First Interstate BancSystem (FIBK) 10-K27 Feb 192018 FY Annual reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2018	Jan. 31, 2019	Jun. 30, 2018
Entity Registrant Name	FIRST INTERSTATE BANCSYSTEM INC
Entity Central Index Key	860,413
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Public Float			$ 1,544,721,547
Class A Common Stock
Entity Common Stock, Shares Outstanding		38,179,174
Class B Common Stock
Entity Common Stock, Shares Outstanding		22,451,963

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 244,100	$ 196,500
Interest bearing deposits in banks	577,800	562,300
Federal funds sold	100	100
Total cash and cash equivalents	822,000	758,900
Investment securities:
Available-for-sale	2,270,700	2,208,700
Held-to-maturity (estimated fair values of $400.7 and $483.3 at December 31, 2018 and 2017, respectively)	406,800	484,500
Total investment securities	2,677,500	2,693,200
Loans held for investment	8,470,400	7,567,700
Mortgage loans held for sale	33,300	46,600
Total loans	8,503,700	7,614,300
Less allowance for loan losses	73,000	72,100
Net loans	8,430,700	7,542,200
Goodwill	546,700	444,700
Goodwill	245,200	241,900
Indefinite-lived Intangible Assets (Excluding Goodwill)	56,900	49,100
Premises and equipment, net of accumulated depreciation	275,100	260,600
Core deposit intangibles, net of accumulated amortization	14,400	10,100
Accrued interest receivable	44,900	38,000
Mortgage servicing rights, net of accumulated amortization and impairment reserve	27,700	24,800
Other real estate owned (“OREO”)	0	4,000
Other assets	159,100	145,800
Total assets	13,300,200	12,213,300
Deposits:
Non-interest bearing	3,158,300	2,900,000
Interest bearing	7,522,400	7,034,900
Total deposits	10,680,700	9,934,900
Securities sold under repurchase agreements	712,400	643,000
Accounts payable and accrued expenses	94,100	86,600
Accrued interest payable	7,800	5,600
Deferred tax liability, net	8,600	0
Long-term debt	15,800	13,100
Other borrowed funds	0	20,000
Subordinated debentures held by subsidiary trusts	86,900	82,500
Total liabilities	11,606,300	10,785,700
Stockholders’ equity:
Nonvoting noncumulative preferred stock without par value; authorized 100,000 shares; no shares issued or outstanding as of December 31, 2018 and 2017	0	0
Common stock	866,700	687,000
Retained earnings	851,800	752,600
Accumulated other comprehensive income (loss), net	(24,600)	(12,000)
Total stockholders’ equity	1,693,900	1,427,600
Total liabilities and stockholders’ equity	$ 13,300,200	$ 12,213,300

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Assets:
Held-to-maturity investment securities, estimated fair value	$ 400.7	$ 483.3

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Consolidated Statements of Income - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income:
Interest and fees on loans		$ 404.3	$ 324.7	$ 259.2
Interest and dividends on investment securities:
Taxable		55.4	42.8	32.2
Exempt from federal taxes		2.4	3.2	3.4
Interest on deposits in banks		11.3	7.1	2.6
Total interest income		473.4	377.8	297.4
Interest expense:
Interest on deposits		32.6	21.4	12.7
Interest on securities sold under repurchase agreements		2.7	1.3	0.4
Interest on other borrowed funds		0.2	0.5	0
Interest on long-term debt		1.3	1.7	1.8
Interest on subordinated debentures held by subsidiary trusts		4.1	3.1	2.7
Total interest expense		40.9	28	17.6
Net interest income		432.5	349.8	279.8
Provision for loan losses		8.6	11	10
Net interest income after provision for loan losses		423.9	338.8	269.8
Non-interest income:
Fees and Commissions, Mortgage Banking and Servicing	$ 24.9		28.9	37.2
Loss on termination of interest rate swap	0		(1.1)	0
Investment securities (losses) gains, net	(0.1)	(0.1)	0.7	0.3
Other income	15.1		14.3	10
Non-recurring litigation recovery		0	0	4.2
Total non-interest income		143.3	141.8	136.5
Non-interest expense:
Salaries and wages		146.4	122.7	108.7
Employee benefits		47.9	37.6	35.2
Information Technology and Data Processing		28.7	25.1	20.5
Occupancy, Net		25.4	22.4	17.7
Equipment Expense		12.7	11.5	9.6
FDIC insurance premiums		6.9	6.8	5
Federal Deposit Insurance Corporation Premium Expense		5.6	4.7	4.5
Mortgage servicing rights impairment recovery		3.1	3	3
OREO expense, net of income		0	(0.1)	0
Other Real Estate Owned Expense Net Of Income		0.3	0.4	0
Core deposit intangibles amortization		7.9	5.5	3.4
Other expenses		63.6	57.1	50.6
Acquisition related expenses		12.4	27.2	2.8
Total non-interest expense		360.9	323.9	261
Income before income tax expense		206.3	156.7	145.3
Income tax expense		46.1	50.2	49.6
Net income		$ 160.2	$ 106.5	$ 95.7
Basic earnings per common share (in dollars per share)		$ 2.77	$ 2.07	$ 2.15
Diluted earnings per common share (in dollars per share)		$ 2.75	$ 2.05	$ 2.13
Credit and Debit Card [Member]
Interest expense:
Revenue from Contract with Customer, Excluding Assessed Tax	43.3		$ 43.3	$ 34.4
Financial Service, Other [Member]
Interest expense:
Revenue from Contract with Customer, Excluding Assessed Tax	15.1		13.3	11.5
Investment Advisory, Management and Administrative Service [Member]
Non-interest income:
Investment Banking, Advisory, Brokerage, and Underwriting Fees and Commissions	23.2		21.1	20.5
Deposit Account [Member]
Interest expense:
Revenue from Contract with Customer, Excluding Assessed Tax	$ 21.8		$ 21.3	$ 18.4

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 160.2	$ 106.5	$ 95.7
Investment securities available-for-sale:
Change in net unrealized gains (losses) during the period	(13.9)	(6.5)	(19.4)
Reclassification adjustment for net losses (gains) included in income	0.1	(0.7)	(0.3)
Change in unamortized loss on available-for-sale investment securities transferred into held-to-maturity	1.6	1.9	1.9
Change in net unrealized gain (loss) on derivatives	0	(1.1)	(0.2)
Reclassification adjustment for derivative net (gains) losses included in net income	0	1.1	0
Defined benefit post-retirement benefit plans:
Change in net actuarial loss	(0.6)	(1.3)	3.9
Other comprehensive income (loss), before tax	(12.8)	(6.6)	(14.1)
Deferred tax benefit (expense) related to other comprehensive income (loss)	3.3	2.8	5.5
Other comprehensive income (loss), net of tax	(9.5)	(3.8)	(8.6)
Comprehensive income	$ 150.7	$ 102.7	$ 87.1

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2015	$ 950.5	$ 311.7	$ 638.4	$ 0.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	95.7		95.7
Other comprehensive loss, net of tax	(8.6)			(8.6)
Common stock transactions:
Common shares purchased and retired	(26.9)	(26.9)
Common shares issued	0
Non-vested common shares issued	0
Non-vested common shares forfeited or canceled	0
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	4.7	4.7
Tax benefit of stock-based compensation	2.2	2.2
Stock-based compensation expense	4.4	4.4
Cash dividends declared:
Common (per share)	(39.4)		(39.4)
Ending Balance at Dec. 31, 2016	982.6	296.1	694.7	(8.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	106.5		106.5
Other comprehensive loss, net of tax	(3.8)			(3.8)
Common stock transactions:
Common shares purchased and retired	(1.3)	(1.3)
Non-vested common shares issued	0
Non-vested common shares forfeited or canceled	0
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	2.4	2.4
Tax benefit of stock-based compensation		2.6
Stock-based compensation expense	3.8	3.8
Cash dividends declared:
Common (per share)	(48.6)		(48.6)
Ending Balance at Dec. 31, 2017	1,427.6	687	752.6	(12)
Common stock transactions:
Common Stock, Value, Issued	386	386
Net income	160.2		160.2
Reclassifications Of Income Tax Effects				(3.1)
Other comprehensive loss, net of tax	(9.5)			(9.5)
Common shares purchased and retired	(1)	(1)
Non-vested common shares issued	0
Non-vested common shares forfeited or canceled	0
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	1.8	1.8
Tax benefit of stock-based compensation		1.1
Stock-based compensation expense	5.6
Cash dividends declared:
Common (per share)	(64.1)		(64.1)
Ending Balance at Dec. 31, 2018	1,693.9	866.7	$ 851.8	$ (24.6)
Common stock transactions:
Common Stock, Value, Issued	$ 173.3	$ 173.3

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical)	12 Months Ended
	Dec. 31, 2018shares
Common stock transactions:
Stock options exercised (in shares)	199,667

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 160,200	$ 106,500	$ 95,700
Adjustments to reconcile net income from operations to net cash provided by operating activities:
Provision for loan losses	8,600	11,000	10,000
Net (gain) loss on disposal of property and equipment	0	200	600
Depreciation and amortization	27,600	18,400	19,500
Net premium amortization on investment securities	10,000	11,600	12,500
Net (gain) loss on investment securities transactions	100	(700)	(300)
Realized and unrealized net gains on mortgage banking activities	(23,000)	(25,200)	(26,800)
Net loss (gain) on sale of OREO	(800)	100	(900)
Write-down of OREO and other assets pending disposal	100	400	800
Net (gain) on sale of Health Savings Accounts	0	(3,100)	0
Mortgage servicing rights recovery	0	(100)	0
Deferred income tax expense (benefit)	15,800	20,900	3,400
Net increase in cash surrender value of company-owned life insurance policies	(5,000)	(5,400)	(4,500)
Stock-based compensation expense	5,600	3,900	4,400
Tax benefits from stock-based compensation	0	0	2,100
Excess tax benefits from stock-based compensation	0	0	(1,600)
Originations of mortgage loans held for sale	(768,100)	(815,000)	(1,042,500)
Proceeds from sales of mortgage loans held for sale	798,400	860,100	1,054,500
Changes in operating assets and liabilities:
(Increase) decrease in interest receivable	(3,300)	(600)	(1,100)
Decrease (increase) in other assets	(8,000)	(6,100)	(2,200)
Increase (decrease) in interest payable	2,200	200	400
Increase (decrease) in accounts payable and accrued expenses	(200)	(22,500)	(6,000)
Net cash provided by operating activities	220,200	154,600	118,000
Purchases of investment securities:
Held-to-maturity	(2,000)	(12,800)	(18,200)
Available-for-sale	(541,000)	(614,300)	(905,900)
Proceeds from maturities, pay-downs, calls and sales of investment securities:
Held-to-maturity	79,300	97,400	112,600
Available-for-sale	460,000	426,200	814,600
Extensions of credit to customers, net of repayments	(221,700)	(99,700)	(168,300)
Recoveries of loans charged-off	12,000	7,800	9,200
Proceeds from sales of OREO	9,100	5,900	5,300
Acquisition of intangible assets	0	(28,000)	0
Proceeds from the sale of Health Savings Accounts	0	6,100	0
Proceeds from sale of loan production office	0	0	900
Acquisition of bank and bank holding company, net of cash and cash equivalents received	28,100	91,800	18,600
Capital expenditures, net of proceeds from sales	(6,100)	(11,000)	(11,900)
Net cash provided by (used in) investing activities	(182,300)	(130,600)	(143,100)
Cash flows from financing activities:
Net increase (decrease) in deposits	49,500	(110,200)	77,600
Net increase (decrease) in securities sold under repurchase agreements	69,400	105,400	8,900
Net increase (decrease) in other borrowed funds	(26,100)	100	0
Repayments of long-term debt	(7,100)	100	(100)
Advances on long-term debt	2,800	5,000	200
Proceeds from issuance of common stock	1,800	2,400	4,700
Excess tax benefits from stock-based compensation	0	0	1,600
Purchase and retirement of common stock	(1,000)	(1,300)	(26,900)
Dividends paid to common stockholders	(64,100)	(48,600)	(39,400)
Net cash used in financing activities	25,200	(47,100)	26,600
Net change in cash and cash equivalents	63,100	(23,100)	1,500
Cash and cash equivalents at beginning of period	758,900	782,000	780,500
Cash and cash equivalents at end of period	822,000	758,900	782,000
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	(25,300)	(28,800)	(54,400)
Cash paid during the period for interest expense	(38,700)	(27,800)	(17,200)
Supplemental disclosures of noncash investing and financing activities:
Transfer from long-term debt to other borrowed funds	0	20,000	0
Transfer of loans to other real estate owned	12,100	5,200	7,600
Capitalization of internally originated mortgage servicing rights	6,100	5,600	5,800
Supplemental schedule of noncash investing activities from acquisitions:
Investment securities available for sale	3,100	424,300	0
Investment securities held to maturity	0	57,300	0
Loans held for sale	0	10,300	0
Loans	713,100	2,079,300	0
Premises and equipment	14,000	47,700	0
Goodwill	101,100	231,900	0
Core deposit intangible	15,700	48,000	0
Mortgage servicing rights	0	3,500	0
Deferred tax assets	3,600	7,600	0
Interest receivable	9,500	57,000	0
Deferred tax assets	0	28,600	0
Other real estate owned	600	1,200	0
Other assets	6,200	31,600	0
Total noncash assets acquired	866,900	3,028,300	0
Deposits	696,300	2,669,000	0
Deferred tax liability	7,700	64,200	0
Noncash or Part Noncash Acquisition, Debt Assumed	7,000	0	0
Noncash or Part Noncash Acquisition, Other Liabilities Assumed	6,100	0	0
Noncash or Part Noncash Acquisition, Trust Preferred Securities Assumed	4,400	0	0
Noncash or Part Noncash Acquisition, Deferred Tax Liability	300	0	0
Total liabilities assumed	$ (721,800)	$ (2,733,200)	$ 0

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Business . First Interstate BancSystem, Inc. (the “Parent Company” and collectively with its subsidiaries, the “Company”) is a financial and bank holding company that, through the branch offices of its bank subsidiary, provides a comprehensive range of banking products and services to individuals, businesses, municipalities and other entities throughout Idaho, Montana, Oregon, South Dakota, Washington, and Wyoming. In addition to its primary emphasis on commercial and consumer banking services, the Company also offers trust, employee benefit, investment and insurance services through its bank subsidiary. The Company is subject to competition from other financial institutions and nonbank financial companies, and is also subject to the regulations of various government agencies and undergoes periodic examinations by those regulatory authorities. Basis of Presentation . The Company’s consolidated financial statements include the accounts of the Parent Company and its operating subsidiaries. As of December 31, 2018 , the Company had one significant subsidiary, First Interstate Bank (“FIB”). All significant intercompany balances and transactions have been eliminated in consolidation. Certain reclassifications, none of which were material, have been made in the consolidated financial statements for 2017 and 2016 to conform to the 2018 presentation. These reclassifications did not change previously reported net income or stockholders’ equity. Equity Method Investments. The Company has investments in real estate joint ventures that are not consolidated because the Company does not own a majority voting interest, control the operations or receive a majority of the losses or earnings of the joint venture. These joint ventures are accounted for using the equity method of accounting whereby the Company initially records its investment at cost (or fair value at the date of acquisition) and then subsequently adjusts the carrying value for the Company’s proportionate share of distributions and earnings or losses of the joint ventures. Variable Interest Entities. The Company’s wholly-owned business trusts, FI Statutory Trust I (“Trust I”), FI Capital Trust II (“Trust II”), FI Statutory Trust III (“Trust III”), FI Capital Trust IV (“Trust IV”), FI Statutory Trust V (“Trust V”), FI Statutory Trust VI (“Trust VI”), and Northwest Bancorporation Capital Trust I (“Trust VII”) are variable interest entities for which the Company is not a primary beneficiary. Accordingly, the accounts of Trust I, Trust II, Trust III, Trust IV, Trust V, Trust VI, and Trust VII are not included in the accompanying consolidated financial statements, and are instead accounted for using the equity method of accounting. The Company has equity investments in variable interest Certified Development Entities (“CDEs”) which have received allocations under the New Markets Tax Credits Program. The underlying activities of the CDEs are community development projects designed primarily to promote community welfare, such as economic rehabilitation and development of low-income areas by providing housing, services, or jobs for residents. The maximum exposure to loss in the CDEs is the amount of equity invested and credit extended by the Company. The Company has credit protection in the form of indemnification agreements, guarantees, and collateral arrangements. As the primary beneficiary of these variable interest entities, the Company’s consolidated financial statements include the assets, liabilities, and results of operations of the CDEs. The primary activities of the CDEs are recognized in interest and fees on loans, other non-interest income and long-term debt interest expense on the Company’s statements of operations. Related cash flows are recognized in loans originated, principal collected on loans and advances or repayments of long-term debt. Assets Held in Fiduciary or Agency Capacity. The Company holds certain trust assets in a fiduciary or agency capacity. The Company also purchases and sells federal funds as an agent. These and other assets held in an agency or fiduciary capacity are not assets of the Company and, accordingly, are not included in the accompanying consolidated financial statements. Use of Estimates. The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and income and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to change relate to the determination of the allowance for loan losses, the valuation of goodwill, fair valuations of investment securities and other financial instruments and the status of loss contingencies. Cash and Cash Equivalents . For purposes of reporting cash flows, cash and cash equivalents include cash on hand, amounts due from banks, federal funds sold for one day periods and interest bearing deposits in banks with original maturities of less than three months. As of December 31, 2018 and 2017 , the Company had cash of $574.4 million and $552.0 million , respectively, on deposit with the Federal Reserve Bank. In addition, the Company maintained compensating balances with the Federal Reserve Bank of approximately $28.1 million and $16.1 million as of December 31, 2018 and 2017 , respectively, to reduce service charges for check clearing services. Investment Securities . Investments in debt securities that the Company has the positive intent and ability to hold to maturity are classified as held-to-maturity and carried at amortized cost. Investments in debt securities that may be sold in response to or in anticipation of changes in interest rates and resulting prepayment risk, or other factors, and marketable equity securities are classified as available-for-sale and carried at fair value. The unrealized gains and losses on these securities are reported, net of applicable income taxes, as a separate component of stockholders’ equity and comprehensive income. Management determines the appropriate classification of securities at the time of purchase and at each reporting date management reassesses the appropriateness of the classification. The amortized cost of debt securities classified as held-to-maturity or available-for-sale is adjusted for accretion of discounts to maturity and amortization of premiums over the estimated average life of the security, or in the case of callable securities, through the first call date, using the effective yield method. Such amortization and accretion is included in interest income. Realized gains and losses are included in investment securities gains. Declines in the fair value of securities below their cost that are judged to be other-than-temporary are included in other expenses if the decline is related to credit losses. Other-than-temporary impairment losses related to other factors are recognized in other comprehensive income, net of income taxes. In estimating other-than-temporary impairment losses, the Company considers, among other things, the length of time and the extent to which the fair value has been less than cost, the financial condition and near-term prospects of the issuer and the intent and ability of the Company to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. The cost of securities sold is based on the specific identification method. Loans . Loans are reported at the principal amount outstanding. Interest income on loans is calculated using the simple interest method on the daily balance of the principal amount outstanding. Loan origination fees and certain direct origination costs are deferred, and the net amount is amortized as an adjustment of the related loan’s yield using a level yield method over the expected lives of the related loans. The accrual of interest on loans is discontinued when, in management’s opinion, the borrower may be unable to meet payment obligations as they become due or when a loan becomes contractually past due ninety days or more with respect to interest or principal, unless such past due loan is well secured and in the process of collection. When interest accrual is discontinued, all unpaid accrued interest is reversed against current period interest income. Interest income is subsequently recognized only to the extent cash payments are received in excess of principal due. Loans are returned to accrual status when all principal and interest amounts contractually due are brought current and when, in the opinion of management, the loans are estimated to be fully collectible as to both principal and interest. A loan is considered impaired when, based upon current information and events, it is probable that the Company will be unable to collect, on a timely basis, all amounts due according to the contractual terms of the loan’s original agreement. The amount of the impairment is measured using cash flows discounted at the loan’s effective interest rate, except when it is determined that the primary source of repayment for the loan is the operation or liquidation of the underlying collateral. In such cases, the current fair value of the collateral, reduced by anticipated selling costs, is used to measure impairment. The Company considers impaired loans to include all loans, except consumer loans, that are risk rated as doubtful or on which interest accrual has been discontinued or that have been renegotiated in a troubled debt restructuring. Interest payments received on impaired loans are applied based on whether they are on accrual or non-accrual status. Interest income recognized by the Company on impaired loans primarily relates to loans modified in troubled debt restructurings that remain on accrual status. 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. Loans acquired in a business combination are recorded and initially measured at their estimated fair value as of the acquisition date, with no carryover of the related allowance for credit losses. Credit risks are included in the determination of fair value. For loans with no significant evidence of credit deterioration since origination, the difference between the fair value and the unpaid principal balance of the loan at the acquisition date is amortized into interest income using the effective interest method over the remaining period to contractual maturity. The accounting for loans acquired with evidence of a deterioration of credit quality is described below. Loans acquired through the completion of a transfer, including loans acquired in business combinations, that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all contractually required payments receivable are initially recorded at fair value (as determined by the present value of expected future cash flows) with no valuation allowance. The difference between the undiscounted cash flows expected at acquisition and the recorded fair value of the loan, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment, a loss accrual or a valuation allowance. Increases in expected cash flows subsequent to the initial measurement are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition. A loan is considered a troubled debt restructuring when a borrower is experiencing financial difficulties that leads to a restructuring of the loan and the Company grants concessions to the borrower in the restructuring that it would not otherwise consider. These concessions may include rate reductions, principal forgiveness, extension of maturity date and other actions to minimize potential losses. Certain troubled debt restructurings are on non-accrual status at the time of restructuring and are returned to accrual status only after considering the borrower’s sustained repayment performance in accordance with the restructuring agreement for a reasonable 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 no longer be disclosed as a troubled debt restructuring although they continue to be individually evaluated for impairment and disclosed as impaired loans. Loans held for sale include residential mortgage loans originated for immediate sale. The Company has elected to account for loans held for sale using the fair value option. Under the fair value option, net loan origination fees are recognized in non-interest income at the time of origination. Subsequent changes in the estimated fair values of loans held for sale are recorded as unrealized gains and losses in non-interest income. Estimated fair values of loans held for sale are determined based upon current secondary market prices for loans with similar coupons, maturities and credit quality, or in the case of committed loans, on current delivery prices. Gains and losses on loans held for sale are recognized based on the difference between the net sales proceeds, including the estimated value associated with servicing assets or liabilities, and the net carrying value of the loans sold. Adjustments to reflect unrealized gains and losses resulting from changes in fair value of loans held for sale, as well as realized gains and losses on the sale of loans, are included in non-interest income - mortgage banking revenues on the accompanying consolidated statements of income. Loans held for sale were $33.3 million and $46.6 million as of December 31, 2018 and 2017 , respectively. As of December 31, 2018 , the Company had $0.4 million recorded investments in consumer mortgage loans secured by residential real estate for which formal foreclosure proceedings were in process. Allowance for Loan Losses . The allowance for loan losses is established through a provision for loan losses which is charged to expense. Loans, or portions thereof, are charged against the allowance for loan losses when management believes that the collectability of the principal is unlikely or, with respect to consumer installment and credit card loans, according to established delinquency schedules. The allowance balance is an amount that management believes will be adequate to absorb known and inherent losses in the loan portfolio based upon quarterly analysis of the current risk characteristics of the loan portfolio, an assessment of individual problem loans and actual loss experience, industry concentrations and current economic factors and the estimated impact of current economic and environmental conditions on historical loss rates. Loans acquired in business combinations are recorded at their estimated fair values on the date of acquisition. Accordingly, no allowance for loan losses related to these loans is recorded at the date of transfer. An allowance for loan losses is recorded for credit deterioration occurring subsequent to the transfer date. Goodwill . The excess purchase price over the fair value of net assets from acquisitions, or goodwill, is evaluated for impairment at least annually and on an interim basis if an event or circumstance indicates that it is likely impairment has occurred. Goodwill impairment is determined by comparing the fair value of a reporting unit to its carrying amount. In any given year the Company may elect to perform a qualitative assessment to determine whether it is more likely than not that the fair value of a reporting unit is in excess of its carrying value. If it is not more likely than not that the fair value of the reporting unit is in excess of the carrying value, or if the Company elects to bypass the qualitative assessment, a quantitative impairment test is performed. In performing a quantitative test for impairment, the fair value of net assets is estimated based on analyses of the Company’s market value, discounted cash flows and peer values. The determination of goodwill impairment is sensitive to market-based economics and other key assumptions used in determining or allocating fair value. Variability in the market and changes in assumptions or subjective measurements used to allocate fair value are reasonably possible and may have a material impact on our consolidated financial statements or results of operations. Core Deposit Intangibles. Core deposit intangibles represent the intangible value of depositor relationships resulting from deposit liabilities assumed, as a result of acquisitions, and are amortized using an accelerated method based on the estimated weighted average useful lives of the related deposits. Mortgage Servicing Rights . The Company recognizes the rights to service mortgage loans for others, whether acquired or internally originated. Mortgage servicing rights are initially recorded at fair value based on comparable market data and are amortized in proportion to and over the period of estimated net servicing income. Mortgage servicing rights are evaluated quarterly for impairment by discounting the expected future cash flows, taking into consideration the estimated level of prepayments based on current industry expectations and the predominant risk characteristics of the underlying loans including loan type, note rate and loan term. Impairment adjustments, if any, are recorded through a valuation allowance. Premises and Equipment . Buildings, furniture and equipment are stated at cost less accumulated depreciation. Depreciation expense is computed using straight-line methods over estimated useful lives of 5 to 45 years for buildings and improvements and 4 to 15 years for furniture and equipment. Leasehold improvements and assets acquired under capital lease are amortized over the shorter of their estimated useful lives or the terms of the related leases. Land is recorded at cost. Costs incurred for maintenance and repairs are expensed as incurred. Company-Owned Life Insurance . Key executive and group life insurance policies are recorded at their cash surrender value. Separate account group life insurance policies are subject to a stable value contract that offsets the impact of interest rate fluctuations on the market value of the policies and are recorded at the stabilized investment value. Increases in the cash surrender or stabilized investment value of insurance policies, as well as insurance proceeds received, are recorded as other non-interest income, and are not subject to income taxes. Deferred Compensation Plan. The Company has a deferred compensation plan for the benefit of certain highly compensated officers and directors of the Company. The plan allows for discretionary employer contributions in excess of tax limits applicable to the Company’s 401(k) and profit sharing plans and the deferral of salary, short-term incentives or director fees subject to certain limitations. Deferred compensation plan assets and liabilities are included in the Company’s consolidated balance sheets at fair value. As of December 31, 2018 and 2017 , deferred compensation plan assets were $12.1 million and $12.2 million , respectively. Corresponding deferred compensation plan liabilities were $12.1 million and $12.2 million as of December 31, 2018 and 2017 , respectively. Impairment of Long-Lived Assets. Long-lived assets, including premises and equipment and certain identifiable intangibles, are reviewed for impairment whenever events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. The amount of the impairment loss, if any, is based on the asset’s fair value. No impairment losses were recognized in 2018 and 2017 , respectively. Impairment losses of $0.2 million were recognized in other non-interest expense in 2016 . Other Real Estate Owned . Real estate acquired in satisfaction of loans is initially carried at current fair value less estimated selling costs. Any excess of loan carrying value over the fair value of the real estate acquired is recorded as a charge to the allowance for loan losses. Subsequent declines in fair value less estimated selling costs are included in OREO expense. Subsequent increases in fair value less estimated selling costs are recorded as a reduction in OREO expense to the extent of recognized losses. Operating expenses, net of related income, and gains or losses on sales are included in OREO expense. Write-downs of $0.1 million , $0.4 million and $0.6 million were recorded in 2018 , 2017 and 2016 , respectively. The carrying value of foreclosed residential real estate properties included in other real estate owned was $2.0 million as of December 31, 2018 , and $2.7 million as of December 31, 2017 . Restricted Equity Securities. The Company, as a member of the Federal Reserve Bank and the Federal Home Loan Bank (“FHLB”), is required to maintain investments in each of the organization’s capital stock. As of December 31, 2018 , restricted equity securities of the Federal Reserve Bank and the FHLB of $37.5 million and $10.7 million , respectively, were included in other assets at cost. As of December 31, 2017 , restricted equity securities of the Federal Reserve Bank and the FHLB were $31.8 million and $10.2 million , respectively. No ready market exists for these restricted equity securities, and they have no quoted market values. Restricted equity securities are periodically reviewed for impairment based on ultimate recovery of par value. The determination of whether a decline affects the ultimate recovery of par value is influenced by the significance of the decline compared to the cost basis of the restricted equity securities, the length of time a decline has persisted, the impact of legislative and regulatory changes on the issuing organizations and the liquidity positions of the issuing organizations. Based on management’s assessment, no impairment losses were recorded on restricted equity securities during 2018 , 2017 or 2016 . Derivatives and Hedging Activities. For asset and liability management purposes, the Company enters into interest rate swap contracts to hedge against changes in forecasted cash flows due to interest rate exposures. Interest rate swaps are contracts in which a series of interest payments are exchanged over a prescribed period. The notional amount upon which the interest payments are based is not exchanged. The swap agreements are derivative instruments and convert a portion of the Company’s forecasted variable rate debt to a fixed rate (i.e., cash flow hedge) over the payment term of the interest rate swap. The effective portion of the gain or loss on cash flow hedging instruments is initially reported as a component of other comprehensive income and subsequently reclassified into earnings in the same period during which the transaction affects earnings. The ineffective portion of the gain or loss on derivative instruments, if any, is recognized in earnings. The Company does not enter into interest rate swap agreements for trading or speculative purposes. As of December 31, 2018 , the Company does not have an existing agreement. The Company also 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. Earnings Per Common Share . Basic and diluted earnings per common share are calculated using a two-class method. Under the two-class method, basic earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period, excluding outstanding participating securities. Participating securities include non-vested performance restricted stock awards granted and all non-vested time restricted stock awards. Diluted earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding determined for the basic earnings per share calculation plus the dilutive effect of stock compensation using the treasury stock method. Income Taxes . The Parent Company and its subsidiaries have elected to be included in a consolidated federal income tax return. For state income tax purposes, the combined taxable income of the Parent Company and its subsidiaries is apportioned among the states in which operations take place. Federal and state income taxes attributable to the subsidiaries, computed on a separate return basis, are paid to or received from the Parent Company. The Company accounts for income taxes using the liability method. Under the liability method, deferred tax assets and liabilities are determined based on enacted income tax rates which will be in effect when the differences between the financial statement carrying values and tax bases of existing assets and liabilities are expected to be reported in taxable income. Positions taken in the Company’s tax returns may be subject to challenge by the taxing authorities upon examination. Uncertain tax positions are initially recognized in the financial statements when it is more likely than not the position will be sustained upon examination by the tax authorities. Such tax positions are both initially and subsequently measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon settlement with the tax authority, assuming full knowledge of the position and all relevant facts. The Company provides for interest and, in some cases, penalties on tax positions that may be challenged by the taxing authorities. Interest expense is recognized beginning in the first period that such interest would begin accruing. Penalties are recognized in the period that the Company claims the position in the tax return. Interest and penalties on income tax uncertainties are classified within income tax expense in the consolidated statements of income. With few exceptions, the Company is no longer subject to U.S. federal and state examinations by tax authorities for years before 2015 . The Company had no material penalties as of December 31, 2018 , 2017 or 2016 . Revenue Recognition. The Company recognizes revenue as it is earned based on contractual terms, as transactions occur, or as services are provided and collectability is reasonably assured. The principal source of revenue is interest income from loans and investments. The Company also earns non-interest income from various banking and financial services offered to its customers. Certain specific policies related to non-interest income include the following: Wealth management and trust fee income Wealth management and trust fee income represents monthly fees due from wealth management customers as consideration for managing the customers’ assets. Wealth management and trust services include custody of assets, investment management, fees for trust services and similar fiduciary activities. Revenue is recognized when our performance obligation is completed. The Company does not earn performance-based incentives. Optional services such as settlement, court, and regulatory fees are also available to existing trust and asset management customers. The Company’s performance obligation for these transactional-based services is generally satisfied, and related revenue recognized, at a point in time (i.e., as incurred). Service charges on deposit accounts Service charges on deposit accounts represent general service fees for account maintenance and activity- or transaction-based fees and consist of transaction-based revenue, time-based revenue (service period), item-based revenue or some other individual attribute-based revenue. Revenue is recognized when our performance obligation is completed for account maintenance services or when a transaction has been completed (such as a wire transfer or check orders). Payment for such performance obligations are generally received at a point in time when the performance obligations are satisfied. Interchange and other fees Interchange and other fees primarily represent debit and credit card income comprised of interchange fees earned whenever the Company’s debit and credit cards are processed through card payment networks such as MasterCard. ATM fees are primarily generated when a Company cardholder uses a non-Company ATM or a non-Company cardholder uses a Company ATM. Merchant services income primarily represents fees charged to merchants to process their debit and credit card transactions, in addition to account management fees. Swap fee income primarily represents income associated with the execution of dealer bank swap agreements. Other service charges include revenue from processing wire transfers, bill pay service, cashier’s checks, and other services. The Company’s performance obligation for interchange and other service charges are largely satisfied, and related revenue recognized, when completion of the services are rendered at a point in time. Annuity and insurance commissions Annuity and insurance commissions primarily re

