.19%		0.24%
[1]	Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.
[2]	Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.
[3]	Unrealized gains (losses) attributable to changes in the fair value of junior subordinated debt are recorded as part of OCI, net of tax, and totaled $(0.3) million and $6.6 million for three months ended March 31, 2021 and 2020, respectively.

Fair Value Accounting - Fair Va

Fair Value Accounting - Fair Value of Assets and Liabilities (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021		Mar. 31, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		$ 6,939.9	[1]		$ 4,708.5	[2]
Investment securities - equity		192.9	[1]		167.3	[2]
Subordinated Debt Obligations, Fair Value Disclosure		66.3	[3]		65.9	[4]
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		6,939.9			4,708.5
Investment securities - equity		192.9			167.3
Derivative Liability		58.6	[5]		87.5	[6]
Fair Value, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		77.3			26.5
Investment securities - equity		162.9			141.7
Subordinated Debt Obligations, Fair Value Disclosure		0	[3]		0	[4]
Derivative Liability		0	[5]		0	[6]
Fair Value, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		6,862.6			4,682
Investment securities - equity		30			25.6
Subordinated Debt Obligations, Fair Value Disclosure		0	[3]		0	[4]
Derivative Liability		58.6	[5]		87.5	[6]
Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Investment securities - equity		0			0
Subordinated Debt Obligations, Fair Value Disclosure		66.3	[3]		65.9	[4]
Derivative Liability		0	[5]		0	[6]
Fair Value, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		2,249.6			1,486.6
Fair Value, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		2,249.6			1,486.6
Fair Value, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Nontaxable Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		1,329.7			1,187.4
Fair Value, Recurring [Member] | Nontaxable Municipal Bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Nontaxable Municipal Bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		1,329.7			1,187.4
Fair Value, Recurring [Member] | Nontaxable Municipal Bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		1,900.6			1,476.9
Fair Value, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		1,900.6			1,476.9
Fair Value, Recurring [Member] | Residential Mortgage Backed Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		87.8			84.6
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		87.8			84.6
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities Issued By US Government Sponsored Enterprise [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		285.1			270.2
Fair Value, Recurring [Member] | Corporate Bond Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Corporate Bond Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		285.1			270.2
Fair Value, Recurring [Member] | Corporate Bond Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity		135.5			113.9
Fair Value, Recurring [Member] | Preferred Stock [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity		135.5			113.9
Fair Value, Recurring [Member] | Preferred Stock [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity		0			0
Fair Value, Recurring [Member] | Preferred Stock [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity		0			0
Fair Value, Recurring [Member] | CRA investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity		57.4			53.4
Fair Value, Recurring [Member] | CRA investments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity		27.4			27.8
Fair Value, Recurring [Member] | CRA investments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity		30			25.6
Fair Value, Recurring [Member] | CRA investments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities - equity		0			0
Fair Value, Recurring [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		50
Fair Value, Recurring [Member] | US Treasury Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		50
Fair Value, Recurring [Member] | US Treasury Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0
Fair Value, Recurring [Member] | US Treasury Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0
Fair Value, Recurring [Member] | Other Security Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		56.4			55.9
Fair Value, Recurring [Member] | Other Security Investments | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		27.3			26.5
Fair Value, Recurring [Member] | Other Security Investments | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		29.1			29.4
Fair Value, Recurring [Member] | Other Security Investments | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		980.7			146.9
Fair Value, Recurring [Member] | Collateralized Loan Obligations | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Fair Value, Recurring [Member] | Collateralized Loan Obligations | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		980.7			146.9
Fair Value, Recurring [Member] | Collateralized Loan Obligations | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Reported Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		6,939.9			4,708.5
Investment securities - equity		192.9			167.3
Derivative Liability		58.6			87.5
Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		6,939.9			4,708.5
Investment securities - equity		192.9			167.3
Derivative Liability		58.6			87.5
Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		77.3			26.5
Investment securities - equity		162.9			141.7
Derivative Liability		0			0
Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		6,862.6			4,682
Investment securities - equity		30			25.6
Derivative Liability		58.6			87.5
Estimate of Fair Value Measurement [Member] | Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale		0			0
Investment securities - equity		0			0
Derivative Liability		0			0
Junior Subordinated Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss)		(0.4)		$ 8.7
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	[7]	(0.4)		$ 8.7
Junior Subordinated Debt [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Subordinated Debt Obligations, Fair Value Disclosure		$ 66.3			$ 65.9
[1]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.
[2]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.
[3]	Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.
[4]	Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.
[5]	Derivative assets and liabilities relate primarily to interest rate swaps, see "Note 8. Derivatives and Hedging Activities." In addition, the carrying value of loans is increased by $46.8 million and the net carrying value of subordinated debt is increased by $3.0 million as of March 31, 2021 for the effective portion of the hedge, which relates to the fair value of the hedges put in place to mitigate against fluctuations in interest rates.
[6]	Derivative assets and liabilities relate primarily to interest rate swaps, see "Note 8. Derivatives and Hedging Activities." In addition, the carrying value of loans is increased by $85.5 million and the net carrying value of subordinated debt is increased by $2.7 million as of December 31, 2020 for the effective portion of the hedge, which relates to the fair value of the hedges put in place to mitigate against fluctuations in interest rates.
[7]	Unrealized gains (losses) attributable to changes in the fair value of junior subordinated debt are recorded as part of OCI, net of tax, and totaled $(0.3) million and $6.6 million for three months ended March 31, 2021 and 2020, respectively.

