First Interstate BancSystem (FIBK) 10-Q 8 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2019shares
Entity Registrant Name	FIRST INTERSTATE BANCSYSTEM INC
Trading Symbol	FIBK
Entity Central Index Key	0000860413
Document Fiscal Year Focus	2019
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Fiscal Period Focus	Q1
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Class A Common Stock
Entity Common Stock, Shares Outstanding	38,461,948
Class B Common Stock
Entity Common Stock, Shares Outstanding	22,374,171

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets
Cash and due from banks	$ 213.6	$ 244.1
Interest bearing deposits in banks	0.1	0.1
Federal Funds Sold	741.5	577.8
Total cash and cash equivalents	955.2	822
Investment securities:
Available-for-sale	2,572	2,270.7
Held-to-maturity (estimated fair values of $118.0 and $400.7 at March 31, 2019 and December 31, 2018, respectively)	117	406.8
Debt Securities	2,689	2,677.5
Loans held for investment	8,459.2	8,470.4
Mortgage loans held for sale	34	33.3
Total loans	8,493.2	8,503.7
Less allowance for loan losses	72.4	73
Net loans	8,420.8	8,430.7
Goodwill	546.3	546.7
Life Insurance, Corporate or Bank Owned, Amount	275.8	275.1
Premises and equipment, net of accumulated depreciation	298.2	245.2
Indefinite-lived Intangible Assets (Excluding Goodwill)	54.6	56.9
Accrued interest receivable	46.5	44.9
Mortgage servicing rights, net of accumulated amortization and impairment reserve	27.9	27.7
Other real estate owned (“OREO”)	21.1	14.4
Other assets	162.8	159.1
Total assets	13,498.2	13,300.2
Deposits:
Non-interest bearing	3,158.7	3,158.3
Interest bearing	7,656	7,522.4
Total deposits	10,814.7	10,680.7
Securities sold under repurchase agreements	672.6	712.4
Accounts payable and accrued expenses	142.6	94.1
Accrued interest payable	10	7.8
Deferred tax liability, net	18.7	8.6
Long-term debt	15.8	15.8
Subordinated debentures held by subsidiary trusts	86.9	86.9
Total liabilities	11,761.3	11,606.3
Stockholders’ equity:
Nonvoting noncumulative preferred stock without par value; authorized 100,000 shares; no shares issued and outstanding as of March 31, 2019 or December 31, 2018	0	0
Common stock	866.6	866.7
Retained earnings	874.7	851.8
Accumulated other comprehensive loss, net	(4.4)	(24.6)
Total stockholders’ equity	1,736.9	1,693.9
Total liabilities and stockholders’ equity	$ 13,498.2	$ 13,300.2

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Investment securities:
Estimated fair value	$ 118,000	$ 400,700
Stockholders' equity:
Nonvoting, noncumulative preferred stock, shares authorized	100,000	100,000
Nonvoting, noncumulative preferred stock, shares issued	0	0
Nonvoting, noncumulative preferred stock, shares outstanding	0	0

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Interest income:
Interest and fees on loans	$ 111.4	$ 91.7
Interest and dividends on investment securities:
Taxable	15.1	13.2
Exempt from federal taxes	0.5	0.6
Interest on deposits in banks	3.6	2.1
Total interest income	130.6	107.6
Interest expense:
Interest on deposits	12.1	6.2
Interest on securities sold under repurchase agreements	1	0.4
Interest on other borrowed funds	0	0.1
Interest on other debt	0.3	0.2
Interest on subordinated debentures held by subsidiary trusts	1.2	0.9
Total interest expense	14.6	7.8
Net interest income	116	99.8
Provision for loan losses	3.7	2.1
Net interest income after provision for loan losses	112.3	97.7
Non-interest income:
Mortgage banking revenues	5.4	5.4
Investment securities gains (losses), net	0	0
Other income	4.3	3.9
Total non-interest income	34.5	35.2
Non-interest expense:
Salaries and wages	36.1	34.6
Employee benefits	14.4	11.3
Outsourced technology services	7.9	7
Occupancy, net	7	6.3
Furniture and equipment	3.5	3.1
OREO expense, net of income	0.1	0.2
Professional fees	1.9	1.2
FDIC insurance premiums	1.5	1.5
Mortgage servicing rights amortization	0.9	0.8
Core deposit intangibles amortization	2.3	1.8
Other expenses	15.9	15.8
Acquisition related expenses	2.3	2.3
Total non-interest expense	93.8	85.9
Income before income tax expense	53	47
Income tax expense	11.4	10.3
Net income	$ 41.6	$ 36.7
Basic earnings per common share (in dollars per share)	$ 0.69	$ 0.65
Diluted earnings per common share (in dollars per share)	$ 0.69	$ 0.65
Weighted average common shares outstanding for basic earnings per share computation	60,311,171	56,241,201
Weighted Average Number of Shares Outstanding, Diluted	60,598,070	56,652,178
Credit and Debit Card [Member]
Non-interest income:
Payment services revenues	$ 9.4	$ 10.5
Investment Advisory, Management and Administrative Service [Member]
Non-interest income:
Wealth management revenues	6.1	5.9
Deposit Account [Member]
Non-interest income:
Payment services revenues	5	5.6
Financial Service, Other [Member]
Non-interest income:
Payment services revenues	$ 4.3	$ 3.9

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 41.6	$ 36.7
Other comprehensive income (loss), before tax:
Change in net unrealized gains (losses) during period	33.6	(23.7)
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity	(6)	0
Other Comprehensive Income (Loss), Transfers from Available-for-Sale to Held-to-Maturity Securities, before Tax	0	0.5
Defined benefit post-retirement benefits plans:
Change in net actuarial gain	(0.2)	(0.1)
Other comprehensive income (loss), before tax	27.4	(23.3)
Deferred tax (expense) benefit related to other comprehensive income	(7.2)	6.1
Other comprehensive income (loss), net of tax	20.2	(17.2)
Comprehensive income, net of tax	$ 61.8	$ 19.5

Consolidated Statement of Chang

Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Common stock	Retained earnings	Accumulated other comprehensive income (loss)
Beginning Balance at Dec. 31, 2017	$ 1,427.6	$ 687	$ 752.6	$ (12)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36.7		36.7
Tax Cuts And Jobs Act Of 2017, Reclassification From AOCI To Retained Earnings			3.1	(3.1)
Other comprehensive income, net of tax expense	(17.2)			(17.2)
Common stock transactions:
Common shares purchased and retired	(0.9)	(0.9)
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	0.8	0.8
Stock-based compensation expense	1.1	1.1
Common cash dividend declared	(15.7)		(15.7)
Ending Balance at Mar. 31, 2018	1,432.4	688	776.7	(32.3)
Beginning Balance at Dec. 31, 2018	1,693.9	866.7	851.8	(24.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	41.6		41.6
Other comprehensive income, net of tax expense	20.2			20.2
Common stock transactions:
Common shares purchased and retired	(2.4)	(2.4)
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	0.4	0.4
Stock-based compensation expense	1.9	1.9
Common cash dividend declared	(18.7)		(18.7)
Ending Balance at Mar. 31, 2019	$ 1,736.9	$ 866.6	$ 874.7	$ (4.4)

Consolidated Statement of Cha_2

Consolidated Statement of Changes in Stockholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Common stock
Common stock transactions:
Common shares purchased and retired	38,753	24,271
Common shares issued	0	3,848,929
Non-vested common shares issued	200,028	214,892
Non-vested common shares forfeited	5,385	43,079
stock options exercised	56,982	161,217
net of shares tendered	19,004	38,450
Retained earnings
Common stock transactions:
Common dividends (in dollars per share)	$ 0.31	$ 1.12

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	$ 41.6	$ 36.7
Adjustments to reconcile net income to net cash provided by operating activities:
Increase (Decrease) in Mortgage Loans Held-for-sale	129.8	204.1
Provision for Loan and Lease Losses	3.7	2.1
Depreciation and amortization	7.5	6.6
Net premium amortization on investment securities	2	2.8
Realized and unrealized net gains on mortgage banking activities	(4.7)	(1.6)
Impairment of Real Estate and Other Assets Pending Disposal	0.3	0
Net loss (gain) on sale of OREO	(0.4)	0
Deferred income tax expense	2.7	10.1
Net increase in cash surrender value of company-owned life insurance	(0.7)	(1.3)
Stock-based compensation expense	1.9	1.1
Proceeds from sales of mortgage loans held for sale	132.7	218.8
Changes in operating assets and liabilities, net of effects of acquisition:
Increase in interest receivable	(1.6)	(0.9)
(Increase) decrease in other assets	(3.7)	3.9
Increase in accrued interest payable	2.2	0.1
Decrease in accounts payable and accrued expenses	(6.1)	(10.9)
Net cash provided by operating activities	47.6	63.4
Cash flows from investing activities:
Purchase of investment securities, Available-for-sale	(161.3)	(212.9)
Proceeds from maturities and paydowns of held-to-maturity investment securities	11.3	22.2
Proceeds from maturities and paydowns of available-for-sale investment securities	164	114.9
Extensions of credit to customers, net of repayments	(3.2)	(53.3)
Recoveries of loans charged-off	1.7	4.5
Proceeds from sale of OREO	1.8	0.3
Capital expenditures, net of sales	(2.2)	(2.4)
Net cash provided by (used in) investing activities	12.1	(126.7)
Cash flows from financing activities:
Proceeds from Issuance of Unsecured Debt	0	2.6
Net increase (decrease) in deposits	134	91
Net (decrease) increase in securities sold under repurchase agreements	(39.8)	(9.2)
Net decrease in other borrowed funds	0	(20)
Proceeds from issuance of common stock	0.4	0.8
Purchase and retirement of common stock	(2.4)	(0.9)
Dividends paid to common stockholders	(18.7)	(15.7)
Net cash provided by financing activities	73.5	48.6
Net increase (decrease) in cash and cash equivalents	133.2	(14.7)
Cash and cash equivalents at beginning of period	822	758.9
Cash and cash equivalents at end of period	955.2	744.2
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	0	4.6
Cash paid during the period for interest expense	12.4	7.7
Noncash or Part Noncash Acquisition, Value of Assets Acquired [Abstract]
Amortization of unrealized gains and losses on transfers of securities	0	0.5
Right-of-use assets obtained in exchange for operating lease liabilities	54.6	0
Transfer of loans to other real estate owned	8.4	1.2
Capitalization of internally originated mortgage servicing rights	$ 1.1	$ 1.3

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation In the opinion of management, the accompanying unaudited consolidated financial statements of First Interstate BancSystem, Inc., First Interstate Bank (“FIB”), and its other subsidiaries (together, the “Company”) contain all adjustments (all of which are of a normal recurring nature) necessary to present fairly the financial position of the Company at March 31, 2019 and December 31, 2018 , the results of operations for each of the three month periods ended March 31, 2019 and 2018 , and cash flows and changes in stockholders’ equity for each of the three month periods ended March 31, 2019 and 2018 , in conformity with U.S. generally accepted accounting principles (“GAAP”). The balance sheet information at December 31, 2018 is derived from audited consolidated financial statements. Certain reclassifications, none of which were material, have been made to conform prior year financial statements to the March 31, 2019 presentation. These reclassifications did not change previously reported net income or stockholders’ equity. These unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 . Operating results for the three months ended March 31, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019 . Leases We have leased branches and office space and have entered into various other agreements in conducting our business. At inception, we determine whether an agreement represents a lease and at commencement we evaluate each lease agreement to determine whether the lease is an operating or financing lease. Some of our lease agreements have contained renewal options, tenant improvement allowances, rent holidays and rent escalation clauses. As discussed in “Note 16 – Recent Authoritative Accounting Guidance” included in this report, we adopted ASU 2016-02, as of January 1, 2019. Pursuant to ASU 2016-02, all of our long-term operating leases outstanding on December 31, 2018 continued to be classified as operating leases. Our capital lease outstanding at December 31, 2018 is classified as a financing lease. With the adoption of ASU 2016-02, we recorded an operating lease right-of-use asset, within the Premises and Equipment line item, and an operating lease liability, within the Other Liabilities line item, on our balance sheet. Right-of-use lease assets represent our right to use the underlying asset for the lease term and the lease obligation represents our commitment to make the lease payments arising from the lease. Right-of-use lease assets and obligations are recognized at the commencement date based on the present value of remaining lease payments over the lease term. As the Company’s leases do not provide an implicit rate, we have used an estimated incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. The right-of-use lease asset includes any lease payments made prior to commencement and excludes any lease incentives. The lease term may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term, subject to any changes in the lease or expectations regarding the terms. Variable lease costs such as property taxes are expensed as incurred. Leases with an initial term of 12 months or less are not recorded on the balance sheet. Prior to our adoption of ASU 2016-02, when our lease agreements contained renewal options, tenant improvement allowances, rent holidays and rent escalation clauses, we recorded a deferred rent asset or liability equal to the difference between the rent expense and the future minimum lease payments due. The lease expense related to operating leases was recognized on a straight-line basis in the statements of operations over the term of each lease. In cases where the lessor granted us leasehold improvement allowances that reduced our lease expense, we capitalized the improvements as incurred and recognized deferred rent, which was amortized over the shorter of the lease term or the expected useful life of the improvements.

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Acquisitions	Acquisitions Idaho Independent Bank. On October 11, 2018 , the Company entered into a definitive agreement to acquire all of the outstanding stock of Idaho Independent Bank (“IIBK”), a community bank headquartered in Coeur d' Alene, Idaho with 11 banking offices across Idaho. The acquisition was completed on April 8, 2019, and conversion of the data processing systems will occur in June 2019. Consideration for the acquisition was $157.3 million , consisting of the issuance of 3.871 million shares of the Company's Class A common stock valued at $40.64 per share, the closing price of the Company's Class A common stock as quoted on the NASDAQ stock market on the acquisition date. Holders of each share of IIBK common stock received 0.50 shares of First Interstate Class A common stock for each share of IIBK common stock. Previously unvested IIBK restricted stock awards outstanding immediately prior to the close of the transaction vested and were considered issued and outstanding at acquisition close and included in the consideration. Community 1 st Bank. On October 11, 2018 , the Company also entered into a definitive agreement to acquire all of the outstanding stock of Community 1st Bank (“CMYF”), a community bank headquartered in Post Falls, Idaho with three banking offices in North Idaho. The acquisition was completed on April 8, 2019, and conversion of the data processing systems will occur in June 2019. Consideration for the acquisition was $18.8 million , consisting of the issuance of 0.463 million shares of the Company's Class A common stock valued at $40.64 per share, the closing price of the Company's Class A common stock as quoted on the NASDAQ stock market on the acquisition date. Holders of each share of CMYF common stock received 0.3784 shares of First Interstate Class A common stock for each share of CMYF common stock. Previously unvested CMYF restricted stock awards outstanding immediately prior to the close of the transaction vested and were considered issued and outstanding at acquisition close and included in consideration. Northwest Bancorporation, Inc. On April 25, 2018 , the Company entered into a definitive agreement to acquire all of the outstanding stock of Northwest Bancorporation, Inc. (“Northwest”), the parent company of Inland Northwest Bank (“INB”), a Spokane, Washington based community bank with 20 banking offices across Idaho, Oregon and Washington. The acquisition was completed on August 16, 2018 , and the Company merged INB with its existing bank subsidiary, First Interstate Bank, on November 9, 2018 . Consideration for the acquisition was $176.3 million , consisting of the issuance of 3.84 million shares of the Company's Class A common stock valued at $45.15 per share, the closing price of the Company's Class A common stock as quoted on the NASDAQ stock market on the acquisition date. The Company paid approximately $3.0 million in cash related to Northwest warrants, which were included in the consideration paid. Holders of each share of Northwest common stock received 0.516 shares of First Interstate Class A common stock for each share of Northwest common stock. Additionally, all Northwest stock purchase warrants outstanding immediately prior to the close of the transaction were canceled in exchange for the right to receive a cash payment as provided in the Agreement. Previously unvested Northwest restricted stock awards outstanding immediately prior to the close of the transaction vested and were considered issued and outstanding at acquisition close. The assets and liabilities of Northwest were provisionally recorded in the Company’s consolidated financial statements at their estimated fair values as of the acquisition date and will be finalized in the coming months. The excess value of the consideration paid over the fair value of assets acquired and liabilities assumed is recorded as provisional goodwill. The preliminary purchase price allocation resulted in provisional goodwill of $100.7 million , which is not deductible for income tax purposes. Goodwill resulting from the acquisition was allocated to the Company’s one operating segment, community banking, and consists largely of the synergies and economies of scale expected from combining the operations of Northwest and the Company. The following table summarizes the consideration paid, fair values of the Northwest assets acquired and liabilities assumed, and the resulting goodwill. The amounts reported for net deferred tax assets and goodwill are provisional pending completion of the Company's review of tax items. As Recorded Fair Value As Recorded As of August 16, 2018 by Northwest Adjustments by the Company Assets acquired: Cash and cash equivalents $ 31.2 $ — $ 31.2 Investment securities 3.1 — 3.1 Loans held for investment 727.9 (14.8 ) (1) 713.1 Allowance for loan loss (8.0 ) 8.0 (2) — Premises and equipment 14.5 — 14.5 Other real estate owned (“OREO”) 0.3 0.3 0.6 Core deposit intangible assets 2.4 13.3 (3) 15.7 Other assets 29.3 (10.0 ) (4) 19.3 Total assets acquired 800.7 (3.2 ) 797.5 Liabilities assumed: Deposits 696.1 0.2 (5) 696.3 Accounts payable and accrued expense 8.1 (0.4 ) (6) 7.7 Long term debt 13.0 0.1 13.1 Trust preferred securities 5.2 (0.8 ) (7) 4.4 Deferred tax liability, net (1.2 ) 1.6 (8) 0.4 Total liabilities assumed 721.2 0.7 721.9 Net assets acquired $ 79.5 $ (3.9 ) $ 75.6 Consideration paid: Cash $ 3.0 Class A common stock 173.3 Total consideration paid 176.3 Goodwill $ 100.7 Explanation of fair value adjustments and the removal of previously recorded fair value marks recorded by Northwest. Note adjustments to the marks for deferred tax assets and premises and equipment were made since the prior quarter, none of which were material. The adjustments had no impact on 2018 earnings and a net decrease to goodwill of $0.4 million from the December 31, 2018 reported balances. (1) Write down of the book value of loans to their estimated fair values. The fair value of the loans was estimated using cash flow projections based on the remaining maturity and repricing terms, adjusted for estimated future credit losses and prepayments and discounted to present value using a risk-adjusted market rate for similar loans. The fair value of collateral dependent loans acquired with deteriorated credit quality was estimated based on the Company’s analysis of the fair value of each loan’s underlying collateral, discounted using market-derived rates of return with consideration given to the period of time and costs associated with foreclosure and disposition of the collateral. (2) Adjustment to remove the Northwest allowance for loan losses at acquisition date, as the credit risk is included in the fair value adjustment for loans receivable described in (1) above. (3) Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm. (4) Adjustment consists of reductions to the fair value of other items, including the removal of Northwest previously recorded goodwill. (5) Increase in book value of time deposits to their estimated fair values based upon interest rates of similar time deposits with similar terms on the date of acquisition based upon valuation from an independent accounting and advisory firm. (6) Decrease due to the write-off of off balance sheet reserves. (7) Write down of the book value of debt to the estimated fair values on the date of acquisition based upon favorable interest rates in the market. (8) Adjustment consists of the write-off of pre-existing deferred tax assets and purchase accounting adjustments as a result of the acquisition. Core deposit intangible assets of $15.7 million are being amortized using an accelerated method over the estimated useful lives of the related deposits of 10 years. The Company acquired certain loans that are subject to Accounting Standards Codification ("ASC") Topic 310-30 "Loans and Debt Securities Acquired with Deteriorated Credit Quality." ASC Topic 310-30 provides recognition, measurement and disclosure guidance for acquired loans that have evidence of deterioration in credit quality since origination for which it is probable, at acquisition, the Company will be unable to collect all contractual amounts owed. For loans that meet the criteria stipulated in ASC Topic 310-30, the excess of all cash flows expected at acquisition over the initial fair value of the loans acquired ("accretable yield") is amortized to interest income over the expected remaining lives of the underlying loans using the effective interest method. The accretable yield will fluctuate due to changes in (i) estimated lives of underling credit-impaired loans, (ii) assumptions regarding future principal and interest amounts collected, and (iii) indices used to fair value variable rate loans. Information regarding Northwest loans acquired deemed credit-impaired as of the August 16, 2018 acquisition date are as follows: Contractually required principal and interest payments $ 27.5 Contractual cash flows not expected to be collected (“non-accretable discount”) 4.4 Cash flows expected to be collected 23.1 Interest component of cash flows expected to be collected (“accretable discount”) 3.2 Fair value of acquired credit-impaired loans $ 19.9 Information regarding Northwest acquired loans not deemed credit-impaired at the August 16, 2018 acquisition date are as follows: Contractually required principal and interest payments $ 894.8 Contractual cash flows not expected to be collected 26.1 Fair value at acquisition $ 693.2 Unaudited pro forma consolidated revenues and net income as if the Northwest acquisition had occurred as of January 1, 2018, are not presented because the effect of this acquisition was not considered significant. The accompanying consolidated statements of income for the three months ended March 31, 2019 , include the results of operations of the acquired entity from the August 16, 2018 acquisition date. The acquired entity continued to operate as INB until November 9, 2018 at which point INB’s operations were integrated with the Company’s operations, and INB merged with FIB. The Company recorded $2.3 million and $2.3 million in pre-tax acquisition related expenses for the three months ended March 31, 2019 and 2018 . These costs are incorporated in non-interest expenses in the Company’s consolidated statements of income. Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Legal and Professional Fees $ 0.3 $ 0.5 Employee Expenses 0.6 0.1 Technology Conversion and Contract Termination 0.8 1.5 Other 0.6 0.2 Total Acquisition Related Expenses $ 2.3 $ 2.3

Goodwill and Intangibles

Goodwill and Intangibles	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangibles	Goodwill and Core Deposit Intangibles Management analyzes its goodwill for impairment on an annual basis and between annual tests in certain circumstances, such as upon material adverse changes in legal, business, regulatory and economic factors. An impairment loss is recorded to the extent that the carrying amount of goodwill exceeds its implied fair value. The Company performed an impairment assessment as of July 1, 2018 and 2017 and concluded that there was no impairment to goodwill. Goodwill As of March 31, 2019 2018 Net carrying value at beginning of three month period $ 546.7 $ 444.7 Measurement period adjustment to previously recorded goodwill (0.4 ) 0.9 Net carrying value at end of period $ 546.3 $ 445.6 Core deposit intangibles (“CDI”) As of March 31, 2019 2018 Gross CDI, beginning of period $ 89.7 $ 74.0 Accumulated amortization (35.1 ) (26.7 ) Net CDI, end of period $ 54.6 $ 47.3 The Company recorded $2.3 million and $1.8 million of CDI amortization expense for the three months ended March 31, 2019 and 2018 . CDI are evaluated for impairment if events and circumstances indicate a possible impairment and are amortized using an accelerated method based on the estimated weighted average useful lives of the related deposits, which is generally ten years. The following table provides the estimated future CDI amortization expense: Years Ending December 31, 2019 remaining $ 6.6 2020 8.1 2021 7.5 2022 6.9 2023 6.3 Thereafter 19.2 Total $ 54.6