Acquisitions

Acquisitions	12 Months Ended
Acquisitions	Dec. 31, 2018
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 IIBK, a community bank headquartered in Coeur d' Alene, Idaho with 11 banking offices across Idaho, in an all-stock transaction valued at approximately $181.3 million in aggregate, or $22.73 per share of IIBK stock, based on a per share price of First Interstate Class A common stock of $45.45 per share as of October 5, 2018. IIBK shareholders will be entitled to receive 0.50 shares of First Interstate Class A common stock for each share of IIBK common stock they own. The transaction has been approved by the boards of directors of both companies and is expected to close and convert data processing systems in the second quarter of 2019, subject to customary conditions, including regulatory and shareholder approvals. Community 1 st Bank. On October 11, 2018 , the Company also entered into a definitive agreement to acquire all of the outstanding stock of CMYF, a community bank headquartered in Post Falls, Idaho with three banking offices in North Idaho, in an all-stock transaction valued at approximately $21.5 million in aggregate, or $17.20 per share of CMYF stock, based on a per share price of First Interstate Class A common stock of $45.45 per share as of October 5, 2018. CMYF stockholders will be entitled to receive 0.3784 shares of First Interstate Class A common stock for each share of CMYF common stock they own. The transaction has been approved by the boards of directors of both companies and is expected to close and convert data processing systems in the second quarter of 2019, subject to customary conditions, including regulatory and shareholder approvals. 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 exchange 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 $101.1 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. Due to the recent closing of the transaction, all amounts reported are provisional pending the review of valuations obtained from third parties. 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 (0.5 ) (3) 14.0 Other real estate owned (“OREO”) 0.3 0.3 0.6 Core deposit intangible assets 2.4 13.3 (4) 15.7 Other assets 29.3 (10.0 ) (5) 19.3 Total assets acquired 800.7 (3.7 ) 797.0 Liabilities assumed: Deposits 696.1 0.2 (6) 696.3 Accounts payable and accrued expense 8.1 (0.4 ) (7) 7.7 Long term debt 13.0 0.1 13.1 Trust preferred securities 5.2 (0.8 ) (8) 4.4 Deferred tax liability, net (1.2 ) 1.5 (9) 0.3 Total liabilities assumed 721.2 0.6 721.8 Net assets acquired $ 79.5 $ (4.3 ) $ 75.2 Consideration paid: Cash $ 3.0 Class A common stock 173.3 Total consideration paid 176.3 Goodwill $ 101.1 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, other assets, and long term debt were made since the prior quarter, none of which were material. The adjustments had no impact on 2018 earnings and a net increase to goodwill of $0.3 million from the third quarter 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) 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) Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm. (5) Adjustment consists of reductions to the fair value of other items, including the removal of Northwest previously recorded goodwill. (6) 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) Decrease due to the write-off of off balance sheet reserves. (8) 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. (9) 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, 2017, are not presented because the effect of this acquisition was not considered significant. The accompanying consolidated statements of income include the results of operations of the acquired entity from the August 16, 2018 acquisition date. For the period from August 16, 2018 to September 30, 2018, Northwest reported revenues of $5.9 million and net income of $2.1 million . 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. Standalone amounts for INB were no longer available after that date. Cascade Bancorp. On November 17, 2016 , the Company entered into an agreement and plan of merger (the “Agreement”) to acquire all of the outstanding stock of Cascade Bancorp (“Cascade”), parent company of Bank of the Cascades, an Oregon-based community bank with 46 banking offices across Oregon, Idaho, and Washington. This transaction was strategic in allowing the Company to expand its community banking footprint in the Northwest corridor of the United States. The merger was completed on May 30, 2017 . Holders of each share of Cascade common stock received 0.14864 shares of First Interstate Class A common stock and $1.91 in cash, without interest, for each share of Cascade common stock. In connection with the merger, the Company issued approximately 11.3 million shares of First Interstate Class A common stock, which was valued at $34.30 per share, which was the closing price of First Interstate Class A common stock on the acquisition date. Cash paid by First Interstate was approximately $155.0 million , which included the cash portion of the merger consideration and the cash in lieu of fractional shares that Cascade Bancorp shareholders would have otherwise been entitled to receive. Total consideration exchanged in connection with the merger amounted to $541.0 million . All “in-the-money” Cascade options and all Cascade restricted stock units outstanding immediately prior to the transaction close were canceled in exchange for the right to receive a cash payment as provided in the Agreement. The Company paid approximately $9.3 million in cash related to Cascade options and restricted stock units, which was included in the consideration paid. Unvested Cascade restricted stock awards outstanding immediately prior to the transaction close were canceled in exchange for the right to receive a cash payment and Company shares as provided in the Agreement. The Company paid a total of approximately $2.2 million in cash and issued approximately 168 thousand Company shares, valued at $34.30 per share, related to Cascade unvested restricted stock awards. Of the cash paid and shares issued related to Cascade unvested restricted stock awards, approximately $2.4 million was allocated to expense and excluded from consideration paid due to the acceleration of award vesting at the Company’s discretion. The remaining balance of approximately $5.5 million related to unvested Cascade restricted stock awards is included in the consideration paid. The assets and liabilities of Cascade were recorded in the Company’s consolidated financial statements at their estimated fair values as of the acquisition date. The excess value of the consideration paid over the fair value of assets acquired and liabilities assumed is recorded as goodwill. The purchase price allocation resulted in goodwill of $232.8 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 Cascade and the Company. The following table summarizes the consideration paid, fair values of the Cascade assets acquired and liabilities assumed, and the resulting goodwill. All amounts were finalized in the first quarter of 2018. As Recorded Fair Value As Recorded As of May 30, 2017 by Cascade Adjustments by the Company Assets acquired: Cash and cash equivalents $ 246.8 $ — $ 246.8 Investment securities 476.7 4.9 (1) 481.6 Loans held for investment 2,111.0 (31.7 ) (2) 2,079.3 Mortgage loans held for sale 10.3 — 10.3 Allowance for loan losses (24.0 ) 24.0 (3) — Premises and equipment 46.6 0.1 (4) 46.7 Other real estate owned (“OREO”) 1.2 — 1.2 Core deposit intangible assets — 48.0 (5) 48.0 Deferred tax assets, net 47.6 (20.9 ) (6) 26.7 Other assets 98.6 2.1 (7) 100.7 Total assets acquired 3,014.8 26.5 3,041.3 Liabilities assumed: Deposits 2,669.9 (0.9 ) (8) 2,669.0 Accounts payable and accrued expense 62.2 1.9 (9) 64.1 Total liabilities assumed 2,732.1 1.0 2,733.1 Net assets acquired $ 282.7 $ 25.5 $ 308.2 Consideration paid: Cash $ 155.0 Class A common stock 386.0 Total consideration paid $ 541.0 Goodwill $ 232.8 Explanation of fair value adjustments: (1) Write up of the book value of investments to their estimated fair values on the date of acquisition based upon quotes obtained from an independent third party pricing service. (2) Write down of the book value of loans to their estimated fair values. Shared National Credits (SNC) were recorded at quoted sales prices where available. The fair value of the remaining 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. (3) Adjustment to remove the Cascade allowance for loan losses at acquisition date, as the credit risk is included in the fair value adjustment for loans receivable described in (2) above. (4) Write up of the book value of premises and equipment to their estimated fair values on the date of acquisition based upon appraisals obtained from an independent third party appraiser or broker’s opinion of value. (5) Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm. (6) Adjustment consists of the write-off of pre-existing deferred tax assets and purchase accounting adjustments as a result of the acquisition. (7) Adjustment consists of various other assets recorded as a result of the acquisition, including mortgage servicing rights, SBA servicing rights, and favorable leases offset by reductions to the fair value of other items. (8) Decrease 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. (9) Increase in fair value due to credit card incentive program, unfavorable leases, write-off of balance sheet reserve, and swap liability offset. Core deposit intangible assets of $48.0 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 ASC Topic 310-30. For loans that meet the criteria stipulated in 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 Cascade loans acquired deemed credit-impaired as of the May 30, 2017 acquisition date is as follows: Contractually required principal and interest payments $ 49.7 Contractual cash flows not expected to be collected (“non-accretable discount”) 24.7 Cash flows expected to be collected 25.0 Interest component of cash flows expected to be collected (“accretable discount”) 1.9 Fair value of acquired credit-impaired loans $ 23.1 Information regarding Cascade acquired loans not deemed credit-impaired at the May 30, 2017 acquisition date is as follows: Contractually required principal and interest payments $ 2,098.1 Contractual cash flows not expected to be collected 23.3 Fair value at acquisition $ 2,066.5 The accompanying consolidated statements of income include the results of operations of the acquired entity from the May 30, 2017 acquisition date. For the period from May 30, 2017 to June 30, 2017, Cascade reported revenues of $12.9 million and net income of $3.0 million . The acquired entities continued to operate as Bank of the Cascades until August 11, 2017 at which point Cascade’s operations were integrated with the Company’s operations, and Bank of the Cascades merged with FIB. Standalone amounts for the Bank of the Cascades were no longer available after that date. The following table presents unaudited pro forma consolidated revenues and net income as if the Cascade acquisition had occurred as of January 1, 2016. Year ended December 31, (unaudited) 2018 2017 Interest income $ 473.4 $ 420.8 Non-interest income 143.3 153.3 Total revenues $ 616.7 $ 574.1 Net income $ 162.5 $ 126.4 EPS - basic $ 2.81 $ 2.03 EPS - diluted 2.79 2.01 The unaudited pro forma net income presented in the table above for 2018 and 2017 was adjusted to exclude acquisition-related costs, including change in control expenses related to employee benefit plans and legal and professional expenses, of $2.3 million and $21.8 million , respectively, net of tax. The unaudited pro forma net income presented in the table above for 2018 and 2017 includes adjustments for scheduled amortization of core deposit intangible assets acquired in the acquisition. The unaudited supplemental pro forma net income presented in the table above for 2018 and 2017 does not capture operating costs savings and other business synergies expected as a result of the acquisition. Acquisition related expenses The Company recorded third party acquisition related costs of $12.4 million , $27.2 million and $2.8 million in 2018 , 2017 and 2016 , respectively. These costs are incorporated in non-interest expense in the Company’s consolidated statements of income and are summarized below. Dec 31, 2018 Dec 31, 2017 Dec 31, 2016 Legal and professional fees $ 4.0 $ 9.6 $ 2.1 Employee expenses 1.1 5.1 0.2 Technology conversion and contract termination 6.6 10.2 0.2 Other 0.7 2.3 0.3 Total acquisition related expenses $ 12.4 $ 27.2 $ 2.8

Goodwill and Core Deposit Intan

Goodwill and Core Deposit Intangibles	12 Months Ended
Goodwill and Core Deposit Intangibles	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Core Deposit Intangibles	GOODWILL AND CORE DEPOSIT INTANGIBLES Goodwill Year Ended December 31, 2018 2017 Net carrying value at beginning of period $ 444.7 $ 212.8 Acquisitions and measurement period adjustments 102.0 231.9 Net carrying value at end of period $ 546.7 $ 444.7 The Company performed its annual goodwill impairment qualitative assessment as of July 1, 2018 , 2017 , and 2016 and determined the Company’s goodwill was no t considered impaired. In addition, there were no events or circumstances that occurred during the second half of 2018 that would more-likely-than-not reduce the fair value of a reporting unit below its carrying value, the Company did not perform interim testing as of December 31, 2018 . Core deposit intangibles (“CDI”) The following table sets forth activity for identifiable core deposit intangibles subject to amortization: Year Ended December 31, 2018 2017 Gross CDI, beginning of period $ 74.0 $ 29.2 Established through acquisitions 15.7 48.0 Reductions due to sale of accounts — (3.2 ) Accumulated amortization (32.8 ) (24.9 ) Net CDI, end of period $ 56.9 $ 49.1 Amortization expense of CDI assets was $7.9 million , $5.5 million and $3.4 million for the fiscal years ended December 31, 2018 , 2017 and 2016 , respectively. CDI are evaluated for impairment if events and circumstances indicate a possible impairment. The CDI are amortized using an accelerated method based on the estimated weighted average useful lives of the related deposits, which is generally ten years. In 2017, the Company sold the custodial rights to our Health Savings Account (“HSA”) portfolio to HealthEquity, Inc. for $6.2 million , of which $3.2 million was attributable to BOTC acquired deposits which were sold at fair market value. The following table provides estimated future CDI amortization expense: Years ending December 31, 2019 $ 8.9 2020 8.1 2021 7.5 2022 6.9 2023 6.3 Thereafter 19.2 Total $ 56.9

Investment Securities

Investment Securities	12 Months Ended
Investment Securities	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Investment Securities	INVESTMENT SECURITIES The amortized cost and approximate fair values of investment securities are summarized as follows: 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 U.S agency residential mortgage-backed securities & 189.7 0.3 (6.5 ) 183.5 Corporate securities 46.3 0.1 (0.6 ) 45.8 Obligations of U.S. government agencies 19.8 — (0.3 ) 19.5 Other investments 0.1 — — 0.1 Total $ 406.8 $ 2.2 $ (8.3 ) $ 400.7 December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale U.S. Treasury notes $ 3.2 $ — $ — $ 3.2 Obligations of U.S. government agencies 569.5 — (8.0 ) 561.5 U.S. agency residential mortgage-backed securities & 1,474.1 3.8 (15.4 ) 1,462.5 Private mortgage-backed securities 91.5 — (0.8 ) 90.7 Corporate Securities 88.0 0.1 (0.3 ) 87.8 Other investments 3.0 — — 3.0 Total $ 2,229.3 $ 3.9 $ (24.5 ) $ 2,208.7 December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to Maturity State, county and municipal securities $ 172.4 $ 2.6 $ (0.6 ) $ 174.4 Obligations of U.S. government agencies 19.8 — (0.2 ) 19.6 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 230.5 8.8 (11.6 ) 227.7 Corporate securities 61.6 0.1 (0.3 ) 61.4 Other investments 0.2 — — 0.2 Total $ 484.5 $ 11.5 $ (12.7 ) $ 483.3 There were no material gross gains and $0.1 million of gross losses realized on the disposition of available-for-sale securities in 2018 . Gross gains of $1.1 million and $0.4 million were realized on the disposition of available-for-sale securities in 2017 and 2016 , respectively. Gross losses of $0.4 million and $0.1 million were realized on the disposition of available-for-sale securities in 2017 and 2016 , respectively. As of December 31, 2018 , the Company had general obligation securities with amortized costs of $115.5 million included in state, county and municipal securities, of which $66.8 million were issued by political subdivisions or agencies within the states of Idaho, Montana, Oregon, South Dakota, Washington, and Wyoming. 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 December 31, 2018 and 2017 . 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 Value 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 ) U.S. agency residential mortgage-backed 45.0 (2.2 ) 120.2 (4.3 ) 165.2 (6.5 ) Corporate securities — — 39.6 (0.6 ) 39.6 (0.6 ) Obligations of U.S. government agencies 19.5 (0.3 ) — — 19.5 (0.3 ) Total $ 90.4 $ (2.8 ) $ 216.9 $ (5.5 ) $ 307.3 $ (8.3 ) Less than 12 Months 12 Months or More Total December 31, 2017 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale Obligations of U.S. government agencies 284.9 (3.4 ) 266.1 (4.6 ) 551.0 (8.0 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 670.1 (6.2 ) 439.2 (9.2 ) 1,109.3 (15.4 ) Private mortgage-backed securities 74.0 (0.8 ) — — 74.0 (0.8 ) Corporate securities 51.3 (0.3 ) — — 51.3 (0.3 ) Total $ 1,080.3 $ (10.7 ) $ 705.3 $ (13.8 ) $ 1,785.6 $ (24.5 ) Less than 12 Months 12 Months or More Total December 31, 2017 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity State, county and municipal securities $ 53.3 $ (0.4 ) $ 12.3 $ (0.2 ) $ 65.6 $ (0.6 ) U.S. agency residential mortgage-backed 76.4 (9.1 ) 60.5 (2.5 ) $ 136.9 $ (11.6 ) Corporate securities $ 41.2 $ (0.2 ) $ 5.0 $ (0.1 ) $ 46.2 $ (0.3 ) Obligations of U.S. government agencies $ 9.7 $ — $ 9.9 $ (0.2 ) $ 19.6 $ (0.2 ) Total $ 180.6 $ (9.7 ) $ 87.7 $ (3.0 ) $ 268.3 $ (12.7 ) The investment portfolio is evaluated quarterly for other-than-temporary declines in the market value of each individual investment security. Consideration is given to the length of time and the extent to which the fair value has been less than cost; the financial condition and near term prospects of the issuer; and, the intent and ability of the Company to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. The Company had 760 and 581 individual investment securities that were in an unrealized loss position as of December 31, 2018 and 2017 , respectively. Unrealized losses as of December 31, 2018 and 2017 related primarily to fluctuations in the current interest rates. The fair value of these investment securities is expected to recover as the securities approach their maturity or repricing date or if market yields for such investments decline. As of December 31, 2018 , 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 2018 , 2017 or 2016 . Maturities of investment securities at December 31, 2018 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 December 31, 2018 Amortized Cost Estimated Fair Value Amortized Cost Estimated Fair Value Within one year $ 477.8 $ 472.3 $ 64.1 $ 63.0 After one year but within five years 1,519.2 1,495.0 221.6 216.7 After five years but within ten years 154.5 151.9 94.4 94.9 After ten years 153.7 151.5 26.7 26.1 Total $ 2,305.2 $ 2,270.7 $ 406.8 $ 400.7 At December 31, 2018 , the Company had investment securities callable within one year with amortized costs and estimated fair values of $64.7 million and $64.8 million , respectively. These investment securities are primarily classified as available-for-sale and included in the after one year but within five years category in the table above. At December 31, 2018 , 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 and included in the after one year but within five years category in the table above. Maturities of securities do not reflect rate repricing opportunities present in adjustable rate mortgage-backed securities. At December 31, 2018 and 2017 , the Company had variable rate mortgage-backed securities with amortized costs of $219.5 million and $247.9 million , respectively, classified as available-for-sale in the table above. There are no significant concentrations of investments at December 31, 2018 , (greater than 10 percent of stockholders’ equity) in any individual security issuer, except for U.S. government or agency-backed securities. Investment securities with amortized cost of $1,943.1 million and $2,087.7 million at December 31, 2018 and 2017 , respectively, were pledged to secure public deposits and securities sold under repurchase agreements. The approximate fair value of securities pledged at December 31, 2018 and 2017 was $1,908.4 million and $2,062.6 million , respectively. All securities sold under repurchase agreements are with customers and mature on the next banking day. The Company retains possession of the underlying securities sold under repurchase agreements.