Fair Value Accounting - Change

Fair Value Accounting - Change in Level 3 Liabilities Measured at Fair Value on Recurring Basis (Detail) $ in Millions		3 Months Ended			12 Months Ended
		Mar. 31, 2021USD ($)		Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax		$ 0.3		$ 6.6
Junior subordinated debt		66.3	[1]		$ 65.9	[2]
Fair Value, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt		$ 66.3	[1]		$ 65.9	[2]
Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description		Discounted cash flow method			Discounted cash flow method
Other Assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description		Collateral method			Collateral method
Junior Subordinated Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	[3]	$ (0.4)		8.7
Debt Instrument, Measurement Input		0.0278			0.0287
Junior Subordinated Debt [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior subordinated debt		$ 66.3			$ 65.9
Fair Value Measurements, Valuation Processes, Description		Implied credit rating of the Company			Implied credit rating of the Company
Junior Subordinated Debt [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance		$ (65.9)		61.7	$ 61.7
Closing balance		$ (66.3)		$ (53)	$ (65.9)
Valuation Technique, Discounted Cash Flow [Member] | Junior Subordinated Debt [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description		Discounted cash flow			Discounted cash flow
Collateral Method [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description		Collateral method			Collateral method
Third Party Appraisal [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description		Third party appraisal			Third party appraisal
Third Party Appraisal [Member] | Other Assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description		Third party appraisal			Third party appraisal
Discount Rate [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description		Discount rate			Discount rate
[1]	Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.
[2]	Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.
[3]	Unrealized gains (losses) attributable to changes in the fair value of junior subordinated debt are recorded as part of OCI, net of tax, and totaled $(0.3) million and $6.6 million for three months ended March 31, 2021 and 2020, respectively.

Fair Value Accounting - Assets

Fair Value Accounting - Assets Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans with an allowance recorded	$ (9.5)
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans with an allowance recorded		$ (8.9)
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets acquired through foreclosure	4.2	1.4
Collateral Dependent Loans, Net of Allowance	183	187.3
Fair Value, Nonrecurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets acquired through foreclosure	0	0
Collateral Dependent Loans, Net of Allowance	0	0
Fair Value, Nonrecurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets acquired through foreclosure	0	0
Collateral Dependent Loans, Net of Allowance	0	0
Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets acquired through foreclosure	4.2	1.4
Collateral Dependent Loans, Net of Allowance	$ 183	$ 187.3
Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description	Discounted cash flow method	Discounted cash flow method
Other Assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description	Collateral method	Collateral method
Collateral Method [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description	Collateral method	Collateral method
Third Party Appraisal [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description	Third party appraisal	Third party appraisal
Level 3 Fair Value Measurement Inputs	Costs to sell	Costs to sell
Third Party Appraisal [Member] | Other Assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description	Third party appraisal	Third party appraisal
Level 3 Fair Value Measurement Inputs	Costs to sell	Costs to sell
Discount Rate [Member] | Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description	Discount rate	Discount rate
Level 3 Fair Value Measurement Inputs	Contractual loan rate	Contractual loan rate