Investment Securities

Investment Securities	3 Months Ended
	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities The amortized cost and approximate fair values of investment securities are summarized as follows: March 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale: U.S. Treasury notes $ 4.0 $ — $ — $ 4.0 State, county and municipal securities 77.7 0.8 (0.1 ) 78.4 Obligations of U.S. government agencies 601.4 0.3 (4.0 ) 597.7 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 1,735.9 9.4 (12.4 ) 1,732.9 Private mortgage-backed securities 66.2 — (0.9 ) 65.3 Corporate securities 92.1 0.2 (0.3 ) 92.0 Other investments 1.7 — — 1.7 Total $ 2,579.0 $ 10.7 $ (17.7 ) $ 2,572.0 March 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to-Maturity: State, county and municipal securities $ 67.6 $ 1.5 $ (0.2 ) $ 68.9 Obligations of U.S. government agencies 19.8 — (0.2 ) 19.6 U.S agency residential mortgage-backed securities & collateralized mortgage obligations 1.3 — — 1.3 Corporate securities 28.2 — (0.1 ) 28.1 Other investments 0.1 — — 0.1 Total $ 117.0 $ 1.5 $ (0.5 ) $ 118.0 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale: U.S. Treasury notes $ 2.6 $ — $ — $ 2.6 Obligations of U.S. government agencies 569.3 0.1 (10.2 ) 559.2 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 1,566.4 2.5 (24.1 ) 1,544.8 Private mortgage-backed securities 72.0 — (1.8 ) 70.2 Corporate securities 92.9 — (1.0 ) 91.9 Other investments 2.0 — — 2.0 Total $ 2,305.2 $ 2.6 $ (37.1 ) $ 2,270.7 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to-Maturity: State, county and municipal securities $ 150.9 $ 1.8 $ (0.9 ) $ 151.8 Obligations of U.S. government agencies 19.8 — (0.3 ) 19.5 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 189.7 0.3 (6.5 ) 183.5 Corporate securities 46.3 0.1 (0.6 ) 45.8 Other investments 0.1 — — 0.1 Total $ 406.8 $ 2.2 $ (8.3 ) $ 400.7 At December 31, 2018, we had $406.8 million of investment securities classified as held to maturity. As a result of the adoption of ASU 2017-12 discussed in “Note 16 – Recent Authoritative Accounting Guidance” included in this report, the Company transferred investment securities classified as held-to-maturity to investment securities available-for-sale. At the time of transfer, the amortized cost and fair value of these securities totaled $281.1 million and $275.0 million , respectively. In addition, the unrealized loss of $6.0 million was recorded in the consolidated statement of comprehensive income. There were no material gross realized gains and losses from the disposition of available-for-sale investment securities for the three month periods ended March 31, 2019 and 2018 . The following tables show the gross unrealized losses and fair values of investment securities, aggregated by investment category, and the length of time individual investment securities have been in a continuous unrealized loss position, as of March 31, 2019 and December 31, 2018 : Less than 12 Months 12 Months or More Total March 31, 2019 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale: State, county and municipal securities $ — $ — $ 16.2 $ (0.1 ) $ 16.2 $ (0.1 ) Obligations of U.S. government agencies 336.8 (2.8 ) 129.7 (1.2 ) 466.5 (4.0 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 535.9 (6.9 ) 450.3 (5.5 ) 986.2 (12.4 ) Private mortgage-backed securities — — 64.5 (0.9 ) 64.5 (0.9 ) Corporate securities — — 36.9 (0.3 ) 36.9 (0.3 ) Total $ 872.7 $ (9.7 ) $ 697.6 $ (8.0 ) $ 1,570.3 $ (17.7 ) Less than 12 Months 12 Months or More Total March 31, 2019 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity: State, county and municipal securities $ 9.0 $ (0.1 ) $ 16.6 $ (0.1 ) $ 25.6 $ (0.2 ) Obligations of U.S. government agencies 19.6 (0.2 ) — — 19.6 (0.2 ) Corporate securities — — 28.0 (0.1 ) 28.0 (0.1 ) Total $ 28.6 $ (0.3 ) $ 44.6 $ (0.2 ) $ 73.2 $ (0.5 ) Less than 12 Months 12 Months or More Total December 31, 2018 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale: Obligations of U.S. government agencies $ 363.1 $ (7.9 ) $ 154.5 $ (2.3 ) $ 517.6 $ (10.2 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 735.2 (14.5 ) 503.7 (9.6 ) 1,238.9 (24.1 ) Private mortgage-backed securities — — 69.4 (1.8 ) 69.4 (1.8 ) Corporate securities 24.9 (0.2 ) 51.4 (0.8 ) 76.3 (1.0 ) Total $ 1,123.2 $ (22.6 ) $ 779.0 $ (14.5 ) $ 1,902.2 $ (37.1 ) Less than 12 Months 12 Months or More Total December 31, 2018 Fair Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity: State, county and municipal securities $ 25.9 $ (0.3 ) $ 57.1 $ (0.6 ) $ 83.0 $ (0.9 ) Obligations of U.S. government agencies 19.5 (0.3 ) — — 19.5 (0.3 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 45.0 (2.2 ) 120.2 (4.3 ) 165.2 (6.5 ) Corporate securities — — 39.6 (0.6 ) 39.6 (0.6 ) Total $ 90.4 $ (2.8 ) $ 216.9 $ (5.5 ) $ 307.3 $ (8.3 ) The investment portfolio is evaluated quarterly for other-than-temporary declines in the market value of each individual investment security. The Company had 551 and 760 individual investment securities that were in an unrealized loss position as of March 31, 2019 and December 31, 2018 , respectively, related primarily to fluctuations in the current interest rates. As of March 31, 2019 , the Company had the intent and ability to hold these investment securities for a period of time sufficient to allow for an anticipated recovery. Furthermore, the Company does not have the intent to sell any of the available-for-sale securities in the above table and it is more likely than not that the Company will not have to sell any securities before a recovery in cost. No impairment losses were recorded during the three month periods ended March 31, 2019 or 2018 . Maturities of investment securities at March 31, 2019 are shown below. Maturities of mortgage-backed securities have been adjusted to reflect shorter maturities based upon estimated prepayments of principal. All other investment securities maturities are shown at contractual maturity dates. Available-for-Sale Held-to-Maturity March 31, 2019 Amortized Cost Estimated Fair Value Amortized Cost Estimated Fair Value Within one year $ 497.2 $ 496.0 $ 44.9 $ 44.8 After one year but within five years 1,509.8 1,504.9 44.2 44.1 After five years but within ten years 395.3 395.5 24.3 25.5 After ten years 176.7 175.6 3.6 3.6 Total $ 2,579.0 $ 2,572.0 $ 117.0 $ 118.0 As of March 31, 2019 , the Company had investment securities callable within one year with amortized costs and estimated fair values of $121.3 million and $121.5 million , respectively. These investment securities are primarily included in the after one year but within five years category in the table above. As of March 31, 2019 , the Company had callable structured notes with amortized costs and estimated fair values of $2.0 million and $2.0 million , respectively. These callable structured notes, which are classified as available-for-sale, are included in the after one year but within five years category in the table above.

Loans

Loans	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Loans	Loans The following table presents loans by class as of the dates indicated: March 31, December 31, Real estate loans: Commercial $ 3,255.8 $ 3,235.4 Construction: Land acquisition & development 292.7 321.6 Residential 233.1 242.8 Commercial 312.1 274.3 Total construction loans 837.9 838.7 Residential 1,529.5 1,542.0 Agricultural 210.4 217.4 Total real estate loans 5,833.6 5,833.5 Consumer: Indirect consumer 775.7 787.8 Other consumer 194.1 200.6 Credit card 77.2 81.8 Total consumer loans 1,047.0 1,070.2 Commercial 1,342.1 1,310.3 Agricultural 234.7 254.8 Other, including overdrafts 1.8 1.6 Loans held for investment 8,459.2 8,470.4 Mortgage loans held for sale 34.0 33.3 Total loans $ 8,493.2 $ 8,503.7 The following tables present the Company’s recorded investment and contractual aging of the Company’s recorded investment in loans by class as of the dates indicated. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of March 31, 2019 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 12.6 $ 7.2 $ 2.5 $ 22.3 $ 3,222.4 $ 11.1 $ 3,255.8 Construction: Land acquisition & development 1.2 0.7 0.4 2.3 286.6 3.8 292.7 Residential 2.2 — — 2.2 229.6 1.3 233.1 Commercial — — — — 311.9 0.2 312.1 Total construction loans 3.4 0.7 0.4 4.5 828.1 5.3 837.9 Residential 4.6 1.6 0.2 6.4 1,517.2 5.9 1,529.5 Agricultural 4.0 0.9 0.3 5.2 202.8 2.4 210.4 Total real estate loans 24.6 10.4 3.4 38.4 5,770.5 24.7 5,833.6 Consumer: Indirect consumer 6.5 1.1 0.5 8.1 765.6 2.0 775.7 Other consumer 1.4 0.7 0.3 2.4 191.2 0.5 194.1 Credit card 0.6 0.5 0.7 1.8 75.4 — 77.2 Total consumer loans 8.5 2.3 1.5 12.3 1,032.2 2.5 1,047.0 Commercial 4.0 4.1 1.7 9.8 1,317.0 15.3 1,342.1 Agricultural 1.3 1.3 0.5 3.1 229.0 2.6 234.7 Other, including overdrafts — — — — 1.8 — 1.8 Loans held for investment 38.4 18.1 7.1 63.6 8,350.5 45.1 8,459.2 Mortgage loans originated for sale — — — — 34.0 — 34.0 Total loans $ 38.4 $ 18.1 $ 7.1 $ 63.6 $ 8,384.5 $ 45.1 $ 8,493.2 Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of December 31, 2018 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 10.4 $ 1.0 $ 0.8 $ 12.2 $ 3,214.0 $ 9.2 $ 3,235.4 Construction: Land acquisition & development 1.6 0.1 0.2 1.9 316.0 3.7 321.6 Residential 1.0 0.4 — 1.4 240.4 1.0 242.8 Commercial 0.4 — — 0.4 273.7 0.2 274.3 Total construction loans 3.0 0.5 0.2 3.7 830.1 4.9 838.7 Residential 8.8 1.1 0.2 10.1 1,525.3 6.6 1,542.0 Agricultural 2.2 — — 2.2 202.6 12.6 217.4 Total real estate loans 24.4 2.6 1.2 28.2 5,772.0 33.3 5,833.5 Consumer: Indirect consumer 6.8 2.1 0.4 9.3 776.8 1.7 787.8 Other consumer 1.4 0.5 0.1 2.0 198.1 0.5 200.6 Credit card 0.9 0.4 0.8 2.1 79.7 — 81.8 Total consumer loans 9.1 3.0 1.3 13.4 1,054.6 2.2 1,070.2 Commercial 8.3 1.2 1.3 10.8 1,283.7 15.8 1,310.3 Agricultural 2.1 0.3 — 2.4 249.4 3.0 254.8 Other, including overdrafts — — — — 1.6 — 1.6 Loans held for investment 43.9 7.1 3.8 54.8 8,361.3 54.3 8,470.4 Mortgage loans originated for sale — — — — 33.3 — 33.3 Total loans $ 43.9 $ 7.1 $ 3.8 $ 54.8 $ 8,394.6 $ 54.3 $ 8,503.7 Loans from business combinations included in the tables above include certain loans that had evidence of deterioration in credit quality since origination and for which it was probable, at acquisition, that all contractually required payments would not be collected. The following table displays the outstanding unpaid balances and accrual status of loans acquired with credit impairment as of the dates indicated: March 31, 2019 December 31, 2018 Outstanding balance $ 40.9 $ 43.4 Carrying value Loans on accrual status 28.0 30.2 Total carrying value $ 28.0 $ 30.2 The following table summarizes changes in the accretable yield for loans acquired deemed credit impaired for the three month periods ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 2018 Beginning balance $ 8.9 $ 7.3 Accretion income (0.7 ) (0.7 ) Reductions due to exit events (0.3 ) (0.2 ) Reclassifications from non-accretable differences 0.5 0.8 Ending balance $ 8.4 $ 7.2 Acquired loans that met the criteria for non-accrual of interest prior to acquisition were considered performing upon acquisition. If interest on non-accrual loans had been accrued, such income would have been approximately $0.6 million and $0.8 million for the three months ended March 31, 2019 and 2018 , respectively. The Company considers impaired loans to include all originated loans, except consumer loans, that are risk rated as doubtful, or have been placed on non-accrual status or renegotiated in troubled debt restructurings, and all loans acquired with evidence of deterioration in credit quality and for which it was probable, at acquisition, that the Company would be unable to collect all contractual amounts owed. The following tables present information on the Company’s recorded investment in impaired loans as of the dates indicated: As of March 31, 2019 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 27.0 $ 10.7 $ 10.6 $ 21.3 $ 0.7 Construction: Land acquisition & development 10.0 0.4 3.4 3.8 0.3 Residential 1.5 0.9 0.4 1.3 — Commercial 0.6 0.1 — 0.1 — Total construction loans 12.1 1.4 3.8 5.2 0.3 Residential 8.9 4.2 3.3 7.5 0.5 Agricultural 2.7 2.4 0.2 2.6 — Total real estate loans 50.7 18.7 17.9 36.6 1.5 Commercial 24.3 5.8 14.0 19.8 5.1 Agricultural 5.0 1.6 3.2 4.8 0.5 Total $ 80.0 $ 26.1 $ 35.1 $ 61.2 $ 7.1 As of December 31, 2018 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 22.2 $ 8.6 $ 7.7 $ 16.3 $ 0.7 Construction: Land acquisition & development 10.0 0.4 3.5 3.9 0.2 Residential 1.1 0.6 0.4 1.0 0.1 Commercial 0.7 0.2 — 0.2 — Total construction loans 11.8 1.2 3.9 5.1 0.3 Residential 8.8 5.7 2.0 7.7 0.3 Agricultural 12.9 12.5 0.2 12.7 — Total real estate loans 55.7 28.0 13.8 41.8 1.3 Commercial 24.1 5.5 14.4 19.9 5.2 Agricultural 3.2 2.5 0.6 3.1 0.3 Total $ 83.0 $ 36.0 $ 28.8 $ 64.8 $ 6.8 The following table presents the average recorded investment in and income recognized on impaired loans for the periods indicated: Three Months Ended March 31, 2019 2018 Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Real estate $ 39.3 $ — $ 56.1 $ — Commercial 19.9 — 22.1 — Agricultural 3.9 — 1.5 — Total $ 63.1 $ — $ 79.7 $ — Interest payments received on non-accrual impaired loans are applied to principal. Interest income is subsequently recognized only to the extent cash payments are received in excess of principal due. If interest on impaired loans had been accrued, interest income on impaired loans would have been approximately $0.6 million and $0.8 million for the three months ended March 31, 2019 and 2018 , respectively. Collateralized impaired loans are generally recorded at the fair value of the underlying collateral using discounted cash flows, independent appraisals and management estimates based upon current market conditions. For loans measured under the present value of cash flows method, the change in present value attributable to the passage of time, if applicable, is recognized in the provision for loan losses and thus no interest income is recognized. Modifications of performing loans are made in the ordinary course of business and are completed on a case-by-case basis as negotiated with the borrower. Loan modifications typically include interest rate changes, interest only periods of less than twelve months, short-term payment deferrals and extension of amortization periods to provide payment relief. A loan modification is considered a troubled debt restructuring if the borrower is experiencing financial difficulties and the Company, for economic or legal reasons, grants a concession to the borrower that it would not otherwise consider. Certain troubled debt restructurings are on non-accrual status at the time of restructuring and may be returned to accrual status after considering the borrower’s sustained repayment performance in accordance with the restructuring agreement for a period of at least six months and management is reasonably assured of future performance. If the troubled debt restructuring meets these performance criteria and the interest rate granted at the modification is equal to or greater than the rate that the Company was willing to accept at the time of the restructuring for a new loan with comparable risk, then the loan will return to performing status and the accrual of interest will resume, although they continue to be individually evaluated for impairment and disclosed as impaired loans. The Company had loans renegotiated in troubled debt restructurings of $22.7 million as of March 31, 2019 , of which $16.9 million were included in non-accrual loans and $5.8 million were on accrual status. The Company had loans renegotiated in troubled debt restructurings of $23.4 million as of December 31, 2018 , of which $17.8 million were included in non-accrual loans and $5.6 million were on accrual status. The Company had no material troubled debt restructurings that occurred during the three months ended March 31, 2019 . For troubled debt restructurings that were on non-accrual status or otherwise deemed impaired before the modification, a specific reserve may already be recorded. In periods subsequent to modification, the Company continues to evaluate all troubled debt restructurings for possible impairment and recognizes impairment through the allowance. Additionally these loans continue to work their way through the credit cycle through charge-off, pay-off or foreclosure. Financial effects of modifications of troubled debt restructurings may include principal loan forgiveness or other charge-offs directly related to the restructuring. The Company had no charge-offs directly related to modifying troubled debt restructurings during the three months ended March 31, 2019 or 2018 . The Company had no material troubled debt restructurings during the previous 12 months for which there was a payment default during the three months ended March 31, 2019 . The Company considers a payment default to occur on troubled debt restructurings when the loan is 90 days or more past due or was placed on non-accrual status after the modification. At March 31, 2019 , there were no material commitments to lend additional funds to borrowers whose existing loans have been renegotiated or are classified as non-accrual. As part of the on-going and continuous monitoring of the credit quality of the Company’s loan portfolio, management tracks internally assigned risk classifications of loans. The Company adheres to a Uniform Classification System developed jointly by the various bank regulatory agencies to internally risk rate loans. The Uniform Classification System defines three broad categories of criticized assets, which the Company uses as credit quality indicators: Other Assets Especially Mentioned — includes loans that exhibit weaknesses in financial condition, loan structure or documentation, which if not promptly corrected, may lead to the development of abnormal risk elements. Substandard — includes loans that are inadequately protected by the current sound worth and paying capacity of the borrower. Although the primary source of repayment for a substandard loan is not currently sufficient, collateral or other sources of repayment are sufficient to satisfy the debt. Continuance of a substandard loan is not warranted unless positive steps are taken to improve the worthiness of the credit. Doubtful — includes loans that exhibit pronounced weaknesses to a point where collection or liquidation in full, on the basis of currently existing facts, conditions and values, is highly questionable and improbable. Doubtful loans are required to be placed on non-accrual status and are assigned specific loss exposure. Company management undertakes the same process for assigning risk ratings to acquired loans as it does for originated loans. Acquired loans rated as substandard or lower or that were on non-accrual status or designated as troubled debt restructurings at the time of acquisition are deemed to be acquired credit impaired loans accounted for under ASC Topic 310-30, regardless of whether they are classified as performing or non-performing loans. The following tables present the Company’s recorded investment in criticized loans by class and credit quality indicator based on the most recent analysis performed as of the dates indicated: As of March 31, 2019 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 100.4 $ 90.9 $ 2.8 $ 194.1 Construction: Land acquisition & development 5.1 2.2 3.4 10.7 Residential 0.9 2.2 0.9 4.0 Commercial 1.8 4.1 — 5.9 Total construction loans 7.8 8.5 4.3 20.6 Residential 2.6 8.9 1.9 13.4 Agricultural 15.7 18.0 0.1 33.8 Total real estate loans 126.5 126.3 9.1 261.9 Consumer: Indirect consumer 0.3 2.7 0.1 3.1 Direct consumer 0.3 0.8 0.1 1.2 Total consumer loans 0.6 3.5 0.2 4.3 Commercial 42.3 46.5 11.3 100.1 Agricultural 16.8 18.3 1.1 36.2 Total $ 186.2 $ 194.6 $ 21.7 $ 402.5 As of December 31, 2018 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 102.5 $ 87.4 $ 2.9 $ 192.8 Construction: Land acquisition & development 5.0 7.0 3.3 15.3 Residential 2.8 2.0 0.4 5.2 Commercial 1.7 3.9 — 5.6 Total construction loans 9.5 12.9 3.7 26.1 Residential 3.0 10.8 0.7 14.5 Agricultural 9.0 24.0 0.1 33.1 Total real estate loans 124.0 135.1 7.4 266.5 Consumer: Indirect consumer 0.7 2.1 0.1 2.9 Direct consumer 0.3 0.8 0.1 1.2 Total consumer loans 1.0 2.9 0.2 4.1 Commercial 39.4 45.8 11.8 97.0 Agricultural 14.4 17.8 1.5 33.7 Total $ 178.8 $ 201.6 $ 20.9 $ 401.3 The Company maintains a credit review function, which is independent of the credit approval process, to assess assigned internal risk classifications and monitor compliance with internal lending policies and procedures. Written action plans with firm target dates for resolution of identified problems are maintained and reviewed on a quarterly basis for all categories of criticized loans.