Loans

Loans	12 Months Ended
Loans	Dec. 31, 2018
Loans Receivable, Net [Abstract]
Loans	LOANS The following table presents loans by class as of the dates indicated: December 31, 2018 2017 Real estate loans: Commercial $ 3,235.4 $ 2,822.9 Construction: Land acquisition & development 321.6 348.7 Residential 242.8 240.2 Commercial 274.3 119.4 Total construction loans 838.7 708.3 Residential 1,542.0 1,487.4 Agricultural 217.4 158.2 Total real estate loans 5,833.5 5,176.8 Consumer: Indirect consumer 787.8 784.7 Other consumer 200.6 175.1 Credit card 81.8 74.6 Total consumer loans 1,070.2 1,034.4 Commercial 1,310.3 1,215.4 Agricultural 254.8 136.2 Other, including overdrafts 1.6 4.9 Loans held for investment 8,470.4 7,567.7 Mortgage loans held for sale 33.3 46.6 Total loans $ 8,503.7 $ 7,614.3 The Company has lending policies and procedures in place that are designed to maximize loan income within an acceptable level of risk. Management reviews and approves these policies and procedures on a regular basis. A reporting system supplements the review process by providing management with frequent reports related to loan production, loan quality, concentrations of credit, loan delinquencies and internally risk-classified loans. Real estate loans include construction and permanent financing for both single-family and multi-unit properties, term loans for commercial, agricultural and industrial property and/or buildings and home equity loans and lines of credit secured by real estate. Longer-term residential real estate loans are generally sold in the secondary market. Those residential real estate loans not sold are typically secured by first liens on the financed property and generally mature in less than fifteen years . Home equity loans and lines of credit are typically secured by first or second liens on residential real estate and generally do not exceed a loan to value ratio of 80% . The Company had home equity loans and lines of credit of $409.5 million and $397.0 million as of December 31, 2018 and 2017 , respectively, included in residential real estate loans. Commercial and agricultural real estate loans are generally secured by first liens on income-producing real estate and generally mature in less than 5 years . Construction loans are primarily to commercial builders for residential lot development and the construction of single-family residences and commercial real estate properties. Construction loans are generally underwritten pursuant to pre-approved permanent financing. During the construction phase the borrower pays interest only. Consumer loans include direct personal loans, credit card loans, lines of credit and indirect dealer loans for the purchase of automobiles, recreational vehicles, boats and other consumer goods. Personal loans and indirect dealer loans are generally secured by automobiles, boats and other types of personal property and are made on an installment basis. Credit cards are offered to individuals in our market areas. Lines of credit are generally floating rate loans that are unsecured or secured by personal property. Commercial loans include a mix of variable and fixed rate loans made to small and medium-sized manufacturing, wholesale, retail and service businesses for working capital needs and business expansions. Commercial loans generally include lines of credit, business credit cards and loans with maturities of five years or less. The loans are generally made with business operations as the primary source of repayment, but also include collateralization by inventory, accounts receivable, equipment and/or personal guarantees. Agricultural loans generally consist of short and medium-term loans and lines of credit that are primarily used for crops, livestock, equipment and general operations. Agricultural loans are ordinarily secured by assets such as livestock or equipment and are repaid from the operations of the farm or ranch. Agricultural loans generally have maturities of five years or less, with operating lines for one production season. Included in the loan table above, are loans acquired in business combinations including 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 principal balance and accrual status of loans acquired with credit impairment as of December 31, 2018 and 2017 . December 31, 2018 2017 Outstanding principal $ 43.4 $ 38.2 Carrying value: Loans on accrual status 30.2 24.9 Total carrying value $ 30.2 $ 24.9 The following table summarizes changes in the accretable yield for loans acquired credit impaired for the years ended December 31, 2018 , 2017 , and 2016 : Year Ended December 31, 2018 2017 2016 Beginning balance $ 7.3 $ 6.8 $ 6.7 Acquisitions 3.2 1.9 1.1 Additions 0.6 0.1 — Accretion income (3.1 ) (2.9 ) (2.5 ) Reductions due to exit events (1.1 ) (1.5 ) (1.1 ) Reclassifications from nonaccretable differences 2.0 2.9 2.6 Ending balance $ 8.9 $ 7.3 $ 6.8 Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. The following tables present the contractual aging of the Company’s recorded investment in past due loans by class as of the period indicated: 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 Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of December 31, 2017 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 2.9 $ 0.5 $ 0.3 $ 3.7 $ 2,792.4 $ 26.8 $ 2,822.9 Construction: Land acquisition & development 7.3 0.3 0.3 7.9 337.8 3.0 348.7 Residential 2.1 — — 2.1 236.4 1.7 240.2 Commercial — — — — 115.6 3.8 119.4 Total construction loans 9.4 0.3 0.3 10.0 689.8 8.5 708.3 Residential 13.3 1.4 0.4 15.1 1,464.1 8.2 1,487.4 Agricultural 0.3 — 0.2 0.5 154.3 3.4 158.2 Total real estate loans 25.9 2.2 1.2 29.3 5,100.6 46.9 5,176.8 Consumer: Indirect consumer 7.8 2.1 0.4 10.3 772.6 1.8 784.7 Other consumer 1.6 0.5 0.1 2.2 172.6 0.3 175.1 Credit card 0.9 0.6 0.7 2.2 72.4 — 74.6 Total consumer loans 10.3 3.2 1.2 14.7 1,017.6 2.1 1,034.4 Commercial 3.9 1.7 0.7 6.3 1,189.5 19.6 1,215.4 Agricultural 1.8 0.1 — 1.9 133.5 0.8 136.2 Other, including overdrafts — — — — 4.9 — 4.9 Loans held for investment 41.9 7.2 3.1 52.2 7,446.1 69.4 7,567.7 Mortgage loans originated for sale — — — — 46.6 — 46.6 Total loans $ 41.9 $ 7.2 $ 3.1 $ 52.2 $ 7,492.7 $ 69.4 $ 7,614.3 Acquired loans that meet the criteria for non-accrual of interest prior to the acquisition were considered performing upon acquisition. If interest on non-accrual loans had been accrued, such income would have approximated $3.0 million , $3.5 million and $3.4 million during the years ended December 31, 2018 , 2017 , and 2016 , 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 the 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 dates indicated: 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 December 31, 2017 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 45.6 $ 20.9 $ 14.1 $ 35.0 $ 3.9 Construction: Land acquisition & development 10.0 3.4 0.5 3.9 — Residential 1.8 1.7 — 1.7 — Commercial 4.7 0.4 3.5 3.9 2.2 Total construction loans 16.5 5.5 4.0 9.5 2.2 Residential 11.5 8.2 2.0 10.2 0.1 Agricultural 3.7 3.6 — 3.6 — Total real estate loans 77.3 38.2 20.1 58.3 6.2 Commercial 29.5 12.4 11.4 23.8 4.4 Agricultural 1.1 0.8 0.3 1.1 0.2 Total $ 107.9 $ 51.4 $ 31.8 $ 83.2 $ 10.8 December 31, 2016 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 57.0 $ 24.4 $ 21.4 $ 45.8 $ 2.8 Construction: Land acquisition & development 12.1 4.3 1.8 6.1 0.8 Residential 1.6 0.2 0.6 0.8 — Commercial 4.8 3.9 0.7 4.6 0.7 Total construction loans 18.5 8.4 3.1 11.5 1.5 Residential 8.2 4.1 2.5 6.6 0.3 Agricultural 5.1 4.5 0.2 4.7 — Total real estate loans 88.8 41.4 27.2 68.6 4.6 Commercial 40.3 13.2 19.2 32.4 9.3 Agricultural 3.7 3.3 0.4 3.7 0.1 Total $ 132.8 $ 57.9 $ 46.8 $ 104.7 $ 14.0 The following tables present the average recorded investment in and income recognized on impaired loans for the periods indicated: Year Ended December 31, 2018 2017 2016 Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Real estate 50.0 0.1 63.5 0.3 69.2 0.3 Commercial 21.9 0.2 28.1 0.2 30.1 0.3 Agricultural 2.1 — 2.4 — 1.8 — Total $ 74.0 $ 0.3 $ 94.0 $ 0.5 $ 101.1 $ 0.6 The amount of interest income recognized by the Company within the period that the loans were impaired was primarily related to loans modified in troubled debt restructurings that remained on accrual status. 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 during 2018 , 2017 , and 2016 would have been approximately $3.0 million , $3.5 million and $ 4.2 million , respectively. Collateral dependent impaired loans are recorded at the fair value less selling costs of the underlying collateral determined 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 $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 loans renegotiated in troubled debt restructurings of $44.5 million as of December 31, 2017 , of which $31.9 million were included in non-accrual loans and $12.6 million were on accrual status. The following table presents information on the Company’s troubled debt restructurings that occurred during the periods indicated: Number of Notes Type of Concession Principal Balance at Restructure Date Year Ended December 31, 2018 Interest only period Extension of terms or maturity Interest rate adjustment Other Commercial real estate 3 $ 3.6 $ — $ — $ — $ 3.6 Agriculture real estate 1 — — — 0.2 0.2 Consumer 1 — — — 0.3 0.3 Total loans restructured 5 $ 3.6 $ — $ — $ 0.5 $ 4.1 Number of Notes Type of Concession Principal Balance at Restructure Date Year Ended December 31, 2017 Interest only period Extension of terms or maturity Interest rate adjustment Other Commercial real estate 5 $ 1.5 $ 0.4 $ — $ 0.9 $ 2.8 Agriculture real estate 1 — 0.8 — — 0.8 Commercial 17 1.2 2.0 — 6.0 9.2 Agriculture 1 — 0.1 — — 0.1 Total loans restructured 24 $ 2.7 $ 3.3 $ — $ 6.9 $ 12.9 Number of Notes Type of Concession Principal Balance at Restructure Date Year Ended December 31, 2016 Interest only period Extension of terms or maturity Interest rate adjustment Other Commercial real estate 18 $ 0.4 $ 5.5 $ 0.2 $ 1.8 $ 7.9 Commercial construction 1 — 3.7 — — 3.7 Residential real estate 1 — 0.1 — — 0.1 Commercial 13 4.4 0.4 — 3.3 8.1 Agriculture 2 — 0.3 — — 0.3 Total loans restructured 35 $ 4.8 $ 10.0 $ 0.2 $ 5.1 $ 20.1 Other concessions include payment reductions or deferrals for a specified period of time or the extension of amortization schedules. A specific reserve may have been previously recorded for loans modified in troubled debt restructurings that were on non-accrual status or otherwise deemed impaired before the modification. In periods subsequent to modification, the Company continues to evaluate all loans modified in troubled debt restructurings for possible impairment, which is recognized through the allowance for loan losses. Financial effects of modifications may include principal loan forgiveness or other charge-offs directly related to the restructuring. The Company had no charge-offs directly related to loans modified in troubled debt restructurings taken at the time of restructuring during 2018 , 2017 , and 2016 . The Company considers a payment default to occur on loans modified in troubled debt restructurings when the loan is 90 days or more past due or was placed on non-accrual status after the modification. The Company’s loans modified in troubled debt restructurings within the previous 12 months for which there was a payment default during the period were no t significant as of December 31, 2018 and December 31, 2016 . As of December 31, 2017 , the Company had one $1.3 million commercial loan modified in troubled debt restructurings within the previous 12 months for which there was a payment default during the period. As of December 31, 2018 , 2017 , and 2016 all of the loans modified in troubled debt restructurings with payment defaults during the previous twelve months were on non-accrual status. At December 31, 2018 , 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 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. 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 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 As of December 31, 2017 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 78.0 $ 96.4 $ 10.3 $ 184.7 Construction: Land acquisition & development 3.2 16.4 — 19.6 Residential 2.3 1.7 0.5 4.5 Commercial 2.4 3.6 3.5 9.5 Total construction loans 7.9 21.7 4.0 33.6 Residential 3.9 12.5 1.9 18.3 Agricultural 4.3 19.1 — 23.4 Total real estate loans 94.1 149.7 16.2 260.0 Consumer: Indirect consumer 0.8 2.2 0.3 3.3 Direct consumer 0.4 0.7 0.2 1.3 Total consumer loans 1.2 2.9 0.5 4.6 Commercial 54.7 56.3 11.1 122.1 Agricultural 5.1 8.3 0.4 13.8 Total $ 155.1 $ 217.2 $ 28.2 $ 400.5 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	12 Months Ended
Allowance for Loan Losses	Dec. 31, 2018
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: Year Ended December 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 (credited) to operating expense (0.7 ) 6.8 1.9 0.6 — 8.6 Less loans charged-off (3.7 ) (11.3 ) (4.7 ) — — (19.7 ) Add back recoveries of loans previously charged-off 3.7 4.5 3.6 0.2 — 12.0 Ending balance $ 31.0 $ 8.7 $ 31.3 $ 2.0 $ — $ 73.0 Individually evaluated for impairment $ 1.3 $ — $ 5.2 $ 0.3 $ — $ 6.8 Collectively evaluated for impairment 29.7 8.7 26.1 1.7 — 66.2 Ending balance $ 31.0 $ 8.7 $ 31.3 $ 2.0 $ — $ 73.0 Total loans: 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 Year Ended December 31, 2017 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 28.6 $ 7.7 $ 38.1 $ 1.8 $ — $ 76.2 Provision charged (credited) to operating expense 6.0 8.1 (2.9 ) (0.2 ) — 11.0 Less loans charged-off (4.3 ) (11.3 ) (6.8 ) (0.4 ) — (22.8 ) Add back recoveries of loans previously charged-off 1.4 4.2 2.1 — — 7.7 Ending balance $ 31.7 $ 8.7 $ 30.5 $ 1.2 $ — $ 72.1 Individually evaluated for impairment $ 6.2 $ — $ 4.4 $ 0.2 $ — $ 10.8 Collectively evaluated for impairment 25.5 8.7 26.1 1.0 — 61.3 Ending balance $ 31.7 $ 8.7 $ 30.5 $ 1.2 $ — $ 72.1 Total loans: Individually evaluated for impairment $ 58.3 $ — $ 23.8 $ 1.1 $ — $ 83.2 Collectively evaluated for impairment 5,118.5 1,034.4 1,191.6 135.1 4.9 7,484.5 Total loans held for investment $ 5,176.8 $ 1,034.4 $ 1,215.4 $ 136.2 $ 4.9 $ 7,567.7 Year Ended December 31, 2016 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 52.3 $ 5.1 $ 18.8 $ 0.6 $ — $ 76.8 Provision charged (credited) to operating expense (21.7 ) 8.4 21.9 1.4 — 10.0 Less loans charged-off (5.2 ) (8.6 ) (5.8 ) (0.2 ) — (19.8 ) Add back recoveries of loans previously charged-off 3.2 2.8 3.2 — — 9.2 Ending balance $ 28.6 $ 7.7 $ 38.1 $ 1.8 $ — $ 76.2 Individually evaluated for impairment $ 4.6 $ — $ 9.3 $ 0.1 $ — $ 14.0 Collectively evaluated for impairment 24.0 7.7 28.8 1.7 — 62.2 Ending balance $ 28.6 $ 7.7 $ 38.1 $ 1.8 $ — $ 76.2 Total loans: Individually evaluated for impairment $ 68.6 $ — $ 32.4 $ 3.7 $ — $ 104.7 Collectively evaluated for impairment 3,445.4 970.3 765.5 129.2 1.6 5,312.0 Total loans held for investment $ 3,514.0 $ 970.3 $ 797.9 $ 132.9 $ 1.6 $ 5,416.7 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 BOTC 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 December 31, 2018 and 2017 , the Company’s allowance for loan losses included $0.8 million and $1.0 million , respectively, related to loans acquired credit impaired.

Premises and Equipment

Premises and Equipment	12 Months Ended
Premises and Equipment	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Premises and Equipment	PREMISES AND EQUIPMENT Premises and equipment and related accumulated depreciation are as follows: December 31, 2018 2017 Land $ 49.9 $ 49.4 Buildings and improvements 268.1 257.1 Furniture and equipment 104.0 97.7 Total premises and equipment 422.0 404.2 Less accumulated depreciation (176.8 ) (162.3 ) Premises and equipment, net $ 245.2 $ 241.9 The Parent Company and a FIB branch office lease premises from an affiliated entity. See Note 17—Commitments and Contingencies.

Company-Owned Life Insurance

Company-Owned Life Insurance	12 Months Ended
Company-Owned Life Insurance	Dec. 31, 2018
Investments, All Other Investments [Abstract]
Company-Owned Life Insurance	COMPANY-OWNED LIFE INSURANCE Company-owned life insurance consists of the following: December 31, 2018 2017 Key executive, principal shareholder $ 4.7 $ 4.2 Key executive split dollar 9.4 4.9 Group life 261.0 251.5 Total $ 275.1 $ 260.6 The Company maintains key executive life insurance policies on certain principal shareholders. Under these policies, the Company receives benefits payable upon the death of the insured. The net cash surrender value of key executive, principal shareholder insurance policies was $4.7 million and $4.2 million at December 31, 2018 and 2017 , respectively. The Company also has life insurance policies covering selected other key officers. The net cash surrender value of these policies was $9.4 million and $4.9 million at December 31, 2018 and 2017 , respectively. Under these policies, the Company receives benefits payable upon death of the insured. An endorsement split dollar agreement has been executed with the selected key officers whereby a portion of the policy death benefit is payable to their designated beneficiaries. The endorsement split dollar agreement will provide post-retirement coverage for those selected key officers meeting specified retirement qualifications. The Company expenses the earned portion of the post-employment benefit through the vesting period. The Company has group life insurance policies covering selected officers of FIB. The net cash surrender value of these policies was $261.0 million and $251.5 million at December 31, 2018 and 2017 , respectively. Under these policies, the Company receives benefits payable upon death of the insured. The Company has entered into either an endorsement split dollar agreement or a survivor income benefit agreement with each insured officer. Under the endorsement split dollar agreements, a portion of the policy death benefit is payable to the insured’s designated beneficiary if the insured is employed by the Company at the time of death. Under the survivor income benefit agreements, the Company makes a lump-sum payment to the insured’s designated beneficiary if the insured is employed by the Company at the time of death.

Other Real Estate Owned

Other Real Estate Owned	12 Months Ended
Other Real Estate Owned	Dec. 31, 2018
Repossessed Assets [Abstract]
Other Real Estate Owned	OTHER REAL ESTATE OWNED Information with respect to the Company’s other real estate owned follows: Year Ended December 31, 2018 2017 2016 Balance at beginning of year $ 10.1 $ 10.0 $ 6.3 Acquisitions 0.6 1.2 1.1 Additions 12.1 5.4 7.6 Valuation adjustments (0.1 ) (0.4 ) (0.6 ) Dispositions (8.3 ) (6.1 ) (4.4 ) Balance at end of year $ 14.4 $ 10.1 $ 10.0 Write-downs of $0.1 million during 2018 were adjustments based on other sources, including management estimates of the current fair value of properties. Write-downs of $0.4 million and $0.6 million during 2017 and 2016 , respectively, were adjustments based on other sources, including management estimates of the current fair value of properties and adjustments directly related to receipt of updated appraisals.

Derivatives and Hedging Activit

Derivatives and Hedging Activities	12 Months Ended
Derivatives and Hedging Activities	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging Activities	DERIVATIVES AND HEDGING ACTIVITIES 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. December 31, 2018 December 31, 2017 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 $ 403.3 $ 8.8 $ 344.2 $ 7.5 Interest rate lock commitments 51.0 1.3 60.7 1.3 Total derivative assets $ 454.3 $ 10.1 $ 404.9 $ 8.8 Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets) Non-hedging interest rate derivatives: Interest rate swap contracts $ 403.3 $ 8.8 $ 344.2 $ 7.8 Forward loan sales contracts 64.6 0.6 88.8 0.1 Total derivative liabilities $ 467.9 $ 9.4 $ 433.0 $ 7.9 On September 6, 2017, the Company paid $1.1 million to terminate an existing interest rate swap contract designated as a cash flow hedge, originally entered into on September 22, 2015, with a notional amount of $100 million . Under the terms of the interest rate swap contract, the Company would have paid a fixed interest rate of 1.94% and the counterparty would have paid to the Company a variable interest rate equal to the three-month LIBOR. As the contract was terminated prior to the effective date of September 15, 2017, no cash was exchanged outside of the termination payment. The effective portion of changes in the fair value of derivatives designated and that qualify as cash flow hedges is recorded in Accumulated Other Comprehensive Income and is subsequently reclassified into earnings in the period that the hedged forecasted transaction affects earnings. The ineffective portion of the change in fair value of the derivatives is recognized directly in earnings. The Company did not record any hedge ineffectiveness at December 31, 2018 and 2017 . 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 December 31, 2018 and December 31, 2017 : 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 December 31, 2017 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 $ 7.5 $ — $ 7.5 $ 2.4 $ — $ 5.1 Mortgage related derivatives 1.3 — 1.3 — — 1.3 Total derivatives 8.8 — 8.8 2.4 — 6.4 Total assets $ 8.8 $ — $ 8.8 $ 2.4 $ — $ 6.4 Financial Liabilities Interest rate swap contracts $ 7.8 $ — $ 7.8 $ 2.4 $ 3.3 $ 2.1 Mortgage related derivatives 0.1 — 0.1 — — 0.1 Total derivatives 7.9 — 7.9 2.4 3.3 2.2 Repurchase agreements 643.0 — 643.0 — 643.0 — Total liabilities $ 650.9 $ — $ 650.9 $ 2.4 $ 646.3 $ 2.2 The following table presents the pre-tax gains or losses related to derivative contracts that were recorded in accumulated other comprehensive income and other non-interest income in the Company’s statements of income: As of or For The Year Ended December 31, 2018 2017 2016 Derivatives designated as hedges: Amount of loss recognized in other comprehensive income (effective portion) $ — $ (1.1 ) $ (0.2 ) Reclassification adjustment for derivative net (gains) losses included in income — 1.1 — Non-hedging interest rate derivatives: Amount of gain (loss) recognized in other non-interest income 0.3 — 0.1 Amount of net fee income recognized in other non-interest income 1.3 0.8 0.9 Amount of net gains (losses) recognized in mortgage banking revenues (0.5 ) (1.7 ) 1.4

Mortgage Servicing Rights

Mortgage Servicing Rights	12 Months Ended
Mortgage Servicing Rights	Dec. 31, 2018
Transfers and Servicing [Abstract]
Mortgage Servicing Rights	MORTGAGE SERVICING RIGHTS Information with respect to the Company’s mortgage servicing rights follows: Year Ended December 31, 2018 2017 2016 Balance at beginning of year $ 24.8 $ 18.7 $ 15.9 Acquisitions of mortgage servicing rights — 3.5 — Originations of mortgage servicing rights 6.0 5.6 5.8 Amortization expense (3.1 ) (3.0 ) (3.0 ) Balance at end of year 27.7 24.8 18.7 Less valuation reserve — — (0.2 ) Balance at end of year, net of valuation reserve $ 27.7 $ 24.8 $ 18.5 Principal balance of serviced loans underlying mortgage servicing rights $ 3,698.2 $ 3,636.7 $ 3,127.5 Mortgage servicing rights as a percentage of serviced loans 0.75 % 0.68 % 0.59 % At December 31, 2018 , the estimated fair value and weighted average remaining life of the Company’s mortgage servicing rights were $42.4 million and 8.0 years, respectively. The fair value of mortgage servicing rights was determined using discount rates ranging from 10.4% to 12.1% and monthly prepayment speeds ranging from 0.4% to 1.5% depending upon the risk characteristics of the underlying loans. At December 31, 2017 , the estimated fair value and weighted average remaining life of the Company’s mortgage servicing rights were $40.1 million and 7.3 years, respectively. The fair value of mortgage servicing rights was determined using discount rates ranging from 9.5% to 11.3% and monthly prepayment speeds ranging from 0.5% to 1.8% depending upon the risk characteristics of the underlying loans. There were no material impairments reversed in 2018 , 2017 and 2016 , respectively. No permanent impairment was recorded in 2018 , 2017 or 2016 .