Fair Value Accounting - Estimat

Fair Value Accounting - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2021		Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Repossessed Assets	$ 4.2		$ 1.4
Financial assets
Debt Securities, Held-to-maturity	698		568.8
Available-for-sale Securities	6,939.9	[1]	4,708.5	[2]
Investment securities - equity	192.9	[1]	167.3	[2]
Loans, net	28,463.9		26,774.1
Accrued Investment Income Receivable	2.4		2
Financial liabilities
Deposits	38,393.1		31,930.5
Customer repurchase agreements	15.9		16
Other borrowings	5		5
Junior subordinated debt	66.3	[3]	65.9	[4]
Fair Value, Nonrecurring [Member] | Reported Value Measurement [Member]
Financial assets
Debt Securities, Held-to-maturity	698		568.8
Loans, net	28,463.9		26,774.1
Financial liabilities
Deposits	38,393.1		31,930.5
Junior subordinated debt	543.7		548.7
Fair Value, Nonrecurring [Member] | Estimate of Fair Value Measurement [Member]
Financial assets
Debt Securities, Held-to-maturity	740.4		611.8
Loans, net	29,244.8		27,231
Financial liabilities
Deposits	38,397.4		31,935.9
Junior subordinated debt	572.4		567.4
Fair Value, Nonrecurring [Member] | Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Financial assets
Debt Securities, Held-to-maturity	0		0
Loans, net	0		0
Financial liabilities
Deposits	0		0
Junior subordinated debt	0		0
Fair Value, Nonrecurring [Member] | Estimate of Fair Value Measurement [Member] | Level 2 [Member]
Financial assets
Debt Securities, Held-to-maturity	740.4		611.8
Loans, net	0		0
Financial liabilities
Deposits	38,397.4		31,935.9
Junior subordinated debt	492.6		488.1
Fair Value, Nonrecurring [Member] | Estimate of Fair Value Measurement [Member] | Level 3 [Member]
Financial assets
Debt Securities, Held-to-maturity	0		0
Loans, net	29,244.8		27,231
Financial liabilities
Deposits	0		0
Junior subordinated debt	79.8		79.3
Fair Value, Recurring [Member]
Financial assets
Available-for-sale Securities	6,939.9		4,708.5
Investment securities - equity	192.9		167.3
Derivative Asset	9.1	[5]	4.2	[6]
Financial liabilities
Derivative Liability	58.6	[5]	87.5	[6]
Fair Value, Recurring [Member] | Level 1 [Member]
Financial assets
Available-for-sale Securities	77.3		26.5
Investment securities - equity	162.9		141.7
Derivative Asset	0	[5]	0	[6]
Financial liabilities
Junior subordinated debt	0	[3]	0	[4]
Derivative Liability	0	[5]	0	[6]
Fair Value, Recurring [Member] | Level 2 [Member]
Financial assets
Available-for-sale Securities	6,862.6		4,682
Investment securities - equity	30		25.6
Derivative Asset	9.1	[5]	4.2	[6]
Financial liabilities
Junior subordinated debt	0	[3]	0	[4]
Derivative Liability	58.6	[5]	87.5	[6]
Fair Value, Recurring [Member] | Level 3 [Member]
Financial assets
Available-for-sale Securities	0		0
Investment securities - equity	0		0
Derivative Asset	0	[5]	0	[6]
Financial liabilities
Junior subordinated debt	66.3	[3]	65.9	[4]
Derivative Liability	0	[5]	0	[6]
Fair Value, Recurring [Member] | Reported Value Measurement [Member]
Financial assets
Available-for-sale Securities	6,939.9		4,708.5
Investment securities - equity	192.9		167.3
Derivative Asset	9.1		4.2
Accrued Investment Income Receivable	169.9		166.1
Financial liabilities
Customer repurchase agreements	15.9		16
Other borrowings	5		5
Derivative Liability	58.6		87.5
Interest Payable, Current	12.7		11
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial assets
Available-for-sale Securities	6,939.9		4,708.5
Investment securities - equity	192.9		167.3
Derivative Asset	9.1		4.2
Accrued Investment Income Receivable	169.9		166.1
Financial liabilities
Customer repurchase agreements	15.9		16
Other borrowings	5		5
Derivative Liability	58.6		87.5
Interest Payable, Current	12.7		11
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Financial assets
Available-for-sale Securities	77.3		26.5
Investment securities - equity	162.9		141.7
Derivative Asset	0		0
Accrued Investment Income Receivable	0		0
Financial liabilities
Customer repurchase agreements	0		0
Other borrowings	0		0
Derivative Liability	0		0
Interest Payable, Current	0		0
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Level 2 [Member]
Financial assets
Available-for-sale Securities	6,862.6		4,682
Investment securities - equity	30		25.6
Derivative Asset	9.1		4.2
Accrued Investment Income Receivable	169.9		166.1
Financial liabilities
Customer repurchase agreements	15.9		16
Other borrowings	5		5
Derivative Liability	58.6		87.5
Interest Payable, Current	12.7		11
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Level 3 [Member]
Financial assets
Available-for-sale Securities	0		0
Investment securities - equity	0		0
Derivative Asset	0		0
Accrued Investment Income Receivable	0		0
Financial liabilities
Customer repurchase agreements	0		0
Other borrowings	0		0
Derivative Liability	0		0
Interest Payable, Current	$ 0		$ 0
[1]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.
[2]	Where ratings differ, the Company uses an average of the available ratings by major credit agencies.
[3]	Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.
[4]	Includes only the portion of junior subordinated debt that is recorded at fair value at each reporting period pursuant to the election of FVO treatment.
[5]	Derivative assets and liabilities relate primarily to interest rate swaps, see "Note 8. Derivatives and Hedging Activities." In addition, the carrying value of loans is increased by $46.8 million and the net carrying value of subordinated debt is increased by $3.0 million as of March 31, 2021 for the effective portion of the hedge, which relates to the fair value of the hedges put in place to mitigate against fluctuations in interest rates.
[6]	Derivative assets and liabilities relate primarily to interest rate swaps, see "Note 8. Derivatives and Hedging Activities." In addition, the carrying value of loans is increased by $85.5 million and the net carrying value of subordinated debt is increased by $2.7 million as of December 31, 2020 for the effective portion of the hedge, which relates to the fair value of the hedges put in place to mitigate against fluctuations in interest rates.