Allowance for Loan Losses

Allowance for Loan Losses	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Allowance for Loan Losses	Allowance for Loan Losses The following tables present a summary of changes in the allowance for loan losses by portfolio segment for the periods indicated: Three Months Ended March 31, 2019 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 31.0 $ 8.7 $ 31.3 $ 2.0 $ — $ 73.0 Provision charged to operating expense (1.7 ) 2.0 3.6 (0.2 ) — 3.7 Less loans charged-off (2.1 ) (3.0 ) (0.8 ) (0.1 ) — (6.0 ) Add back recoveries of loans previously charged-off 0.2 1.1 0.4 — — 1.7 Ending balance $ 27.4 $ 8.8 $ 34.5 $ 1.7 $ — $ 72.4 As of March 31, 2019 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Loans individually evaluated for impairment $ 1.5 $ — $ 5.1 $ 0.5 $ — $ 7.1 Loans collectively evaluated for impairment 25.9 8.8 29.4 1.2 — 65.3 Allowance for loan losses $ 27.4 $ 8.8 $ 34.5 $ 1.7 $ — $ 72.4 As of March 31, 2019 Real Estate Consumer Commercial Agriculture Other Total Loans held for investment: Individually evaluated for impairment $ 36.6 $ — $ 19.8 $ 4.8 $ — $ 61.2 Collectively evaluated for impairment 5,797.0 1,047.0 1,322.3 229.9 1.8 8,398.0 Total loans held for investment $ 5,833.6 $ 1,047.0 $ 1,342.1 $ 234.7 $ 1.8 $ 8,459.2 Three Months Ended March 31, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 31.7 $ 8.7 $ 30.5 $ 1.2 $ — $ 72.1 Provision charged to operating expense 1.8 0.7 (0.7 ) 0.3 — 2.1 Less loans charged-off (0.8 ) (2.7 ) (1.7 ) — — (5.2 ) Add back recoveries of loans previously charged-off 1.2 1.1 2.0 0.2 — 4.5 Ending balance $ 33.9 $ 7.8 $ 30.1 $ 1.7 $ — $ 73.5 As of December 31, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Loans individually evaluated for impairment $ 1.3 $ — $ 5.2 $ 0.3 $ — $ 6.8 Loans collectively evaluated for impairment 29.7 8.7 26.1 1.7 — 66.2 Allowance for loan losses $ 31.0 $ 8.7 $ 31.3 $ 2.0 $ — $ 73.0 As of December 31, 2018 Real Estate Consumer Commercial Agriculture Other Total Loans held for investment: Individually evaluated for impairment $ 41.8 $ — $ 19.9 $ 3.1 $ — $ 64.8 Collectively evaluated for impairment 5,791.7 1,070.2 1,290.4 251.7 1.6 8,405.6 Total loans held for investment $ 5,833.5 $ 1,070.2 $ 1,310.3 $ 254.8 $ 1.6 $ 8,470.4 The Company performs a quarterly assessment of the adequacy of its allowance for loan losses in accordance with GAAP. The methodology used to assess the adequacy is consistently applied to the Company’s loan portfolio and consists of three elements: (1) specific valuation allowances based on probable losses on impaired loans; (2) historical valuation allowances based on loan loss experience for similar loans with similar characteristics and trends; and (3) general valuation allowances determined based on changes in the nature of the loan portfolio, overall portfolio quality, industry concentrations, delinquency trends, general economic conditions and other qualitative risk factors both internal and external to the Company. Specific allowances are established for loans where management has determined that probability of a loss exists by analyzing the borrower’s ability to repay amounts owed, collateral deficiencies and any relevant qualitative or economic factors impacting the loan. Historical valuation allowances are determined by applying percentage loss factors to the credit exposures from outstanding loans. For commercial, agricultural and real estate loans, loss factors are applied based on the internal risk classifications of these loans. For consumer loans, loss factors are applied on a portfolio basis. For commercial, agriculture and real estate loans, loss factor percentages are based on a migration analysis of our historical loss experience, designed to account for credit deterioration. For consumer loans, the loss factor percentages are based on a three-year loss history for the 2018 period and on a one-year loss history for the comparable periods. The loan loss rates for 2018 also incorporate the available loss history data from Bank of the Cascades prior to the merger date to represent a consolidated institutional loss rate for both originated and acquired portfolios. General valuation allowances are determined by evaluating, on a quarterly basis, changes in the nature and volume of the loan portfolio, overall portfolio quality, industry concentrations, current economic and regulatory conditions and the estimated impact of these factors on historical loss rates. An allowance for loan losses is established for loans acquired deemed credit impaired and for which the Company projects a decrease in the expected cash flows in periods subsequent to the acquisition of such loans. As of March 31, 2019 and December 31, 2018 , the Company’s allowance for loan losses included $0.9 million and $0.8 million related to loans acquired credit impaired.

Other Real Estate Owned

Other Real Estate Owned	3 Months Ended
	Mar. 31, 2019
Repossessed Assets [Abstract]
Other Real Estate Owned	Other Real Estate Owned Information with respect to the Company’s other real estate owned follows: Three Months Ended March 31, 2019 2018 Beginning balance $ 14.4 $ 10.1 Additions 8.4 1.2 Valuation adjustments (0.3 ) — Dispositions (1.4 ) (0.3 ) Ending balance $ 21.1 $ 11.0 The carrying values of foreclosed residential real estate properties included in other real estate owned were $1.7 million and $2.0 million as of March 31, 2019 and December 31, 2018 , respectively. The Company had $0.5 million of consumer mortgage loans collateralized by residential real estate property that were in the process of foreclosure as of March 31, 2019 and $0.4 million as of December 31, 2018 .

Derivatives and Hedging Activit

Derivatives and Hedging Activities	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative and Hedging Activities	Derivatives and Hedging Activities The Company enters into certain interest rate swap contracts that are not designated as hedging instruments. These derivative contracts relate to transactions in which the Company enters into an interest rate swap with a customer while at the same time entering into an offsetting interest rate swap with a third party financial institution. Because the Company acts as an intermediary for the customer, changes in the fair value of the underlying derivative contracts for the most part offset each other and do not significantly impact the Company’s results of operations. In the normal course of business, the Company enters into interest rate lock commitments to finance residential mortgage loans that are not designated as accounting hedges. These commitments, which contain fixed expiration dates, offer the borrower an interest rate guarantee provided the loan meets underwriting guidelines and closes within the timeframe established by the Company. Interest rate risk arises on these commitments and subsequently closed loans if interest rates change between the time of the interest rate lock and the delivery of the loan to the investor. Loan commitments related to residential mortgage loans intended to be sold are considered derivatives and are marked to market through earnings. In addition to the effects of the change in market interest rate, the fair value measurement of the derivative also contemplates the expected cash flows to be received from the counterparty from the future sale of the loan. The Company sells residential mortgage loans on either a best efforts or mandatory delivery basis. The Company mitigates the effect of the interest rate risk inherent in providing interest rate lock commitments by entering into forward loan sales contracts. During the interest rate lock commitment period, these forward loan sales contracts are marked to market through earnings and are not designated as accounting hedges. Exclusive of the fair value component associated with the projected cash flows from the loan delivery to the investor, the changes in fair value related to movements in market rates of the interest rate lock commitments and the forward loan sales contracts generally move in opposite directions, and the net impact of changes in these valuations on net income during the loan commitment period is generally inconsequential. When the loan is funded to the borrower, the interest rate lock commitment derivative expires and the Company records a loan held for sale. The forward loan sales contract acts as a hedge against the variability in cash to be received from the loan sale. The changes in measurement of the estimated fair values of the interest rate lock commitments and forward loan sales contracts are included in mortgage banking revenues in the accompanying consolidated statements of income. The notional amounts and estimated fair values of the Company’s derivatives are presented in the following table. Fair value estimates are obtained from third parties and are based on pricing models. March 31, 2019 December 31, 2018 Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Derivative Assets (included in other assets on the consolidated balance sheets): Non-hedging interest rate derivatives: Interest rate swap contracts $ 449.2 $ 12.7 $ 403.3 $ 8.8 Interest rate lock commitments 76.9 1.9 51.0 1.3 Total derivative assets $ 526.1 $ 14.6 $ 454.3 $ 10.1 Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets): Non-hedging interest rate derivatives: Interest rate swap contracts $ 449.2 $ 12.7 $ 403.3 $ 8.8 Forward loan sales contracts 90.4 0.8 64.6 0.6 Total derivative liabilities $ 539.6 $ 13.5 $ 467.9 $ 9.4 Derivative assets and liabilities are recorded at fair value on the balance sheet and do not take into account the effects of master netting arrangements. Master netting arrangements allow the Company to settle all contracts held with a single counterparty on a net basis and to offset net contract position with related collateral where applicable. The following table illustrates the potential effect of the Company’s master netting arrangements, by type of financial instrument, on the Company’s consolidated balance sheets as of March 31, 2019 and December 31, 2018 : March 31, 2019 Gross Amounts Recognized Gross Amounts Offset in the Balance Sheet Net Amounts in the Balance Sheet Financial Instruments Fair Value of Financial Collateral in the Balance Sheet Net Amount Financial Assets Interest rate swap contracts $ 12.7 $ — $ 12.7 $ 2.0 $ 7.5 $ 3.2 Mortgage related derivatives 1.9 — 1.9 — — 1.9 Total derivatives 14.6 — 14.6 2.0 7.5 5.1 Total assets $ 14.6 $ — $ 14.6 $ 2.0 $ 7.5 $ 5.1 Financial Liabilities Interest rate swap contracts $ 12.7 $ — $ 12.7 $ 2.0 $ 0.2 $ 10.5 Mortgage related derivatives 0.8 — 0.8 — — 0.8 Total derivatives 13.5 — 13.5 2.0 0.2 11.3 Repurchase agreements 672.6 — 672.6 — 672.6 — Total liabilities $ 686.1 $ — $ 686.1 $ 2.0 $ 672.8 $ 11.3 December 31, 2018 Gross Amounts Recognized Gross Amounts Offset in the Balance Sheet Net Amounts in the Balance Sheet Financial Instruments Fair Value of Financial Collateral in the Balance Sheet Net Amount Financial Assets Interest rate swap contracts $ 8.8 $ — $ 8.8 $ 2.7 $ 2.4 $ 3.7 Mortgage related derivatives 1.3 — 1.3 — — 1.3 Total derivatives 10.1 — 10.1 2.7 2.4 5.0 Total assets $ 10.1 $ — $ 10.1 $ 2.7 $ 2.4 $ 5.0 Financial Liabilities Interest rate swap contracts $ 8.8 $ — $ 8.8 $ 2.7 $ 4.1 $ 2.0 Mortgage related derivatives 0.6 — 0.6 — — 0.6 Total derivatives 9.4 — 9.4 2.7 4.1 2.6 Repurchase agreements 712.4 — 712.4 — 712.4 — Total liabilities $ 721.8 $ — $ 721.8 $ 2.7 $ 716.5 $ 2.6 The following table presents the pre-tax gains or losses related to derivative contracts that were recorded in other non-interest income in the Company’s statements of income for the periods indicated: Three Months Ended March 31, 2019 2018 Non-hedging interest rate derivatives: Amount of gain recognized in other non-interest income $ — $ 0.3 Amount of net fee income recognized in other non-interest income 0.8 0.5 Amount of net gains recognized in mortgage banking revenues 0.4 (0.1 )

Capital Stock

Capital Stock	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Capital Stock	Capital Stock The Company had 38,461,948 shares of Class A common stock and 22,374,171 shares of Class B common stock outstanding as of March 31, 2019 . The Company had 38,169,575 shares of Class A common stock and 22,453,672 shares of Class B common stock outstanding as of December 31, 2018 . During the three months ended March 31, 2019 and 2018 , the Company did not repurchase any shares of its Class A common stock other than stock repurchases which were redemptions of vested restricted shares tendered in lieu of cash for payment of income tax withholding amounts by participants in the Company’s equity compensation plans.

Earnings per Common Share

Earnings per Common Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Earnings per Common Share	Earnings per Common Share Basic earnings per common share is calculated by dividing net income by the weighted average number of common shares outstanding during the period presented, excluding unvested restricted stock. Diluted earnings per share is calculated by dividing net income by the weighted average number of common shares determined for the basic earnings per share computation plus the dilutive effects of stock-based compensation using the treasury stock method. The following table sets forth the computation of basic and diluted earnings per share for the three month periods ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 2018 Net income $ 41.6 $ 36.7 Weighted average common shares outstanding for basic earnings per share computation 60,311,171 56,241,201 Dilutive effects of stock-based compensation 286,899 410,977 Weighted average common shares outstanding for diluted earnings per common share computation 60,598,070 56,652,178 Basic earnings per common share $ 0.69 $ 0.65 Diluted earnings per common share $ 0.69 $ 0.65 Anti-dilutive unvested time restricted stock 121,452 139,943 The Company had 154,387 and 164,019 shares of unvested restricted stock as of March 31, 2019 and 2018 , respectively, that were not included in the computation of diluted earnings per common share because performance conditions for vesting had not been met.

Regulatory Capital

Regulatory Capital	3 Months Ended
	Mar. 31, 2019
Banking and Thrift [Abstract]
Regulatory Capital	Regulatory Capital On July 2, 2013, the Board of Governors of the Federal Reserve Bank issued a final rule implementing a revised regulatory capital framework for U.S. banks in accordance with the Basel III international accord and satisfying related mandates under the Dodd-Frank Wall Street Reform and Consumer Protection Act. The revised regulatory capital framework (the “Basel III Capital Rules”) substantially revised the risk-based capital requirements applicable to bank holding companies and depository institutions by defining the components of capital and addressing other issues affecting the numerator in banking institutions’ regulatory capital ratios, addressing risk weights and other issues affecting the denominator in banking institutions’ regulatory capital ratios and replacing the existing risk-weighting approach with a more risk-sensitive approach. The Basel III Capital Rules became effective for the Company on January 1, 2015, subject to a phase-in period for certain provisions. The capital conservation buffer required under Basel III began to phase in starting January 1, 2016 and became fully implemented on January 1, 2019. As of March 31, 2019 and December 31, 2018 , the Company exceeded all capital adequacy requirements to which it is subject. Actual capital amounts and ratios for the Company and its subsidiary Bank, as of March 31, 2019 and December 31, 2018 are presented in the following tables: Actual Minimum Required for Capital Adequacy Purposes For Capital Adequacy Purposes Plus Capital Conservation Buffer Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements(1) March 31, 2019 Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total risk-based capital: Consolidated $ 1,310.3 13.23 % $ 792.4 8.000 % $ 1,040.0 10.50 % $ 990.5 10.00 % FIB 1,201.4 12.16 790.2 8.000 1,037.1 10.50 987.8 10.00 Tier 1 risk-based capital: Consolidated 1,237.9 12.50 594.3 6.000 841.9 8.50 792.4 8.00 FIB 1,129.0 11.43 592.7 6.000 839.6 8.50 790.2 8.00 Common equity tier 1 risk-based capital: Consolidated 1,153.7 11.65 445.7 4.500 693.4 7.00 643.8 6.50 FIB 1,129.0 11.43 444.5 4.500 691.4 7.00 642.0 6.50 Leverage capital ratio: Consolidated 1,237.9 9.76 507.5 4.000 507.5 4.00 634.4 5.00 FIB 1,129.0 8.92 506.3 4.000 506.3 4.00 632.8 5.00 Actual Minimum Required for Capital Adequacy Purposes For Capital Adequacy Purposes Plus Capital Conservation Buffer Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements(1) December 31, 2018 Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total risk-based capital: Consolidated $ 1,285.0 12.99 % $ 791.2 8.00 % $ 976.6 9.875 % $ 989.0 10.00 % FIB 1,184.5 12.01 788.8 8.00 973.7 9.875 986.0 10.00 Tier 1 risk-based capital: Consolidated 1,212.0 12.26 593.4 6.00 778.8 7.875 791.2 8.00 FIB 1,111.6 11.27 591.6 6.00 776.5 7.875 788.8 8.00 Common equity tier 1 risk-based capital: Consolidated 1,127.8 11.40 445.0 4.50 630.5 6.375 642.8 6.50 FIB 1,111.6 11.27 443.7 4.50 628.6 6.375 640.9 6.50 Leverage capital ratio: Consolidated 1,212.0 9.47 511.9 4.00 511.9 4.000 639.9 5.00 FIB 1,111.6 8.97 495.9 4.00 495.9 4.000 619.8 5.00 (1) The ratios for the requirements to be deemed “well capitalized” are only applicable to FIB. However, the Company manages its capital position as if the requirements apply to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies In the normal course of business, the Company is involved in various other claims and litigation. In the opinion of management, following consultation with legal counsel, the ultimate liability or disposition thereof of all other claims and litigation is not expected to have a material adverse effect on the consolidated financial condition, results of operations or liquidity of the Company. As of March 31, 2019 , the Company had commitments under construction contracts of $1.5 million . Residential mortgage loans sold to investors in the secondary market are sold with varying recourse provisions. Essentially all of the loan sales agreements require the repurchase of a mortgage loan by the seller in situations such as breach of representation, warranty or covenant; untimely document delivery; false or misleading statements; failure to obtain certain certificates or insurance; unmarketability; etc. Certain loan sales agreements contain repurchase requirements based on payment-related defects that are defined in terms of the number of days or months since the purchase, the sequence number of the payment, and/or the number of days of payment delinquency. Based on the specific terms stated in the agreements, the Company had $1.5 million of sold residential mortgage loans with recourse provisions still in effect as of March 31, 2019 .

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk	3 Months Ended
	Mar. 31, 2019
Financial Instruments with Off-Balance Sheet Risk [Abstract]
Financial Instruments with Off-Balance Sheet Risk	Financial Instruments with Off-Balance Sheet Risk The Company is a party to financial instruments with off-balance sheet risk in the normal course of business to meet the financing needs of its customers. These financial instruments include commitments to extend credit and standby letters of credit. Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the commitment contract. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. At March 31, 2019 , commitments to extend credit to existing and new borrowers approximated $2,637.1 million , which included $720.7 million on unused credit card lines and $1,058.9 million with commitment maturities beyond one year. Standby letters of credit are conditional commitments issued by the Company to guarantee the performance of a customer to a third party. At March 31, 2019 , the Company had outstanding standby letters of credit of $47.6 million . The estimated fair value of the obligation undertaken by the Company in issuing the standby letters of credit is included in other liabilities in the Company’s consolidated balance sheet.

Other Comprehensive Income_Loss

Other Comprehensive Income/Loss	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Other Comprehensive Income/Loss	Other Comprehensive Income/Loss The gross amounts of each component of other comprehensive income and the related tax effects are as follows: Pre-tax Tax Expense (Benefit) Net of Tax Three Months Ended March 31, 2019 2018 2019 2018 2019 2018 Investment securities available-for sale: Change in net unrealized gains during period $ 33.6 $ (23.7 ) $ 8.8 $ (6.2 ) $ 24.8 $ (17.5 ) Reclassification adjustment for securities transferred from held-to-maturity to available-for-sale (6.0 ) — (1.6 ) — (4.4 ) — Change in unamortized loss on available-for-sale securities transferred into held-to-maturity — 0.5 — 0.2 — 0.3 Defined benefits post-retirement benefit plan: Change in net actuarial (gain) loss (0.2 ) (0.1 ) — (0.1 ) (0.2 ) — Total other comprehensive income (loss) $ 27.4 $ (23.3 ) $ 7.2 $ (6.1 ) $ 20.2 $ (17.2 ) The components of accumulated other comprehensive loss, net of related tax effects, are as follows: March 31, 2019 December 31, 2018 Net unrealized gain (loss) on investment securities available-for-sale $ (5.1 ) $ (25.5 ) Net actuarial gain (loss) on defined benefit post-retirement benefit plans 0.7 0.9 Net accumulated other comprehensive gain (loss) $ (4.4 ) $ (24.6 )