Deposits

Deposits	12 Months Ended
Deposits	Dec. 31, 2018
Deposits [Abstract]
Deposits	DEPOSITS Deposits are summarized as follows: December 31, 2018 2017 Non-interest bearing demand $ 3,158.3 $ 2,900.0 Interest bearing: Demand 2,957.5 2,787.5 Savings 3,247.9 3,095.4 Time, $100 and over 547.6 432.0 Time, other 769.4 720.0 Total interest bearing 7,522.4 7,034.9 Total deposits $ 10,680.7 $ 9,934.9 Other time deposits include $24.1 million and zero brokered deposits as of December 31, 2018 and 2017 , respectively, and deposits obtained through the Company’s participation in the Certificate of Deposit Account Registry Service (“CDARS”). CDARS deposits totaled $87.1 million and $94.2 million as of December 31, 2018 and 2017 , respectively. As of December 31, 2018 and 2017 , the Company had time deposits of $221.0 million and $182.0 million , respectively, that met or exceeded the FDIC insurance limit of $250,000 . Maturities of time deposits at December 31, 2018 are as follows: Time, $100 and Over Total Time Due within 3 months or less $ 45.0 $ 253.8 Due after 3 months and within 6 months 49.0 149.2 Due after 6 months and within 12 months 217.5 420.4 Due within 2020 159.7 323.7 Due within 2021 63.5 128.8 Due within 2022 9.8 30.3 Due within 2023 and thereafter 3.1 10.8 Total $ 547.6 $ 1,317.0 Interest expense on time deposits of $100 and over was $7.0 million , $4.3 million and $3.7 million for the years ended December 31, 2018 , 2017 and 2016 , respectively.

Long-Term Debt and Other Borrow

Long-Term Debt and Other Borrowed Funds	12 Months Ended
Long-Term Debt and Other Borrowed Funds	Dec. 31, 2018
Debt Disclosure [Abstract]
Long-Term Debt and Other Borrowed Funds	LONG-TERM DEBT AND OTHER BORROWED FUNDS A summary of long-term debt follows: December 31, 2018 2017 Subsidiaries: 8.00% capital lease obligation with term ending October 25, 2029 1.3 1.4 6.24% note payable maturing September 6, 2032, principal due at maturity, interest payable monthly 1.8 1.6 2.28% note payable maturing July 29, 2022, principal due at maturity, interest payable monthly 5.0 5.0 1.00% note payable maturing December 31, 2041, interest only payable quarterly until December 31, 2025 and then principal and interest until maturity 5.1 5.1 Note payable maturing March 31, 2038, interest only payable at 1.30% monthly until March 31, 2025 and then principal and interest at 3.25% until maturity 2.0 — 1.30% note payable maturing June 1, 2034, interest only payable monthly until March 31, 2025 and then principal and interest until maturity 0.6 — Total long-term debt $ 15.8 $ 13.1 Maturities of long-term debt at December 31, 2018 are as follows: 2019 $ 0.1 2020 0.1 2021 0.1 2022 5.1 2023 0.1 Thereafter 10.3 Total $ 15.8 The Company has available lines of credit with the FHLB of approximately $1,399.0 million , subject to collateral availability. As of December 31, 2018 and 2017 , there were no long or short-term advances outstanding with the FHLB. The Company has a capital lease obligation on a banking office. Assets acquired under capital lease, consisting solely of a building and leasehold improvements, are included in premises and equipment and are subject to depreciation. The Company borrowed or assumed through acquisitions $14.4 million and $11.7 million as of December 31, 2018 and 2017 , respectively, related to New Market Tax Credits. The long-term debt obligations consists of fixed rate note payables with various interest rates from 1.00% to 6.24% and maturities from July 29, 2022 through March 31, 2038 , collateralized by the Company’s equity interest in various CDEs, which are 99.9% owned by the Company. The Company had no material other borrowed funds as of December 31, 2018 . As of December 31, 2017 , the Company had other borrowed funds of $20.0 million , primarily consisting of a fixed rate subordinated term loan which was redeemed during the first quarter of 2018. The Company has federal funds lines of credit with third parties amounting to $205.0 million , subject to funds availability. These lines are subject to cancellation without notice. The Company also has a line of credit with the Federal Reserve Bank for borrowings up to $461.7 million secured by a blanket pledge of indirect consumer loans, and has an unused $50.0 million revolving line of credit with U.S. Bank National Association.

Subordinated Debentures Held by

Subordinated Debentures Held by Subsidiary Trusts	12 Months Ended
Subordinated Debentures Held by Subsidiary Trusts	Dec. 31, 2018
Subordinated Borrowings [Abstract]
Subordinated Debentures Held by Subsidiary Trusts	SUBORDINATED DEBENTURES HELD BY SUBSIDIARY TRUSTS The Company sponsors seven wholly-owned business trusts, Trust I, Trust II, Trust III, Trust IV, Trust V, Trust VI, and Trust VII (collectively, the “Trusts”). The Trusts were formed for the exclusive purpose of issuing an aggregate of $84.3 million of 30 -year floating rate mandatorily redeemable capital trust preferred securities (“Trust Preferred Securities”) to third-party investors. The Trusts also issued, in aggregate, $2.6 million of common equity securities to the Parent Company. Proceeds from the issuance of the Trust Preferred Securities and common equity securities were invested in 30 -year junior subordinated deferrable interest debentures (“Subordinated Debentures”) issued by the Parent Company. A summary of Subordinated Debenture issuances follows: Principal Amount Outstanding as of December 31, Issuance Maturity Date 2018 2017 October 2007 January 1, 2038 $ 10.3 $ 10.3 November 2007 December 15, 2037 15.5 15.5 December 2007 December 15, 2037 20.6 20.6 December 2007 April 1, 2038 15.5 15.5 January 2008 April 1, 2038 10.3 10.3 January 2008 April 1, 2038 10.3 10.3 June 2005 June 30, 2035 4.4 — Total subordinated debentures held by subsidiary trusts $ 86.9 $ 82.5 In October 2007 , the Company issued $10.3 million of Subordinated Debentures to Trust II. The Subordinated Debentures bear a cumulative floating interest rate equal to LIBOR plus 2.25% per annum. As of December 31, 2018 , the interest rate on the Subordinated Debentures was 5.05% . In November 2007 , the Company issued $15.5 million of Subordinated Debentures to Trust I. The Subordinated Debentures bore interest at a fixed rate of 7.50% for five years after issuance until December 16, 2012, and thereafter at a variable rate equal to LIBOR plus 2.75% per annum. As of December 31, 2018 , the interest rate on the Subordinated Debentures was 5.54% . In December 2007 , the Company issued $20.6 million of Subordinated Debentures to Trust III. The Subordinated Debentures bore interest at a fixed rate of 6.88% for five years after issuance until December 15, 2012, and thereafter at a variable rate equal to LIBOR plus 2.40% per annum. As of December 31, 2018 , the interest rate on the Subordinated Debentures was 5.19% . In December 2007 , the Company issued $15.5 million of Subordinated Debentures to Trust IV. The Subordinated Debentures bear a cumulative floating interest rate equal to LIBOR plus 2.70% per annum. As of December 31, 2018 the interest rate on the Subordinated Debentures was 5.50% . In January 2008 , the Company issued $10.3 million of Subordinated Debentures to Trust V. The Subordinated Debentures bore interest at a fixed rate of 6.78% for five years after issuance until April 1, 2013, and thereafter at a variable rate equal to LIBOR plus 2.75% per annum. As of December 31, 2018 the interest rate on the Subordinated Debentures was 5.55% . In January 2008 , the Company issued $10.3 million of Subordinated Debentures to Trust VI. The Subordinated Debentures bear a cumulative floating interest rate equal to LIBOR plus 2.75% per annum. As of December 31, 2018 , the interest rate on the Subordinated Debentures was 5.55% . In conjunction with the acquisition of Northwest in August 2018, the Company acquired Northwest Bancorporation Capital Trust I (“Trust VII”). The Northwest Trust was formed for the exclusive purpose of issuing an aggregate of $5.0 million of 30-year floating rate mandatorily redeemable capital trust preferred securities (“Northwest Trust Preferred Securities”) to third-party investors. The Trusts also issued, in aggregate, $0.2 million of common equity securities to Northwest. Proceeds from the issuance of the Trust Preferred Securities and common equity securities were invested in 30-year junior subordinated deferrable interest debentures (“Northwest Subordinated Debentures”) issued by Northwest. The Subordinated Debentures bore interest at a fixed rate of 5.95% for five years after issuance until June 30, 2010, and thereafter at a variable rate equal to LIBOR plus 1.70% per annum. As of December 31, 2018 the interest rate on the Subordinated Debentures was 4.50% . The Subordinated Debentures are unsecured with interest distributions payable quarterly. The Company may defer the payment of interest at any time provided that the deferral period does not extend past the stated maturity. During any such deferral period, distributions on the Trust Preferred Securities will also be deferred and the Company’s ability to pay dividends on its common and preferred shares is restricted. The Subordinated Debentures may be redeemed, subject to approval by the Federal Reserve Bank, at the Company’s option on or after five years from the date of issue, or at any time in the event of unfavorable changes in laws or regulations. Debt issuance costs consisting primarily of underwriting discounts and professional fees were capitalized and are being amortized through maturity to interest expense using the straight-line method, which approximates level yield. The terms of the Trust Preferred Securities are identical to those of the Subordinated Debentures. The Trust Preferred Securities are subject to mandatory redemption upon repayment of the Subordinated Debentures at their stated maturity dates or earlier redemption in an amount equal to their liquidation amount plus accumulated and unpaid distributions to the date of redemption. The Company guarantees the payment of distributions and payments for redemption or liquidation of the Trust Preferred Securities to the extent of funds held by the Trusts. Subject to certain limitations, the Trust Preferred Securities qualify as tier 1 capital of the Parent Company under the Federal Reserve Board’s capital adequacy guidelines. Proceeds from the issuance of the Trust Preferred Securities were used to fund acquisitions.

Capital Stock and Dividend Rest

Capital Stock and Dividend Restrictions	12 Months Ended
Capital Stock and Dividend Restrictions	Dec. 31, 2018
Equity [Abstract]
Capital Stock and Dividend Restrictions	CAPITAL STOCK AND DIVIDEND RESTRICTIONS The Company’s authorized common stock consists of 200,000,000 shares, of which, 100,000,000 shares are designated as Class A common stock and 100,000,000 are designated as Class B common stock. The Class A common stock has one vote per share. The Class B common stock has five votes per share and is convertible to Class A common stock on a share-for-share basis at any time. 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 . The Company had 33,560,202 shares of Class A common stock and 22,905,357 shares of Class B common stock outstanding as of December 31, 2017 . During 2018 , the Company issued 11,389 shares of its Class A common stock with an aggregate value of $0.5 million to directors for their service on the Company’s board of directors during 2018 . During 2017 , the Company issued 14,926 shares of its Class A common stock with an aggregate value of $0.5 million to directors for their service on the Company’s board of directors during 2017 . The aggregate value of the shares issued to directors of is included in stock-based compensation expense in the accompanying consolidated statements of changes in stockholders’ equity. During 2018 and 2017 , the Company did no t 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. On November 28, 2018, we filed a registration statement on Form S-4, as amended on January 16, 2019, to register 492,069 shares of Class A common stock to be issued as consideration for our acquisition of CMYF. On November 28, 2018, we filed a registration statement on Form S-4, as amended on January 16, 2019, to register 4,045,302 shares of Class A common stock to be issued as consideration for our acquisition of IIBK. On June 8, 2018, we filed a registration statement on Form S-4, as amended on July 2, 2018 with registration statement on Form S-4/A, to register 3,982,842 shares of Class A common stock to be issued as consideration for our acquisition of Northwest. On August 16, 2018 , the Company issued 3,837,540 shares of its Class A common stock with an aggregate value of $173.3 million as consideration for the acquisition of Northwest. On September 25, 2017, the Company filed a shelf registration statement on Form S-3, which was subsequently declared effective by the SEC. The registration statement permits us to offer and sell up to $ 250.0 million of our Class A common shares in one or more future public offerings. At the present time, we have no specific plans to offer any of the securities covered by the registration statement. The payment of dividends by subsidiary banks is subject to various federal and state regulatory limitations. In general, a bank is limited, without the prior consent of its regulators, to paying dividends that do not exceed current year net profits together with retained earnings from the two preceding calendar years. The Company’s debt instruments also include limitations on the payment of dividends.

Earnings per Common Share

Earnings per Common Share	12 Months Ended
Earnings per Common Share	Dec. 31, 2018
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 common share: Year Ended December 31, 2018 2017 2016 Net income, basic and diluted $ 160.2 $ 106.5 $ 95.7 Weighted average common shares outstanding for basic earnings per share computation 57,778,857 51,429,366 44,511,774 Dilutive effects of stock-based compensation 438,266 473,843 398,622 Weighted average common shares outstanding for diluted earnings per common share computation 58,217,123 51,903,209 44,910,396 Basic earnings per common share $ 2.77 $ 2.07 $ 2.15 Diluted earnings per common share 2.75 2.05 2.13 The Company had 448 , 83,635 and 7,215 unvested time restricted stock outstanding as of December 31, 2018 , 2017 , and 2016 respectively, that were not included in the computation of diluted earnings per common share because their effect would be anti-dilutive. The Company had 83,475 , 113,874 and 155,637 shares of unvested restricted stock as of December 31, 2018 , 2017 , and 2016 , 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	12 Months Ended
Regulatory Capital	Dec. 31, 2018
Banking and Thrift [Abstract]
Regulatory Capital	REGULATORY CAPITAL The Company and the Bank are subject to various regulatory capital requirements administered by federal banking regulators and the Federal Reserve. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company’s and the Bank’s financial statements. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, the Company and the Bank must meet specific capital guidelines that involve quantitative measures of the Company’s and Bank’s assets, liabilities and certain off-balance sheet items as calculated under regulatory accounting practices. The Parent Company, like all bank holding companies, is not subject to the prompt corrective action provisions. The Company’s and the Bank’s capital amounts and classification are also subject to qualitative judgments by the regulators about components, risk weightings and other factors. Quantitative measures established by regulation to ensure capital adequacy require the Company to maintain minimum amounts and ratios of total and tier 1 capital to risk-weighted assets, and of tier 1 capital to average assets, as defined in the regulations. As of December 31, 2018 , the Company exceeded all capital adequacy requirements to which it is subject. As of December 31, 2018 , the most recent notification from the regulatory agencies categorized the Bank as well capitalized under the regulatory framework for prompt corrective action. To be categorized as well-capitalized, the institution must maintain minimum total risk-based, Tier 1 risk-based, and Tier 1 leverage ratios as set forth in the following table. There are no conditions or events since the most recent notification that management believes have changed the Bank's categories. As an approved mortgage seller, the Bank is required to maintain a minimum level of capital specified by the United States Department of Housing and Urban Development. At December 31, 2018 and 2017 , the Bank met these requirements. The Company’s actual capital amounts and ratios and selected minimum regulatory thresholds and prompt corrective action provisions as of December 31, 2018 and 2017 are presented in the following tables: Actual Adequately Capitalized Basel III Phase-In Schedule Adequately Capitalized Basel III Fully Phased-In Well Capitalized (1) Amount Ratio Amount Ratio Amount Ratio Amount Ratio December 31, 2018 Total risk-based capital: Consolidated $ 1,285.0 12.99 % $ 976.6 9.875 % $ 1,038.4 10.50 % $ 989.0 10.00 % FIB 1,184.5 12.01 973.7 9.875 1,035.3 10.50 986.0 10.00 Tier 1 risk-based capital: Consolidated 1,212.0 12.26 778.8 7.875 840.6 8.50 791.2 8.00 FIB 1,111.6 11.27 776.5 7.875 838.1 8.50 788.8 8.00 Common equity tier 1 risk-based capital: Consolidated 1,127.8 11.40 630.5 6.375 692.3 7.00 642.8 6.50 FIB 1,111.6 11.27 628.6 6.375 690.2 7.00 640.9 6.50 Leverage capital ratio: Consolidated 1,212.0 9.47 511.9 4.00 511.9 4.00 639.9 5.00 FIB 1,111.6 8.97 495.9 4.00 495.9 4.00 619.8 5.00 Actual Adequately Capitalized Basel III Phase-In Schedule Adequately Capitalized Basel III Fully Phased-In Well Capitalized (1) Amount Ratio Amount Ratio Amount Ratio Amount Ratio December 31, 2017 Total risk-based capital: Consolidated $ 1,112.5 12.76 % $ 806.5 9.25 % $ 915.5 10.50 % $ 871.9 10.00 % FIB 1,066.6 12.29 802.7 9.25 911.2 10.50 867.8 10.00 Tier 1 risk-based capital: Consolidated 1,040.3 11.93 632.1 7.25 741.1 8.50 697.5 8.00 FIB 994.4 11.46 629.1 7.25 737.6 8.50 694.2 8.00 Common equity tier 1 risk-based capital: Consolidated 962.4 11.04 501.3 5.75 610.3 7.00 566.7 6.50 FIB 994.4 11.46 499.0 5.75 607.4 7.00 564.1 6.50 Leverage capital ratio: Consolidated 1,040.3 8.86 469.9 4.00 469.9 4.00 587.4 5.00 FIB 994.4 8.48 469.1 4.00 469.1 4.00 586.3 5.00 (1) The ratios for the well capitalized requirement are only applicable to FIB. However, the Company manages its capital position as if the requirement applies to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis. 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. When fully phased in on January 1, 2019, the Basel III Capital Rules will require the Company to maintain (i) a minimum ratio of common equity tier 1 capital to risk-weighted assets of at least 4.5% , plus a 2.5% “capital conservation buffer” (which is added to the 4.5% tier 1 capital to risk-weighted assets of at least 7.0% upon full implementation), (ii) a minimum ratio of tier 1 capital to risk-weighted assets of at least 6.0% , plus the capital conservation buffer (which is added to the 6.0% tier 1 capital ratio as that buffer is phased in, effectively resulting in a minimum tier 1 capital ratio of 8.5% upon full implementation), (iii) a minimum ratio of total capital to risk-weighted assets of at least 8.0% , plus the capital conservation buffer (which is added to the 8.0% total capital ratio as that buffer is phased in, effectively resulting in a minimum total capital ratio of 10.5% upon full implementation) and (iv) a minimum leverage ratio of 4.0% , calculated as the ratio of tier 1 capital to average quarterly assets. The implementation of the capital conservation buffer began on January 1, 2016 at the 0.625% level and will be phased in over a four-year period (increasing by that amount on each subsequent January 1, until it reaches 2.5% on January 1, 2019). The Basel III Capital Rules also provide for a “countercyclical capital buffer” that is applicable to only certain covered institutions and does not have any current applicability to us. The capital conservation buffer is designed to absorb losses during periods of economic stress and, as detailed above, effectively increases the minimum required risk-weighted capital ratios. Banking institutions with a ratio of common equity tier 1 capital to risk-weighted assets below the effective minimum ( 4.5% plus the capital conservation buffer and, if applicable, the countercyclical capital buffer) will face constraints on dividends, equity repurchases and compensation based on the amount of the shortfall. As of December 31, 2018 , the Company’s capital conservation buffer was 4.99% for the consolidated company and 4.01% for FIB.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES The Company had commitments under construction contracts of $2.7 million as of December 31, 2018 . The Parent Company and the Billings office of FIB are the anchor tenants in a building owned by an entity in which FIB has a 50.0% ownership interest. The Company leases certain premises and equipment from third parties under operating leases. Total rental expense to third parties was $3.2 million , $2.5 million , and $1.9 million , in 2018 , 2017 and 2016 , respectively. The total future minimum rental commitments, exclusive of maintenance and operating costs, required under operating leases that have initial or remaining noncancelable lease terms in excess of one year at December 31, 2018 , are as follows: Third Parties Related Entity Total For the year ending December 31: 2019 $ 4.4 $ 1.6 $ 6.0 2020 4.2 1.5 5.7 2021 4.1 1.4 5.5 2022 4.1 1.2 5.3 2023 3.9 1.2 5.1 Thereafter 15.3 2.8 18.1 Total $ 36.0 $ 9.7 $ 45.7 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 and $1.9 million of sold residential mortgage loans with recourse provisions still in effect as of December 31, 2018 and 2017 , respectively. The Company did not repurchase any significant amount of loans from secondary market investors under the terms of loan sales agreements during the years ended December 31, 2018 , 2017 and 2016 . In the opinion of management, the risk of recourse and the subsequent requirement of loan repurchase to the Company is not significant, and accordingly no liabilities have been established related to such. In addition, the Company made various representations and warranties associated with the sale of loans. The Company has not incurred significant losses resulting from these provisions. On October 11, 2018 , the Company entered into a definitive agreement to acquire all of the outstanding stock of IIBK, a community bank headquartered in Coeur d' Alene, Idaho with 11 banking offices across Idaho, in an all-stock transaction valued at approximately $181.3 million in aggregate, or $22.73 per share of IIBK stock, based on a per share price of First Interstate Class A common stock of $45.45 per share as of October 5, 2018. IIBK shareholders will be entitled to receive 0.50 shares of First Interstate Class A common stock for each share of IIBK common stock they own. The transaction has been approved by the boards of directors of both companies and is expected to close and convert data processing systems in the second quarter of 2019, subject to customary conditions, including regulatory and shareholder approvals. Also on October 11, 2018 , the Company entered into a definitive agreement to acquire all of the outstanding stock of CMYF, a community bank headquartered in Post Falls, Idaho with three banking offices in North Idaho, in an all-stock transaction valued at approximately $21.5 million in aggregate, or $17.20 per share of CMYF stock, based on a per share price of First Interstate Class A common stock of $45.45 per share as of October 5, 2018. CMYF stockholders will be entitled to receive 0.3784 shares of First Interstate Class A common stock for each share of CMYF common stock they own. The transaction has been approved by the boards of directors of both companies and is expected to close and convert data processing systems in the second quarter of 2019, subject to customary conditions, including regulatory and shareholder approvals. A substantial portion of the Company’s customers’ ability to honor their contracts is dependent on the economy in Idaho, Montana, Oregon, South Dakota, Washington, and Wyoming. The Company’s loan portfolio is diversified and assigned to risk classifications by industry concentrations and the current economic conditions. These industry concentrations of credit are taken into consideration by management in determining the allowance for loan and lease losses. 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 is not expected to have a material adverse effect on the consolidated financial condition, results of operations or liquidity of the Company.

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk	12 Months Ended
Financial Instruments with Off-Balance Sheet Risk	Dec. 31, 2018
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. These instruments involve, to varying degrees, elements of credit and interest rate risk in excess of amounts recorded in the consolidated balance sheets. The Company evaluates each customer’s creditworthiness on a case-by-case basis. The amount of collateral obtained is based on management’s credit evaluation of the customer. Collateral held varies but may include accounts receivable, inventory, premises and equipment, and income-producing commercial properties. 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. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. Generally, commitments to extend credit are subject to annual renewal. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. Commitments to extend credit to borrowers approximated $2,620.4 million at December 31, 2018 , which included $726.7 million on unused credit card lines and $1,058.5 million with commitment maturities beyond one year. Commitments to extend credit to borrowers approximated $2,179.5 million at December 31, 2017 , which included $635.3 million on unused credit card lines and $775.0 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. Most commitments extend for no more than two years and are generally subject to annual renewal. The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loan facilities to customers. The Company’s policy for obtaining collateral, and the nature of such collateral, is essentially the same as that involved in making commitments to extend credit. At December 31, 2018 and 2017 , the Company had outstanding stand-by letters of credit of $46.7 million and $50.5 million , respectively. The estimated fair value of the obligation undertaken by the Company in issuing standby letters of credit is included in accounts payable and accrued expenses in the Company’s consolidated balance sheets.