Fair Value Accounting - Additio

Fair Value Accounting - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets acquired through foreclosure	$ 4.2		$ 1.4
Common Stock, Shares, Issued	105,771,103		103,013,290
Junior Subordinated Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Period of basis point spread	2.59%	2.64%
Percentage of LIBOR	0.19%	0.24%
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral Dependent Loans, Net of Allowance	$ 183		$ 187.3
Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral Dependent Loans, Net of Allowance	$ 183		$ 187.3

Segments - Operating Segment In

Segments - Operating Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Operating Statistics [Line Items]
Service charges and fees	$ 6.7	$ 6.4
Cash, Cash Equivalents and Investment Securities	13,235.3		$ 8,176.5
Loans and Leases Receivable, Net of Deferred Income	28,711		27,053
Less: Allowance for credit losses	(247.1)		(278.9)
Loans and Leases Receivable Including Held for Sale, Net	28,463.9		26,774.1
Other Repossessed Assets	4.2		1.4
Goodwill and intangible assets, net	298		298.5
Other Assets Segment	1,395.6		1,210.5
Assets	43,397		36,461
Deposits	38,393.1		31,930.5
Other borrowings	548.7		553.7
Other Liabilities Segment	742.5		563.3
Total liabilities	39,684.3		33,047.5
Stockholders' equity	3,712.7	2,999.6	3,413.5	$ 2,991.8	$ 3,016.7
Liabilities and Equity	43,397		36,461
Excess Funds Provided by (Used in) Segment Basis	0		0
Net interest income	317.3	269
Provision for Loan, Lease, and Other Losses	32.4	(51.2)
Net interest income (loss) after provision for credit losses	349.7	217.8
Total non-interest income	19.7	5.1
Non-interest expense	(135)	(120.5)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	234.4	102.4
Income tax expense (benefit)	41.9	18.5
Net income	192.5	83.9
Debit and credit card interchange fees	1.3	1.4
Success fees (2)	1	0.1
Other income	0.2	0.1
Total revenue from contracts with customers	9.2	8
Revenues outside the scope of ASC 606 (3)	10.5	(2.9)
Operating Segments [Member] | Commercial Segment
Operating Statistics [Line Items]
Service charges and fees	6.2	6
Cash, Cash Equivalents and Investment Securities	13.4		12
Loans and Leases Receivable, Net of Deferred Income	20,660.4		20,245.8
Less: Allowance for credit losses	229.8		263.4
Loans and Leases Receivable Including Held for Sale, Net	20,430.6		19,982.4
Other Repossessed Assets	4.2		1.4
Goodwill and intangible assets, net	295.7		296.1
Other Assets Segment	251.5		257
Assets	20,995.4		20,548.9
Deposits	24,126		21,448
Other borrowings	0		0
Other Liabilities Segment	226.4		170.4
Total liabilities	24,352.4		21,618.4
Stockholders' equity	2,100.3		1,992.2
Liabilities and Equity	26,452.7		23,610.6
Excess Funds Provided by (Used in) Segment Basis	5,457.3		3,061.7
Net interest income	263.7	228.5
Provision for Loan, Lease, and Other Losses	36.3	(47.9)
Net interest income (loss) after provision for credit losses	300	180.6