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. There is a fair value hierarchy which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The three levels of inputs that may be used to measure fair value are as follows: • Level 1 - Quoted prices in active markets for identical assets or liabilities • Level 2 - Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities • Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of assets or liabilities The methodologies used by the Company in determining the fair values of each class of financial instruments are based primarily on the use of independent, market-based data to reflect a value that would be reasonably expected in an orderly transaction between market participants at the measurement date, and therefore are classified within Level 2 of the valuation hierarchy. The Company’s policy is to recognize transfers between levels as of the end of the reporting period. There were no transfers between Level 1 and Level 2 during the three months ended March 31, 2019 and 2018 . Further details on the methods used to estimate the fair value of each class of financial instruments above are discussed below: Investment Debt Securities Available-for-Sale . The Company obtains fair value measurements for investment securities from an independent pricing service. The fair value measurements consider observable data that may include 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 investment’s terms and conditions, among other things. Vendors chosen by the Company are widely recognized vendors whose evaluations support the pricing functions of financial institutions, investment and mutual funds, and portfolio managers. If needed, a broker may be utilized to determine the reported fair value of investment securities. Loans Held for Sale. Fair value measurements for loans held for sale are obtained from an independent pricing service. The fair value measurements consider observable data that may include binding contracts or quotes or bids from third party investors as well as loan level pricing adjustments. Interest Rate Swap Contracts. Fair values for derivative interest rate swap contracts are based upon the estimated amounts to settle the contracts considering current interest rates and are calculated using discounted cash flows that are observable or that can be corroborated by observable market data. The inputs used to determine fair value include the 3 month LIBOR forward curve to estimate variable rate cash inflows and the federal funds effective swap rate to estimate the discount rate. The estimated variable rate cash inflows are compared to the fixed rate outflows and such difference is discounted to a present value to estimate the fair value of the interest rate swaps. The change in the value of derivative assets attributable to basis risk, or the risk that offsetting investments in a hedging strategy will not experience price changes in entirely opposite directions from each other, was not significant in the reported periods. The Company also obtains and compares the reasonableness of the pricing from an independent third party. Interest Rate Lock Commitments. Fair value measurements for interest rate lock commitments are obtained from an independent pricing service. The fair value measurements consider observable data that may include prices available from secondary market investors taking into consideration various characteristics of the loan, including the loan amount, interest rate, value of the servicing and loan to value ratio, among other things. Observable data is then adjusted to reflect changes in interest rates, the Company’s estimated pull-through rate and estimated direct costs necessary to complete the commitment into a closed loan net of origination and processing fees collected from the borrower. Forward Loan Sales Contracts. The fair value measurements for forward loan sales contracts are obtained from an independent pricing service. The fair value measurements consider observable data that includes sales of similar loans. Deferred Compensation Plan Assets and Liabilities. The fair values of deferred compensation plan assets are based primarily on the use of independent, market-based data to reflect a value that would be reasonably expected in an orderly transaction between market participants at the measurement date. These investments are in the same funds and purchased in the same amounts as the participants’ selected investments, which represent the underlying liabilities to plan participants. Deferred compensation plan liabilities are recorded at amounts due to participants, based on the fair value of participants’ selected investments. Financial assets and liabilities measured at fair value on a recurring basis are as follows: Fair Value Measurements at Reporting Date Using As of March 31, 2019 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Investment debt securities available-for-sale: U.S. Treasury Notes $ 4.0 $ — $ 4.0 $ — State, county and municipal securities 78.4 — 78.4 — Obligations of U.S. government agencies 597.7 — 597.7 — U.S. agencies mortgage-backed securities & collateralized mortgage obligations 1,732.9 — 1,732.9 — Private mortgage-backed securities 65.3 — 65.3 — Corporate securities 92.0 — 92.0 — Other investments 1.7 — 1.7 — Loans held for sale 34.0 — 34.0 — Derivative assets: Interest rate swap contracts 12.7 — 12.7 — Interest rate lock commitments 1.9 — 1.9 — Derivative liabilities: Interest rate swap contracts 12.7 — 12.7 — Forward loan sale contracts 0.8 — 0.8 — Deferred compensation plan assets 12.4 — 12.4 — Deferred compensation plan liabilities $ 12.4 $ — $ 12.4 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2018 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Investment debt securities available-for-sale: U.S. Treasury notes $ 2.6 $ — $ 2.6 $ — Obligations of U.S. government agencies 559.2 — 559.2 — U.S. agencies mortgage-backed securities & collateralized mortgage obligations 1,544.8 — 1,544.8 — Private mortgage-backed securities 70.2 — 70.2 — Corporate securities 91.9 — 91.9 — Other investments 2.0 — 2.0 — Loans held for sale 33.3 — 33.3 — Derivative assets: Interest rate swap contracts 8.8 — 8.8 — Interest rate lock commitments 1.3 — 1.3 — Derivative liabilities Interest rate swap contracts 8.8 — 8.8 — Forward loan sales contracts 0.6 — 0.6 — Deferred compensation plan assets 12.1 — 12.1 — Deferred compensation plan liabilities $ 12.1 $ — $ 12.1 $ — Additionally, from time to time, certain assets are measured at fair value on a non-recurring basis. Adjustments to fair value generally result from the application of lower-of-cost-or-market accounting or write-downs of individual assets due to impairment. The following table presents information about the Company’s assets and liabilities measured at fair value on a non-recurring basis: Fair Value Measurements at Reporting Date Using As of March 31, 2019 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Impaired loans $ 30.9 $ — $ — $ 30.9 Other real estate owned 2.0 — — 2.0 Long-lived assets to be disposed of by sale $ 5.5 $ — $ — $ 5.5 Fair Value Measurements at Reporting Date Using As of December 31, 2018 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Impaired loans $ 24.1 $ — $ — $ 24.1 Other real estate owned 0.6 — — 0.6 Long-lived assets to be disposed of by sale $ 4.9 $ — $ — $ 4.9 Impaired Loans. Collateralized impaired loans are reported at the fair value of the underlying collateral if repayment is expected solely from collateral. The impaired loans are reported at fair value through specific valuation allowance allocations. In addition, when it is determined that the fair value of an impaired loan is less than the recorded investment in the loan, the carrying value of the loan is adjusted to fair value through a charge to the allowance for loan losses. Collateral values are estimated using independent appraisals and management estimates of current market conditions. As of March 31, 2019 , certain impaired loans with a carrying value of $44.2 million were reduced by specific valuation allowance allocations of $7.1 million and partial loan charge-offs of $6.2 million resulting in a reported fair value of $30.9 million . As of December 31, 2018 , certain impaired loans with a carrying value of $36.3 million were reduced by specific valuation allowance allocations of $6.8 million and partial loan charge-offs of $5.4 million resulting in a reported fair value of $24.1 million . OREO. The fair values of OREO are estimated using independent appraisals and management estimates of current market conditions. Upon initial recognition, write-downs based on the foreclosed asset’s fair value at foreclosure are reported through charges to the allowance for loan losses. Periodically, the fair value of foreclosed assets is remeasured with any subsequent write-downs charged to OREO expense in the period in which they are identified. The Company had $0.3 million and zero write downs on OREO properties during the three months ended March 31, 2019 and 2018 , respectively. Long-lived Assets to be Disposed of by Sale. Long-lived assets to be disposed of by sale are carried at the lower of carrying value or fair value less estimated costs to sell. The fair values of long-lived assets to be disposed of by sale are based upon observable market data and management estimates of current market conditions. As of March 31, 2019 , the Company had long-lived assets to be disposed of by sale with carrying values aggregating $6.0 million , which was reduced by write-downs of $0.5 million , resulting in a fair value of $5.5 million . As of December 31, 2018 , the Company had long-lived assets to be disposed of by sale with carrying values aggregating $5.4 million , reduced by write-downs of $0.5 million , resulting in a fair value of $4.9 million . The following table presents additional quantitative information about assets measured at fair value on a non-recurring basis and for which the Company has utilized Level 3 inputs to determine fair values: Fair Value As of March 31, 2019 December 31, 2018 Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 30.9 $ 24.1 Appraisal Appraisal adjustment 0% - 26% (13%) Other real estate owned 2.0 0.6 Appraisal Appraisal adjustment 8% - 96% (39%) Long-lived assets to be disposed of by sale $ 5.5 $ 4.9 Appraisal Appraisal adjustment 0% - 43% (10%) The Company is required to disclose the fair value of financial instruments for which it is practical to estimate fair value. The methodologies for estimating the fair value of financial instruments that are measured at fair value on a recurring or non-recurring basis are discussed above. The methodologies for estimating the fair value of other financial instruments are discussed below. For financial instruments bearing a variable interest rate where no credit risk exists, it is presumed that recorded book values are reasonable estimates of fair value. Financial Assets. Carrying values of cash, cash equivalents and accrued interest receivable approximate fair values due to the liquid and/or short-term nature of these instruments. Fair values for investment securities held-to-maturity are obtained from an independent pricing service, which considers observable data that may include 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 investment’s terms and conditions, among other things. Fair values of fixed rate loans and variable rate loans that reprice on an infrequent basis are estimated by discounting future cash flows using current interest rates at which similar loans with similar terms would be made to borrowers of similar credit quality using an exit price notion. Carrying values of variable rate loans that reprice frequently, and with no change in credit risk, approximate the fair values of these instruments. Financial Liabilities. The fair values of demand deposits, savings accounts, securities sold under repurchase agreements and accrued interest payable are the amounts payable on demand at the reporting date. The fair values of fixed-maturity certificates of deposit are estimated using external market rates currently offered for deposits with similar remaining maturities. The fair values of derivative liabilities are obtained from an independent pricing service, which considers observable data that may include the three-month LIBOR forward curve, the federal funds effective swap rate and cash flows, among other things. The carrying values of the interest bearing demand notes to the United States Treasury are deemed an approximation of fair values due to the frequent repayment and repricing at market rates. The fixed and floating rate subordinated debentures, floating rate subordinated term loan, notes payable to the FHLB, fixed rate subordinated term debt, and capital lease obligation are estimated by discounting future cash flows using current rates for advances with similar characteristics. Commitments to Extend Credit and Standby Letters of Credit. The fair value of commitments to extend credit and standby letters of credit, based on fees currently charged to enter into similar agreements, is not significant. The estimated fair values of financial instruments that are reported in the Company’s consolidated balance sheets, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value, are as follows: Fair Value Measurements at Reporting Date Using As of March 31, 2019 Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets: Cash and cash equivalents $ 955.2 $ 955.2 $ 955.2 $ — $ — Investment debt securities available-for-sale 2,572.0 2,572.0 — 2,572.0 — Investment debt securities held-to-maturity 117.0 118.0 — 118.0 — Accrued interest receivable 46.5 46.5 — 46.5 — Mortgage servicing rights, net 27.9 40.5 — 40.5 — Loans held for sale 34.0 34.0 — 34.0 — Net loans held for investment 8,386.8 8,408.6 — 8,377.7 30.9 Derivative assets 14.6 14.6 — 14.6 — Deferred compensation plan assets 12.4 12.4 — 12.4 — Total financial assets $ 12,166.4 $ 12,201.8 $ 955.2 $ 11,215.7 $ 30.9 Financial liabilities: Total deposits, excluding time deposits $ 9,408.3 $ 9,408.3 $ 9,408.3 $ — $ — Time deposits 1,406.4 1,393.2 — 1,393.2 — Securities sold under repurchase agreements 672.6 672.6 — 672.6 — Accrued interest payable 10.0 10.0 — 10.0 — Long-term debt 15.8 13.9 — 13.9 — Subordinated debentures held by subsidiary trusts 86.9 85.1 — 85.1 — Derivative liabilities 13.5 13.5 — 13.5 — Deferred compensation plan liabilities 12.4 12.4 — 12.4 — Total financial liabilities $ 11,625.9 $ 11,609.0 $ 9,408.3 $ 2,200.7 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2018 Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets: Cash and cash equivalents $ 822.0 $ 822.0 $ 822.0 $ — $ — Investment debt securities available-for-sale 2,270.7 2,270.7 — 2,270.7 — Investment debt securities held-to-maturity 406.8 400.7 — 400.7 — Accrued interest receivable 44.9 44.9 — 44.9 — Mortgage servicing rights, net 27.7 42.4 — 42.4 — Loans held for sale 33.3 33.3 — 33.3 — Net loans held for investment 8,397.4 8,439.7 — 8,415.6 24.1 Derivative assets 10.1 10.1 — 10.1 — Deferred compensation plan assets 12.1 12.1 — 12.1 — Total financial assets $ 12,025.0 $ 12,075.9 $ 822.0 $ 11,229.8 $ 24.1 Financial liabilities: Total deposits, excluding time deposits $ 9,363.7 $ 9,363.7 $ 9,363.7 $ — $ — Time deposits 1,317.0 1,299.0 — 1,299.0 — Securities sold under repurchase agreements 712.4 712.4 — 712.4 — Accrued interest payable 7.8 7.8 — 7.8 — Long-term debt 15.8 13.0 — 13.0 — Subordinated debentures held by subsidiary trusts 86.9 84.9 — 84.9 — Derivative liabilities 9.4 9.4 — 9.4 — Deferred compensation plan liabilities 12.1 12.1 — 12.1 — Total financial liabilities $ 11,525.1 $ 11,502.3 $ 9,363.7 $ 2,138.6 $ —

Recent Authoritative Accounting

Recent Authoritative Accounting Guidance	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Recent Authoritative Accounting Guidance	Recent Authoritative Accounting Guidance ASU 2016-02, “Leases (Topic 842).” In February 2016, the FASB issued ASU 2016-02, “Leases (Topic 842).” Under the new guidance, lessees will be required to recognize a lease liability and a right of use asset for all leases (with the exception of short-term leases) at the commencement date of the lease and disclose key information about leasing arrangements. Accounting by lessors is largely unchanged. In July 2018, the FASB issued ASU 2018-11 to provide entities with an additional (and optional) transition method to adopt the new leases standard. Under this new transition method, an entity initially applies the new leases standard at the adoption date and recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. Additionally, in December 2018, the FASB issued ASU 2018-20, “Leases (Topic 842) - Narrow-Scope Improvements for Lessors,” which provides for certain policy elections and changes lessor accounting for sales and similar taxes and certain lessor costs. Upon adoption of ASU 2016-02, ASU 2018-11 and ASU 2018-20 on January 1, 2019, the Company recognized right-of-use assets and related lease liabilities totaling $54.6 million and $54.6 million , respectively, with an immaterial impact on its consolidated results of operations and liquidity. The Company elected to apply certain practical expedients provided under ASU 2016-02 whereby we did not reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) initial direct costs for any existing leases. The Company elected the hindsight practical expedient to determine the lease term for existing leases. We also did not apply the recognition requirements of ASU 2016-02 to any short-term leases (as defined by related accounting guidance). Lease and non-lease components are accounted for separately as the amounts are readily determinable under our lease contracts. ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” The amendments in ASU 2016-13 require a financial asset or group of financial assets measured at amortized cost basis to be presented on a company’s financial statements at the net amount expected to be collected based on historical experience, current conditions and reasonable and supportable forecasts. ASU 2016-13 requires a company’s income statement to reflect the measurement of credit losses for newly recognized financial assets as well as the expected increases or decreases of expected credit losses that have taken place during the period. The amendments in ASU 2016-13 require that the allowance for credit losses for purchased financial assets with a more-than-insignificant amount of credit deterioration since origination be measured at amortized cost basis with the initial allowance for credit losses added to the purchase price rather than being reported as a credit loss expense. ASU 2016-13 also requires that credit losses relating to available-for-sale debt securities be recorded through an allowance for credit losses. The amendments in ASU 2016-13 are effective for the Company for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. The amendments will be applied through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period. A prospective transition approach is required for debt securities for which other-than-temporary impairment was recognized before the effective date. Amounts previously recognized in accumulated other comprehensive income as of the date of adoption that relate to improvement in cash flows expected to be collected will continue to be accreted into income over the remaining life of the asset. Recoveries of amounts previously written off relating to improvements in cash flows after the date of adoption will be recorded in earnings when received. We are currently evaluating the potential impact of ASU 2016-13 on our financial statements, which will be effective on January 1, 2020. We have formed a cross-functional working group comprised of individuals from various functional areas including credit, risk management, finance and information technology, among others. We are currently working through our implementation plan which includes assessment and documentation of processes, internal controls and data sources; model development and documentation; and system configuration, among other things. We are in the process of implementing a third-party vendor solution. The adoption of ASU 2016-13 could result in an increase in the allowance for loan losses as a result of changing from an “incurred loss” model, which encompasses allowances for current known and inherent losses within the portfolio, to an “expected loss” model, which encompasses allowances for losses expected to be incurred over the life of the portfolio. The adoption will also necessitate that we establish an allowance for expected credit losses for certain debt securities and other financial assets. While we are currently unable to reasonably estimate the impact of adopting ASU 2016-13, we expect that the impact of adoption will be significantly influenced by the composition, characteristics and quality of our loan and securities portfolios as well as the prevailing economic conditions and forecasts as of the adoption date. ASU 2017-08, “Receivables – Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities.” The amendments in ASU 2017-08 shorten the amortization period for the premium on certain purchased callable debt securities to the earliest call date. The new guidance does not change the accounting for purchased callable debt securities held at a discount; the discount continues to be amortized to maturity. ASU No. 2017-08 is effective for interim and annual reporting periods beginning after December 15, 2018. As the Company amortized premiums on callable debt securities to the earliest call date, the amendments in ASU 2017-08 became effective for the Company on January 1, 2019, and did not have a significant impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities.” In August 2017, the FASB issued ASU 2017-12, Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities (ASU 2017-12). The purpose of this updated guidance is to better align a company’s financial reporting for hedging activities with the economic objectives of those activities. In addition, this ASU makes certain targeted improvements to simplify the application of the hedge accounting, including to derivative instruments as well as allow a one-time election to reclassify fixed-rate, prepayable debt securities from a held-to-maturity classification to an available-for-sale classification. ASU 2017-12 is effective for public business entities for fiscal years beginning after December 15, 2018. Guidance related to existing cash flow hedges and, if elected, fair value hedges is to be applied under a modified retrospective approach and guidance related to amended presentation and disclosures is to be applied under a prospective approach. Upon adoption of ASU 2017-12 on January 1, 2019, the guidance did not have an impact on the Company's derivatives and, thus, no adjustments were made related to derivatives. In conjunction with the adoption of ASU 2017-12, the Company made the transition election to reclassify $281.1 million in book value of securities, that qualified, from held-to-maturity to available-for-sale. ASU 2018-13, “Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement.” In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement: Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (ASU 2018-13). The amendments in this Update removes, modifies, and adds to the disclosure requirements on fair value measurements in Topic 820, Fair Value Measurement, based on the concepts in the Concepts Statement, including the consideration of costs and benefits. The amendments in this Update are effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively to all periods presented upon their effective date. Early adoption is permitted. An entity is permitted to early adopt any removed or modified disclosures upon issuance of this Update and delay adoption of the additional disclosures until their effective date. While the Company continues to assess all potential impacts of the standard, we currently expect adoption to have an immaterial impact on our consolidated financial statements disclosures. ASU 2018-14, “Compensation – Retirement Benefits – Defined Benefit Plans – General (Subtopic 715-20): Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans.” In August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General: Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans (ASU 2018-14). The amendments in this Update remove disclosures that no longer are considered cost beneficial, clarify the specific requirements of disclosures, and add disclosure requirements identified as relevant. Although narrow in scope, the amendments are considered an important part of the Board’s efforts to improve the effectiveness of disclosures in the notes to financial statements by applying concepts in the Concepts Statement. The amendments in this Update are effective for fiscal years ending after December 15, 2020, for public business entities. Early adoption is permitted. While the Company continues to assess all potential impacts of the standard, we currently expect adoption to have an immaterial impact on our consolidated financial statements disclosures. ASU 2018-15, “Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40) - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract.” In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other- Internal-Use Software (Subtopic 350-40). The amendments in this Update clarifies certain aspects of ASU 2015-05, “Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement,” which was issued in April 2015. ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The accounting for the service element of a hosting arrangement that is a service contract is not affected by the Update. The amendments in this Update are effective for fiscal years beginning after December 15, 2019, for public business entities. Early adoption is permitted. While the Company continues to assess all potential impacts of the standard, we currently expect adoption to have an immaterial impact on our consolidated financial statements disclosures. ASU 2018-16, “Derivatives and Hedging (Topic 815) - Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes.” In October 2018, the FASB issued ASU 2018-16, Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes. The amendments in this Update permit use of the OIS rate based on SOFR as a U.S. benchmark interest rate for hedge accounting purposes under Topic 815 in addition to the interest rates on direct U.S. Treasury obligations, the LIBOR swap rate, the OIS rate based on the Fed Funds Effective Rate and the Securities Industry and Financial Markets Association (SIFMA) Municipal Swap Rate. The amendments in ASU 2018-16 became effective for the Company in conjunction with the adoption of ASU 2017-12 on January 1, 2019, and did not have a significant impact on the Company’s consolidated financial statements, results of operations or liquidity.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Subsequent events have been evaluated for potential recognition and disclosure through the date financial statements were filed with the SEC. On May 3, 2019 , the Company declared a quarterly dividend to common shareholders of $0.31 per share, to be paid on May 23, 2019 to shareholders of record as of May 13, 2019 . No other undisclosed events requiring recognition or disclosure were identified.

Basis of Presentation Basis of

Basis of Presentation Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Revenue Recognition, Policy [Policy Text Block]	Leases We have leased branches and office space and have entered into various other agreements in conducting our business. At inception, we determine whether an agreement represents a lease and at commencement we evaluate each lease agreement to determine whether the lease is an operating or financing lease. Some of our lease agreements have contained renewal options, tenant improvement allowances, rent holidays and rent escalation clauses. As discussed in “Note 16 – Recent Authoritative Accounting Guidance” included in this report, we adopted ASU 2016-02, as of January 1, 2019. Pursuant to ASU 2016-02, all of our long-term operating leases outstanding on December 31, 2018 continued to be classified as operating leases. Our capital lease outstanding at December 31, 2018 is classified as a financing lease. With the adoption of ASU 2016-02, we recorded an operating lease right-of-use asset, within the Premises and Equipment line item, and an operating lease liability, within the Other Liabilities line item, on our balance sheet. Right-of-use lease assets represent our right to use the underlying asset for the lease term and the lease obligation represents our commitment to make the lease payments arising from the lease. Right-of-use lease assets and obligations are recognized at the commencement date based on the present value of remaining lease payments over the lease term. As the Company’s leases do not provide an implicit rate, we have used an estimated incremental borrowing rate based on the information available at the commencement date in determining the present value of lease payments. The right-of-use lease asset includes any lease payments made prior to commencement and excludes any lease incentives. The lease term may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term, subject to any changes in the lease or expectations regarding the terms. Variable lease costs such as property taxes are expensed as incurred. Leases with an initial term of 12 months or less are not recorded on the balance sheet. Prior to our adoption of ASU 2016-02, when our lease agreements contained renewal options, tenant improvement allowances, rent holidays and rent escalation clauses, we recorded a deferred rent asset or liability equal to the difference between the rent expense and the future minimum lease payments due. The lease expense related to operating leases was recognized on a straight-line basis in the statements of operations over the term of each lease. In cases where the lessor granted us leasehold improvement allowances that reduced our lease expense, we capitalized the improvements as incurred and recognized deferred rent, which was amortized over the shorter of the lease term or the expected useful life of the improvements.

Acquisitions (Tables)

Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table summarizes the consideration paid, fair values of the Northwest assets acquired and liabilities assumed, and the resulting goodwill. The amounts reported for net deferred tax assets and goodwill are provisional pending completion of the Company's review of tax items. As Recorded Fair Value As Recorded As of August 16, 2018 by Northwest Adjustments by the Company Assets acquired: Cash and cash equivalents $ 31.2 $ — $ 31.2 Investment securities 3.1 — 3.1 Loans held for investment 727.9 (14.8 ) (1) 713.1 Allowance for loan loss (8.0 ) 8.0 (2) — Premises and equipment 14.5 — 14.5 Other real estate owned (“OREO”) 0.3 0.3 0.6 Core deposit intangible assets 2.4 13.3 (3) 15.7 Other assets 29.3 (10.0 ) (4) 19.3 Total assets acquired 800.7 (3.2 ) 797.5 Liabilities assumed: Deposits 696.1 0.2 (5) 696.3 Accounts payable and accrued expense 8.1 (0.4 ) (6) 7.7 Long term debt 13.0 0.1 13.1 Trust preferred securities 5.2 (0.8 ) (7) 4.4 Deferred tax liability, net (1.2 ) 1.6 (8) 0.4 Total liabilities assumed 721.2 0.7 721.9 Net assets acquired $ 79.5 $ (3.9 ) $ 75.6 Consideration paid: Cash $ 3.0 Class A common stock 173.3 Total consideration paid 176.3 Goodwill $ 100.7 Explanation of fair value adjustments and the removal of previously recorded fair value marks recorded by Northwest. Note adjustments to the marks for deferred tax assets and premises and equipment were made since the prior quarter, none of which were material. The adjustments had no impact on 2018 earnings and a net decrease to goodwill of $0.4 million from the December 31, 2018 reported balances. (1) Write down of the book value of loans to their estimated fair values. The fair value of the loans was estimated using cash flow projections based on the remaining maturity and repricing terms, adjusted for estimated future credit losses and prepayments and discounted to present value using a risk-adjusted market rate for similar loans. The fair value of collateral dependent loans acquired with deteriorated credit quality was estimated based on the Company’s analysis of the fair value of each loan’s underlying collateral, discounted using market-derived rates of return with consideration given to the period of time and costs associated with foreclosure and disposition of the collateral. (2) Adjustment to remove the Northwest allowance for loan losses at acquisition date, as the credit risk is included in the fair value adjustment for loans receivable described in (1) above. (3) Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm. (4) Adjustment consists of reductions to the fair value of other items, including the removal of Northwest previously recorded goodwill. (5) Increase in book value of time deposits to their estimated fair values based upon interest rates of similar time deposits with similar terms on the date of acquisition based upon valuation from an independent accounting and advisory firm. (6) Decrease due to the write-off of off balance sheet reserves. (7) Write down of the book value of debt to the estimated fair values on the date of acquisition based upon favorable interest rates in the market. (8) Adjustment consists of the write-off of pre-existing deferred tax assets and purchase accounting adjustments as a result of the acquisition.
Schedule of Acquired Loans with Credit Impairment	Contractually required principal and interest payments $ 27.5 Contractual cash flows not expected to be collected (“non-accretable discount”) 4.4 Cash flows expected to be collected 23.1 Interest component of cash flows expected to be collected (“accretable discount”) 3.2 Fair value of acquired credit-impaired loans $ 19.9 The following table displays the outstanding unpaid balances and accrual status of loans acquired with credit impairment as of the dates indicated: March 31, 2019 December 31, 2018 Outstanding balance $ 40.9 $ 43.4 Carrying value Loans on accrual status 28.0 30.2 Total carrying value $ 28.0 $ 30.2 The following table summarizes changes in the accretable yield for loans acquired deemed credit impaired for the three month periods ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 2018 Beginning balance $ 8.9 $ 7.3 Accretion income (0.7 ) (0.7 ) Reductions due to exit events (0.3 ) (0.2 ) Reclassifications from non-accretable differences 0.5 0.8 Ending balance $ 8.4 $ 7.2
Schedule of Acquired Loans not Deemed to Have Credit Impairment	Information regarding Northwest acquired loans not deemed credit-impaired at the August 16, 2018 acquisition date are as follows: Contractually required principal and interest payments $ 894.8 Contractual cash flows not expected to be collected 26.1 Fair value at acquisition $ 693.2
Summary of Pre-tax Merger Related Expenses	The Company recorded $2.3 million and $2.3 million in pre-tax acquisition related expenses for the three months ended March 31, 2019 and 2018 . These costs are incorporated in non-interest expenses in the Company’s consolidated statements of income. Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Legal and Professional Fees $ 0.3 $ 0.5 Employee Expenses 0.6 0.1 Technology Conversion and Contract Termination 0.8 1.5 Other 0.6 0.2 Total Acquisition Related Expenses $ 2.3 $ 2.3