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES Income tax expense consists of the following: Year ended December 31, 2018 2017 2016 Current: Federal $ 23.1 $ 24.3 $ 40.3 State 7.2 5.0 5.9 Total current 30.3 29.3 46.2 Deferred: Federal 12.3 18.4 2.9 State 3.5 2.5 0.5 Total deferred 15.8 20.9 3.4 Total income tax expense $ 46.1 $ 50.2 $ 49.6 Total income tax provision differs from the amount of income tax determined by applying the statutory federal income tax rate of 21% for 2018 and 35% for 2017 and 2016 , respectively, to income before income taxes due to the following: Year ended December 31, 2018 2017 2016 Tax expense at the statutory tax rate $ 43.3 $ 54.9 $ 50.8 Increase (decrease) in tax resulting from: Tax-exempt income (2.8 ) (4.5 ) (4.4 ) State income tax, net of federal income tax benefit 8.5 4.9 4.3 Benefit of stock-based compensation plans (1.1 ) (2.6 ) — Federal tax credits (2.6 ) (2.5 ) (2.1 ) Benefit due to enactment of federal tax reform — (2.2 ) — Other, net 0.8 2.2 1.0 Tax expense at effective tax rate $ 46.1 $ 50.2 $ 49.6 The tax effects of temporary differences between the financial statement carrying amounts and tax bases of assets and liabilities that give rise to significant portions of the net deferred tax asset (liability) relate to the following: December 31, 2018 2017 Deferred tax assets: Loans, principally due to allowance for loan losses $ 18.4 $ 18.0 Loan discount 8.3 6.7 Investment securities, unrealized losses 8.9 5.6 Deferred compensation 17.0 13.1 Non-performing loan interest 1.2 1.1 Other real estate owned write-downs and carrying costs 0.3 0.6 Tax credit carryforwards (1) 0.1 3.7 Net operating loss carryforwards (2) 3.9 8.7 Other 0.1 3.1 Deferred tax assets 58.2 60.6 Deferred tax liabilities: Fixed assets, principally differences in bases and depreciation (6.9 ) (6.7 ) Deferred loan costs (2.6 ) (1.7 ) Investment in joint venture partnership, principally due to differences in depreciation of partnership assets (0.8 ) (0.8 ) Prepaid amounts (0.6 ) (0.6 ) Government agency stock dividends (1.5 ) (1.6 ) Goodwill and core deposit intangibles (44.2 ) (38.1 ) Mortgage servicing rights (6.4 ) (5.7 ) Other (3.8 ) (1.4 ) Deferred tax liabilities (66.8 ) (56.6 ) Net deferred tax assets (liabilities) $ (8.6 ) $ 4.0 (1) Based on filed tax returns and amounts expected to be reported in current year tax returns ( December 31, 2018 ), we had remaining federal tax credit carryforwards of $0.1 million from acquired companies. The remaining federal tax credits were primarily generated from AMT tax credit carryforwards, and their use is subject to annual limitations. (2) As of December 31, 2018 , we had remaining federal net operating loss carryforwards of $5.4 million from acquired companies, which is available to offset federal taxable income and state net operating loss carryforwards in amounts which vary by state. The federal net operating losses will expire beginning in 2029 and ending in 2037 and the state net operating losses will expire beginning in 2019 and ending in 2034. The use of these carryforwards is subject to annual limitations. The Company had current net income tax receivables of $2.0 million and $5.7 million at December 31, 2018 and 2017 , respectively.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
Stock-Based Compensation	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	STOCK-BASED COMPENSATION The Company has equity awards outstanding under two stock-based compensation plans; the 2015 Equity Incentive Plan (the “2015 Plan”) and the 2006 Equity Compensation Plan, as amended and restated (the “2006 Plan”). These plans were primarily established to enhance the Company’s ability to attract, retain and motivate employees. The Company’s Board of Directors or, upon delegation, the Compensation Committee of the Board of Directors (“Compensation Committee”) has exclusive authority to select employees, advisors and others, including directors, to receive awards and to establish the terms and conditions of each award made pursuant to the Company’s stock-based compensation plans. The 2015 Plan, approved by the Company’s shareholders in May 2015, was established to provide the Company with flexibility to select from various equity-based performance compensation methods, and to be able to address changing accounting and tax rules and corporate governance practices by optimally utilizing performance based compensation. The 2015 Plan did not increase the number of shares of common stock available for awards under the 2006 Plan. The 2006 Plan, approved by the Company’s shareholders in May 2006 and May 2014, was established to consolidate into one plan the benefits available under all other than existing share-based award plans. The 2006 Plan continues with respect to awards made prior to June 2015. All shares of common stock available for future grant under the 2006 Plan were transferred into the 2015 Plan. At December 31, 2018 , there were 1,727,765 common shares available for future grant under the 2015 Plan. Stock Options. All options granted have an exercise price equal to fair market value, which is currently defined as the closing sales price for the stock as quoted on the NASDAQ Stock Market for the last market trading day preceding the date that the Company’s Board of Directors awards the benefit. Options may be subject to vesting as determined by the Company’s Board of Directors or Compensation Committee, and can be exercised for periods of up to ten years from the date of grant. No stock option awards were granted in 2018 or 2017 . All outstanding stock option awards were fully vested as of December 31, 2016. As such, there was no compensation expense or related income tax benefits recognized related to stock option awards in 2018 or 2017 . Compensation expense related to stock option awards and the related income tax benefits for the year ended December 31, 2016 were not considered material. The following table summarizes stock option activity under the Company’s active stock option plans: Year Ended December 31, 2018 Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contract Life Outstanding options, beginning of year 642,255 $ 16.13 Granted — — Exercised (199,667 ) 17.12 Forfeited (14,412 ) 20.87 Expired — — Outstanding options, end of year 428,176 $ 15.61 1.56 years Outstanding options exercisable, end of year 428,176 $ 15.61 1.56 years The total intrinsic value of fully-vested stock options outstanding as of December 31, 2018 was $9.0 million . The total intrinsic value of options exercised was $4.9 million , $6.3 million and $5.6 million during the years ended December 31, 2018 , 2017 and 2016 , respectively. The actual tax benefit realized for the tax deduction from option exercises totaled $0.9 million , $2.0 million and $2.1 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. The Company received cash of $1.8 million , $2.4 million and $4.7 million from stock option exercises during the years ended December 31, 2018 , 2017 and 2016 , respectively. The Company redeemed common stock with aggregate values of $1.6 million , $2.8 million and $3.1 million tendered in payment for stock option exercises during the years ended December 31, 2018 , 2017 and 2016 , respectively. Restricted Stock Awards. Common stock issued under the Company’s restricted stock plan may not be sold or otherwise transferred until restrictions have lapsed or performance objectives have been obtained. During the vesting periods, participants have voting rights and receive dividends on all time restricted shares and vesting performance restricted shares. Upon termination of employment, common shares upon which restrictions have not lapsed must be returned to the Company. All restricted share awards are classified as equity awards. The fair value of equity-classified restricted stock awards is amortized as compensation expense on a straight-line basis over the period restrictions lapse or performance goals are met. Compensation expense related to restricted stock awards of $5.6 million , $3.3 million and $3.9 million was included in benefits on the Company’s consolidated statements of income for the years ended December 31, 2018 , 2017 and 2016 , respectively. Related income tax benefits recognized for the years ended December 31, 2018 , 2017 and 2016 were $0.2 million , $0.6 million and $1.5 million , respectively. The following table presents information regarding the Company’s restricted stock: As of December 31, 2018 Number of Shares Weighted-Average Measurement Date Fair Value Restricted stock, beginning of year 292,506 $ 33.24 Granted 214,893 40.97 Vested (83,736 ) 32.42 Forfeited (43,079 ) 36.64 Canceled — — Restricted stock, end of year 380,584 $ 37.46 During 2018 , the Company issued 214,893 restricted common shares. The 2018 restricted share awards included 59,464 performance restricted shares, of which 29,732 vest in varying percentages upon achievement of defined return on equity performance goals, and 29,732 vest in varying percentages upon achievement of defined total return to shareholder goals. Vesting of the performance restricted shares is also contingent on employment as of December 31, 2020 . Additionally, 155,429 time-restricted shares were issued during 2018 that vest one-third on each annual anniversary of the grant date through February 15, 2021 , contingent on continued employment through the vesting date. As of December 31, 2018 , there was $7.9 million of unrecognized compensation cost related to non-vested, restricted stock awards expected to be recognized over a period of 1.91 years .

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
Employee Benefit Plans	Dec. 31, 2018
Compensation Related Costs [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS Profit Sharing Plan. The Company has a noncontributory profit sharing plan. All employees, other than temporary employees, working 20 hours or more per week are eligible to participate in the profit sharing plan. The Company’s Board of Directors authorizes all contributions to the profit sharing plan. Participants become 100% vested upon the completion of two years of vesting service. Accrued contribution expense for this plan of $2.4 million , $1.6 million and $2.7 million in 2018 , 2017 and 2016 , respectively, is included in employee benefits expense in the Company’s consolidated statements of income. Savings Plan. In addition, the Company has a contributory employee savings plan. Eligibility requirements for this plan are the same as those for the profit sharing plan discussed in the preceding paragraph. Employee participation in the plan is at the option of the employee. The Company contributes $1.25 for each $1.00 of employee contributions up to 4% of the participating employee’s compensation. Contribution expense for this plan of $6.3 million , $5.5 million and $4.8 million in 2018 , 2017 and 2016 , respectively, is included in employee benefits expense in the Company’s consolidated statements of income. Post-Retirement Healthcare Plan. The Company sponsors a contributory defined benefit healthcare plan (the “Plan”) for active employees and employees and directors retiring from the Company at the age of at least 55 years and with at least 15 years of continuous service. Retired Plan participants contribute the full cost of benefits based on the average per capita cost of benefit coverage for both active employees and retired Plan participants. In 2016, the Company amended the Plan to discontinue offering healthcare benefits to future retirees beginning July 1, 2016, with current retirees as of July 1, 2016 continuing in the Plan. The Company recorded a $2.8 million gain in conjunction with the Plan amendment, which was recorded in other comprehensive income and is being amortized as a reduction in net periodic benefit cost over the weighted average remaining service period of active employees expected to receive post-retirement healthcare benefits under the Plan of approximately four years . The Plan amendment triggered a curtailment, which immediately reduced the Company’s accumulated post-retirement benefit obligation and net periodic benefit cost by $2.8 million and $0.3 million , respectively. The Plan’s unfunded benefit obligation of $0.5 million and $0.7 million as of December 31, 2018 and 2017 , respectively, is included in accounts payable and accrued expenses in the Company’s consolidated balance sheets. Net periodic benefit costs of $0.8 million , $0.4 million and $0.2 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, are included in employee benefits expense in the Company’s consolidated statements of income. Weighted average actuarial assumptions used to determine the post-retirement benefit obligation at December 31, 2018 , and the net periodic benefit costs for the year then ended, included a discount rate of 3.6% and a 6.0% annual increase in the per capita cost of covered healthcare benefits. Weighted average actuarial assumptions used to determine the post-retirement benefit obligation at December 31, 2017 , and the net periodic benefit costs for the year then ended, included a discount rate of 2.4% and a 6.0% annual increase in the per capita cost of covered healthcare benefits. The estimated effect of a one percent increase or a one percent decrease in the assumed healthcare cost trend rate would not significantly impact the service and interest cost components of the net periodic benefit cost or the accumulated post-retirement benefit obligation. Future benefit payments are expected to be $0.14 million , $0.12 million , $0.09 million , $0.06 million , $0.05 million and $0.10 million for 2019 , 2020 , 2021 , 2022 , 2023 , and 2024 through 2028 , respectively. At December 31, 2018 , the Company had accumulated other comprehensive gain related to the plan of $1.2 million , or $0.9 million net of related income tax benefit, comprised primarily of an unamortized transition asset of $0.7 million .

Other Comprehensive Income

Other Comprehensive Income	12 Months Ended
Other Comprehensive Income	Dec. 31, 2018
Equity [Abstract]
Other Comprehensive Income	OTHER COMPREHENSIVE INCOME The gross amounts of each component of other comprehensive income and the related tax effects for the periods indicated are as follows: Year Ended December 31, 2018 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized loss during period $ (13.9 ) $ (3.6 ) $ (10.3 ) Reclassification adjustment for net loss included in net income 0.1 — 0.1 Change in unamortized loss on available-for-sale securities transferred into held-to-maturity 1.6 0.4 1.2 Defined benefits post-retirement benefit plan: Change in net actuarial loss (gain) (0.6 ) (0.1 ) (0.5 ) Total other comprehensive loss $ (12.8 ) $ (3.3 ) $ (9.5 ) Year Ended December 31, 2017 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized loss during period $ (6.5 ) $ (2.7 ) $ (3.8 ) Reclassification adjustment for net gains included in net income (0.7 ) (0.3 ) (0.4 ) Change in unamortized loss on available-for-sale securities transferred into held-to-maturity 1.9 0.7 1.2 Change in net unrealized loss on derivatives (1.1 ) (0.4 ) (0.7 ) Reclassification adjustment for derivative net (gains) losses included in net income 1.1 0.4 0.7 Defined benefits post-retirement benefit plan: Change in net actuarial loss (gain) (1.3 ) (0.5 ) (0.8 ) Total other comprehensive loss $ (6.6 ) $ (2.8 ) $ (3.8 ) Year Ended December 31, 2016 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized loss during period $ (19.4 ) $ (7.6 ) $ (11.8 ) Reclassification adjustment for net gains included in net income (0.3 ) (0.1 ) (0.2 ) Change in unamortized gain on available-for-sale securities transferred into held-to-maturity 1.9 0.7 1.2 Change in net unrealized loss on derivatives (0.2 ) (0.1 ) (0.1 ) Defined benefits post-retirement benefit plan: Change in net actuarial loss (gain) 3.9 1.6 2.3 Total other comprehensive income $ (14.1 ) $ (5.5 ) $ (8.6 ) The components of accumulated other comprehensive income (loss), net of income taxes, are as follows: Year ended December 31, 2018 2017 Net unrealized gain (loss) on investment securities available-for-sale $ (25.5 ) $ (13.3 ) Net actuarial gain (loss) on defined benefit post-retirement benefit plans 0.9 1.3 Net accumulated other comprehensive income (loss) $ (24.6 ) $ (12.0 )

Condensed Financial Information

Condensed Financial Information (Parent Company Only)	12 Months Ended
Condensed Financial Information (Parent Company Only)	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Condensed Financial Information (Parent Company Only)	CONDENSED FINANCIAL INFORMATION (PARENT COMPANY ONLY) Following is condensed financial information of First Interstate BancSystem, Inc. December 31, 2018 2017 Condensed balance sheets: Cash and cash equivalents $ 72.9 $ 42.3 Investment in bank subsidiary 1,648.9 1,432.3 Advances to subsidiaries, net 46.0 25.7 Other assets 59.0 61.7 Total assets $ 1,826.8 $ 1,562.0 Other liabilities $ 46.0 $ 51.9 Subordinated debentures held by subsidiary trusts 86.9 82.5 Total liabilities 132.9 134.4 Stockholders’ equity 1,693.9 1,427.6 Total liabilities and stockholders’ equity $ 1,826.8 $ 1,562.0 Years Ended December 31, 2018 2017 2016 Condensed statements of income: Dividends from subsidiaries $ 148.5 $ 150.0 $ 140.0 Other interest income 0.1 0.1 — Other income, primarily management fees from subsidiaries 17.0 18.0 15.1 Total income 165.6 168.1 155.1 Salaries and benefits 25.3 21.8 18.8 Interest expense 4.5 4.7 4.1 Acquisition expenses 8.1 25.3 1.5 Other operating expenses, net 14.5 13.0 10.4 Total expenses 52.4 64.8 34.8 Earnings before income tax benefit 113.2 103.3 120.3 Income tax benefit (9.3 ) (14.2 ) (7.7 ) Income before undistributed earnings of subsidiaries 122.5 117.5 128.0 Undistributed earnings of subsidiaries 37.7 (11.0 ) (32.4 ) Net income $ 160.2 $ 106.5 $ 95.6 Years Ended December 31, 2018 2017 2016 Condensed statements of cash flows: Cash flows from operating activities: Net income $ 160.2 $ 106.5 $ 95.6 Adjustments to reconcile net income to cash provided by operating activities: Undistributed earnings of subsidiaries (37.7 ) 11.0 32.4 Stock-based compensation expense 5.6 3.9 4.4 Tax benefits from stock-based compensation — — 2.1 Excess tax benefits from stock-based compensation — — (1.6 ) Other, net 16.4 14.7 (0.8 ) Net cash provided by operating activities 144.5 136.1 132.1 Cash flows from investing activities: Capital distributions from nonbank subsidiaries — 18.0 2.0 Acquisition of intangible assets — (28.0 ) — Acquisition of bank holding company, net of cash and cash equivalents received (14.7 ) (128.3 ) — Investment in subsidiary — (18.0 ) — Net cash (used) provided in investing activities (14.7 ) (156.3 ) 2.0 Cash flows from financing activities: Net (decrease) increase in advances from subsidiaries (9.9 ) (28.4 ) 9.1 Repayment of long-term debt (26.0 ) — — Proceeds from issuance of common stock, net of stock issuance costs 1.8 2.4 4.7 Excess tax benefits from stock-based compensation — — 1.6 Purchase and retirement of common stock (1.0 ) (1.3 ) (26.9 ) Dividends paid to common stockholders (64.1 ) (48.6 ) (39.4 ) Net cash used in financing activities (99.2 ) (75.9 ) (50.9 ) Net change in cash and cash equivalents 30.6 (96.1 ) 83.2 Cash and cash equivalents, beginning of year 42.3 138.4 55.2 Cash and cash equivalents, end of year $ 72.9 $ 42.3 $ 138.4 There was $173.3 million and $386.0 million in 2018 and 2017 , respectively, of noncash financing activities for the issuance of common stock related to the INB and BOTC acquisitions, respectively. There was no noncash investing or financing activities during 2016 .

Fair Value Measurements

Fair Value Measurements	12 Months Ended
Fair Value Measurements	Dec. 31, 2018
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. There have been no significant changes in the valuation techniques during the periods ended December 31, 2018 and 2017 . The Company’s policy is to recognize transfers between levels as of the end of the reporting period. Transfers in and out of Level 1, Level 2 and Level 3 are recognized on the actual transfer date. There were no transfers between fair value hierarchy levels during the years ended December 31, 2018 and 2017 . 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. The Company has documented and evaluated the pricing methodologies used by the vendors and maintains internal processes that regularly test valuations. These internal processes include obtaining and reviewing available reports on internal controls, evaluating the prices for reasonableness given market changes, obtaining and evaluating the inputs used in the model for a sample of securities, investigating anomalies and confirming determinations through discussions with the vendor. 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. For purposes of potential valuation adjustments to our derivative positions, we evaluate the credit risk of our counterparties as well as ours. Accordingly, we have considered factors such as the likelihood of our default and the default of our counterparties, our net exposures and remaining contractual life, among other things, in determining if any fair value adjustments related to credit risk are required. The change in value of derivative assets and derivative liabilities attributable to credit risk was not significant during the reported periods. 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 and liabilities 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 financial liabilities measured at fair value on a recurring basis are as follows: 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. agency 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 — Fair Value Measurements at Reporting Date Using As of December 31, 2017 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 $ 3.2 $ — $ 3.2 $ — Obligations of U.S. government agencies 561.5 — 561.5 — U.S. agency mortgage-backed securities & collateralized mortgage obligations 1,462.5 — 1,462.5 — Private mortgage-backed securities 90.7 — 90.7 — Corporate securities 87.9 — 87.9 — Other investments 3.0 — 3.0 — Loans held for sale 46.6 — 46.6 — Derivative assets: Interest rate swap contracts 7.5 — 7.5 — Interest rate lock commitments 1.3 — 1.3 — Derivative liabilities: Interest rate swap contracts 7.8 — 7.8 — Forward loan sales contracts 0.1 — 0.1 — Deferred compensation plan assets 12.2 — 12.2 — Deferred compensation plan liabilities 12.2 — 12.2 — 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 December 31, 2018 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Gains (Losses) Impaired loans $ 24.1 $ — $ — $ 24.1 $ (12.2 ) Other real estate owned 0.6 — — 0.6 (0.6 ) Long-lived assets to be disposed of by sale 4.9 — — 4.9 (0.5 ) Fair Value Measurements at Reporting Date Using As of December 31, 2017 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Gains (Losses) Impaired loans $ 32.6 $ — $ — $ 32.6 $ (22.2 ) Other real estate owned 1.3 — — 1.3 (1.6 ) Long-lived assets to be disposed of by sale 0.8 — — 0.8 — 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 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 . As of December 31, 2017 , certain impaired loans with a carrying value of $54.8 million were reduced by specific valuation allowance allocations of $10.8 million and partial loan charge-offs of $11.4 million resulting in a reported fair value of $32.6 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. 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 December 31, 2018 , the Company had long-lived assets to be disposed of by sale with carrying values aggregating $5.4 million , which was reduced by write-downs of $0.5 million charged to other expense, resulting in a reported fair value of $4.9 million . As of December 31, 2017 , the Company had long-lived assets to be disposed of by sale with carrying values of $0.8 million , had zero write-downs, resulting in a reported fair value of $0.8 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: As of December 31, 2018 Fair Value Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 24.1 Appraisal Appraisal adjustment 0% - 26% (13%) Other real estate owned 0.6 Appraisal Appraisal adjustment 8% - 96% (39%) Long-lived assets to be disposed of by sale 4.9 Appraisal Appraisal adjustment 0% - 43% (10%) As of December 31, 2017 Fair Value Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 32.6 Appraisal Appraisal adjustment 0% - 78% (26%) Other real estate owned 1.3 Appraisal Appraisal adjustment 8% - 96% (12%) Long-lived assets to be disposed of by sale 0.8 Appraisal Appraisal adjustment 0% - 0% 0% 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. 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 December 31, 2018 Carrying Amount Estimated Fair Value Quoted Prices in Significant Other Significant 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 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2017 Carrying Amount Estimated Fair Value Quoted Prices in Significant Other Significant Financial assets: Cash and cash equivalents $ 759.0 $ 759.0 $ 759.0 $ — $ — Investment debt securities available-for-sale 2,208.7 2,208.7 — 2,208.7 — Investment debt securities held-to-maturity 484.5 483.3 — 483.3 — Accrued interest receivable 38.0 38.0 — 38.0 — Mortgage servicing rights, net 24.8 40.1 — 40.1 — Loans held for sale 46.6 46.6 — 46.6 — Net loans held for investment 7,495.6 7,252.2 — 7,219.6 32.6 Derivative assets 8.8 8.8 — 8.8 — Deferred compensation plan assets 12.2 12.2 — 12.2 — Total financial assets $ 11,078.2 $ 10,848.9 $ 759.0 $ 10,057.3 $ 32.6 Financial liabilities: Total deposits, excluding time deposits $ 8,783.0 $ 8,783.0 $ 8,783.0 $ — $ — Time deposits 1,151.9 1,137.9 — 1,137.9 — Securities sold under repurchase agreements 643.0 643.0 — 643.0 — Other borrowed funds 20.0 20.0 — 20.0 — Accrued interest payable 5.6 5.6 — 5.6 — Long-term debt 13.1 11.3 — 11.3 — Subordinated debentures held by subsidiary trusts 82.5 76.7 — 76.7 — Derivative liabilities 7.9 7.9 — 7.9 — Deferred compensation plan liabilities 12.2 12.2 — 12.2 — Total financial liabilities $ 10,719.2 $ 10,697.6 $ 8,783.0 $ 1,914.6 $ —

Related Party Transactions

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	RELATED PARTY TRANSACTIONS Certain executive officers, directors and greater than 5% shareholders of the Company and certain entities and individuals related to such persons, incurred indebtedness in the form of loans, as customers, of $43.2 million and $54.6 million at December 31, 2018 and 2017 , respectively. During 2018 , new loans and advances on existing loans of $7.6 million were funded and loan repayments totaled $17.4 million . In addition, $1.6 million of loans were removed due to changes in related parties during the year. These loans were made on substantially the same terms, including interest rates and collateral, as those prevailing at the time for comparable loans with persons not related to the Company and do not involve more than a normal risk of collectability or present other unfavorable features. The Company leases an aircraft from an entity wholly-owned by the chairman of the Board of Directors of the Company. Under the terms of the lease, we pay a fee for each flight hour plus certain third party operating expenses related to the aircraft. During 2018 , 2017 and 2016 , the Company paid total fees and operating expenses of $53 thousand , $45 thousand and $121 thousand respectively, for its use of the aircraft. In addition, we lease a portion or our hanger and provide pilot services to the related entity. During 2018 , 2017 and 2016 , the Company received payments from the related entity of $25 thousand , $17 thousand and $19 thousand , respectively, for hangar use, pilot fees, and reimbursement of certain third party operating expenses related to the chairman’s personal use of the aircraft. The Company purchases services from an entity which includes certain members of the Company’s control group. Services provided for the Company’s benefit include shareholder education and communication, strategic enterprise planning and corporate governance consultation. During 2018 , 2017 and 2016 , the Company paid $80 thousand , $73 thousand and $100 thousand , respectively, for these services.