Total non-interest income	19.2	11.4
Non-interest expense	(98.3)	(82.4)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	220.9	109.6
Income tax expense (benefit)	52.7	26
Net income	168.2	83.6
Debit and credit card interchange fees	1.3	1.4
Success fees (2)	1	0.1
Other income	0.2	0.1
Total revenue from contracts with customers	8.7	7.6
Revenues outside the scope of ASC 606 (3)	10.5	3.8
Operating Segments [Member] | Consumer Related Segment
Operating Statistics [Line Items]
Service charges and fees	0.5	0.4
Cash, Cash Equivalents and Investment Securities	33.1		45.6
Loans and Leases Receivable, Net of Deferred Income	8,048.9		6,798.2
Less: Allowance for credit losses	17.3		15.4
Loans and Leases Receivable Including Held for Sale, Net	8,031.6		6,782.8
Other Repossessed Assets	0		0
Goodwill and intangible assets, net	2.3		2.4
Other Assets Segment	113.1		96.6
Assets	8,180.1		6,927.4
Deposits	13,286.5		9,936.8
Other borrowings	0		0
Other Liabilities Segment	6		3.3
Total liabilities	13,292.5		9,940.1
Stockholders' equity	702.9		579.1
Liabilities and Equity	13,995.4		10,519.2
Excess Funds Provided by (Used in) Segment Basis	5,815.3		3,591.8
Net interest income	107.9	55.7
Provision for Loan, Lease, and Other Losses	1.7	3
Net interest income (loss) after provision for credit losses	106.2	52.7
Total non-interest income	0.5	0.4
Non-interest expense	(35.2)	(25.8)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	71.5	27.3
Income tax expense (benefit)	17.5	6.4
Net income	54	20.9
Debit and credit card interchange fees	0	0
Success fees (2)	0	0
Other income	0	0
Total revenue from contracts with customers	0.5	0.4
Revenues outside the scope of ASC 606 (3)	0	0
Corporate & Other
Operating Statistics [Line Items]
Service charges and fees	0	0
Cash, Cash Equivalents and Investment Securities	13,188.8		8,118.9
Loans and Leases Receivable, Net of Deferred Income	1.7		9
Less: Allowance for credit losses	0		0.1
Loans and Leases Receivable Including Held for Sale, Net	1.7		8.9
Other Repossessed Assets	0		0
Goodwill and intangible assets, net	0		0
Other Assets Segment	1,031		856.9
Assets	14,221.5		8,984.7
Deposits	980.6		545.7
Other borrowings	548.7		553.7
Other Liabilities Segment	510.1		389.6
Total liabilities	2,039.4		1,489
Stockholders' equity	909.5		842.2
Liabilities and Equity	2,948.9		2,331.2
Excess Funds Provided by (Used in) Segment Basis	(11,272.6)		$ (6,653.5)
Net interest income	(54.3)	(15.2)
Provision for Loan, Lease, and Other Losses	(2.2)	(0.3)
Net interest income (loss) after provision for credit losses	(56.5)	(15.5)
Total non-interest income	0	(6.7)
Non-interest expense	(1.5)	(12.3)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(58)	(34.5)
Income tax expense (benefit)	(28.3)	(13.9)
Net income	(29.7)	(20.6)
Debit and credit card interchange fees	0	0
Success fees (2)	0	0
Other income	0	0
Total revenue from contracts with customers	0	0
Revenues outside the scope of ASC 606 (3)	$ 0	$ (6.7)