Goodwill and Intangibles (Table

Goodwill and Intangibles (Tables)	3 Months Ended
	Mar. 31, 2019
Goodwill [Line Items]
Schedule of Goodwill [Table Text Block]	As of March 31, 2019 2018 Net carrying value at beginning of three month period $ 546.7 $ 444.7 Measurement period adjustment to previously recorded goodwill (0.4 ) 0.9 Net carrying value at end of period $ 546.3 $ 445.6
Schedule of Finite-Lived Intangible Assets	As of March 31, 2019 2018 Gross CDI, beginning of period $ 89.7 $ 74.0 Accumulated amortization (35.1 ) (26.7 ) Net CDI, end of period $ 54.6 $ 47.3
Schedule of Future Amortization Expense	The following table provides the estimated future CDI amortization expense: Years Ending December 31, 2019 remaining $ 6.6 2020 8.1 2021 7.5 2022 6.9 2023 6.3 Thereafter 19.2 Total $ 54.6

Investment Securities (Tables)

Investment Securities (Tables)	3 Months Ended
	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Amortized Cost and Approximate Fair Values of Investment Securities	The amortized cost and approximate fair values of investment securities are summarized as follows: March 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale: U.S. Treasury notes $ 4.0 $ — $ — $ 4.0 State, county and municipal securities 77.7 0.8 (0.1 ) 78.4 Obligations of U.S. government agencies 601.4 0.3 (4.0 ) 597.7 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 1,735.9 9.4 (12.4 ) 1,732.9 Private mortgage-backed securities 66.2 — (0.9 ) 65.3 Corporate securities 92.1 0.2 (0.3 ) 92.0 Other investments 1.7 — — 1.7 Total $ 2,579.0 $ 10.7 $ (17.7 ) $ 2,572.0 March 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to-Maturity: State, county and municipal securities $ 67.6 $ 1.5 $ (0.2 ) $ 68.9 Obligations of U.S. government agencies 19.8 — (0.2 ) 19.6 U.S agency residential mortgage-backed securities & collateralized mortgage obligations 1.3 — — 1.3 Corporate securities 28.2 — (0.1 ) 28.1 Other investments 0.1 — — 0.1 Total $ 117.0 $ 1.5 $ (0.5 ) $ 118.0 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale: U.S. Treasury notes $ 2.6 $ — $ — $ 2.6 Obligations of U.S. government agencies 569.3 0.1 (10.2 ) 559.2 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 1,566.4 2.5 (24.1 ) 1,544.8 Private mortgage-backed securities 72.0 — (1.8 ) 70.2 Corporate securities 92.9 — (1.0 ) 91.9 Other investments 2.0 — — 2.0 Total $ 2,305.2 $ 2.6 $ (37.1 ) $ 2,270.7 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to-Maturity: State, county and municipal securities $ 150.9 $ 1.8 $ (0.9 ) $ 151.8 Obligations of U.S. government agencies 19.8 — (0.3 ) 19.5 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 189.7 0.3 (6.5 ) 183.5 Corporate securities 46.3 0.1 (0.6 ) 45.8 Other investments 0.1 — — 0.1 Total $ 406.8 $ 2.2 $ (8.3 ) $ 400.7
Gross Unrealized Losses and Fair Values of Investment Securities	The following tables show the gross unrealized losses and fair values of investment securities, aggregated by investment category, and the length of time individual investment securities have been in a continuous unrealized loss position, as of March 31, 2019 and December 31, 2018 : Less than 12 Months 12 Months or More Total March 31, 2019 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale: State, county and municipal securities $ — $ — $ 16.2 $ (0.1 ) $ 16.2 $ (0.1 ) Obligations of U.S. government agencies 336.8 (2.8 ) 129.7 (1.2 ) 466.5 (4.0 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 535.9 (6.9 ) 450.3 (5.5 ) 986.2 (12.4 ) Private mortgage-backed securities — — 64.5 (0.9 ) 64.5 (0.9 ) Corporate securities — — 36.9 (0.3 ) 36.9 (0.3 ) Total $ 872.7 $ (9.7 ) $ 697.6 $ (8.0 ) $ 1,570.3 $ (17.7 ) Less than 12 Months 12 Months or More Total March 31, 2019 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity: State, county and municipal securities $ 9.0 $ (0.1 ) $ 16.6 $ (0.1 ) $ 25.6 $ (0.2 ) Obligations of U.S. government agencies 19.6 (0.2 ) — — 19.6 (0.2 ) Corporate securities — — 28.0 (0.1 ) 28.0 (0.1 ) Total $ 28.6 $ (0.3 ) $ 44.6 $ (0.2 ) $ 73.2 $ (0.5 ) Less than 12 Months 12 Months or More Total December 31, 2018 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale: Obligations of U.S. government agencies $ 363.1 $ (7.9 ) $ 154.5 $ (2.3 ) $ 517.6 $ (10.2 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 735.2 (14.5 ) 503.7 (9.6 ) 1,238.9 (24.1 ) Private mortgage-backed securities — — 69.4 (1.8 ) 69.4 (1.8 ) Corporate securities 24.9 (0.2 ) 51.4 (0.8 ) 76.3 (1.0 ) Total $ 1,123.2 $ (22.6 ) $ 779.0 $ (14.5 ) $ 1,902.2 $ (37.1 ) Less than 12 Months 12 Months or More Total December 31, 2018 Fair Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity: State, county and municipal securities $ 25.9 $ (0.3 ) $ 57.1 $ (0.6 ) $ 83.0 $ (0.9 ) Obligations of U.S. government agencies 19.5 (0.3 ) — — 19.5 (0.3 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 45.0 (2.2 ) 120.2 (4.3 ) 165.2 (6.5 ) Corporate securities — — 39.6 (0.6 ) 39.6 (0.6 ) Total $ 90.4 $ (2.8 ) $ 216.9 $ (5.5 ) $ 307.3 $ (8.3 )
Maturities of Investment Securities	Maturities of investment securities at March 31, 2019 are shown below. Maturities of mortgage-backed securities have been adjusted to reflect shorter maturities based upon estimated prepayments of principal. All other investment securities maturities are shown at contractual maturity dates. Available-for-Sale Held-to-Maturity March 31, 2019 Amortized Cost Estimated Fair Value Amortized Cost Estimated Fair Value Within one year $ 497.2 $ 496.0 $ 44.9 $ 44.8 After one year but within five years 1,509.8 1,504.9 44.2 44.1 After five years but within ten years 395.3 395.5 24.3 25.5 After ten years 176.7 175.6 3.6 3.6 Total $ 2,579.0 $ 2,572.0 $ 117.0 $ 118.0

Loans (Tables)

Loans (Tables)	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Schedule of Loans by Class	The following table presents loans by class as of the dates indicated: March 31, December 31, Real estate loans: Commercial $ 3,255.8 $ 3,235.4 Construction: Land acquisition & development 292.7 321.6 Residential 233.1 242.8 Commercial 312.1 274.3 Total construction loans 837.9 838.7 Residential 1,529.5 1,542.0 Agricultural 210.4 217.4 Total real estate loans 5,833.6 5,833.5 Consumer: Indirect consumer 775.7 787.8 Other consumer 194.1 200.6 Credit card 77.2 81.8 Total consumer loans 1,047.0 1,070.2 Commercial 1,342.1 1,310.3 Agricultural 234.7 254.8 Other, including overdrafts 1.8 1.6 Loans held for investment 8,459.2 8,470.4 Mortgage loans held for sale 34.0 33.3 Total loans $ 8,493.2 $ 8,503.7
Schedule of Recorded Investment in Past Due Loans by Class	The following tables present the Company’s recorded investment and contractual aging of the Company’s recorded investment in loans by class as of the dates indicated. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of March 31, 2019 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 12.6 $ 7.2 $ 2.5 $ 22.3 $ 3,222.4 $ 11.1 $ 3,255.8 Construction: Land acquisition & development 1.2 0.7 0.4 2.3 286.6 3.8 292.7 Residential 2.2 — — 2.2 229.6 1.3 233.1 Commercial — — — — 311.9 0.2 312.1 Total construction loans 3.4 0.7 0.4 4.5 828.1 5.3 837.9 Residential 4.6 1.6 0.2 6.4 1,517.2 5.9 1,529.5 Agricultural 4.0 0.9 0.3 5.2 202.8 2.4 210.4 Total real estate loans 24.6 10.4 3.4 38.4 5,770.5 24.7 5,833.6 Consumer: Indirect consumer 6.5 1.1 0.5 8.1 765.6 2.0 775.7 Other consumer 1.4 0.7 0.3 2.4 191.2 0.5 194.1 Credit card 0.6 0.5 0.7 1.8 75.4 — 77.2 Total consumer loans 8.5 2.3 1.5 12.3 1,032.2 2.5 1,047.0 Commercial 4.0 4.1 1.7 9.8 1,317.0 15.3 1,342.1 Agricultural 1.3 1.3 0.5 3.1 229.0 2.6 234.7 Other, including overdrafts — — — — 1.8 — 1.8 Loans held for investment 38.4 18.1 7.1 63.6 8,350.5 45.1 8,459.2 Mortgage loans originated for sale — — — — 34.0 — 34.0 Total loans $ 38.4 $ 18.1 $ 7.1 $ 63.6 $ 8,384.5 $ 45.1 $ 8,493.2 Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of December 31, 2018 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 10.4 $ 1.0 $ 0.8 $ 12.2 $ 3,214.0 $ 9.2 $ 3,235.4 Construction: Land acquisition & development 1.6 0.1 0.2 1.9 316.0 3.7 321.6 Residential 1.0 0.4 — 1.4 240.4 1.0 242.8 Commercial 0.4 — — 0.4 273.7 0.2 274.3 Total construction loans 3.0 0.5 0.2 3.7 830.1 4.9 838.7 Residential 8.8 1.1 0.2 10.1 1,525.3 6.6 1,542.0 Agricultural 2.2 — — 2.2 202.6 12.6 217.4 Total real estate loans 24.4 2.6 1.2 28.2 5,772.0 33.3 5,833.5 Consumer: Indirect consumer 6.8 2.1 0.4 9.3 776.8 1.7 787.8 Other consumer 1.4 0.5 0.1 2.0 198.1 0.5 200.6 Credit card 0.9 0.4 0.8 2.1 79.7 — 81.8 Total consumer loans 9.1 3.0 1.3 13.4 1,054.6 2.2 1,070.2 Commercial 8.3 1.2 1.3 10.8 1,283.7 15.8 1,310.3 Agricultural 2.1 0.3 — 2.4 249.4 3.0 254.8 Other, including overdrafts — — — — 1.6 — 1.6 Loans held for investment 43.9 7.1 3.8 54.8 8,361.3 54.3 8,470.4 Mortgage loans originated for sale — — — — 33.3 — 33.3 Total loans $ 43.9 $ 7.1 $ 3.8 $ 54.8 $ 8,394.6 $ 54.3 $ 8,503.7
Schedule of Acquired Loans with Credit Impairment	Contractually required principal and interest payments $ 27.5 Contractual cash flows not expected to be collected (“non-accretable discount”) 4.4 Cash flows expected to be collected 23.1 Interest component of cash flows expected to be collected (“accretable discount”) 3.2 Fair value of acquired credit-impaired loans $ 19.9 The following table displays the outstanding unpaid balances and accrual status of loans acquired with credit impairment as of the dates indicated: March 31, 2019 December 31, 2018 Outstanding balance $ 40.9 $ 43.4 Carrying value Loans on accrual status 28.0 30.2 Total carrying value $ 28.0 $ 30.2 The following table summarizes changes in the accretable yield for loans acquired deemed credit impaired for the three month periods ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 2018 Beginning balance $ 8.9 $ 7.3 Accretion income (0.7 ) (0.7 ) Reductions due to exit events (0.3 ) (0.2 ) Reclassifications from non-accretable differences 0.5 0.8 Ending balance $ 8.4 $ 7.2
Schedule of Recorded Investment in Impaired Loans	The following tables present information on the Company’s recorded investment in impaired loans as of the dates indicated: As of March 31, 2019 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 27.0 $ 10.7 $ 10.6 $ 21.3 $ 0.7 Construction: Land acquisition & development 10.0 0.4 3.4 3.8 0.3 Residential 1.5 0.9 0.4 1.3 — Commercial 0.6 0.1 — 0.1 — Total construction loans 12.1 1.4 3.8 5.2 0.3 Residential 8.9 4.2 3.3 7.5 0.5 Agricultural 2.7 2.4 0.2 2.6 — Total real estate loans 50.7 18.7 17.9 36.6 1.5 Commercial 24.3 5.8 14.0 19.8 5.1 Agricultural 5.0 1.6 3.2 4.8 0.5 Total $ 80.0 $ 26.1 $ 35.1 $ 61.2 $ 7.1 As of December 31, 2018 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 22.2 $ 8.6 $ 7.7 $ 16.3 $ 0.7 Construction: Land acquisition & development 10.0 0.4 3.5 3.9 0.2 Residential 1.1 0.6 0.4 1.0 0.1 Commercial 0.7 0.2 — 0.2 — Total construction loans 11.8 1.2 3.9 5.1 0.3 Residential 8.8 5.7 2.0 7.7 0.3 Agricultural 12.9 12.5 0.2 12.7 — Total real estate loans 55.7 28.0 13.8 41.8 1.3 Commercial 24.1 5.5 14.4 19.9 5.2 Agricultural 3.2 2.5 0.6 3.1 0.3 Total $ 83.0 $ 36.0 $ 28.8 $ 64.8 $ 6.8 The following table presents the average recorded investment in and income recognized on impaired loans for the periods indicated: Three Months Ended March 31, 2019 2018 Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Real estate $ 39.3 $ — $ 56.1 $ — Commercial 19.9 — 22.1 — Agricultural 3.9 — 1.5 — Total $ 63.1 $ — $ 79.7 $ —
Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator	The following tables present the Company’s recorded investment in criticized loans by class and credit quality indicator based on the most recent analysis performed as of the dates indicated: As of March 31, 2019 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 100.4 $ 90.9 $ 2.8 $ 194.1 Construction: Land acquisition & development 5.1 2.2 3.4 10.7 Residential 0.9 2.2 0.9 4.0 Commercial 1.8 4.1 — 5.9 Total construction loans 7.8 8.5 4.3 20.6 Residential 2.6 8.9 1.9 13.4 Agricultural 15.7 18.0 0.1 33.8 Total real estate loans 126.5 126.3 9.1 261.9 Consumer: Indirect consumer 0.3 2.7 0.1 3.1 Direct consumer 0.3 0.8 0.1 1.2 Total consumer loans 0.6 3.5 0.2 4.3 Commercial 42.3 46.5 11.3 100.1 Agricultural 16.8 18.3 1.1 36.2 Total $ 186.2 $ 194.6 $ 21.7 $ 402.5 As of December 31, 2018 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 102.5 $ 87.4 $ 2.9 $ 192.8 Construction: Land acquisition & development 5.0 7.0 3.3 15.3 Residential 2.8 2.0 0.4 5.2 Commercial 1.7 3.9 — 5.6 Total construction loans 9.5 12.9 3.7 26.1 Residential 3.0 10.8 0.7 14.5 Agricultural 9.0 24.0 0.1 33.1 Total real estate loans 124.0 135.1 7.4 266.5 Consumer: Indirect consumer 0.7 2.1 0.1 2.9 Direct consumer 0.3 0.8 0.1 1.2 Total consumer loans 1.0 2.9 0.2 4.1 Commercial 39.4 45.8 11.8 97.0 Agricultural 14.4 17.8 1.5 33.7 Total $ 178.8 $ 201.6 $ 20.9 $ 401.3

Allowance for Loan Losses (Tabl

Allowance for Loan Losses (Tables)	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Schedule of Allowance for Loan Losses by Portfolio Segment	The following tables present a summary of changes in the allowance for loan losses by portfolio segment for the periods indicated: Three Months Ended March 31, 2019 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 31.0 $ 8.7 $ 31.3 $ 2.0 $ — $ 73.0 Provision charged to operating expense (1.7 ) 2.0 3.6 (0.2 ) — 3.7 Less loans charged-off (2.1 ) (3.0 ) (0.8 ) (0.1 ) — (6.0 ) Add back recoveries of loans previously charged-off 0.2 1.1 0.4 — — 1.7 Ending balance $ 27.4 $ 8.8 $ 34.5 $ 1.7 $ — $ 72.4 As of March 31, 2019 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Loans individually evaluated for impairment $ 1.5 $ — $ 5.1 $ 0.5 $ — $ 7.1 Loans collectively evaluated for impairment 25.9 8.8 29.4 1.2 — 65.3 Allowance for loan losses $ 27.4 $ 8.8 $ 34.5 $ 1.7 $ — $ 72.4 As of March 31, 2019 Real Estate Consumer Commercial Agriculture Other Total Loans held for investment: Individually evaluated for impairment $ 36.6 $ — $ 19.8 $ 4.8 $ — $ 61.2 Collectively evaluated for impairment 5,797.0 1,047.0 1,322.3 229.9 1.8 8,398.0 Total loans held for investment $ 5,833.6 $ 1,047.0 $ 1,342.1 $ 234.7 $ 1.8 $ 8,459.2 Three Months Ended March 31, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 31.7 $ 8.7 $ 30.5 $ 1.2 $ — $ 72.1 Provision charged to operating expense 1.8 0.7 (0.7 ) 0.3 — 2.1 Less loans charged-off (0.8 ) (2.7 ) (1.7 ) — — (5.2 ) Add back recoveries of loans previously charged-off 1.2 1.1 2.0 0.2 — 4.5 Ending balance $ 33.9 $ 7.8 $ 30.1 $ 1.7 $ — $ 73.5 As of December 31, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Loans individually evaluated for impairment $ 1.3 $ — $ 5.2 $ 0.3 $ — $ 6.8 Loans collectively evaluated for impairment 29.7 8.7 26.1 1.7 — 66.2 Allowance for loan losses $ 31.0 $ 8.7 $ 31.3 $ 2.0 $ — $ 73.0 As of December 31, 2018 Real Estate Consumer Commercial Agriculture Other Total Loans held for investment: Individually evaluated for impairment $ 41.8 $ — $ 19.9 $ 3.1 $ — $ 64.8 Collectively evaluated for impairment 5,791.7 1,070.2 1,290.4 251.7 1.6 8,405.6 Total loans held for investment $ 5,833.5 $ 1,070.2 $ 1,310.3 $ 254.8 $ 1.6 $ 8,470.4

Other Real Estate Owned (Tables

Other Real Estate Owned (Tables)	3 Months Ended
	Mar. 31, 2019
Repossessed Assets [Abstract]
Other Real Estate Owned Roll Forward	Information with respect to the Company’s other real estate owned follows: Three Months Ended March 31, 2019 2018 Beginning balance $ 14.4 $ 10.1 Additions 8.4 1.2 Valuation adjustments (0.3 ) — Dispositions (1.4 ) (0.3 ) Ending balance $ 21.1 $ 11.0

Derivatives and Hedging Activ_2

Derivatives and Hedging Activities (Tables)	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amounts and Estimated Fair Values of Derivatives	The notional amounts and estimated fair values of the Company’s derivatives are presented in the following table. Fair value estimates are obtained from third parties and are based on pricing models. March 31, 2019 December 31, 2018 Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Derivative Assets (included in other assets on the consolidated balance sheets): Non-hedging interest rate derivatives: Interest rate swap contracts $ 449.2 $ 12.7 $ 403.3 $ 8.8 Interest rate lock commitments 76.9 1.9 51.0 1.3 Total derivative assets $ 526.1 $ 14.6 $ 454.3 $ 10.1 Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets): Non-hedging interest rate derivatives: Interest rate swap contracts $ 449.2 $ 12.7 $ 403.3 $ 8.8 Forward loan sales contracts 90.4 0.8 64.6 0.6 Total derivative liabilities $ 539.6 $ 13.5 $ 467.9 $ 9.4
Offsetting Assets and Liabilities	The following table illustrates the potential effect of the Company’s master netting arrangements, by type of financial instrument, on the Company’s consolidated balance sheets as of March 31, 2019 and December 31, 2018 : March 31, 2019 Gross Amounts Recognized Gross Amounts Offset in the Balance Sheet Net Amounts in the Balance Sheet Financial Instruments Fair Value of Financial Collateral in the Balance Sheet Net Amount Financial Assets Interest rate swap contracts $ 12.7 $ — $ 12.7 $ 2.0 $ 7.5 $ 3.2 Mortgage related derivatives 1.9 — 1.9 — — 1.9 Total derivatives 14.6 — 14.6 2.0 7.5 5.1 Total assets $ 14.6 $ — $ 14.6 $ 2.0 $ 7.5 $ 5.1 Financial Liabilities Interest rate swap contracts $ 12.7 $ — $ 12.7 $ 2.0 $ 0.2 $ 10.5 Mortgage related derivatives 0.8 — 0.8 — — 0.8 Total derivatives 13.5 — 13.5 2.0 0.2 11.3 Repurchase agreements 672.6 — 672.6 — 672.6 — Total liabilities $ 686.1 $ — $ 686.1 $ 2.0 $ 672.8 $ 11.3 December 31, 2018 Gross Amounts Recognized Gross Amounts Offset in the Balance Sheet Net Amounts in the Balance Sheet Financial Instruments Fair Value of Financial Collateral in the Balance Sheet Net Amount Financial Assets Interest rate swap contracts $ 8.8 $ — $ 8.8 $ 2.7 $ 2.4 $ 3.7 Mortgage related derivatives 1.3 — 1.3 — — 1.3 Total derivatives 10.1 — 10.1 2.7 2.4 5.0 Total assets $ 10.1 $ — $ 10.1 $ 2.7 $ 2.4 $ 5.0 Financial Liabilities Interest rate swap contracts $ 8.8 $ — $ 8.8 $ 2.7 $ 4.1 $ 2.0 Mortgage related derivatives 0.6 — 0.6 — — 0.6 Total derivatives 9.4 — 9.4 2.7 4.1 2.6 Repurchase agreements 712.4 — 712.4 — 712.4 — Total liabilities $ 721.8 $ — $ 721.8 $ 2.7 $ 716.5 $ 2.6
Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss)	The following table presents the pre-tax gains or losses related to derivative contracts that were recorded in other non-interest income in the Company’s statements of income for the periods indicated: Three Months Ended March 31, 2019 2018 Non-hedging interest rate derivatives: Amount of gain recognized in other non-interest income $ — $ 0.3 Amount of net fee income recognized in other non-interest income 0.8 0.5 Amount of net gains recognized in mortgage banking revenues 0.4 (0.1 )

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Computation of Basic and Diluted Earnings per Share	The following table sets forth the computation of basic and diluted earnings per share for the three month periods ended March 31, 2019 and 2018 : Three Months Ended March 31, 2019 2018 Net income $ 41.6 $ 36.7 Weighted average common shares outstanding for basic earnings per share computation 60,311,171 56,241,201 Dilutive effects of stock-based compensation 286,899 410,977 Weighted average common shares outstanding for diluted earnings per common share computation 60,598,070 56,652,178 Basic earnings per common share $ 0.69 $ 0.65 Diluted earnings per common share $ 0.69 $ 0.65 Anti-dilutive unvested time restricted stock 121,452 139,943

Regulatory Capital (Tables)

Regulatory Capital (Tables)	3 Months Ended
	Mar. 31, 2019
Banking and Thrift [Abstract]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations	Actual capital amounts and ratios for the Company and its subsidiary Bank, as of March 31, 2019 and December 31, 2018 are presented in the following tables: Actual Minimum Required for Capital Adequacy Purposes For Capital Adequacy Purposes Plus Capital Conservation Buffer Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements(1) March 31, 2019 Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total risk-based capital: Consolidated $ 1,310.3 13.23 % $ 792.4 8.000 % $ 1,040.0 10.50 % $ 990.5 10.00 % FIB 1,201.4 12.16 790.2 8.000 1,037.1 10.50 987.8 10.00 Tier 1 risk-based capital: Consolidated 1,237.9 12.50 594.3 6.000 841.9 8.50 792.4 8.00 FIB 1,129.0 11.43 592.7 6.000 839.6 8.50 790.2 8.00 Common equity tier 1 risk-based capital: Consolidated 1,153.7 11.65 445.7 4.500 693.4 7.00 643.8 6.50 FIB 1,129.0 11.43 444.5 4.500 691.4 7.00 642.0 6.50 Leverage capital ratio: Consolidated 1,237.9 9.76 507.5 4.000 507.5 4.00 634.4 5.00 FIB 1,129.0 8.92 506.3 4.000 506.3 4.00 632.8 5.00 Actual Minimum Required for Capital Adequacy Purposes For Capital Adequacy Purposes Plus Capital Conservation Buffer Minimum to Be Well Capitalized Under Prompt Corrective Action Requirements(1) December 31, 2018 Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total risk-based capital: Consolidated $ 1,285.0 12.99 % $ 791.2 8.00 % $ 976.6 9.875 % $ 989.0 10.00 % FIB 1,184.5 12.01 788.8 8.00 973.7 9.875 986.0 10.00 Tier 1 risk-based capital: Consolidated 1,212.0 12.26 593.4 6.00 778.8 7.875 791.2 8.00 FIB 1,111.6 11.27 591.6 6.00 776.5 7.875 788.8 8.00 Common equity tier 1 risk-based capital: Consolidated 1,127.8 11.40 445.0 4.50 630.5 6.375 642.8 6.50 FIB 1,111.6 11.27 443.7 4.50 628.6 6.375 640.9 6.50 Leverage capital ratio: Consolidated 1,212.0 9.47 511.9 4.00 511.9 4.000 639.9 5.00 FIB 1,111.6 8.97 495.9 4.00 495.9 4.000 619.8 5.00 (1) The ratios for the requirements to be deemed “well capitalized” are only applicable to FIB. However, the Company manages its capital position as if the requirements apply to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis.