Authoritative Accounting Guidan

Authoritative Accounting Guidance	12 Months Ended
Authoritative Accounting Guidance	Dec. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Authoritative Accounting Guidance	RECENT AUTHORITATIVE ACCOUNTING GUIDANCE ASU 2014-09, “Revenue from Contracts with Customers.” In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers (Topic 606).” ASU 2014-09 introduced a new five-step revenue recognition model in which an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 also requires disclosures sufficient to enable users to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers, including qualitative and quantitative disclosures about contracts with customers, significant judgments and changes in judgments, and assets recognized from the costs to obtain or fulfill a contract. ASU 2015-14, “Revenue from Contracts with Customers (Topic 606) – Deferral of the Effective Date” was released in August of 2015 deferring the effective date of ASU 2014-09 for all entities by one year until January 1, 2018. ASU 2016-08, “Revenue from Contracts with Customers (Topic 606): Principal vs Agent Considerations (Reporting Revenue Gross versus Net)” was released in March of 2016 to clarify certain principal versus agent considerations within the implementation guidance of ASC Topic 606, “Revenue from Contracts with Customers.” The effective date and transition of ASU 2016-08 is the same as the effective date and transition of ASU 2014-09, Revenue from Contracts with Customers (Topic 606), as discussed above. ASU 2016-10, “Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing” was released in April 2016 to clarify ASC Topic 606, “Revenue from Contracts with Customers” related to (i) identifying performance obligations; and (ii) the licensing implementation guidance. The effective date and transition of ASU 2016-10 is the same as the effective date and transition of ASU 2014-09, “Revenue from Contracts with Customers (Topic 606),” as discussed above. The new revenue recognition standards became effective for the Company on January 1, 2018, and did not have a material impact to our net income, or have a significant impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2016-01 “Financial Instruments – Overall : Recognition and Measurement of Financial Assets and Financial Liabilities.” In January 2016, the FASB issued ASU 2016-01, “Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities.” The amendments in ASU 2016-01, among other things, (i) require equity investments, with certain exceptions, to be measured at fair value with changes in fair value recognized in net income, (ii) simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment, (iii) eliminates the requirement for public business entities to disclose the methods and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet, (iv) requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes, (v) requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments, (vi) requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or the accompanying notes to the financial statements and (viii) clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale investment securities. The amendments in ASU 2016-01 became effective for the Company on January 1, 2018, and did not have a significant impact on the Company’s consolidated financial statements, results of operations or liquidity. 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. ASU 2016-02 will be effective for the Company on January 1, 2019 and will be applied using a modified retrospective approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. Additionally, 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. In December 2018, the FASB also 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, we expect to recognize right-of-use assets and related lease liabilities totaling $54.6 million and $54.6 million , respectively. We expect to elect to apply certain practical expedients provided under ASU 2016-02 whereby we will 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. We also do not expect to apply the recognition requirements of ASU 2016-02 to any short-term leases (as defined by related accounting guidance). We expect to account for lease and non-lease components separately because such amounts are readily determinable under our lease contracts. The Company has determined the new guidance in ASU 2016-02 will have an immaterial impact on its consolidated results of operations and liquidity. ASU No. 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 have selected and 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 No. 2016-15 “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments.” The amendments in ASU 2016-15 are intended to reduce diversity in practice in how eight particular transactions are classified in the statement of cash flows. The amendments in ASU 2016-15 became effective for the Company on January 1, 2018, and did not have a significant impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU No. 2017-01, “Business Combinations (Topic 805): Clarifying the Definition of a Business.” ASU 2017-01 clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The amendments in this update provide a screen to determine when a set is not a business. The screen requires that when substantially all of the fair value of the gross assets acquired (or disposed of) is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. This screen reduces the number of transactions that need to be further evaluated. If the screen is not met, the amendments in this update (1) require that to be considered a business, a set must include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create output and (2) remove the evaluation of whether a market participant could replace missing elements. The amendments provide a framework to assist entities in evaluating whether both an input and a substantive process are present. The framework includes two sets of criteria to consider that depend on whether a set has outputs. ASU 2017-01 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The amendments in ASU 2017-01 became effective for the Company on January 1, 2018, and did not have a significant impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU No. 2017-04, “Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment.” The amendments in ASU 2017-04 remove Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. Goodwill impairment will now be the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. All other goodwill impairment guidance will remain largely unchanged. ASU No. 2017-04 is effective for interim and annual reporting periods beginning after December 15, 2019, applied prospectively. Early adoption is permitted for any impairment tests performed after January 1, 2017. The amendments in ASU 2017-04 were early adopted by the Company in the third quarter of 2018, in conjunction with its annual goodwill impairment test. The annual test did not result in any impairment. ASU No. 2017-07, “Compensation – Retirement Benefits (Topic 750): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.” The amendments in ASU 2017-07 requires employers to present the service cost component of the net periodic benefit cost in the same income statement line item as other employee compensation costs arising from services rendered during the period. The other components of net benefit cost are required to be presented in the income separately from the service cost component and outside a subtotal of income from operations, if one is presented. The amendments in ASU 2017-07 also allow only the service cost component to be eligible for capitalization. The amendments in ASU 2017-07 are applied retrospectively for the presentation of the service cost and other components of net periodic benefit cost in the income statement and prospectively for the capitalization of the service cost in other assets. ASU 2017-07 allows the use of a practical expedient that permits an employer to use the amounts disclosed in its pension and other post-retirement benefits plan footnote for the prior comparative periods as the estimation basis for applying the retrospective presentation requirements. ASU 2017-07 is effective for the Company for interim and annual reporting periods beginning after December 15, 2017. The amendments in ASU 2017-07 became effective for the Company on January 1, 2018, and did not have a significant impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU No. 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, with early adoption permitted. The guidance calls for a modified retrospective transition approach under which a cumulative-effect adjustment will be made to retained earnings as of the beginning of the first reporting period in which the guidance is adopted. The Company currently amortizes premiums on callable debt securities to the earliest call date. As such, the amendments in ASU 2017-08 will not impact the Company’s consolidated financial statements, results of operations and liquidity. ASU 2017-09, “Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting.” In May 2017, the FASB issued ASU 2017-09, which clarifies when a change to the terms or conditions of a share-based payment award must be accounted for as a modification. Under the new guidance, an entity will not apply modification accounting to a share-based payment award if there is no change to the award’s fair value, vesting conditions and classification as an equity or liability instrument. The guidance is effective prospectively for all companies for annual periods beginning after December 15, 2017. The amendments in ASU 2017-09 became effective for the Company on January 1, 2018, 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. ASU 2017-12 is effective for public business entities for fiscal years beginning after December 15, 2018, with early adoption, including adoption in an interim period, permitted. ASU 2017-12 requires a modified retrospective transition method in which the Company will recognize the cumulative effect of the change on the beginning balance of each affected component of equity in the statement of financial position as of the date of adoption. ASU 2017-12 will be effective for us on January 1, 2019 and is not expected to have a significant impact on our financial statements. ASU 2018-02, “Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” In February 2018, the FASB issued ASU 2018-02, Income Statement - Reporting Comprehensive Income: Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (ASU 2018-02). The purpose of this updated guidance is to allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. However, because the amendments only relate to the reclassification of the income tax effects of the Tax Cuts and Jobs Act, the underlying guidance that requires that the effect of a change in tax laws or rates be included in income from continuing operations is not affected. The updated amendments are effective for all entities for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted and should be applied either in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act is recognized. The Company early adopted ASU 2018-02, which resulted in the reclassification from accumulated other comprehensive income to retained earnings totaling $3.1 million , reflected in the Consolidated Statements of Changes in Stockholders’ Equity. 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 this Update are required to be adopted concurrently with the amendments in Update 2017-12 and will be effective for us on January 1, 2019. The adoption of the Update is not expected to have a significant impact on our financial statements.

Subsequent Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2018
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 Securities and Exchange Commission. On January 29, 2019 , the Company declared a quarterly dividend to common shareholders of $0.31 per share, which was paid on February 21, 2019 to shareholders of record as of February 11, 2019 . No other events requiring recognition or disclosure were identified.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2018
Accounting Policies [Abstract]
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition. The Company recognizes revenue as it is earned based on contractual terms, as transactions occur, or as services are provided and collectability is reasonably assured. The principal source of revenue is interest income from loans and investments. The Company also earns non-interest income from various banking and financial services offered to its customers. Certain specific policies related to non-interest income include the following: Wealth management and trust fee income Wealth management and trust fee income represents monthly fees due from wealth management customers as consideration for managing the customers’ assets. Wealth management and trust services include custody of assets, investment management, fees for trust services and similar fiduciary activities. Revenue is recognized when our performance obligation is completed. The Company does not earn performance-based incentives. Optional services such as settlement, court, and regulatory fees are also available to existing trust and asset management customers. The Company’s performance obligation for these transactional-based services is generally satisfied, and related revenue recognized, at a point in time (i.e., as incurred). Service charges on deposit accounts Service charges on deposit accounts represent general service fees for account maintenance and activity- or transaction-based fees and consist of transaction-based revenue, time-based revenue (service period), item-based revenue or some other individual attribute-based revenue. Revenue is recognized when our performance obligation is completed for account maintenance services or when a transaction has been completed (such as a wire transfer or check orders). Payment for such performance obligations are generally received at a point in time when the performance obligations are satisfied. Interchange and other fees Interchange and other fees primarily represent debit and credit card income comprised of interchange fees earned whenever the Company’s debit and credit cards are processed through card payment networks such as MasterCard. ATM fees are primarily generated when a Company cardholder uses a non-Company ATM or a non-Company cardholder uses a Company ATM. Merchant services income primarily represents fees charged to merchants to process their debit and credit card transactions, in addition to account management fees. Swap fee income primarily represents income associated with the execution of dealer bank swap agreements. Other service charges include revenue from processing wire transfers, bill pay service, cashier’s checks, and other services. The Company’s performance obligation for interchange and other service charges are largely satisfied, and related revenue recognized, when completion of the services are rendered at a point in time. Annuity and insurance commissions Annuity and insurance commissions primarily represent commissions received on annuity product sales. The Company acts as an intermediary between the Company’s customer and the insurance carrier. The Company’s performance obligation is generally satisfied upon the issuance of the annuity policy, the carrier then remits the commission payment to the Company, and the Company recognizes the revenue at a point in time.
Consolidation Policy	Basis of Presentation . The Company’s consolidated financial statements include the accounts of the Parent Company and its operating subsidiaries. As of December 31, 2018 , the Company had one significant subsidiary, First Interstate Bank (“FIB”). All significant intercompany balances and transactions have been eliminated in consolidation. Certain reclassifications, none of which were material, have been made in the consolidated financial statements for 2017 and 2016 to conform to the 2018 presentation. These reclassifications did not change previously reported net income or stockholders’ equity.
Equity Method Investments	Equity Method Investments. The Company has investments in real estate joint ventures that are not consolidated because the Company does not own a majority voting interest, control the operations or receive a majority of the losses or earnings of the joint venture. These joint ventures are accounted for using the equity method of accounting whereby the Company initially records its investment at cost (or fair value at the date of acquisition) and then subsequently adjusts the carrying value for the Company’s proportionate share of distributions and earnings or losses of the joint ventures.
Variable Interest Entities	Variable Interest Entities. The Company’s wholly-owned business trusts, FI Statutory Trust I (“Trust I”), FI Capital Trust II (“Trust II”), FI Statutory Trust III (“Trust III”), FI Capital Trust IV (“Trust IV”), FI Statutory Trust V (“Trust V”), FI Statutory Trust VI (“Trust VI”), and Northwest Bancorporation Capital Trust I (“Trust VII”) are variable interest entities for which the Company is not a primary beneficiary. Accordingly, the accounts of Trust I, Trust II, Trust III, Trust IV, Trust V, Trust VI, and Trust VII are not included in the accompanying consolidated financial statements, and are instead accounted for using the equity method of accounting. The Company has equity investments in variable interest Certified Development Entities (“CDEs”) which have received allocations under the New Markets Tax Credits Program. The underlying activities of the CDEs are community development projects designed primarily to promote community welfare, such as economic rehabilitation and development of low-income areas by providing housing, services, or jobs for residents. The maximum exposure to loss in the CDEs is the amount of equity invested and credit extended by the Company. The Company has credit protection in the form of indemnification agreements, guarantees, and collateral arrangements. As the primary beneficiary of these variable interest entities, the Company’s consolidated financial statements include the assets, liabilities, and results of operations of the CDEs. The primary activities of the CDEs are recognized in interest and fees on loans, other non-interest income and long-term debt interest expense on the Company’s statements of operations. Related cash flows are recognized in loans originated, principal collected on loans and advances or repayments of long-term debt.
Assets Held In Fiduciary Or Agency Capacity	Assets Held in Fiduciary or Agency Capacity. The Company holds certain trust assets in a fiduciary or agency capacity. The Company also purchases and sells federal funds as an agent. These and other assets held in an agency or fiduciary capacity are not assets of the Company and, accordingly, are not included in the accompanying consolidated financial statements.
Use of Estimates	Use of Estimates. The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and income and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to change relate to the determination of the allowance for loan losses, the valuation of goodwill, fair valuations of investment securities and other financial instruments and the status of loss contingencies.
Cash and Cash Equivalents	Cash and Cash Equivalents . For purposes of reporting cash flows, cash and cash equivalents include cash on hand, amounts due from banks, federal funds sold for one day periods and interest bearing deposits in banks with original maturities of less than three months.
Investment Securities	Investment Securities . Investments in debt securities that the Company has the positive intent and ability to hold to maturity are classified as held-to-maturity and carried at amortized cost. Investments in debt securities that may be sold in response to or in anticipation of changes in interest rates and resulting prepayment risk, or other factors, and marketable equity securities are classified as available-for-sale and carried at fair value. The unrealized gains and losses on these securities are reported, net of applicable income taxes, as a separate component of stockholders’ equity and comprehensive income. Management determines the appropriate classification of securities at the time of purchase and at each reporting date management reassesses the appropriateness of the classification. The amortized cost of debt securities classified as held-to-maturity or available-for-sale is adjusted for accretion of discounts to maturity and amortization of premiums over the estimated average life of the security, or in the case of callable securities, through the first call date, using the effective yield method. Such amortization and accretion is included in interest income. Realized gains and losses are included in investment securities gains. Declines in the fair value of securities below their cost that are judged to be other-than-temporary are included in other expenses if the decline is related to credit losses. Other-than-temporary impairment losses related to other factors are recognized in other comprehensive income, net of income taxes. In estimating other-than-temporary impairment losses, the Company considers, among other things, the length of time and the extent to which the fair value has been less than cost, the financial condition and near-term prospects of the issuer and the intent and ability of the Company to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. The cost of securities sold is based on the specific identification method.
Loans	Loans . Loans are reported at the principal amount outstanding. Interest income on loans is calculated using the simple interest method on the daily balance of the principal amount outstanding. Loan origination fees and certain direct origination costs are deferred, and the net amount is amortized as an adjustment of the related loan’s yield using a level yield method over the expected lives of the related loans. The accrual of interest on loans is discontinued when, in management’s opinion, the borrower may be unable to meet payment obligations as they become due or when a loan becomes contractually past due ninety days or more with respect to interest or principal, unless such past due loan is well secured and in the process of collection. When interest accrual is discontinued, all unpaid accrued interest is reversed against current period interest income. Interest income is subsequently recognized only to the extent cash payments are received in excess of principal due. Loans are returned to accrual status when all principal and interest amounts contractually due are brought current and when, in the opinion of management, the loans are estimated to be fully collectible as to both principal and interest. A loan is considered impaired when, based upon current information and events, it is probable that the Company will be unable to collect, on a timely basis, all amounts due according to the contractual terms of the loan’s original agreement. The amount of the impairment is measured using cash flows discounted at the loan’s effective interest rate, except when it is determined that the primary source of repayment for the loan is the operation or liquidation of the underlying collateral. In such cases, the current fair value of the collateral, reduced by anticipated selling costs, is used to measure impairment. The Company considers impaired loans to include all loans, except consumer loans, that are risk rated as doubtful or on which interest accrual has been discontinued or that have been renegotiated in a troubled debt restructuring. Interest payments received on impaired loans are applied based on whether they are on accrual or non-accrual status. Interest income recognized by the Company on impaired loans primarily relates to loans modified in troubled debt restructurings that remain on accrual status. 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. Loans acquired in a business combination are recorded and initially measured at their estimated fair value as of the acquisition date, with no carryover of the related allowance for credit losses. Credit risks are included in the determination of fair value. For loans with no significant evidence of credit deterioration since origination, the difference between the fair value and the unpaid principal balance of the loan at the acquisition date is amortized into interest income using the effective interest method over the remaining period to contractual maturity. The accounting for loans acquired with evidence of a deterioration of credit quality is described below. Loans acquired through the completion of a transfer, including loans acquired in business combinations, that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all contractually required payments receivable are initially recorded at fair value (as determined by the present value of expected future cash flows) with no valuation allowance. The difference between the undiscounted cash flows expected at acquisition and the recorded fair value of the loan, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment, a loss accrual or a valuation allowance. Increases in expected cash flows subsequent to the initial measurement are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition. A loan is considered a troubled debt restructuring when a borrower is experiencing financial difficulties that leads to a restructuring of the loan and the Company grants concessions to the borrower in the restructuring that it would not otherwise consider. These concessions may include rate reductions, principal forgiveness, extension of maturity date and other actions to minimize potential losses. Certain troubled debt restructurings are on non-accrual status at the time of restructuring and are returned to accrual status only after considering the borrower’s sustained repayment performance in accordance with the restructuring agreement for a reasonable 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 no longer be disclosed as a troubled debt restructuring although they continue to be individually evaluated for impairment and disclosed as impaired loans. Loans held for sale include residential mortgage loans originated for immediate sale. The Company has elected to account for loans held for sale using the fair value option. Under the fair value option, net loan origination fees are recognized in non-interest income at the time of origination. Subsequent changes in the estimated fair values of loans held for sale are recorded as unrealized gains and losses in non-interest income. Estimated fair values of loans held for sale are determined based upon current secondary market prices for loans with similar coupons, maturities and credit quality, or in the case of committed loans, on current delivery prices. Gains and losses on loans held for sale are recognized based on the difference between the net sales proceeds, including the estimated value associated with servicing assets or liabilities, and the net carrying value of the loans sold. Adjustments to reflect unrealized gains and losses resulting from changes in fair value of loans held for sale, as well as realized gains and losses on the sale of loans, are included in non-interest income - mortgage banking revenues on the accompanying consolidated statements of income.
Allowance for Loan Losses	Allowance for Loan Losses . The allowance for loan losses is established through a provision for loan losses which is charged to expense. Loans, or portions thereof, are charged against the allowance for loan losses when management believes that the collectability of the principal is unlikely or, with respect to consumer installment and credit card loans, according to established delinquency schedules. The allowance balance is an amount that management believes will be adequate to absorb known and inherent losses in the loan portfolio based upon quarterly analysis of the current risk characteristics of the loan portfolio, an assessment of individual problem loans and actual loss experience, industry concentrations and current economic factors and the estimated impact of current economic and environmental conditions on historical loss rates. Loans acquired in business combinations are recorded at their estimated fair values on the date of acquisition. Accordingly, no allowance for loan losses related to these loans is recorded at the date of transfer. An allowance for loan losses is recorded for credit deterioration occurring subsequent to the transfer date.
Goodwill and Core Deposit Intangibles	Goodwill . The excess purchase price over the fair value of net assets from acquisitions, or goodwill, is evaluated for impairment at least annually and on an interim basis if an event or circumstance indicates that it is likely impairment has occurred. Goodwill impairment is determined by comparing the fair value of a reporting unit to its carrying amount. In any given year the Company may elect to perform a qualitative assessment to determine whether it is more likely than not that the fair value of a reporting unit is in excess of its carrying value. If it is not more likely than not that the fair value of the reporting unit is in excess of the carrying value, or if the Company elects to bypass the qualitative assessment, a quantitative impairment test is performed. In performing a quantitative test for impairment, the fair value of net assets is estimated based on analyses of the Company’s market value, discounted cash flows and peer values. The determination of goodwill impairment is sensitive to market-based economics and other key assumptions used in determining or allocating fair value. Variability in the market and changes in assumptions or subjective measurements used to allocate fair value are reasonably possible and may have a material impact on our consolidated financial statements or results of operations. Core Deposit Intangibles. Core deposit intangibles represent the intangible value of depositor relationships resulting from deposit liabilities assumed, as a result of acquisitions, and are amortized using an accelerated method based on the estimated weighted average useful lives of the related deposits.
Mortgage Servicing Rights	Mortgage Servicing Rights . The Company recognizes the rights to service mortgage loans for others, whether acquired or internally originated. Mortgage servicing rights are initially recorded at fair value based on comparable market data and are amortized in proportion to and over the period of estimated net servicing income. Mortgage servicing rights are evaluated quarterly for impairment by discounting the expected future cash flows, taking into consideration the estimated level of prepayments based on current industry expectations and the predominant risk characteristics of the underlying loans including loan type, note rate and loan term. Impairment adjustments, if any, are recorded through a valuation allowance.
Premises and Equipment	Premises and Equipment . Buildings, furniture and equipment are stated at cost less accumulated depreciation. Depreciation expense is computed using straight-line methods over estimated useful lives of 5 to 45 years for buildings and improvements and 4 to 15 years for furniture and equipment. Leasehold improvements and assets acquired under capital lease are amortized over the shorter of their estimated useful lives or the terms of the related leases. Land is recorded at cost.
Company-Owned Life Insurance	Company-Owned Life Insurance . Key executive and group life insurance policies are recorded at their cash surrender value. Separate account group life insurance policies are subject to a stable value contract that offsets the impact of interest rate fluctuations on the market value of the policies and are recorded at the stabilized investment value. Increases in the cash surrender or stabilized investment value of insurance policies, as well as insurance proceeds received, are recorded as other non-interest income, and are not subject to income taxes.
Deferred Compensation Plan	Deferred Compensation Plan. The Company has a deferred compensation plan for the benefit of certain highly compensated officers and directors of the Company. The plan allows for discretionary employer contributions in excess of tax limits applicable to the Company’s 401(k) and profit sharing plans and the deferral of salary, short-term incentives or director fees subject to certain limitations. Deferred compensation plan assets and liabilities are included in the Company’s consolidated balance sheets at fair value.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets. Long-lived assets, including premises and equipment and certain identifiable intangibles, are reviewed for impairment whenever events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. The amount of the impairment loss, if any, is based on the asset’s fair value
Other Real Estate Owned	. Other Real Estate Owned . Real estate acquired in satisfaction of loans is initially carried at current fair value less estimated selling costs. Any excess of loan carrying value over the fair value of the real estate acquired is recorded as a charge to the allowance for loan losses. Subsequent declines in fair value less estimated selling costs are included in OREO expense. Subsequent increases in fair value less estimated selling costs are recorded as a reduction in OREO expense to the extent of recognized losses. Operating expenses, net of related income, and gains or losses on sales are included in OR
Restricted Equity Securities	. Restricted Equity Securities. The Company, as a member of the Federal Reserve Bank and the Federal Home Loan Bank (“FHLB”), is required to maintain investments in each of the organization’s cap ectively. No ready market exists for these restricted equity securities, and they have no quoted market values. Restricted equity securities are periodically reviewed for impairment based on ultimate recovery of par value. The determination of whether a decline affects the ultimate recovery of par value is influenced by the significance of the decline compared to the cost basis of the restricted equity securities, the length of time a decline has persisted, the impact of legislative and regulatory changes on the issuing organizations and the liquidity positions of the issuing orga
Derivatives and Hedging Activities	or 2016 . Derivatives and Hedging Activities. For asset and liability management purposes, the Company enters into interest rate swap contracts to hedge against changes in forecasted cash flows due to interest rate exposures. Interest rate swaps are contracts in which a series of interest payments are exchanged over a prescribed period. The notional amount upon which the interest payments are based is not exchanged. The swap agreements are derivative instruments and convert a portion of the Company’s forecasted variable rate debt to a fixed rate (i.e., cash flow hedge) over the payment term of the interest rate swap. The effective portion of the gain or loss on cash flow hedging instruments is initially reported as a component of other comprehensive income and subsequently reclassified into earnings in the same period during which the transaction affects earnings. The ineffective portion of the gain or loss on derivative instruments, if any, is recognized in earnings. The Company does not enter into interest rate swap agreements for trading or speculative purposes. As of December 31, 2018 , the Company does not have an existing agreement. The Company also 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 o
Earnings Per Common Share	f income. Earnings Per Common Share . Basic and diluted earnings per common share are calculated using a two-class method. Under the two-class method, basic earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period, excluding outstanding participating securities. Participating securities include non-vested performance restricted stock awards granted and all non-vested time restricted stock awards. Diluted earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding determined for the basic earnings per share calculation plus the dilutive effect of stock compensation using the treasury st
Income Taxes	k method. Income Taxes . The Parent Company and its subsidiaries have elected to be included in a consolidated federal income tax return. For state income tax purposes, the combined taxable income of the Parent Company and its subsidiaries is apportioned among the states in which operations take place. Federal and state income taxes attributable to the subsidiaries, computed on a separate return basis, are paid to or received from the Parent Company. The Company accounts for income taxes using the liability method. Under the liability method, deferred tax assets and liabilities are determined based on enacted income tax rates which will be in effect when the differences between the financial statement carrying values and tax bases of existing assets and liabilities are expected to be reported in taxable income. Positions taken in the Company’s tax returns may be subject to challenge by the taxing authorities upon examination. Uncertain tax positions are initially recognized in the financial statements when it is more likely than not the position will be sustained upon examination by the tax authorities. Such tax positions are both initially and subsequently measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon settlement with the tax authority, assuming full knowledge of the position and all relevant facts. The Company provides for interest and, in some cases, penalties on tax positions that may be challenged by the taxing authorities. Interest expense is recognized beginning in the first period that such interest would begin accruing. Penalties are recognized in the period that the Company claims the position in the tax return. Interest and penalties on income tax uncertainties are classified within income tax expense in the consolidated statements of income. With few exceptions, the Company is no longer subject to U.S. federal and state examinations by tax authorities for years b
Comprehensive Income	Comprehensive Income. Comprehensive income includes net income, as well as other changes in stockholders’ equity that result from transactions and economic events other than those with shareholders. In addition to net income, the Company’s comprehensive income includes the after tax effect of changes in unrealized gains and losses on available-for-sale investment securities and derivatives designated as cash flow hedges, changes in the unamortized gain or loss on available-for-sale investment securities transferred to held-to-maturity and changes in net actuarial gains and losses on defined benefit post-retirement benefits plans.
Segment Reporting	s plans. Segment Reporting. An operating segment is defined as a component of a business for which separate financial information is available that is evaluated regularly by the chief operating decision maker in deciding how to allocate resources and evaluate performance. The "Segment Reporting" topic of the FASB ASC requires that public companies report certain information about operating segments. It also requires that public companies report certain information about their products and services, the geographic areas in which they operate, and their major customers. The Company is a holding company for a regional community bank, which offers a wide array of products and services to its customers. The Company has one reporting unit and one operating segment, community banking, which encompasses commercial and consumer banking services offered to individuals, businesses, municipalities and other entities.
Advertising Costs	tities. For additional information concerning community banking, see “Business—Community Banking,” included in Part I, Item 1 of this report. Advertising Costs. Advertising costs are expensed as incurred.
Transfers of Financial Assets	Transfers of Financial Assets. Transfers of financial assets are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when the assets have been isolated from the Company; the transferee obtains the right, free of conditions that constrain it from taking advantage of that right, to pledge or exchange the transferred assets; and, the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
Stock-Based Compensation	Stock-Based Compensation . Compensation cost for all stock-based awards is measured at fair value on the date of grant and is recognized over the requisite service period for awards expected to vest. The impact of forfeitures of stock-based payment awards on compensation expense is recognized as forfeitures occur.
Fair Value Measurements	Fair Value Measurements. In general, fair value measurements are based upon quoted market prices, where available. If quoted market prices are not available, fair value measurements are estimated using relevant market information and other assumptions. Fair value estimates involve uncertainties and require some degree of judgment regarding interest rates, credit risk, prepayments and other factors. The use of different assumptions or estimation techniques may have a significant effect on the fair value amounts reported.