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Service charges and fees	$ 6.7	$ 6.4
Accounts Receivable, after Allowance for Credit Loss	1.7		$ 1.6
Debit and credit card interchange fees	1.3	1.4
Success fees (2)	1	0.1
Other income	0.2	0.1
Total revenue from contracts with customers	9.2	8
Revenues outside the scope of ASC 606 (3)	10.5	(2.9)
Total non-interest income	19.7	5.1
Operating Segments [Member] | Commercial Segment
Disaggregation of Revenue [Line Items]
Service charges and fees	6.2	6
Debit and credit card interchange fees	1.3	1.4
Success fees (2)	1	0.1
Other income	0.2	0.1
Total revenue from contracts with customers	8.7	7.6
Revenues outside the scope of ASC 606 (3)	10.5	3.8
Total non-interest income	19.2	11.4
Operating Segments [Member] | Consumer Related Segment
Disaggregation of Revenue [Line Items]
Service charges and fees	0.5	0.4
Debit and credit card interchange fees	0	0
Success fees (2)	0	0
Other income	0	0
Total revenue from contracts with customers	0.5	0.4
Revenues outside the scope of ASC 606 (3)	0	0
Total non-interest income	0.5	0.4
Corporate & Other
Disaggregation of Revenue [Line Items]
Service charges and fees	0	0
Debit and credit card interchange fees	0	0
Success fees (2)	0	0
Other income	0	0
Total revenue from contracts with customers	0	0
Revenues outside the scope of ASC 606 (3)	0	(6.7)
Total non-interest income	$ 0	$ (6.7)

Subsequent Events (Details)

Subsequent Events (Details) $ in Millions	3 Months Ended
	Jun. 30, 2021USD ($)
Subsequent Event [Line Items]
Payments to Acquire Businesses, Gross	$ 1,220

Uncategorized Items - wal-20210

Label	Element	Value
AOCI Attributable to Parent [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ 25,000,000
Common Stock [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ 0
Shares, Issued	us-gaap_SharesIssued	102,500,000
Retained Earnings [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ 1,655,400,000
Treasury Stock [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	62,700,000
Additional Paid-in Capital [Member]
Stockholders' Equity Attributable to Parent	us-gaap_StockholdersEquity	$ 1,374,100,000