Other Comprehensive Income_Lo_2

Other Comprehensive Income/Loss (Tables)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Schedule of Comprehensive Income (Loss)	The gross amounts of each component of other comprehensive income and the related tax effects are as follows: Pre-tax Tax Expense (Benefit) Net of Tax Three Months Ended March 31, 2019 2018 2019 2018 2019 2018 Investment securities available-for sale: Change in net unrealized gains during period $ 33.6 $ (23.7 ) $ 8.8 $ (6.2 ) $ 24.8 $ (17.5 ) Reclassification adjustment for securities transferred from held-to-maturity to available-for-sale (6.0 ) — (1.6 ) — (4.4 ) — Change in unamortized loss on available-for-sale securities transferred into held-to-maturity — 0.5 — 0.2 — 0.3 Defined benefits post-retirement benefit plan: Change in net actuarial (gain) loss (0.2 ) (0.1 ) — (0.1 ) (0.2 ) — Total other comprehensive income (loss) $ 27.4 $ (23.3 ) $ 7.2 $ (6.1 ) $ 20.2 $ (17.2 )
Schedule of Accumulated Other Comprehensive Income (Loss)	The components of accumulated other comprehensive loss, net of related tax effects, are as follows: March 31, 2019 December 31, 2018 Net unrealized gain (loss) on investment securities available-for-sale $ (5.1 ) $ (25.5 ) Net actuarial gain (loss) on defined benefit post-retirement benefit plans 0.7 0.9 Net accumulated other comprehensive gain (loss) $ (4.4 ) $ (24.6 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis	Financial assets and liabilities measured at fair value on a recurring basis are as follows: Fair Value Measurements at Reporting Date Using As of March 31, 2019 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Investment debt securities available-for-sale: U.S. Treasury Notes $ 4.0 $ — $ 4.0 $ — State, county and municipal securities 78.4 — 78.4 — Obligations of U.S. government agencies 597.7 — 597.7 — U.S. agencies mortgage-backed securities & collateralized mortgage obligations 1,732.9 — 1,732.9 — Private mortgage-backed securities 65.3 — 65.3 — Corporate securities 92.0 — 92.0 — Other investments 1.7 — 1.7 — Loans held for sale 34.0 — 34.0 — Derivative assets: Interest rate swap contracts 12.7 — 12.7 — Interest rate lock commitments 1.9 — 1.9 — Derivative liabilities: Interest rate swap contracts 12.7 — 12.7 — Forward loan sale contracts 0.8 — 0.8 — Deferred compensation plan assets 12.4 — 12.4 — Deferred compensation plan liabilities $ 12.4 $ — $ 12.4 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2018 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Investment debt securities available-for-sale: U.S. Treasury notes $ 2.6 $ — $ 2.6 $ — Obligations of U.S. government agencies 559.2 — 559.2 — U.S. agencies mortgage-backed securities & collateralized mortgage obligations 1,544.8 — 1,544.8 — Private mortgage-backed securities 70.2 — 70.2 — Corporate securities 91.9 — 91.9 — Other investments 2.0 — 2.0 — Loans held for sale 33.3 — 33.3 — Derivative assets: Interest rate swap contracts 8.8 — 8.8 — Interest rate lock commitments 1.3 — 1.3 — Derivative liabilities Interest rate swap contracts 8.8 — 8.8 — Forward loan sales contracts 0.6 — 0.6 — Deferred compensation plan assets 12.1 — 12.1 — Deferred compensation plan liabilities $ 12.1 $ — $ 12.1 $ —
Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Non-Recurring Basis	The following table presents information about the Company’s assets and liabilities measured at fair value on a non-recurring basis: Fair Value Measurements at Reporting Date Using As of March 31, 2019 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Impaired loans $ 30.9 $ — $ — $ 30.9 Other real estate owned 2.0 — — 2.0 Long-lived assets to be disposed of by sale $ 5.5 $ — $ — $ 5.5 Fair Value Measurements at Reporting Date Using As of December 31, 2018 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Impaired loans $ 24.1 $ — $ — $ 24.1 Other real estate owned 0.6 — — 0.6 Long-lived assets to be disposed of by sale $ 4.9 $ — $ — $ 4.9
Fair Value Inputs, Assets, Quantitative Information	The following table presents additional quantitative information about assets measured at fair value on a non-recurring basis and for which the Company has utilized Level 3 inputs to determine fair values: Fair Value As of March 31, 2019 December 31, 2018 Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 30.9 $ 24.1 Appraisal Appraisal adjustment 0% - 26% (13%) Other real estate owned 2.0 0.6 Appraisal Appraisal adjustment 8% - 96% (39%) Long-lived assets to be disposed of by sale $ 5.5 $ 4.9 Appraisal Appraisal adjustment 0% - 43% (10%)
Fair Value, by Balance Sheet Grouping	The estimated fair values of financial instruments that are reported in the Company’s consolidated balance sheets, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value, are as follows: Fair Value Measurements at Reporting Date Using As of March 31, 2019 Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets: Cash and cash equivalents $ 955.2 $ 955.2 $ 955.2 $ — $ — Investment debt securities available-for-sale 2,572.0 2,572.0 — 2,572.0 — Investment debt securities held-to-maturity 117.0 118.0 — 118.0 — Accrued interest receivable 46.5 46.5 — 46.5 — Mortgage servicing rights, net 27.9 40.5 — 40.5 — Loans held for sale 34.0 34.0 — 34.0 — Net loans held for investment 8,386.8 8,408.6 — 8,377.7 30.9 Derivative assets 14.6 14.6 — 14.6 — Deferred compensation plan assets 12.4 12.4 — 12.4 — Total financial assets $ 12,166.4 $ 12,201.8 $ 955.2 $ 11,215.7 $ 30.9 Financial liabilities: Total deposits, excluding time deposits $ 9,408.3 $ 9,408.3 $ 9,408.3 $ — $ — Time deposits 1,406.4 1,393.2 — 1,393.2 — Securities sold under repurchase agreements 672.6 672.6 — 672.6 — Accrued interest payable 10.0 10.0 — 10.0 — Long-term debt 15.8 13.9 — 13.9 — Subordinated debentures held by subsidiary trusts 86.9 85.1 — 85.1 — Derivative liabilities 13.5 13.5 — 13.5 — Deferred compensation plan liabilities 12.4 12.4 — 12.4 — Total financial liabilities $ 11,625.9 $ 11,609.0 $ 9,408.3 $ 2,200.7 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2018 Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets: Cash and cash equivalents $ 822.0 $ 822.0 $ 822.0 $ — $ — Investment debt securities available-for-sale 2,270.7 2,270.7 — 2,270.7 — Investment debt securities held-to-maturity 406.8 400.7 — 400.7 — Accrued interest receivable 44.9 44.9 — 44.9 — Mortgage servicing rights, net 27.7 42.4 — 42.4 — Loans held for sale 33.3 33.3 — 33.3 — Net loans held for investment 8,397.4 8,439.7 — 8,415.6 24.1 Derivative assets 10.1 10.1 — 10.1 — Deferred compensation plan assets 12.1 12.1 — 12.1 — Total financial assets $ 12,025.0 $ 12,075.9 $ 822.0 $ 11,229.8 $ 24.1 Financial liabilities: Total deposits, excluding time deposits $ 9,363.7 $ 9,363.7 $ 9,363.7 $ — $ — Time deposits 1,317.0 1,299.0 — 1,299.0 — Securities sold under repurchase agreements 712.4 712.4 — 712.4 — Accrued interest payable 7.8 7.8 — 7.8 — Long-term debt 15.8 13.0 — 13.0 — Subordinated debentures held by subsidiary trusts 86.9 84.9 — 84.9 — Derivative liabilities 9.4 9.4 — 9.4 — Deferred compensation plan liabilities 12.1 12.1 — 12.1 — Total financial liabilities $ 11,525.1 $ 11,502.3 $ 9,363.7 $ 2,138.6 $ —

Acquisitions - Business Combin

Acquisitions - Business Combination (Narrative) (Details) $ / shares in Units, $ in Millions	Apr. 08, 2019USD ($)$ / sharesshares	Aug. 16, 2018USD ($)$ / sharesshares	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Goodwill			$ 546.3	$ 445.6	$ 546.7	$ 444.7
Acquisition related expenses			2.3	2.3	$ 2.3
Net income			$ 41.6	$ 36.7
Core Deposits
Business Acquisition [Line Items]
Estimated useful lives of related deposits			10 years
Northwest Bank Acquisition, as Recorded by the Company [Member]
Business Acquisition [Line Items]
Core deposit intangible assets		$ 15.7
Cash paid by First Interstate in connection with merger		$ 3
Inland Northwest Bank
Business Acquisition [Line Items]
Number of banking offices acquired		20
Total consideration exchanged in connection with the merger		$ 176.3
Goodwill		$ 100.7
Number of Operating Segments | segment					1
Inland Northwest Bank | Class A Common Stock
Business Acquisition [Line Items]
Business acquisition conversion share rate | shares		0.516
Number of shares issued in connection with Cascade merger | shares		3,840,000
Price per share of First Interstate Class A common stock (in dollars per share) | $ / shares		$ 45.15
Inland Northwest Bank | Core Deposits
Business Acquisition [Line Items]
Estimated useful lives of related deposits		10 years
Subsequent Event | Idaho Independent Bank [Member]
Business Acquisition [Line Items]
Number of banking offices acquired	11
Cash paid by First Interstate in connection with merger	$ 157.3
Subsequent Event | Idaho Independent Bank [Member] | Class A Common Stock
Business Acquisition [Line Items]
Business acquisition conversion share rate | shares	0.5
Number of shares issued in connection with Cascade merger | shares	3,871,000
Price per share of First Interstate Class A common stock (in dollars per share) | $ / shares	$ 40.64
Subsequent Event | Community 1st Bank [Member]
Business Acquisition [Line Items]
Number of banking offices acquired	3
Cash paid by First Interstate in connection with merger	$ 18.8
Subsequent Event | Community 1st Bank [Member] | Class A Common Stock
Business Acquisition [Line Items]
Business acquisition conversion share rate | shares	0.3784
Number of shares issued in connection with Cascade merger | shares	463,000
Price per share of First Interstate Class A common stock (in dollars per share) | $ / shares	$ 40.64

Acquisitions - Schedule of Rec

Acquisitions - Schedule of Recognized Identifiable Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions		Aug. 16, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs			$ 2.3	$ 2.3	$ 2.3
Goodwill			546.3	445.6	$ 546.7	$ 444.7
Net increase to goodwill			(0.4)	$ 0.9
Northwest Bank Acquisition, As Recorded By Inland Northwest Bank [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		$ 31.2
Investment securities		3.1
Loans held for investment		727.9
Allowance for loan loss		(8)
Premises and equipment		14.5
Other real estate owned (“OREO”)		0.3
Core deposit intangible assets		2.4
Other assets		29.3
Total assets acquired		800.7
Deposits		696.1
Accounts Payable and Accrued Expense		8.1
Long term debt		13
Trust preferred securities		5.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Deferred Tax Liability		(1.2)
Total liabilities assumed		721.2
Net assets acquired		79.5
Northwest Bank Acquisition, Fair Value Adjustments [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		0
Investment securities		0
Loans held for investment	[1]	(14.8)
Allowance for loan loss	[2]	8
Premises and equipment		0
Other real estate owned (“OREO”)		0.3
Core deposit intangible assets	[3]	13.3
Other assets	[4]	(10)
Total assets acquired		(3.2)
Deposits	[5]	0.2
Accounts Payable and Accrued Expense	[6]	(0.4)
Long term debt		0.1
Trust preferred securities		(0.8)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Deferred Tax Liability	[7]	1.6
Total liabilities assumed		0.7
Net assets acquired		(3.9)
Northwest Bank Acquisition, as Recorded by the Company [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		31.2
Investment securities		3.1
Loans held for investment		713.1
Allowance for loan loss		0
Premises and equipment		14.5
Other real estate owned (“OREO”)		0.6
Core deposit intangible assets		15.7
Other assets		19.3
Total assets acquired		797.5
Deposits		696.3
Accounts Payable and Accrued Expense		7.7
Long term debt		13.1
Trust preferred securities		4.4
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Deferred Tax Liability		0.4
Total liabilities assumed		721.9
Net assets acquired		75.6
Cash		3
Class A common stock		173.3
Inland Northwest Bank
Business Acquisition [Line Items]
Total consideration paid		176.3
Goodwill		$ 100.7
Cascade Bank Acquisition, as Recorded by the Company [Member]
Business Acquisition [Line Items]
Net increase to goodwill			$ 0.9
[1]	(1) Write down of the book value of loans to their estimated fair values. The fair value of the loans was estimated using cash flow projections based on the remaining maturity and repricing terms, adjusted for estimated future credit losses and prepayments and discounted to present value using a risk-adjusted market rate for similar loans. The fair value of collateral dependent loans acquired with deteriorated credit quality was estimated based on the Company’s analysis of the fair value of each loan’s underlying collateral, discounted using market-derived rates of return with consideration given to the period of time and costs associated with foreclosure and disposition of the collateral.
[2]	(2) Adjustment to remove the Northwest allowance for loan losses at acquisition date, as the credit risk is included in the fair value adjustment for loans receivable described in (1) above.
[3]	(3) Write down of the book value of premises and equipment to their estimated fair values on the date of acquisition based upon broker’s opinion of value.
[4]	(4) Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm.
[5]	(6) Adjustment consists of reductions to the fair value of other items, including the removal of Northwest previously recorded goodwill.
[6]	(7) Increase in book value of time deposits to their estimated fair values based upon interest rates of similar time deposits with similar terms on the date of acquisition based upon valuation from an independent accounting and advisory firm.
[7]	(9) Write down of the book value of debt to the estimated fair values on the date of acquisition based upon favorable interest rates in the market.

Acquisitions - Schedule of Acq

Acquisitions - Schedule of Acquired loans with credit impairment (Details) - Inland Northwest Bank $ in Millions	Aug. 16, 2018USD ($)
Business Acquisition [Line Items]
Contractually required principal and interest payments	$ 27.5
Contractual cash flows not expected to be collected (“non-accretable discount”)	4.4
Cash flows expected to be collected	23.1
Interest component of cash flows expected to be collected (“accretable discount”)	3.2
Fair value of acquired credit-impaired loans	$ 19.9

Acquisitions - Schedule of A_2

Acquisitions - Schedule of Acquired Loans not Deemed to Have Credit Impairment (Details) - Inland Northwest Bank $ in Millions	Aug. 16, 2018USD ($)
Business Acquisition [Line Items]
Contractually required principal and interest payments	$ 894.8
Contractual cash flows not expected to be collected	26.1
Fair value at acquisition	$ 693.2

Acquisitions - Summary of Pre-

Acquisitions - Summary of Pre-tax Merger Related Costs (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs, Legal Fees	$ 0.3	$ 0.5
Business Combination, Acquisition Related Costs, Employee Expense	0.6	0.1
Business Combination, Acquisition Related Costs, Technology and Contract Termination	0.8	1.5
Business Combination, Acquisition Related Costs, Other Expenses	0.6	0.2
Acquisition related expenses	$ 2.3	$ 2.3	$ 2.3

Goodwill and Intangibles - Narr

Goodwill and Intangibles - Narrative (Details) $ in Millions	Aug. 16, 2018USD ($)	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)
Goodwill [Line Items]
Goodwill		$ 546.3	$ 445.6	$ 546.7	$ 444.7
Measurement period adjustment to previously recorded goodwill		$ (0.4)	$ 0.9
Inland Northwest Bank
Goodwill [Line Items]
Goodwill	$ 100.7
Number of Operating Segments | segment				1
Core Deposits
Goodwill [Line Items]
Weighted average useful lives of related deposits		10 years
Core Deposits | Inland Northwest Bank
Goodwill [Line Items]
Weighted average useful lives of related deposits	10 years

Goodwill and Intangibles - Sche

Goodwill and Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Gross CDI, beginning of period	$ 89.7	$ 74
Accumulated amortization	(35.1)	(26.7)
Net CDI, end of period	54.6	47.3
Goodwill [Roll Forward]
Net carrying value at beginning of three month period	546.7	444.7
Net increase to goodwill	(0.4)	0.9
Net carrying value at end of period	$ 546.3	$ 445.6

Goodwill and Intangibles - Sc_2

Goodwill and Intangibles - Schedule of Future Amortization Expense (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Total	$ 54.6	$ 47.3
Core Deposits
Finite-Lived Intangible Assets [Line Items]
2019 remaining	6.6
2018	8.1
2019	7.5
2020	6.9
2021	6.3
Thereafter	19.2
Total	$ 54.6

Investment Securities - Amorti

Investment Securities - Amortized Cost and Approximate Fair Values of Investment Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available for Sale and Held-to-Maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Transfer, Amount	$ 281,100
Debt Securities, Held-to-maturity, transfer, Fair value amount	275,000
Available-for-Sale:
Amortized Cost	2,579,000	$ 2,305,200
Gross Unrealized Gains	10,700	2,600
Gross Unrealized Losses	(17,700)	(37,100)
Estimated Fair Value	2,572,000	2,270,700
Held-to-Maturity:
Amortized Cost	117,000	406,800
Gross Unrealized Gains	1,500	2,200
Gross Unrealized Losses	(500)	(8,300)
Estimated Fair Value	118,000	400,700
Debt Securities, Held-to-maturity, Transfer, Derivative Hedge, Gain (Loss)	6,000
U.S. Treasury notes
Available-for-Sale:
Amortized Cost	4,000	2,600
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	4,000	2,600
Obligations of U.S. government agencies
Available-for-Sale:
Amortized Cost	601,400	569,300
Gross Unrealized Gains	300	100
Gross Unrealized Losses	(4,000)	(10,200)
Estimated Fair Value	597,700	559,200
Held-to-Maturity:
Amortized Cost	19,800	19,800
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(200)	(300)
Estimated Fair Value	19,600	19,500
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Amortized Cost	1,735,900	1,566,400
Gross Unrealized Gains	9,400	2,500
Gross Unrealized Losses	(12,400)	(24,100)
Estimated Fair Value	1,732,900	1,544,800
Held-to-Maturity:
Amortized Cost	1,300	189,700
Gross Unrealized Gains	0	300
Gross Unrealized Losses	0	(6,500)
Estimated Fair Value	1,300	183,500
Private mortgage-backed securities
Available-for-Sale:
Amortized Cost	66,200	72,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(900)	(1,800)
Estimated Fair Value	65,300	70,200
State, county and municipal securities
Available-for-Sale:
Amortized Cost	77,700
Gross Unrealized Gains	800
Gross Unrealized Losses	(100)
Estimated Fair Value	78,400
Held-to-Maturity:
Amortized Cost	67,600	150,900
Gross Unrealized Gains	1,500	1,800
Gross Unrealized Losses	(200)	(900)
Estimated Fair Value	68,900	151,800
Corporate securities
Available-for-Sale:
Amortized Cost	92,100	92,900
Gross Unrealized Gains	200	0
Gross Unrealized Losses	(300)	(1,000)
Estimated Fair Value	92,000	91,900
Held-to-Maturity:
Amortized Cost	28,200	46,300
Gross Unrealized Gains	0	100
Gross Unrealized Losses	(100)	(600)
Estimated Fair Value	28,100	45,800
Other investments
Available-for-Sale:
Amortized Cost	1,700	2,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	1,700	2,000
Other Investments
Held-to-Maturity:
Amortized Cost	100	100
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 100	$ 100