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
Acquisitions (Tables)	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of Recognized Identifiable Assets Acquired and Liabilities Assumed	. As Recorded Fair Value As Recorded As of May 30, 2017 by Cascade Adjustments by the Company Assets acquired: Cash and cash equivalents $ 246.8 $ — $ 246.8 Investment securities 476.7 4.9 (1) 481.6 Loans held for investment 2,111.0 (31.7 ) (2) 2,079.3 Mortgage loans held for sale 10.3 — 10.3 Allowance for loan losses (24.0 ) 24.0 (3) — Premises and equipment 46.6 0.1 (4) 46.7 Other real estate owned (“OREO”) 1.2 — 1.2 Core deposit intangible assets — 48.0 (5) 48.0 Deferred tax assets, net 47.6 (20.9 ) (6) 26.7 Other assets 98.6 2.1 (7) 100.7 Total assets acquired 3,014.8 26.5 3,041.3 Liabilities assumed: Deposits 2,669.9 (0.9 ) (8) 2,669.0 Accounts payable and accrued expense 62.2 1.9 (9) 64.1 Total liabilities assumed 2,732.1 1.0 2,733.1 Net assets acquired $ 282.7 $ 25.5 $ 308.2 Consideration paid: Cash $ 155.0 Class A common stock 386.0 Total consideration paid $ 541.0 Goodwill $ 232.8 Explanation of fair value adjustments: (1) Write up of the book value of investments to their estimated fair values on the date of acquisition based upon quotes obtained from an independent third party pricing service. (2) Write down of the book value of loans to their estimated fair values. Shared National Credits (SNC) were recorded at quoted sales prices where available. The fair value of the remaining 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. (3) Adjustment to remove the Cascade allowance for loan losses at acquisition date, as the credit risk is included in the fair value adjustment for loans receivable described in (2) above. (4) Write up of the book value of premises and equipment to their estimated fair values on the date of acquisition based upon appraisals obtained from an independent third party appraiser or broker’s opinion of value. (5) Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm. (6) Adjustment consists of the write-off of pre-existing deferred tax assets and purchase accounting adjustments as a result of the acquisition. (7) Adjustment consists of various other assets recorded as a result of the acquisition, including mortgage servicing rights, SBA servicing rights, and favorable leases offset by reductions to the fair value of other items. (8) Decrease 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. (9) Increase in fair value due to credit card incentive program, unfavorable leases, write-off of balance sheet reserve, and swap liability offset. The following table summarizes the consideration paid, fair values of the Northwest assets acquired and liabilities assumed, and the resulting goodwill. Due to the recent closing of the transaction, all amounts reported are provisional pending the review of valuations obtained from third parties. 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 (0.5 ) (3) 14.0 Other real estate owned (“OREO”) 0.3 0.3 0.6 Core deposit intangible assets 2.4 13.3 (4) 15.7 Other assets 29.3 (10.0 ) (5) 19.3 Total assets acquired 800.7 (3.7 ) 797.0 Liabilities assumed: Deposits 696.1 0.2 (6) 696.3 Accounts payable and accrued expense 8.1 (0.4 ) (7) 7.7 Long term debt 13.0 0.1 13.1 Trust preferred securities 5.2 (0.8 ) (8) 4.4 Deferred tax liability, net (1.2 ) 1.5 (9) 0.3 Total liabilities assumed 721.2 0.6 721.8 Net assets acquired $ 79.5 $ (4.3 ) $ 75.2 Consideration paid: Cash $ 3.0 Class A common stock 173.3 Total consideration paid 176.3 Goodwill $ 101.1 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, other assets, and long term debt were made since the prior quarter, none of which were material. The adjustments had no impact on 2018 earnings and a net increase to goodwill of $0.3 million from the third quarter 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) 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) Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm. (5) Adjustment consists of reductions to the fair value of other items, including the removal of Northwest previously recorded goodwill. (6) 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) Decrease due to the write-off of off balance sheet reserves. (8) 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. (9) Adjustment consists of the write-off of pre-existing deferred tax assets and purchase accounting adjustments as a result of the acquisition.
Acquisition Related Expenses	These costs are incorporated in non-interest expense in the Company’s consolidated statements of income and are summarized below. Dec 31, 2018 Dec 31, 2017 Dec 31, 2016 Legal and professional fees $ 4.0 $ 9.6 $ 2.1 Employee expenses 1.1 5.1 0.2 Technology conversion and contract termination 6.6 10.2 0.2 Other 0.7 2.3 0.3 Total acquisition related expenses $ 12.4 $ 27.2 $ 2.8
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period	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 Information regarding Cascade loans acquired deemed credit-impaired as of the May 30, 2017 acquisition date is as follows: Contractually required principal and interest payments $ 49.7 Contractual cash flows not expected to be collected (“non-accretable discount”) 24.7 Cash flows expected to be collected 25.0 Interest component of cash flows expected to be collected (“accretable discount”) 1.9 Fair value of acquired credit-impaired loans $ 23.1
Schedule of Acquired Loans not Deemed to Have Credit Impairment	Information regarding Cascade acquired loans not deemed credit-impaired at the May 30, 2017 acquisition date is as follows: Contractually required principal and interest payments $ 2,098.1 Contractual cash flows not expected to be collected 23.3 Fair value at acquisition $ 2,066.5
Business Acquisition, Pro Forma Information	The following table presents unaudited pro forma consolidated revenues and net income as if the Cascade acquisition had occurred as of January 1, 2016. Year ended December 31, (unaudited) 2018 2017 Interest income $ 473.4 $ 420.8 Non-interest income 143.3 153.3 Total revenues $ 616.7 $ 574.1 Net income $ 162.5 $ 126.4 EPS - basic $ 2.81 $ 2.03 EPS - diluted 2.79 2.01

Goodwill and Core Deposit Int_2

Goodwill and Core Deposit Intangibles (Tables)	12 Months Ended
Goodwill and Core Deposit Intangibles (Tables)	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Change in Carrying Amount of Goodwill	Goodwill Year Ended December 31, 2018 2017 Net carrying value at beginning of period $ 444.7 $ 212.8 Acquisitions and measurement period adjustments 102.0 231.9 Net carrying value at end of period $ 546.7 $ 444.7
Schedule of Activity of Identifiable Core Deposit Intangibles	Core deposit intangibles (“CDI”) The following table sets forth activity for identifiable core deposit intangibles subject to amortization: Year Ended December 31, 2018 2017 Gross CDI, beginning of period $ 74.0 $ 29.2 Established through acquisitions 15.7 48.0 Reductions due to sale of accounts — (3.2 ) Accumulated amortization (32.8 ) (24.9 ) Net CDI, end of period $ 56.9 $ 49.1
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	The following table provides estimated future CDI amortization expense: Years ending December 31, 2019 $ 8.9 2020 8.1 2021 7.5 2022 6.9 2023 6.3 Thereafter 19.2 Total $ 56.9

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
Investment Securities (Tables)	Dec. 31, 2018
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: 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 U.S agency residential mortgage-backed securities & 189.7 0.3 (6.5 ) 183.5 Corporate securities 46.3 0.1 (0.6 ) 45.8 Obligations of U.S. government agencies 19.8 — (0.3 ) 19.5 Other investments 0.1 — — 0.1 Total $ 406.8 $ 2.2 $ (8.3 ) $ 400.7 December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale U.S. Treasury notes $ 3.2 $ — $ — $ 3.2 Obligations of U.S. government agencies 569.5 — (8.0 ) 561.5 U.S. agency residential mortgage-backed securities & 1,474.1 3.8 (15.4 ) 1,462.5 Private mortgage-backed securities 91.5 — (0.8 ) 90.7 Corporate Securities 88.0 0.1 (0.3 ) 87.8 Other investments 3.0 — — 3.0 Total $ 2,229.3 $ 3.9 $ (24.5 ) $ 2,208.7 December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to Maturity State, county and municipal securities $ 172.4 $ 2.6 $ (0.6 ) $ 174.4 Obligations of U.S. government agencies 19.8 — (0.2 ) 19.6 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 230.5 8.8 (11.6 ) 227.7 Corporate securities 61.6 0.1 (0.3 ) 61.4 Other investments 0.2 — — 0.2 Total $ 484.5 $ 11.5 $ (12.7 ) $ 483.3
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 December 31, 2018 and 2017 . 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 Value 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 ) U.S. agency residential mortgage-backed 45.0 (2.2 ) 120.2 (4.3 ) 165.2 (6.5 ) Corporate securities — — 39.6 (0.6 ) 39.6 (0.6 ) Obligations of U.S. government agencies 19.5 (0.3 ) — — 19.5 (0.3 ) Total $ 90.4 $ (2.8 ) $ 216.9 $ (5.5 ) $ 307.3 $ (8.3 ) Less than 12 Months 12 Months or More Total December 31, 2017 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale Obligations of U.S. government agencies 284.9 (3.4 ) 266.1 (4.6 ) 551.0 (8.0 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 670.1 (6.2 ) 439.2 (9.2 ) 1,109.3 (15.4 ) Private mortgage-backed securities 74.0 (0.8 ) — — 74.0 (0.8 ) Corporate securities 51.3 (0.3 ) — — 51.3 (0.3 ) Total $ 1,080.3 $ (10.7 ) $ 705.3 $ (13.8 ) $ 1,785.6 $ (24.5 ) Less than 12 Months 12 Months or More Total December 31, 2017 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity State, county and municipal securities $ 53.3 $ (0.4 ) $ 12.3 $ (0.2 ) $ 65.6 $ (0.6 ) U.S. agency residential mortgage-backed 76.4 (9.1 ) 60.5 (2.5 ) $ 136.9 $ (11.6 ) Corporate securities $ 41.2 $ (0.2 ) $ 5.0 $ (0.1 ) $ 46.2 $ (0.3 ) Obligations of U.S. government agencies $ 9.7 $ — $ 9.9 $ (0.2 ) $ 19.6 $ (0.2 ) Total $ 180.6 $ (9.7 ) $ 87.7 $ (3.0 ) $ 268.3 $ (12.7 )
Maturities of Investment Securities	All other investment securities maturities are shown at contractual maturity dates. Available-for-Sale Held-to-Maturity December 31, 2018 Amortized Cost Estimated Fair Value Amortized Cost Estimated Fair Value Within one year $ 477.8 $ 472.3 $ 64.1 $ 63.0 After one year but within five years 1,519.2 1,495.0 221.6 216.7 After five years but within ten years 154.5 151.9 94.4 94.9 After ten years 153.7 151.5 26.7 26.1 Total $ 2,305.2 $ 2,270.7 $ 406.8 $ 400.7

Loans (Tables)

Loans (Tables)	12 Months Ended
Loans (Tables)	Dec. 31, 2018
Loans Receivable, Net [Abstract]
Schedule of Loans by Class	The following table presents loans by class as of the dates indicated: December 31, 2018 2017 Real estate loans: Commercial $ 3,235.4 $ 2,822.9 Construction: Land acquisition & development 321.6 348.7 Residential 242.8 240.2 Commercial 274.3 119.4 Total construction loans 838.7 708.3 Residential 1,542.0 1,487.4 Agricultural 217.4 158.2 Total real estate loans 5,833.5 5,176.8 Consumer: Indirect consumer 787.8 784.7 Other consumer 200.6 175.1 Credit card 81.8 74.6 Total consumer loans 1,070.2 1,034.4 Commercial 1,310.3 1,215.4 Agricultural 254.8 136.2 Other, including overdrafts 1.6 4.9 Loans held for investment 8,470.4 7,567.7 Mortgage loans held for sale 33.3 46.6 Total loans $ 8,503.7 $ 7,614.3
Deteriorated Loans Transferred in	The following table displays the outstanding unpaid principal balance and accrual status of loans acquired with credit impairment as of December 31, 2018 and 2017 . December 31, 2018 2017 Outstanding principal $ 43.4 $ 38.2 Carrying value: Loans on accrual status 30.2 24.9 Total carrying value $ 30.2 $ 24.9 The following table summarizes changes in the accretable yield for loans acquired credit impaired for the years ended December 31, 2018 , 2017 , and 2016 : Year Ended December 31, 2018 2017 2016 Beginning balance $ 7.3 $ 6.8 $ 6.7 Acquisitions 3.2 1.9 1.1 Additions 0.6 0.1 — Accretion income (3.1 ) (2.9 ) (2.5 ) Reductions due to exit events (1.1 ) (1.5 ) (1.1 ) Reclassifications from nonaccretable differences 2.0 2.9 2.6 Ending balance $ 8.9 $ 7.3 $ 6.8
Schedule of Recorded Investment in Past Due Loans by Class	The following tables present the contractual aging of the Company’s recorded investment in past due loans by class as of the period indicated: 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 Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of December 31, 2017 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 2.9 $ 0.5 $ 0.3 $ 3.7 $ 2,792.4 $ 26.8 $ 2,822.9 Construction: Land acquisition & development 7.3 0.3 0.3 7.9 337.8 3.0 348.7 Residential 2.1 — — 2.1 236.4 1.7 240.2 Commercial — — — — 115.6 3.8 119.4 Total construction loans 9.4 0.3 0.3 10.0 689.8 8.5 708.3 Residential 13.3 1.4 0.4 15.1 1,464.1 8.2 1,487.4 Agricultural 0.3 — 0.2 0.5 154.3 3.4 158.2 Total real estate loans 25.9 2.2 1.2 29.3 5,100.6 46.9 5,176.8 Consumer: Indirect consumer 7.8 2.1 0.4 10.3 772.6 1.8 784.7 Other consumer 1.6 0.5 0.1 2.2 172.6 0.3 175.1 Credit card 0.9 0.6 0.7 2.2 72.4 — 74.6 Total consumer loans 10.3 3.2 1.2 14.7 1,017.6 2.1 1,034.4 Commercial 3.9 1.7 0.7 6.3 1,189.5 19.6 1,215.4 Agricultural 1.8 0.1 — 1.9 133.5 0.8 136.2 Other, including overdrafts — — — — 4.9 — 4.9 Loans held for investment 41.9 7.2 3.1 52.2 7,446.1 69.4 7,567.7 Mortgage loans originated for sale — — — — 46.6 — 46.6 Total loans $ 41.9 $ 7.2 $ 3.1 $ 52.2 $ 7,492.7 $ 69.4 $ 7,614.3
Schedule of Recorded Investment in Impaired Loans	The following tables present information on the Company’s recorded investment in impaired loans as of dates indicated: 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 December 31, 2017 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 45.6 $ 20.9 $ 14.1 $ 35.0 $ 3.9 Construction: Land acquisition & development 10.0 3.4 0.5 3.9 — Residential 1.8 1.7 — 1.7 — Commercial 4.7 0.4 3.5 3.9 2.2 Total construction loans 16.5 5.5 4.0 9.5 2.2 Residential 11.5 8.2 2.0 10.2 0.1 Agricultural 3.7 3.6 — 3.6 — Total real estate loans 77.3 38.2 20.1 58.3 6.2 Commercial 29.5 12.4 11.4 23.8 4.4 Agricultural 1.1 0.8 0.3 1.1 0.2 Total $ 107.9 $ 51.4 $ 31.8 $ 83.2 $ 10.8 December 31, 2016 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 57.0 $ 24.4 $ 21.4 $ 45.8 $ 2.8 Construction: Land acquisition & development 12.1 4.3 1.8 6.1 0.8 Residential 1.6 0.2 0.6 0.8 — Commercial 4.8 3.9 0.7 4.6 0.7 Total construction loans 18.5 8.4 3.1 11.5 1.5 Residential 8.2 4.1 2.5 6.6 0.3 Agricultural 5.1 4.5 0.2 4.7 — Total real estate loans 88.8 41.4 27.2 68.6 4.6 Commercial 40.3 13.2 19.2 32.4 9.3 Agricultural 3.7 3.3 0.4 3.7 0.1 Total $ 132.8 $ 57.9 $ 46.8 $ 104.7 $ 14.0 The following tables present the average recorded investment in and income recognized on impaired loans for the periods indicated: Year Ended December 31, 2018 2017 2016 Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Real estate 50.0 0.1 63.5 0.3 69.2 0.3 Commercial 21.9 0.2 28.1 0.2 30.1 0.3 Agricultural 2.1 — 2.4 — 1.8 — Total $ 74.0 $ 0.3 $ 94.0 $ 0.5 $ 101.1 $ 0.6
Schedule of Loans Renegotiated in Troubled Debt Restructurings	The following table presents information on the Company’s troubled debt restructurings that occurred during the periods indicated: Number of Notes Type of Concession Principal Balance at Restructure Date Year Ended December 31, 2018 Interest only period Extension of terms or maturity Interest rate adjustment Other Commercial real estate 3 $ 3.6 $ — $ — $ — $ 3.6 Agriculture real estate 1 — — — 0.2 0.2 Consumer 1 — — — 0.3 0.3 Total loans restructured 5 $ 3.6 $ — $ — $ 0.5 $ 4.1 Number of Notes Type of Concession Principal Balance at Restructure Date Year Ended December 31, 2017 Interest only period Extension of terms or maturity Interest rate adjustment Other Commercial real estate 5 $ 1.5 $ 0.4 $ — $ 0.9 $ 2.8 Agriculture real estate 1 — 0.8 — — 0.8 Commercial 17 1.2 2.0 — 6.0 9.2 Agriculture 1 — 0.1 — — 0.1 Total loans restructured 24 $ 2.7 $ 3.3 $ — $ 6.9 $ 12.9 Number of Notes Type of Concession Principal Balance at Restructure Date Year Ended December 31, 2016 Interest only period Extension of terms or maturity Interest rate adjustment Other Commercial real estate 18 $ 0.4 $ 5.5 $ 0.2 $ 1.8 $ 7.9 Commercial construction 1 — 3.7 — — 3.7 Residential real estate 1 — 0.1 — — 0.1 Commercial 13 4.4 0.4 — 3.3 8.1 Agriculture 2 — 0.3 — — 0.3 Total loans restructured 35 $ 4.8 $ 10.0 $ 0.2 $ 5.1 $ 20.1
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 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 As of December 31, 2017 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 78.0 $ 96.4 $ 10.3 $ 184.7 Construction: Land acquisition & development 3.2 16.4 — 19.6 Residential 2.3 1.7 0.5 4.5 Commercial 2.4 3.6 3.5 9.5 Total construction loans 7.9 21.7 4.0 33.6 Residential 3.9 12.5 1.9 18.3 Agricultural 4.3 19.1 — 23.4 Total real estate loans 94.1 149.7 16.2 260.0 Consumer: Indirect consumer 0.8 2.2 0.3 3.3 Direct consumer 0.4 0.7 0.2 1.3 Total consumer loans 1.2 2.9 0.5 4.6 Commercial 54.7 56.3 11.1 122.1 Agricultural 5.1 8.3 0.4 13.8 Total $ 155.1 $ 217.2 $ 28.2 $ 400.5

Allowance for Loan Losses (Tabl

Allowance for Loan Losses (Tables)	12 Months Ended
Allowance for Loan Losses (Tables)	Dec. 31, 2018
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: Year Ended December 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 (credited) to operating expense (0.7 ) 6.8 1.9 0.6 — 8.6 Less loans charged-off (3.7 ) (11.3 ) (4.7 ) — — (19.7 ) Add back recoveries of loans previously charged-off 3.7 4.5 3.6 0.2 — 12.0 Ending balance $ 31.0 $ 8.7 $ 31.3 $ 2.0 $ — $ 73.0 Individually evaluated for impairment $ 1.3 $ — $ 5.2 $ 0.3 $ — $ 6.8 Collectively evaluated for impairment 29.7 8.7 26.1 1.7 — 66.2 Ending balance $ 31.0 $ 8.7 $ 31.3 $ 2.0 $ — $ 73.0 Total loans: 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 Year Ended December 31, 2017 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 28.6 $ 7.7 $ 38.1 $ 1.8 $ — $ 76.2 Provision charged (credited) to operating expense 6.0 8.1 (2.9 ) (0.2 ) — 11.0 Less loans charged-off (4.3 ) (11.3 ) (6.8 ) (0.4 ) — (22.8 ) Add back recoveries of loans previously charged-off 1.4 4.2 2.1 — — 7.7 Ending balance $ 31.7 $ 8.7 $ 30.5 $ 1.2 $ — $ 72.1 Individually evaluated for impairment $ 6.2 $ — $ 4.4 $ 0.2 $ — $ 10.8 Collectively evaluated for impairment 25.5 8.7 26.1 1.0 — 61.3 Ending balance $ 31.7 $ 8.7 $ 30.5 $ 1.2 $ — $ 72.1 Total loans: Individually evaluated for impairment $ 58.3 $ — $ 23.8 $ 1.1 $ — $ 83.2 Collectively evaluated for impairment 5,118.5 1,034.4 1,191.6 135.1 4.9 7,484.5 Total loans held for investment $ 5,176.8 $ 1,034.4 $ 1,215.4 $ 136.2 $ 4.9 $ 7,567.7 Year Ended December 31, 2016 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 52.3 $ 5.1 $ 18.8 $ 0.6 $ — $ 76.8 Provision charged (credited) to operating expense (21.7 ) 8.4 21.9 1.4 — 10.0 Less loans charged-off (5.2 ) (8.6 ) (5.8 ) (0.2 ) — (19.8 ) Add back recoveries of loans previously charged-off 3.2 2.8 3.2 — — 9.2 Ending balance $ 28.6 $ 7.7 $ 38.1 $ 1.8 $ — $ 76.2 Individually evaluated for impairment $ 4.6 $ — $ 9.3 $ 0.1 $ — $ 14.0 Collectively evaluated for impairment 24.0 7.7 28.8 1.7 — 62.2 Ending balance $ 28.6 $ 7.7 $ 38.1 $ 1.8 $ — $ 76.2 Total loans: Individually evaluated for impairment $ 68.6 $ — $ 32.4 $ 3.7 $ — $ 104.7 Collectively evaluated for impairment 3,445.4 970.3 765.5 129.2 1.6 5,312.0 Total loans held for investment $ 3,514.0 $ 970.3 $ 797.9 $ 132.9 $ 1.6 $ 5,416.7

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
Premises and Equipment (Tables)	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Premises and Equipment and Related Accumulated Depreciation	Premises and equipment and related accumulated depreciation are as follows: December 31, 2018 2017 Land $ 49.9 $ 49.4 Buildings and improvements 268.1 257.1 Furniture and equipment 104.0 97.7 Total premises and equipment 422.0 404.2 Less accumulated depreciation (176.8 ) (162.3 ) Premises and equipment, net $ 245.2 $ 241.9

Company-Owned Life Insurance (T

Company-Owned Life Insurance (Tables)	12 Months Ended
Company-Owned Life Insurance (Tables)	Dec. 31, 2018
Investments, All Other Investments [Abstract]
Schedule of Life Insurance Corporate or Bank Owned	Company-owned life insurance consists of the following: December 31, 2018 2017 Key executive, principal shareholder $ 4.7 $ 4.2 Key executive split dollar 9.4 4.9 Group life 261.0 251.5 Total $ 275.1 $ 260.6

Other Real Estate Owned (Tables

Other Real Estate Owned (Tables)	12 Months Ended
Other Real Estate Owned (Tables)	Dec. 31, 2018
Repossessed Assets [Abstract]
Other Real Estate Owned	Information with respect to the Company’s other real estate owned follows: Year Ended December 31, 2018 2017 2016 Balance at beginning of year $ 10.1 $ 10.0 $ 6.3 Acquisitions 0.6 1.2 1.1 Additions 12.1 5.4 7.6 Valuation adjustments (0.1 ) (0.4 ) (0.6 ) Dispositions (8.3 ) (6.1 ) (4.4 ) Balance at end of year $ 14.4 $ 10.1 $ 10.0