Investment Securities - Gross

Investment Securities - Gross Unrealized Losses and Fair Values of Investment Securities (Details)	3 Months Ended
	Mar. 31, 2019USD ($)Investments	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)Investments	Dec. 31, 2017USD ($)
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	$ 872,700,000			$ 1,123,200,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	(9,700,000)			(22,600,000)
Available-for-Sale, 12 Months or More, Fair Value	697,600,000			779,000,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(8,000,000)			(14,500,000)
Available-for-Sale, Total Fair Value	1,570,300,000			1,902,200,000
Available-for-Sale, Total Gross Unrealized Losses	$ (17,700,000)			(37,100,000)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value			$ 28,600,000	90,400,000
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses			(300,000)	(2,800,000)
Held-to-Maturity, 12 Months or More, Fair Value			44,600,000	216,900,000
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses			(200,000)	(5,500,000)
Held-to-Maturity, Total Fair Value			73,200,000	307,300,000
Held-to-Maturity, Total Gross Unrealized Losses			$ (500,000)	(8,300,000)
Investment securities in an unrealized loss position (securities) | Investments	551		760
Impairment loss	$ 0	$ 0
Available-for-sale Securities, Gross Realized Gain (Loss)	0	$ 0
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	336,800,000			363,100,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	(2,800,000)			(7,900,000)
Available-for-Sale, 12 Months or More, Fair Value	129,700,000			154,500,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(1,200,000)			(2,300,000)
Available-for-Sale, Total Fair Value	466,500,000			517,600,000
Available-for-Sale, Total Gross Unrealized Losses	(4,000,000)			(10,200,000)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value			$ 0	19,500,000
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses			0	(300,000)
Held-to-Maturity, 12 Months or More, Fair Value			28,000,000	0
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses			(100,000)	0
Held-to-Maturity, Total Fair Value			28,000,000	19,500,000
Held-to-Maturity, Total Gross Unrealized Losses			(100,000)	(300,000)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	535,900,000			735,200,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	(6,900,000)			(14,500,000)
Available-for-Sale, 12 Months or More, Fair Value	450,300,000			503,700,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(5,500,000)			(9,600,000)
Available-for-Sale, Total Fair Value	986,200,000			1,238,900,000
Available-for-Sale, Total Gross Unrealized Losses	(12,400,000)			(24,100,000)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value				45,000,000
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses				(2,200,000)
Held-to-Maturity, 12 Months or More, Fair Value				120,200,000
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses				(4,300,000)
Held-to-Maturity, Total Fair Value				165,200,000
Held-to-Maturity, Total Gross Unrealized Losses				(6,500,000)
Private mortgage-backed securities
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	0			0
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	0			0
Available-for-Sale, 12 Months or More, Fair Value	64,500,000			69,400,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(900,000)			(1,800,000)
Available-for-Sale, Total Fair Value	64,500,000			69,400,000
Available-for-Sale, Total Gross Unrealized Losses	(900,000)			(1,800,000)
State, county and municipal securities
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	0
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	0
Available-for-Sale, 12 Months or More, Fair Value	16,200,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(100,000)
Available-for-Sale, Total Fair Value	16,200,000
Available-for-Sale, Total Gross Unrealized Losses	(100,000)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value			9,000,000	25,900,000
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses			(100,000)	(300,000)
Held-to-Maturity, 12 Months or More, Fair Value			16,600,000	57,100,000
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses			(100,000)	(600,000)
Held-to-Maturity, Total Fair Value			25,600,000	83,000,000
Held-to-Maturity, Total Gross Unrealized Losses			(200,000)	(900,000)
Corporate securities
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	0			24,900,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	0			(200,000)
Available-for-Sale, 12 Months or More, Fair Value	36,900,000			51,400,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(300,000)			(800,000)
Available-for-Sale, Total Fair Value	36,900,000			76,300,000
Available-for-Sale, Total Gross Unrealized Losses	$ (300,000)			(1,000,000)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value			19,600,000	0
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses			(200,000)	0
Held-to-Maturity, 12 Months or More, Fair Value			0	39,600,000
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses			0	(600,000)
Held-to-Maturity, Total Fair Value			19,600,000	39,600,000
Held-to-Maturity, Total Gross Unrealized Losses			$ (200,000)	$ (600,000)

Investment Securities - Maturi

Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity
Available-for-Sale Amortized Cost, Within One Year	$ 497,200
Available-for-Sale Amortized Cost, After One Year but Within Five Years	1,509,800
Available-for-Sale Amortized Cost, After Five Years but Within Ten Years	395,300
Available-for-Sale Amortized Cost, After Ten Years	176,700
Amortized Cost	2,579,000	$ 2,305,200
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity
Available-for-Sale Estimated Fair Value, Within One Year	496,000
Available-for-Sale Estimated Fair Value, After One Year but Within Five Years	1,504,900
Available-for-Sale Estimated Fair Value, After Five Years but Within Ten Years	395,500
Available-for-Sale Estimated Fair Value, After Ten Years	175,600
Available-for-Sale, Estimated Fair Value	2,572,000	2,270,700
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount
Held-to-Maturity Amortized Cost, Within One Year	44,900
Held-to-Maturity Amortized Cost, After One Year but Within Five Years	44,200
Held-to-Maturity Amortized Cost, After Five Years but Within Ten Years	24,300
Held-to-Maturity Amortized Cost, After Ten Years	3,600
Amortized Cost	117,000	406,800
Held-to-maturity Securities, Debt Maturities, Fair Value, Rolling Maturity
Held-to-Maturity Estimated Fair Value, Within One Year	44,800
Held-to-Maturity Estimated Fair Value, After One Year but Within Five Years	44,100
Held-to-Maturity Estimated Fair Value, After Five Years but Within Ten Years	25,500
Held-to-Maturity Estimated Fair Value, After Ten Years	3,600
Held-to-Maturity, Estimated Fair Value	118,000	$ 400,700
Callable Within One Year
Available-for-sale Securities and Held-to-maturity Securities
Amortized cost of investment securities callable after one year but within five years	121,300
Fair value of investment securities callable after one year but within five years	121,500
Investment Securities,Callable Structured, Amortized Cost Basis	2,000
Investment Securities,Callable Structured, Fair Value	$ 2,000

Loans - Schedule of Recorded I

Loans - Schedule of Recorded Investment in Past Due Loans by Class (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans	$ 8,459.2	$ 8,470.4
Mortgage loans held for sale	34	33.3
Total loans	8,493.2	8,503.7
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	22.3	12.2
Current Loans	3,222.4	3,214
Non-accrual Loans	11.1	9.2
Total Loans	3,255.8	3,235.4
Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	2.3	1.9
Current Loans	286.6	316
Non-accrual Loans	3.8	3.7
Total Loans	292.7	321.6
Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	2.2	1.4
Current Loans	229.6	240.4
Non-accrual Loans	1.3	1
Total Loans	233.1	242.8
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0.4
Current Loans	311.9	273.7
Non-accrual Loans	0.2	0.2
Total Loans	312.1	274.3
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	4.5	3.7
Current Loans	828.1	830.1
Non-accrual Loans	5.3	4.9
Total Loans	837.9	838.7
Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	6.4	10.1
Current Loans	1,517.2	1,525.3
Non-accrual Loans	5.9	6.6
Total Loans	1,529.5	1,542
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	5.2	2.2
Current Loans	202.8	202.6
Non-accrual Loans	2.4	12.6
Total Loans	210.4	217.4
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	38.4	28.2
Current Loans	5,770.5	5,772
Non-accrual Loans	24.7	33.3
Total Loans	5,833.6	5,833.5
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	8.1	9.3
Current Loans	765.6	776.8
Non-accrual Loans	2	1.7
Total Loans	775.7	787.8
Direct consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	2.4	2
Current Loans	191.2	198.1
Non-accrual Loans	0.5	0.5
Total Loans	194.1	200.6
Credit card
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.8	2.1
Current Loans	75.4	79.7
Non-accrual Loans	0	0
Total Loans	77.2	81.8
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	12.3	13.4
Current Loans	1,032.2	1,054.6
Non-accrual Loans	2.5	2.2
Total Loans	1,047	1,070.2
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	9.8	10.8
Current Loans	1,317	1,283.7
Non-accrual Loans	15.3	15.8
Total Loans	1,342.1	1,310.3
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	3.1	2.4
Current Loans	229	249.4
Non-accrual Loans	2.6	3
Total Loans	234.7	254.8
Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Current Loans	1.8	1.6
Non-accrual Loans	0	0
Total Loans	1.8	1.6
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	63.6	54.8
Current Loans	8,350.5	8,361.3
Non-accrual Loans	45.1	54.3
Total Loans	8,459.2	8,470.4
Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Current Loans	34	33.3
Non-accrual Loans	0	0
Mortgage loans held for sale	34
Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	63.6	54.8
Current Loans	8,384.5	8,394.6
Non-accrual Loans	45.1	54.3
Total loans	8,493.2	8,503.7
30 to 59 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	12.6	10.4
30 to 59 Days Past Due | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.2	1.6
30 to 59 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	2.2	1
30 to 59 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0.4
30 to 59 Days Past Due | Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	3.4	3
30 to 59 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	4.6	8.8
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	4	2.2
30 to 59 Days Past Due | Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	24.6	24.4
30 to 59 Days Past Due | Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	6.5	6.8
30 to 59 Days Past Due | Direct consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.4	1.4
30 to 59 Days Past Due | Credit card
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.6	0.9
30 to 59 Days Past Due | Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	8.5	9.1
30 to 59 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	4	8.3
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.3	2.1
30 to 59 Days Past Due | Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
30 to 59 Days Past Due | Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	38.4	43.9
30 to 59 Days Past Due | Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
30 to 59 Days Past Due | Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	38.4	43.9
60 to 89 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	7.2	1
60 to 89 Days Past Due | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.7	0.1
60 to 89 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0.4
60 to 89 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
60 to 89 Days Past Due | Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.7	0.5
60 to 89 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.6	1.1
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.9	0
60 to 89 Days Past Due | Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	10.4	2.6
60 to 89 Days Past Due | Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.1	2.1
60 to 89 Days Past Due | Direct consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.7	0.5
60 to 89 Days Past Due | Credit card
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.5	0.4
60 to 89 Days Past Due | Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	2.3	3
60 to 89 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	4.1	1.2
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.3	0.3
60 to 89 Days Past Due | Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
60 to 89 Days Past Due | Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	18.1	7.1
60 to 89 Days Past Due | Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
60 to 89 Days Past Due | Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	18.1	7.1
Equal to Greater than 90 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	2.5	0.8
Equal to Greater than 90 Days Past Due | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.4	0.2
Equal to Greater than 90 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Equal to Greater than 90 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Equal to Greater than 90 Days Past Due | Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.4	0.2
Equal to Greater than 90 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.2	0.2
Equal to Greater than 90 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.3	0
Equal to Greater than 90 Days Past Due | Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	3.4	1.2
Equal to Greater than 90 Days Past Due | Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.5	0.4
Equal to Greater than 90 Days Past Due | Direct consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.3	0.1
Equal to Greater than 90 Days Past Due | Credit card
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.7	0.8
Equal to Greater than 90 Days Past Due | Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.5	1.3
Equal to Greater than 90 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.7	1.3
Equal to Greater than 90 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.5	0
Equal to Greater than 90 Days Past Due | Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Equal to Greater than 90 Days Past Due | Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	7.1	3.8
Equal to Greater than 90 Days Past Due | Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Equal to Greater than 90 Days Past Due | Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	$ 7.1	$ 3.8

Loans - Schedule of Outstandin

Loans - Schedule of Outstanding Unpaid Balances and Accrual Status of Loans Acquired with Credit Impairment (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities [Abstract]
Outstanding balance	$ 40.9	$ 43.4
Total carrying value	28	30.2
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Value, Accrual Status	$ 28	$ 30.2

Loans - Schedule of Changes in

Loans - Schedule of Changes in the Accretable Yield for Loans Acquired (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning Balance	$ 8.9	$ 7.3
Accretion income	(0.7)	(0.7)
Reductions due to exit events	(0.3)	(0.2)
Reclassifications from non-accretable differences	0.5	0.8
Ending Balance	$ 8.4	$ 7.2

Loans - Narrative (Details)

Loans - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Receivables [Abstract]
Loans and Leases Receivable, Impaired, Troubled Debt, Interest Income	$ 600,000	$ 800,000
Loans renegotiated in troubled debt restructurings	22,700,000		$ 23,400,000
Charge-offs directly related to modifying troubled debt restructurings	0	$ 0
Balance of defaulted loans under trouble debt restructurings	$ 0

Loans - Schedule of Recorded_2

Loans - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	$ 80		$ 83
Recorded Investment With No Allowance	26.1		36
Recorded Investment With Allowance	35.1		28.8
Total Recorded Investment	61.2		64.8
Related Allowance	7.1		6.8
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income
Average Recorded Investment	63.1	$ 79.7
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Income Recognized	0	0
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	27		22.2
Recorded Investment With No Allowance	10.7		8.6
Recorded Investment With Allowance	10.6		7.7
Total Recorded Investment	21.3		16.3
Related Allowance	0.7		0.7
Land acquisition & development
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	10		10
Recorded Investment With No Allowance	0.4		0.4
Recorded Investment With Allowance	3.4		3.5
Total Recorded Investment	3.8		3.9
Related Allowance	0.3		0.2
Residential
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	1.5		1.1
Recorded Investment With No Allowance	0.9		0.6
Recorded Investment With Allowance	0.4		0.4
Total Recorded Investment	1.3		1
Related Allowance	0		0.1
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	0.6		0.7
Recorded Investment With No Allowance	0.1		0.2
Recorded Investment With Allowance	0		0
Total Recorded Investment	0.1		0.2
Related Allowance	0		0
Total construction loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	12.1		11.8
Recorded Investment With No Allowance	1.4		1.2
Recorded Investment With Allowance	3.8		3.9
Total Recorded Investment	5.2		5.1
Related Allowance	0.3		0.3
Residential
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	8.9		8.8
Recorded Investment With No Allowance	4.2		5.7
Recorded Investment With Allowance	3.3		2
Total Recorded Investment	7.5		7.7
Related Allowance	0.5		0.3
Agricultural
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	2.7		12.9
Recorded Investment With No Allowance	2.4		12.5
Recorded Investment With Allowance	0.2		0.2
Total Recorded Investment	2.6		12.7
Related Allowance	0		0
Total real estate loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	50.7		55.7
Recorded Investment With No Allowance	18.7		28
Recorded Investment With Allowance	17.9		13.8
Total Recorded Investment	36.6		41.8
Related Allowance	1.5		1.3
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income
Average Recorded Investment	39.3	56.1
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Income Recognized	0	0
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	24.3		24.1
Recorded Investment With No Allowance	5.8		5.5
Recorded Investment With Allowance	14		14.4
Total Recorded Investment	19.8		19.9
Related Allowance	5.1		5.2
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income
Average Recorded Investment	19.9	22.1
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Income Recognized	0	0
Agricultural
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	5		3.2
Recorded Investment With No Allowance	1.6		2.5
Recorded Investment With Allowance	3.2		0.6
Total Recorded Investment	4.8		3.1
Related Allowance	0.5		$ 0.3
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income
Average Recorded Investment	3.9	1.5
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Income Recognized	$ 0	$ 0

Loans - Schedule of Loans Rene

Loans - Schedule of Loans Renegotiated in Troubled Debt Restructurings (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0
Loans renegotiated in troubled debt restructurings	22,700,000		$ 23,400,000
Financing Receivable, Modifications, Recorded Investment, Non Accrual	16,900,000		17,800,000
Loans renegotiated in troubled debt restructurings, accrual loans	5,800,000		$ 5,600,000
Charge-offs directly related to modifying troubled debt restructurings	0	$ 0
Balance of defaulted loans under trouble debt restructurings	0
Commitments to lend additional funds	$ 0

Loans - Schedule of Recorded_3

Loans - Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 8,459.2	$ 8,470.4
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,255.8	3,235.4
Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	292.7	321.6
Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	233.1	242.8
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	312.1	274.3
Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	837.9	838.7
Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,529.5	1,542
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	210.4	217.4
Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	5,833.6	5,833.5
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	775.7	787.8
Direct consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	194.1	200.6
Credit card
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	77.2	81.8
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,047	1,070.2
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,342.1	1,310.3
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	234.7	254.8
Other Assets Especially Mentioned
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	186.2	178.8
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	100.4	102.5
Other Assets Especially Mentioned | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	5.1	5
Other Assets Especially Mentioned | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.9	2.8
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1.8	1.7
Other Assets Especially Mentioned | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	7.8	9.5
Other Assets Especially Mentioned | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2.6	3
Other Assets Especially Mentioned | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	15.7	9
Other Assets Especially Mentioned | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	126.5	124
Other Assets Especially Mentioned | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.3	0.7
Other Assets Especially Mentioned | Direct consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.3	0.3
Other Assets Especially Mentioned | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.6	1
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	42.3	39.4
Other Assets Especially Mentioned | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	16.8	14.4
Substandard
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	194.6	201.6
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	90.9	87.4
Substandard | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2.2	7
Substandard | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2.2	2
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4.1	3.9
Substandard | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	8.5	12.9
Substandard | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	8.9	10.8
Substandard | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	18	24
Substandard | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	126.3	135.1
Substandard | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2.7	2.1
Substandard | Direct consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.8	0.8
Substandard | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3.5	2.9
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	46.5	45.8
Substandard | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	18.3	17.8
Doubtful
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	21.7	20.9
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2.8	2.9
Doubtful | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3.4	3.3
Doubtful | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.9	0.4
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	0
Doubtful | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4.3	3.7
Doubtful | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1.9	0.7
Doubtful | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.1	0.1
Doubtful | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	9.1	7.4
Doubtful | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.1	0.1
Doubtful | Direct consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.1	0.1
Doubtful | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.2	0.2
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	11.3	11.8
Doubtful | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1.1	1.5
Total Criticized Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	402.5	401.3
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	194.1	192.8
Total Criticized Loans | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	10.7	15.3
Total Criticized Loans | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4	5.2
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	5.9	5.6
Total Criticized Loans | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	20.6	26.1
Total Criticized Loans | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	13.4	14.5
Total Criticized Loans | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	33.8	33.1
Total Criticized Loans | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	261.9	266.5
Total Criticized Loans | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3.1	2.9
Total Criticized Loans | Direct consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1.2	1.2
Total Criticized Loans | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4.3	4.1
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	100.1	97
Total Criticized Loans | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 36.2	$ 33.7

Loans Schedule of Loans by Clas

Loans Schedule of Loans by Class (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	$ 8,459.2	$ 8,470.4
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group, Mortgage	34	33.3
Loans and Leases Receivable, Gross	8,493.2	8,503.7
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	3,255.8	3,235.4
Land acquisition & development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	292.7	321.6
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	233.1	242.8
Commercial Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	312.1	274.3
Total construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	837.9	838.7
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	1,529.5	1,542
Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	210.4	217.4
Total real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	5,833.6	5,833.5
Indirect consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	775.7	787.8
Direct consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	194.1	200.6
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	77.2	81.8
Total consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	1,047	1,070.2
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	1,342.1	1,310.3
Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	234.7	254.8
Other, including overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	1.8	1.6
Loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	8,459.2	8,470.4
Mortgage loans originated for sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group, Mortgage	34
Total loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 8,493.2	$ 8,503.7

Allowance for Loan Losses - Sc

Allowance for Loan Losses - Schedule of Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses			$ 0.9	$ 0.8
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 73	$ 72.1
Provision for loan losses	3.7	2.1
Less loans charged-off	(6)	5.2
Add back recoveries of loans previously charged-off	1.7	4.5
Ending balance	72.4	73.5
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment			7.1	6.8
Loans collectively evaluated for impairment			65.3	66.2
Allowance for loan losses	73	72.1	72.4	73
Loans held for investment:
Individually evaluated for impairment			61.2	64.8
Individually evaluated for impairment			8,398	8,405.6
Total loans			8,459.2	8,470.4
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	31	31.7
Provision for loan losses	(1.7)	1.8
Less loans charged-off	(2.1)	0.8
Add back recoveries of loans previously charged-off	0.2	1.2
Ending balance	27.4	33.9
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses	31	31.7	27.4	31
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	8.7	8.7
Provision for loan losses	2	0.7
Less loans charged-off	(3)	2.7
Add back recoveries of loans previously charged-off	1.1	1.1
Ending balance	8.8	7.8
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses	8.7	8.7	8.8	8.7
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	31.3	30.5
Provision for loan losses	3.6	(0.7)
Less loans charged-off	(0.8)	1.7
Add back recoveries of loans previously charged-off	0.4	2
Ending balance	34.5	30.1
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses	31.3	30.5	34.5	31.3
Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2	1.2
Provision for loan losses	(0.2)	0.3
Less loans charged-off	(0.1)	0
Add back recoveries of loans previously charged-off	0	0.2
Ending balance	1.7	1.7
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses	2	1.2	1.7	2
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0
Provision for loan losses	0	0
Less loans charged-off	0	0
Add back recoveries of loans previously charged-off	0	0
Ending balance	0	0
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses	0	$ 0	0	0
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				0
Loans collectively evaluated for impairment				0
Allowance for loan losses	0			0
Loans held for investment:
Individually evaluated for impairment				0
Individually evaluated for impairment				1.6
Total loans				1.6
Other | Other
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	0
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment			0
Loans collectively evaluated for impairment			0
Allowance for loan losses	0		0
Loans held for investment:
Individually evaluated for impairment			0
Individually evaluated for impairment			1.8
Total loans			1.8
Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				0.3
Loans collectively evaluated for impairment				1.7
Allowance for loan losses	2			2
Loans held for investment:
Individually evaluated for impairment				3.1
Individually evaluated for impairment				251.7
Total loans				254.8
Agriculture | Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	1.7
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment			0.5
Loans collectively evaluated for impairment			1.2
Allowance for loan losses	1.7		1.7
Loans held for investment:
Individually evaluated for impairment			4.8
Individually evaluated for impairment			229.9
Total loans			234.7
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	31.3
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				5.2
Loans collectively evaluated for impairment				26.1
Allowance for loan losses	31.3			31.3
Loans held for investment:
Individually evaluated for impairment				19.9
Individually evaluated for impairment				1,290.4
Total loans				1,310.3
Commercial | Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	34.5
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment			5.1
Loans collectively evaluated for impairment			29.4
Allowance for loan losses	34.5		34.5
Loans held for investment:
Individually evaluated for impairment			19.8
Individually evaluated for impairment			1,322.3
Total loans			1,342.1
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	8.7
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				0
Loans collectively evaluated for impairment				8.7
Allowance for loan losses	8.7			8.7
Loans held for investment:
Individually evaluated for impairment				0
Individually evaluated for impairment				1,070.2
Total loans				1,070.2
Consumer | Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	8.8
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment			0
Loans collectively evaluated for impairment			8.8
Allowance for loan losses	8.8		8.8
Loans held for investment:
Individually evaluated for impairment			0
Individually evaluated for impairment			1,047
Total loans			1,047
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	31
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment				1.3
Loans collectively evaluated for impairment				29.7
Allowance for loan losses	31			31
Loans held for investment:
Individually evaluated for impairment				41.8
Individually evaluated for impairment				5,791.7
Total loans				$ 5,833.5
Real Estate | Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Ending balance	27.4
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment			1.5
Loans collectively evaluated for impairment			25.9
Allowance for loan losses	$ 27.4		27.4
Loans held for investment:
Individually evaluated for impairment			36.6
Individually evaluated for impairment			5,797
Total loans			$ 5,833.6

Other Real Estate Owned (Detail

Other Real Estate Owned (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Foreclosed Residential Real Estate included in Other Real Estate Owned	$ 1.7		$ 2
Real Estate Acquired Through Foreclosure [Roll Forward]
Beginning balance	14.4	$ 10.1
Additions	8.4	1.2
Valuation adjustments	0.3	0
Dispositions	1.4	0.3
Ending balance	21.1	$ 11
Consumer mortgage loans collateralized by residential real estate property in the process of foreclosure	$ 0.5		$ 0.4

Derivatives and Hedging Activ_3

Derivatives and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 526.1	$ 454.3
Derivative Asset, Estimated Fair Value	14.6	10.1
Notional amount of terminated commitment	539.6	467.9
Derivative Liabilities, Estimated Fair Value	13.5	9.4
Not Designated as Hedging Instrument | Interest rate swap contracts
Derivative [Line Items]
Derivative Asset, Notional Amount	449.2	403.3
Derivative Asset, Estimated Fair Value	12.7	8.8
Notional amount of terminated commitment	449.2	403.3
Derivative Liabilities, Estimated Fair Value	12.7	8.8
Not Designated as Hedging Instrument | Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	76.9	51
Derivative Asset, Estimated Fair Value	1.9	1.3
Not Designated as Hedging Instrument | Forward loan sales contracts
Derivative [Line Items]
Notional amount of terminated commitment	90.4	64.6
Derivative Liabilities, Estimated Fair Value	$ 0.8	$ 0.6

Derivatives and Hedging Activ_4

Derivatives and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financial Assets
Gross Amounts Recognized	$ 14.6	$ 10.1
Gross Amounts Offset in the Balance Sheet	0	0
Derivative assets:	14.6	10.1
Financial Instruments	2	2.7
Fair Value of Financial Collateral in the Balance Sheet	7.5	2.4
Net Amount	5.1	5
Financial Liabilities
Gross Amounts Recognized	13.5	9.4
Gross Amounts Offset in the Balance Sheet	0	0
Derivative liabilities:	13.5	9.4
Financial Instruments	2	2.7
Fair Value of Financial Collateral in the Balance Sheet	0.2	4.1
Net Amount	11.3	2.6
Repurchase agreements
Gross Amounts Recognized	672.6	712.4
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	672.6	712.4
Financial Instruments	0	0
Fair Value of Financial Collateral in the Balance Sheet	672.6	712.4
Net Amount	0	0
Offsetting Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned
Gross Amounts Recognized	686.1	721.8
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	686.1	721.8
Financial Instruments	2	2.7
Fair Value of Financial Collateral in the Balance Sheet	672.8	716.5
Net Amount	11.3	2.6
Interest Rate Swap
Financial Assets
Gross Amounts Recognized	12.7	8.8
Gross Amounts Offset in the Balance Sheet	0	0
Derivative assets:	12.7	8.8
Financial Instruments	2	2.7
Fair Value of Financial Collateral in the Balance Sheet	7.5	2.4
Net Amount	3.2	3.7
Financial Liabilities
Gross Amounts Recognized	12.7	8.8
Gross Amounts Offset in the Balance Sheet	0	0
Derivative liabilities:	12.7	8.8
Financial Instruments	2	2.7
Fair Value of Financial Collateral in the Balance Sheet	0.2	4.1
Net Amount	10.5	2
Mortgage Related Derivatives
Financial Assets
Gross Amounts Recognized	1.9	1.3
Gross Amounts Offset in the Balance Sheet	0	0
Derivative assets:	1.9	1.3
Financial Instruments	0	0
Fair Value of Financial Collateral in the Balance Sheet	0	0
Net Amount	1.9	1.3
Financial Liabilities
Gross Amounts Recognized	0.8	0.6
Gross Amounts Offset in the Balance Sheet	0	0
Derivative liabilities:	0.8	0.6
Financial Instruments	0	0
Fair Value of Financial Collateral in the Balance Sheet	0	0
Net Amount	$ 0.8	$ 0.6

Derivatives and Hedging Activ_5

Derivatives and Hedging Activities - Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Amount of gain recognized in other non-interest income	$ 0	$ 0.3
Amount of net fee income recognized in other non-interest income	0.8	0.5
Amount of net gains recognized in mortgage banking revenues	$ 0.4	$ (0.1)

Capital Stock (Details)

Capital Stock (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Class A Common Stock
Class of Stock [Line Items]
Common Stock, Shares, Outstanding	38,461,948		38,169,575
Stock repurchased and retired (in shares)	0	0
Class B Common Stock
Class of Stock [Line Items]
Common Stock, Shares, Outstanding	22,374,171		22,453,672

Earnings per Common Share - Co

Earnings per Common Share - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Earnings Per Share, Basic and Diluted [Line Items]
Net income	$ 41.6	$ 36.7
Weighted average common shares outstanding for basic earnings per share computation	60,311,171	56,241,201
Dilutive effects of stock-based compensation	286,899	410,977
Weighted average common shares outstanding for diluted earnings per common share computation	60,598,070	56,652,178
Basic earnings per common share (in dollars per share)	$ 0.69	$ 0.65
Diluted earnings per common share (in dollars per share)	$ 0.69	$ 0.65
Restricted Stock [Member]
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock	121,452	139,943
Restricted stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock	154,387	164,019
Class A Common Stock
Earnings Per Share, Basic and Diluted [Line Items]
Common Stock, Shares, Outstanding	38,461,948		38,169,575
Class B Common Stock
Earnings Per Share, Basic and Diluted [Line Items]
Common Stock, Shares, Outstanding	22,374,171		22,453,672

Regulatory Capital - Schedule

Regulatory Capital - Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Total risk-based capital:
Actual Amount	$ 1,310.3	$ 1,285
Actual Ratio	13.23%	12.99%
Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 1,040	$ 976.6
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	10.50%	9.875%
Well Capitalized Amount	$ 990.5	$ 989
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 1,237.9	$ 1,212
Actual Ratio	12.50%	12.26%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 841.9	$ 778.8
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	8.50%	7.875%
Well Capitalized Amount	$ 792.4	$ 791.2
Well Capitalized Ratio	8.00%	8.00%
Common equity tier one risk-based capital:
Actual Amount	$ 1,153.7	$ 1,127.8
Actual Ratio	11.65%	11.40%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 445.7	$ 445
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	4.50%	4.50%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 693.4	$ 630.5
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%	6.375%
Well Capitalized Amount	$ 643.8	$ 642.8
Well Capitalized Ratio	6.50%	6.50%
Leverage capital ratio:
Actual Amount	$ 1,237.9	$ 1,212
Actual Ratio	9.76%	9.47%
Adequately Capitalized Amount	$ 507.5	$ 511.9
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 634.4	$ 639.9
Well Capitalized Ratio	5.00%	5.00%
Capital Required for Capital Adequacy	$ 792.4	$ 791.2
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Tier One Risk Based Capital Required for Capital Adequacy	$ 594.3	$ 593.4
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%	6.00%
FIB
Total risk-based capital:
Actual Amount	$ 1,201.4	$ 1,184.5
Actual Ratio	12.16%	12.01%
Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 1,037.1	$ 973.7
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	10.50%	9.875%
Well Capitalized Amount	$ 987.8	$ 986
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 1,129	$ 1,111.6
Actual Ratio	11.43%	11.27%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 839.6	$ 776.5
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	8.50%	7.875%
Well Capitalized Amount	$ 790.2	$ 788.8
Well Capitalized Ratio	8.00%	8.00%
Common equity tier one risk-based capital:
Actual Amount	$ 1,129	$ 1,111.6
Actual Ratio	11.43%	11.27%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 444.5	$ 443.7
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	4.50%	4.50%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 691.4	$ 628.6
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%	6.375%
Well Capitalized Amount	$ 642	$ 640.9
Well Capitalized Ratio	6.50%	6.50%
Leverage capital ratio:
Actual Amount	$ 1,129	$ 1,111.6
Actual Ratio	8.92%	8.97%
Adequately Capitalized Amount	$ 506.3	$ 495.9
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 632.8	$ 619.8
Well Capitalized Ratio	5.00%	5.00%
Capital Required for Capital Adequacy	$ 790.2	$ 788.8
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Tier One Risk Based Capital Required for Capital Adequacy	$ 592.7	$ 591.6
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%	6.00%

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Apr. 08, 2019	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Aug. 16, 2018
Loss Contingencies [Line Items]
Notional amount of terminated commitment		$ 539.6	$ 467.9
Mortgage Loans Held for Sale
Loss Contingencies [Line Items]
Mortgage loans with recourse provision in effect		$ 1.5
Inland Northwest Bank
Loss Contingencies [Line Items]
Number of banking offices acquired				20
Subsequent Event | Idaho Independent Bank [Member]
Loss Contingencies [Line Items]
Number of banking offices acquired	11
Subsequent Event | Community 1st Bank [Member]
Loss Contingencies [Line Items]
Number of banking offices acquired	3
Construction Contracts
Loss Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation			$ 1.5

Financial Instruments with Of_2

Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Entity Information [Line Items]
Credit extension commitments		$ 2,637.1
Unused Credit Card Lines
Entity Information [Line Items]
Credit extension commitments		720.7
Credit extension commitments beyond one year	$ 1,058.9
Standby Letters of Credit
Entity Information [Line Items]
Credit extension commitments		$ 47.6

Other Comprehensive Income_Lo_3

Other Comprehensive Income/Loss - Schedule of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	$ 1,736.9	$ 1,432.4	$ 1,693.9	$ 1,427.6
Investment securities available-for sale:
Change in net unrealized gain during period, pre-tax	33.6	(23.7)
Change in net unrealized gain during period, tax expense (benefit)	8.8	(6.2)
Change in net unrealized gain during period, net of tax	24.8	(17.5)
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity, pre-tax	6	0
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity, tax expense (benefit)	(1.6)
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity, net of tax	(4.4)	0
Other Comprehensive Income (Loss), Transfers from Available-for-Sale to Held-to-Maturity Securities, before Tax	0	0.5
Other Comprehensive Income (Loss), Transfers from Available-for-Sale to Held-to-Maturity Securities, Tax	0	0.2
Other Comprehensive Income (Loss), Transfers from Available-for-Sale to Held-to-Maturity Securities, Net of Tax	0	0.3
Defined benefits post-retirement benefit plan:
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax	0	0.1
Other comprehensive income (loss), before tax	27.4	(23.3)
Total other comprehensive income, tax expense (benefit)	7.2	(6.1)
Total other comprehensive income, net of tax amount	20.2	(17.2)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax	(0.2)	(0.1)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax	(0.2)	0
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	(5.1)		(25.5)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	(4.4)	$ (32.3)	(24.6)	$ (12)
Postretirement Health Coverage [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax	$ 0.7		$ 0.9

Other Comprehensive Income_Lo_4

Other Comprehensive Income/Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	$ 1,736.9	$ 1,693.9	$ 1,432.4	$ 1,427.6
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	(5.1)	(25.5)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	(4.4)	(24.6)	$ (32.3)	$ (12)
Postretirement Health Coverage [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax	$ 0.7	$ 0.9

Fair Value Measurements - Sche

Fair Value Measurements - Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring and Non-Recurring Basis (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	$ 14.6		$ 10.1
Derivative liabilities:	13.5		9.4
Real Estate Acquired Through Foreclosure, Valuation Adjustments	(0.3)	$ 0
Related allowance	7.1		6.8
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Amount	0		0
Deferred Compensation Plan Assets	0		0
Deferred Compensation Liability, Current and Noncurrent	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0		0
Other real estate owned	0		0
Long-lived assets to be disposed, fair value disclosure	0		0
Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Amount	34		33.3
Derivative assets:			8.8
Derivative liabilities:			8.8
Deferred Compensation Plan Assets	12.4		12.1
Deferred Compensation Liability, Current and Noncurrent	12.4		12.1
Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0		0
Other real estate owned	0		0
Long-lived assets to be disposed, fair value disclosure	0		0
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Amount	0		0
Deferred Compensation Plan Assets	0		0
Deferred Compensation Liability, Current and Noncurrent	0		0
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans			24.1
Other real estate owned	2		0.6
Long-lived assets to be disposed, fair value disclosure	5.5		4.9
Related allowance			7.1	$ 6.8
Partial loan charge-offs			6.2	5.4
US Treasury Notes Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:			0
US Treasury Notes Securities [Member] | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:			2.6
US Treasury Notes Securities [Member] | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:			0
U.S. Treasury notes | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0
U.S. Treasury notes | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	4
U.S. Treasury notes | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0
State, county and municipal securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0
State, county and municipal securities | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	78.4
State, county and municipal securities | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0
Obligations of U.S. government agencies | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
Obligations of U.S. government agencies | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	597.7		559.2
Obligations of U.S. government agencies | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	1,732.9		1,544.8
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
Private mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
Private mortgage-backed securities | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	65.3		70.2
Private mortgage-backed securities | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
Corporate securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
Corporate securities | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	92		91.9
Corporate securities | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
Other investments | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0
Other investments | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	1.7
Other investments | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0
Other Investments | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:			0
Other Investments | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:			2
Other Investments | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:			0
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	2,572		2,270.7
Loans held for sale	34		33.3
Derivative assets:	14.6		10.1
Derivative liabilities:	13.5		9.4
Deferred Compensation Plan Assets	12.4		12.1
Deferred Compensation Liability, Current and Noncurrent	12.4		12.1
Estimated Fair Value | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable Held-for-sale, Amount	34		33.3
Deferred Compensation Plan Assets	12.4		12.1
Deferred Compensation Liability, Current and Noncurrent	12.4		12.1
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets to be disposed of by sale			5.5	4.9
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
Loans held for sale	0		0
Derivative assets:	0		0
Derivative liabilities:	0		0
Deferred Compensation Plan Assets	0		0
Deferred Compensation Liability, Current and Noncurrent	0		0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	2,572		2,270.7
Loans held for sale	34		33.3
Derivative assets:	14.6		10.1
Derivative liabilities:	13.5		9.4
Deferred Compensation Plan Assets	12.4		12.1
Deferred Compensation Liability, Current and Noncurrent	12.4		12.1
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0		0
Loans held for sale	0		0
Derivative assets:	0		0
Derivative liabilities:	0		0
Deferred Compensation Plan Assets	0		0
Deferred Compensation Liability, Current and Noncurrent	0		0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	30.9		30.9	24.1
Other real estate owned	2
Long-lived assets to be disposed, fair value disclosure	5.5		4.9
Estimated Fair Value | US Treasury Notes Securities [Member] | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:			2.6
Estimated Fair Value | U.S. Treasury notes | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	4
Estimated Fair Value | State, county and municipal securities | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	78.4
Estimated Fair Value | Obligations of U.S. government agencies | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	597.7		559.2
Estimated Fair Value | U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	1,732.9		1,544.8
Estimated Fair Value | Private mortgage-backed securities | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	65.3		70.2
Estimated Fair Value | Corporate securities | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	92		91.9
Estimated Fair Value | Other investments | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	1.7
Estimated Fair Value | Other Investments | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:			2
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	2,572		2,270.7
Derivative assets:	14.6		10.1
Derivative liabilities:	13.5		9.4
Deferred Compensation Plan Assets	12.4		12.1
Deferred Compensation Liability, Current and Noncurrent	12.4		12.1
Carrying Amount | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans			44.2	36.3
Long-lived assets to be disposed of by sale			6	5.4
Change During Period | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets to be disposed of by sale			0.5	$ 0.5
Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	12.7		8.8
Derivative liabilities:	12.7		8.8
Interest Rate Swap | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	0		0
Derivative liabilities:	0		0
Interest Rate Swap | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	12.7
Derivative liabilities:	12.7
Interest Rate Swap | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	0		0
Derivative liabilities:	0		0
Interest Rate Swap | Estimated Fair Value | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	12.7		8.8
Derivative liabilities:	12.7		8.8
Interest Rate Lock Commitments | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	0		0
Interest Rate Lock Commitments | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	1.9		1.3
Interest Rate Lock Commitments | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	0		0
Interest Rate Lock Commitments | Estimated Fair Value | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	1.9		1.3
Forward Contracts | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities:	0		0
Forward Contracts | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities:	0.8		0.6
Forward Contracts | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities:	0		0
Forward Contracts | Estimated Fair Value | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities:	$ 0.8		$ 0.6

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Inputs, Quantitative Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Mar. 31, 2019	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Write downs on OREO properties	$ 0
Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Level 3 Fair Value Disclosure		0.00%
Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Assets HFS Level 3 Fair Value		43.00%
Discount Rate for OREO Level 3 Fair Value		96.00%
Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Assets HFS Level 3 Fair Value		10.00%
Discount Rate for OREO Level 3 Fair Value		39.00%
Discount Rate for Level 3 Fair Value Disclosure		13.00%
Carrying Amount
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Net loans held for investment		$ 8,397,400,000	$ 8,386,800,000
Change During Period | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value of long-lived assets to be disposed of by sale		500,000		$ 500,000
Estimated Fair Value
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Net loans held for investment		8,439,700,000	8,408,600,000
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value of long-lived assets to be disposed of by sale		5,500,000		4,900,000
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Partial loan charge-offs		6,200,000		5,400,000
Long-lived assets to be disposed, fair value disclosure		4,900,000	5,500,000
Impaired loans		24,100,000
Other real estate owned		600,000	2,000,000
Significant Unobservable Inputs (Level 3) | Carrying Amount | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans		44,200,000		36,300,000
Fair Value of long-lived assets to be disposed of by sale		6,000,000		5,400,000
Significant Unobservable Inputs (Level 3) | Estimated Fair Value
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Net loans held for investment		24,100,000	30,900,000
Significant Unobservable Inputs (Level 3) | Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Long-lived assets to be disposed, fair value disclosure		4,900,000	5,500,000
Impaired loans		$ 30,900,000	30,900,000	$ 24,100,000
Other real estate owned			$ 2,000,000
Measurement Input, Discount Rate [Member] | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Assets HFS Level 3 Fair Value		0.00%
Discount Rate for OREO Level 3 Fair Value		8.00%
Measurement Input, Discount Rate [Member] | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Level 3 Fair Value Disclosure		26.00%

Fair Value Measurements - Sc_2

Fair Value Measurements - Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Investment debt securities held-to-maturity	$ 118,000	$ 400,700
Derivative assets	14,600	10,100
Financial liabilities:
Derivative liabilities	13,500	9,400
Carrying Amount
Financial assets:
Cash and cash equivalents	955,200	822,000
Investment debt securities available-for-sale:	2,572,000	2,270,700
Investment debt securities held-to-maturity	117,000	406,800
Accrued interest receivable	46,500	44,900
Mortgage servicing rights, net	27,900	27,700
Loans Held-for-sale, Fair Value Disclosure	34,000	33,300
Net loans held for investment	8,386,800	8,397,400
Derivative assets	14,600	10,100
Deferred Compensation Plan Assets	12,400	12,100
Total financial assets	12,166,400	12,025,000
Financial liabilities:
Total deposits, excluding time deposits	9,408,300	9,363,700
Time deposits	1,406,400	1,317,000
Securities sold under repurchase agreements	672,600	712,400
Accrued interest payable	10,000	7,800
Long-term debt	15,800	15,800
Subordinated debentures held by subsidiary trusts	86,900	86,900
Derivative liabilities	13,500	9,400
Deferred Compensation Liability, Current and Noncurrent	12,400	12,100
Total financial liabilities	11,625,900	11,525,100
Estimated Fair Value
Financial assets:
Cash and cash equivalents	955,200	822,000
Investment debt securities available-for-sale:	2,572,000	2,270,700
Investment debt securities held-to-maturity	118,000	400,700
Accrued interest receivable	46,500	44,900
Mortgage servicing rights, net	40,500	42,400
Loans held for sale	34,000	33,300
Net loans held for investment	8,408,600	8,439,700
Derivative assets	14,600	10,100
Deferred Compensation Plan Assets	12,400	12,100
Total financial assets	12,201,800	12,075,900
Financial liabilities:
Total deposits, excluding time deposits	9,408,300	9,363,700
Time deposits	1,393,200	1,299,000
Securities sold under repurchase agreements	672,600	712,400
Accrued interest payable	10,000	7,800
Long-term debt	13,900	13,000
Subordinated debentures held by subsidiary trusts	85,100	84,900
Derivative liabilities	13,500	9,400
Deferred Compensation Liability, Current and Noncurrent	12,400	12,100
Total financial liabilities	11,609,000	11,502,300
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	955,200	822,000
Investment debt securities available-for-sale:	0	0
Investment debt securities held-to-maturity	0	0
Accrued interest receivable	0	0
Mortgage servicing rights, net	0	0
Loans held for sale	0	0
Net loans held for investment	0	0
Derivative assets	0	0
Deferred Compensation Plan Assets	0	0
Total financial assets	955,200	822,000
Financial liabilities:
Total deposits, excluding time deposits	9,408,300	9,363,700
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Accrued interest payable	0	0
Long-term debt	0	0
Subordinated debentures held by subsidiary trusts	0	0
Derivative liabilities	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Total financial liabilities	9,408,300	9,363,700
Significant Other Observable Inputs (Level 2) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment debt securities available-for-sale:	2,572,000	2,270,700
Investment debt securities held-to-maturity	118,000	400,700
Accrued interest receivable	46,500	44,900
Mortgage servicing rights, net	40,500	42,400
Loans held for sale	34,000	33,300
Net loans held for investment	8,377,700	8,415,600
Derivative assets	14,600	10,100
Deferred Compensation Plan Assets	12,400	12,100
Total financial assets	11,215,700	11,229,800
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	1,393,200	1,299,000
Securities sold under repurchase agreements	672,600	712,400
Accrued interest payable	10,000	7,800
Long-term debt	13,900	13,000
Subordinated debentures held by subsidiary trusts	85,100	84,900
Derivative liabilities	13,500	9,400
Deferred Compensation Liability, Current and Noncurrent	12,400	12,100
Total financial liabilities	2,200,700	2,138,600
Significant Unobservable Inputs (Level 3) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment debt securities available-for-sale:	0	0
Investment debt securities held-to-maturity	0	0
Accrued interest receivable	0	0
Mortgage servicing rights, net	0	0
Loans held for sale	0	0
Net loans held for investment	30,900	24,100
Derivative assets	0	0
Deferred Compensation Plan Assets	0	0
Total financial assets	30,900	24,100
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Accrued interest payable	0	0
Long-term debt	0	0
Subordinated debentures held by subsidiary trusts	0	0
Derivative liabilities	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Total financial liabilities	$ 0	$ 0

Recent Authoritative Accounti_2

Recent Authoritative Accounting Guidance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets obtained in exchange for operating lease liabilities	$ 54.6	$ 0
Operating Lease, Payments	$ 54.6