Derivatives and Hedging Activ_2

Derivatives and Hedging Activities (Tables)	12 Months Ended
Derivatives and Hedging Activities (Tables)	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Offsetting Assets	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 December 31, 2018 and December 31, 2017 : 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 December 31, 2017 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 $ 7.5 $ — $ 7.5 $ 2.4 $ — $ 5.1 Mortgage related derivatives 1.3 — 1.3 — — 1.3 Total derivatives 8.8 — 8.8 2.4 — 6.4 Total assets $ 8.8 $ — $ 8.8 $ 2.4 $ — $ 6.4 Financial Liabilities Interest rate swap contracts $ 7.8 $ — $ 7.8 $ 2.4 $ 3.3 $ 2.1 Mortgage related derivatives 0.1 — 0.1 — — 0.1 Total derivatives 7.9 — 7.9 2.4 3.3 2.2 Repurchase agreements 643.0 — 643.0 — 643.0 — Total liabilities $ 650.9 $ — $ 650.9 $ 2.4 $ 646.3 $ 2.2
Offsetting 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 December 31, 2018 and December 31, 2017 : 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 December 31, 2017 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 $ 7.5 $ — $ 7.5 $ 2.4 $ — $ 5.1 Mortgage related derivatives 1.3 — 1.3 — — 1.3 Total derivatives 8.8 — 8.8 2.4 — 6.4 Total assets $ 8.8 $ — $ 8.8 $ 2.4 $ — $ 6.4 Financial Liabilities Interest rate swap contracts $ 7.8 $ — $ 7.8 $ 2.4 $ 3.3 $ 2.1 Mortgage related derivatives 0.1 — 0.1 — — 0.1 Total derivatives 7.9 — 7.9 2.4 3.3 2.2 Repurchase agreements 643.0 — 643.0 — 643.0 — Total liabilities $ 650.9 $ — $ 650.9 $ 2.4 $ 646.3 $ 2.2
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	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. December 31, 2018 December 31, 2017 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 $ 403.3 $ 8.8 $ 344.2 $ 7.5 Interest rate lock commitments 51.0 1.3 60.7 1.3 Total derivative assets $ 454.3 $ 10.1 $ 404.9 $ 8.8 Derivative Liabilities (included in accounts payable and accrued expenses on the consolidated balance sheets) Non-hedging interest rate derivatives: Interest rate swap contracts $ 403.3 $ 8.8 $ 344.2 $ 7.8 Forward loan sales contracts 64.6 0.6 88.8 0.1 Total derivative liabilities $ 467.9 $ 9.4 $ 433.0 $ 7.9
Derivative Instruments, Gain (Loss)	The following table presents the pre-tax gains or losses related to derivative contracts that were recorded in accumulated other comprehensive income and other non-interest income in the Company’s statements of income: As of or For The Year Ended December 31, 2018 2017 2016 Derivatives designated as hedges: Amount of loss recognized in other comprehensive income (effective portion) $ — $ (1.1 ) $ (0.2 ) Reclassification adjustment for derivative net (gains) losses included in income — 1.1 — Non-hedging interest rate derivatives: Amount of gain (loss) recognized in other non-interest income 0.3 — 0.1 Amount of net fee income recognized in other non-interest income 1.3 0.8 0.9 Amount of net gains (losses) recognized in mortgage banking revenues (0.5 ) (1.7 ) 1.4

Mortgage Servicing Rights (Tabl

Mortgage Servicing Rights (Tables)	12 Months Ended
Mortgage Servicing Rights (Tables)	Dec. 31, 2018
Transfers and Servicing [Abstract]
Schedule of Servicing Assets at Amortized Value	Information with respect to the Company’s mortgage servicing rights follows: Year Ended December 31, 2018 2017 2016 Balance at beginning of year $ 24.8 $ 18.7 $ 15.9 Acquisitions of mortgage servicing rights — 3.5 — Originations of mortgage servicing rights 6.0 5.6 5.8 Amortization expense (3.1 ) (3.0 ) (3.0 ) Balance at end of year 27.7 24.8 18.7 Less valuation reserve — — (0.2 ) Balance at end of year, net of valuation reserve $ 27.7 $ 24.8 $ 18.5 Principal balance of serviced loans underlying mortgage servicing rights $ 3,698.2 $ 3,636.7 $ 3,127.5 Mortgage servicing rights as a percentage of serviced loans 0.75 % 0.68 % 0.59 %

Deposits (Tables)

Deposits (Tables)	12 Months Ended
Deposits (Tables)	Dec. 31, 2018
Deposits [Abstract]
Schedule of Deposits, By Type	Deposits are summarized as follows: December 31, 2018 2017 Non-interest bearing demand $ 3,158.3 $ 2,900.0 Interest bearing: Demand 2,957.5 2,787.5 Savings 3,247.9 3,095.4 Time, $100 and over 547.6 432.0 Time, other 769.4 720.0 Total interest bearing 7,522.4 7,034.9 Total deposits $ 10,680.7 $ 9,934.9
Schedule of Maturities of Time Deposits	Maturities of time deposits at December 31, 2018 are as follows: Time, $100 and Over Total Time Due within 3 months or less $ 45.0 $ 253.8 Due after 3 months and within 6 months 49.0 149.2 Due after 6 months and within 12 months 217.5 420.4 Due within 2020 159.7 323.7 Due within 2021 63.5 128.8 Due within 2022 9.8 30.3 Due within 2023 and thereafter 3.1 10.8 Total $ 547.6 $ 1,317.0

Long-Term Debt and Other Borr_2

Long-Term Debt and Other Borrowed Funds (Tables)	12 Months Ended
Long-Term Debt and Other Borrowed Funds (Tables)	Dec. 31, 2018
Debt Disclosure [Abstract]
Summary of Long-Term Debt	A summary of long-term debt follows: December 31, 2018 2017 Subsidiaries: 8.00% capital lease obligation with term ending October 25, 2029 1.3 1.4 6.24% note payable maturing September 6, 2032, principal due at maturity, interest payable monthly 1.8 1.6 2.28% note payable maturing July 29, 2022, principal due at maturity, interest payable monthly 5.0 5.0 1.00% note payable maturing December 31, 2041, interest only payable quarterly until December 31, 2025 and then principal and interest until maturity 5.1 5.1 Note payable maturing March 31, 2038, interest only payable at 1.30% monthly until March 31, 2025 and then principal and interest at 3.25% until maturity 2.0 — 1.30% note payable maturing June 1, 2034, interest only payable monthly until March 31, 2025 and then principal and interest until maturity 0.6 — Total long-term debt $ 15.8 $ 13.1
Schedule of Maturities of Long-term Debt	Maturities of long-term debt at December 31, 2018 are as follows: 2019 $ 0.1 2020 0.1 2021 0.1 2022 5.1 2023 0.1 Thereafter 10.3 Total $ 15.8

Subordinated Debentures Held _2

Subordinated Debentures Held by Subsidiary Trusts (Tables)	12 Months Ended
Subordinated Debentures Held by Subsidiary Trusts (Tables)	Dec. 31, 2018
Subordinated Borrowings [Abstract]
Schedule of Subordinated Borrowings	A summary of Subordinated Debenture issuances follows: Principal Amount Outstanding as of December 31, Issuance Maturity Date 2018 2017 October 2007 January 1, 2038 $ 10.3 $ 10.3 November 2007 December 15, 2037 15.5 15.5 December 2007 December 15, 2037 20.6 20.6 December 2007 April 1, 2038 15.5 15.5 January 2008 April 1, 2038 10.3 10.3 January 2008 April 1, 2038 10.3 10.3 June 2005 June 30, 2035 4.4 — Total subordinated debentures held by subsidiary trusts $ 86.9 $ 82.5

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	12 Months Ended
Earnings per Common Share (Tables)	Dec. 31, 2018
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 common share: Year Ended December 31, 2018 2017 2016 Net income, basic and diluted $ 160.2 $ 106.5 $ 95.7 Weighted average common shares outstanding for basic earnings per share computation 57,778,857 51,429,366 44,511,774 Dilutive effects of stock-based compensation 438,266 473,843 398,622 Weighted average common shares outstanding for diluted earnings per common share computation 58,217,123 51,903,209 44,910,396 Basic earnings per common share $ 2.77 $ 2.07 $ 2.15 Diluted earnings per common share 2.75 2.05 2.13

Regulatory Capital (Tables)

Regulatory Capital (Tables)	12 Months Ended
Regulatory Capital (Tables)	Dec. 31, 2018
Banking and Thrift [Abstract]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations	The Company’s actual capital amounts and ratios and selected minimum regulatory thresholds and prompt corrective action provisions as of December 31, 2018 and 2017 are presented in the following tables: Actual Adequately Capitalized Basel III Phase-In Schedule Adequately Capitalized Basel III Fully Phased-In Well Capitalized (1) Amount Ratio Amount Ratio Amount Ratio Amount Ratio December 31, 2018 Total risk-based capital: Consolidated $ 1,285.0 12.99 % $ 976.6 9.875 % $ 1,038.4 10.50 % $ 989.0 10.00 % FIB 1,184.5 12.01 973.7 9.875 1,035.3 10.50 986.0 10.00 Tier 1 risk-based capital: Consolidated 1,212.0 12.26 778.8 7.875 840.6 8.50 791.2 8.00 FIB 1,111.6 11.27 776.5 7.875 838.1 8.50 788.8 8.00 Common equity tier 1 risk-based capital: Consolidated 1,127.8 11.40 630.5 6.375 692.3 7.00 642.8 6.50 FIB 1,111.6 11.27 628.6 6.375 690.2 7.00 640.9 6.50 Leverage capital ratio: Consolidated 1,212.0 9.47 511.9 4.00 511.9 4.00 639.9 5.00 FIB 1,111.6 8.97 495.9 4.00 495.9 4.00 619.8 5.00 Actual Adequately Capitalized Basel III Phase-In Schedule Adequately Capitalized Basel III Fully Phased-In Well Capitalized (1) Amount Ratio Amount Ratio Amount Ratio Amount Ratio December 31, 2017 Total risk-based capital: Consolidated $ 1,112.5 12.76 % $ 806.5 9.25 % $ 915.5 10.50 % $ 871.9 10.00 % FIB 1,066.6 12.29 802.7 9.25 911.2 10.50 867.8 10.00 Tier 1 risk-based capital: Consolidated 1,040.3 11.93 632.1 7.25 741.1 8.50 697.5 8.00 FIB 994.4 11.46 629.1 7.25 737.6 8.50 694.2 8.00 Common equity tier 1 risk-based capital: Consolidated 962.4 11.04 501.3 5.75 610.3 7.00 566.7 6.50 FIB 994.4 11.46 499.0 5.75 607.4 7.00 564.1 6.50 Leverage capital ratio: Consolidated 1,040.3 8.86 469.9 4.00 469.9 4.00 587.4 5.00 FIB 994.4 8.48 469.1 4.00 469.1 4.00 586.3 5.00 (1) The ratios for the well capitalized requirement are only applicable to FIB. However, the Company manages its capital position as if the requirement applies to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
Commitments and Contingencies (Tables)	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	The total future minimum rental commitments, exclusive of maintenance and operating costs, required under operating leases that have initial or remaining noncancelable lease terms in excess of one year at December 31, 2018 , are as follows: Third Parties Related Entity Total For the year ending December 31: 2019 $ 4.4 $ 1.6 $ 6.0 2020 4.2 1.5 5.7 2021 4.1 1.4 5.5 2022 4.1 1.2 5.3 2023 3.9 1.2 5.1 Thereafter 15.3 2.8 18.1 Total $ 36.0 $ 9.7 $ 45.7

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Income Tax Expense	Income tax expense consists of the following: Year ended December 31, 2018 2017 2016 Current: Federal $ 23.1 $ 24.3 $ 40.3 State 7.2 5.0 5.9 Total current 30.3 29.3 46.2 Deferred: Federal 12.3 18.4 2.9 State 3.5 2.5 0.5 Total deferred 15.8 20.9 3.4 Total income tax expense $ 46.1 $ 50.2 $ 49.6
Schedule of Effective Income Tax Rate Reconciliation	Total income tax provision differs from the amount of income tax determined by applying the statutory federal income tax rate of 21% for 2018 and 35% for 2017 and 2016 , respectively, to income before income taxes due to the following: Year ended December 31, 2018 2017 2016 Tax expense at the statutory tax rate $ 43.3 $ 54.9 $ 50.8 Increase (decrease) in tax resulting from: Tax-exempt income (2.8 ) (4.5 ) (4.4 ) State income tax, net of federal income tax benefit 8.5 4.9 4.3 Benefit of stock-based compensation plans (1.1 ) (2.6 ) — Federal tax credits (2.6 ) (2.5 ) (2.1 ) Benefit due to enactment of federal tax reform — (2.2 ) — Other, net 0.8 2.2 1.0 Tax expense at effective tax rate $ 46.1 $ 50.2 $ 49.6
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences between the financial statement carrying amounts and tax bases of assets and liabilities that give rise to significant portions of the net deferred tax asset (liability) relate to the following: December 31, 2018 2017 Deferred tax assets: Loans, principally due to allowance for loan losses $ 18.4 $ 18.0 Loan discount 8.3 6.7 Investment securities, unrealized losses 8.9 5.6 Deferred compensation 17.0 13.1 Non-performing loan interest 1.2 1.1 Other real estate owned write-downs and carrying costs 0.3 0.6 Tax credit carryforwards (1) 0.1 3.7 Net operating loss carryforwards (2) 3.9 8.7 Other 0.1 3.1 Deferred tax assets 58.2 60.6 Deferred tax liabilities: Fixed assets, principally differences in bases and depreciation (6.9 ) (6.7 ) Deferred loan costs (2.6 ) (1.7 ) Investment in joint venture partnership, principally due to differences in depreciation of partnership assets (0.8 ) (0.8 ) Prepaid amounts (0.6 ) (0.6 ) Government agency stock dividends (1.5 ) (1.6 ) Goodwill and core deposit intangibles (44.2 ) (38.1 ) Mortgage servicing rights (6.4 ) (5.7 ) Other (3.8 ) (1.4 ) Deferred tax liabilities (66.8 ) (56.6 ) Net deferred tax assets (liabilities) $ (8.6 ) $ 4.0 (1) Based on filed tax returns and amounts expected to be reported in current year tax returns ( December 31, 2018 ), we had remaining federal tax credit carryforwards of $0.1 million from acquired companies. The remaining federal tax credits were primarily generated from AMT tax credit carryforwards, and their use is subject to annual limitations. (2) As of December 31, 2018 , we had remaining federal net operating loss carryforwards of $5.4 million from acquired companies, which is available to offset federal taxable income and state net operating loss carryforwards in amounts which vary by state. The federal net operating losses will expire beginning in 2029 and ending in 2037 and the state net operating losses will expire beginning in 2019 and ending in 2034. The use of these carryforwards is subject to annual limitations.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
Stock-Based Compensation (Tables)	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation, Stock Options, Activity	The following table summarizes stock option activity under the Company’s active stock option plans: Year Ended December 31, 2018 Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contract Life Outstanding options, beginning of year 642,255 $ 16.13 Granted — — Exercised (199,667 ) 17.12 Forfeited (14,412 ) 20.87 Expired — — Outstanding options, end of year 428,176 $ 15.61 1.56 years Outstanding options exercisable, end of year 428,176 $ 15.61 1.56 years
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity	The following table presents information regarding the Company’s restricted stock: As of December 31, 2018 Number of Shares Weighted-Average Measurement Date Fair Value Restricted stock, beginning of year 292,506 $ 33.24 Granted 214,893 40.97 Vested (83,736 ) 32.42 Forfeited (43,079 ) 36.64 Canceled — — Restricted stock, end of year 380,584 $ 37.46

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	12 Months Ended
Other Comprehensive Income (Tables)	Dec. 31, 2018
Equity [Abstract]
Schedule of Comprehensive Income (Loss)	The gross amounts of each component of other comprehensive income and the related tax effects for the periods indicated are as follows: Year Ended December 31, 2018 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized loss during period $ (13.9 ) $ (3.6 ) $ (10.3 ) Reclassification adjustment for net loss included in net income 0.1 — 0.1 Change in unamortized loss on available-for-sale securities transferred into held-to-maturity 1.6 0.4 1.2 Defined benefits post-retirement benefit plan: Change in net actuarial loss (gain) (0.6 ) (0.1 ) (0.5 ) Total other comprehensive loss $ (12.8 ) $ (3.3 ) $ (9.5 ) Year Ended December 31, 2017 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized loss during period $ (6.5 ) $ (2.7 ) $ (3.8 ) Reclassification adjustment for net gains included in net income (0.7 ) (0.3 ) (0.4 ) Change in unamortized loss on available-for-sale securities transferred into held-to-maturity 1.9 0.7 1.2 Change in net unrealized loss on derivatives (1.1 ) (0.4 ) (0.7 ) Reclassification adjustment for derivative net (gains) losses included in net income 1.1 0.4 0.7 Defined benefits post-retirement benefit plan: Change in net actuarial loss (gain) (1.3 ) (0.5 ) (0.8 ) Total other comprehensive loss $ (6.6 ) $ (2.8 ) $ (3.8 ) Year Ended December 31, 2016 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized loss during period $ (19.4 ) $ (7.6 ) $ (11.8 ) Reclassification adjustment for net gains included in net income (0.3 ) (0.1 ) (0.2 ) Change in unamortized gain on available-for-sale securities transferred into held-to-maturity 1.9 0.7 1.2 Change in net unrealized loss on derivatives (0.2 ) (0.1 ) (0.1 ) Defined benefits post-retirement benefit plan: Change in net actuarial loss (gain) 3.9 1.6 2.3 Total other comprehensive income $ (14.1 ) $ (5.5 ) $ (8.6 )
Schedule of Accumulated Other Comprehensive Income (Loss)	The components of accumulated other comprehensive income (loss), net of income taxes, are as follows: Year ended December 31, 2018 2017 Net unrealized gain (loss) on investment securities available-for-sale $ (25.5 ) $ (13.3 ) Net actuarial gain (loss) on defined benefit post-retirement benefit plans 0.9 1.3 Net accumulated other comprehensive income (loss) $ (24.6 ) $ (12.0 )

Condensed Financial Informati_2

Condensed Financial Information (Parent Company Only) (Tables)	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Schedule of Condensed Financial Statements	Following is condensed financial information of First Interstate BancSystem, Inc. December 31, 2018 2017 Condensed balance sheets: Cash and cash equivalents $ 72.9 $ 42.3 Investment in bank subsidiary 1,648.9 1,432.3 Advances to subsidiaries, net 46.0 25.7 Other assets 59.0 61.7 Total assets $ 1,826.8 $ 1,562.0 Other liabilities $ 46.0 $ 51.9 Subordinated debentures held by subsidiary trusts 86.9 82.5 Total liabilities 132.9 134.4 Stockholders’ equity 1,693.9 1,427.6 Total liabilities and stockholders’ equity $ 1,826.8 $ 1,562.0 Years Ended December 31, 2018 2017 2016 Condensed statements of income: Dividends from subsidiaries $ 148.5 $ 150.0 $ 140.0 Other interest income 0.1 0.1 — Other income, primarily management fees from subsidiaries 17.0 18.0 15.1 Total income 165.6 168.1 155.1 Salaries and benefits 25.3 21.8 18.8 Interest expense 4.5 4.7 4.1 Acquisition expenses 8.1 25.3 1.5 Other operating expenses, net 14.5 13.0 10.4 Total expenses 52.4 64.8 34.8 Earnings before income tax benefit 113.2 103.3 120.3 Income tax benefit (9.3 ) (14.2 ) (7.7 ) Income before undistributed earnings of subsidiaries 122.5 117.5 128.0 Undistributed earnings of subsidiaries 37.7 (11.0 ) (32.4 ) Net income $ 160.2 $ 106.5 $ 95.6 Years Ended December 31, 2018 2017 2016 Condensed statements of cash flows: Cash flows from operating activities: Net income $ 160.2 $ 106.5 $ 95.6 Adjustments to reconcile net income to cash provided by operating activities: Undistributed earnings of subsidiaries (37.7 ) 11.0 32.4 Stock-based compensation expense 5.6 3.9 4.4 Tax benefits from stock-based compensation — — 2.1 Excess tax benefits from stock-based compensation — — (1.6 ) Other, net 16.4 14.7 (0.8 ) Net cash provided by operating activities 144.5 136.1 132.1 Cash flows from investing activities: Capital distributions from nonbank subsidiaries — 18.0 2.0 Acquisition of intangible assets — (28.0 ) — Acquisition of bank holding company, net of cash and cash equivalents received (14.7 ) (128.3 ) — Investment in subsidiary — (18.0 ) — Net cash (used) provided in investing activities (14.7 ) (156.3 ) 2.0 Cash flows from financing activities: Net (decrease) increase in advances from subsidiaries (9.9 ) (28.4 ) 9.1 Repayment of long-term debt (26.0 ) — — Proceeds from issuance of common stock, net of stock issuance costs 1.8 2.4 4.7 Excess tax benefits from stock-based compensation — — 1.6 Purchase and retirement of common stock (1.0 ) (1.3 ) (26.9 ) Dividends paid to common stockholders (64.1 ) (48.6 ) (39.4 ) Net cash used in financing activities (99.2 ) (75.9 ) (50.9 ) Net change in cash and cash equivalents 30.6 (96.1 ) 83.2 Cash and cash equivalents, beginning of year 42.3 138.4 55.2 Cash and cash equivalents, end of year $ 72.9 $ 42.3 $ 138.4

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
Fair Value Measurements (Tables)	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis	Financial assets and financial liabilities measured at fair value on a recurring basis are as follows: 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. agency 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 — Fair Value Measurements at Reporting Date Using As of December 31, 2017 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 $ 3.2 $ — $ 3.2 $ — Obligations of U.S. government agencies 561.5 — 561.5 — U.S. agency mortgage-backed securities & collateralized mortgage obligations 1,462.5 — 1,462.5 — Private mortgage-backed securities 90.7 — 90.7 — Corporate securities 87.9 — 87.9 — Other investments 3.0 — 3.0 — Loans held for sale 46.6 — 46.6 — Derivative assets: Interest rate swap contracts 7.5 — 7.5 — Interest rate lock commitments 1.3 — 1.3 — Derivative liabilities: Interest rate swap contracts 7.8 — 7.8 — Forward loan sales contracts 0.1 — 0.1 — Deferred compensation plan assets 12.2 — 12.2 — Deferred compensation plan liabilities 12.2 — 12.2 —
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 December 31, 2018 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Gains (Losses) Impaired loans $ 24.1 $ — $ — $ 24.1 $ (12.2 ) Other real estate owned 0.6 — — 0.6 (0.6 ) Long-lived assets to be disposed of by sale 4.9 — — 4.9 (0.5 ) Fair Value Measurements at Reporting Date Using As of December 31, 2017 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Gains (Losses) Impaired loans $ 32.6 $ — $ — $ 32.6 $ (22.2 ) Other real estate owned 1.3 — — 1.3 (1.6 ) Long-lived assets to be disposed of by sale 0.8 — — 0.8 —
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: As of December 31, 2018 Fair Value Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 24.1 Appraisal Appraisal adjustment 0% - 26% (13%) Other real estate owned 0.6 Appraisal Appraisal adjustment 8% - 96% (39%) Long-lived assets to be disposed of by sale 4.9 Appraisal Appraisal adjustment 0% - 43% (10%) As of December 31, 2017 Fair Value Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 32.6 Appraisal Appraisal adjustment 0% - 78% (26%) Other real estate owned 1.3 Appraisal Appraisal adjustment 8% - 96% (12%) Long-lived assets to be disposed of by sale 0.8 Appraisal Appraisal adjustment 0% - 0% 0%
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 December 31, 2018 Carrying Amount Estimated Fair Value Quoted Prices in Significant Other Significant 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 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2017 Carrying Amount Estimated Fair Value Quoted Prices in Significant Other Significant Financial assets: Cash and cash equivalents $ 759.0 $ 759.0 $ 759.0 $ — $ — Investment debt securities available-for-sale 2,208.7 2,208.7 — 2,208.7 — Investment debt securities held-to-maturity 484.5 483.3 — 483.3 — Accrued interest receivable 38.0 38.0 — 38.0 — Mortgage servicing rights, net 24.8 40.1 — 40.1 — Loans held for sale 46.6 46.6 — 46.6 — Net loans held for investment 7,495.6 7,252.2 — 7,219.6 32.6 Derivative assets 8.8 8.8 — 8.8 — Deferred compensation plan assets 12.2 12.2 — 12.2 — Total financial assets $ 11,078.2 $ 10,848.9 $ 759.0 $ 10,057.3 $ 32.6 Financial liabilities: Total deposits, excluding time deposits $ 8,783.0 $ 8,783.0 $ 8,783.0 $ — $ — Time deposits 1,151.9 1,137.9 — 1,137.9 — Securities sold under repurchase agreements 643.0 643.0 — 643.0 — Other borrowed funds 20.0 20.0 — 20.0 — Accrued interest payable 5.6 5.6 — 5.6 — Long-term debt 13.1 11.3 — 11.3 — Subordinated debentures held by subsidiary trusts 82.5 76.7 — 76.7 — Derivative liabilities 7.9 7.9 — 7.9 — Deferred compensation plan liabilities 12.2 12.2 — 12.2 — Total financial liabilities $ 10,719.2 $ 10,697.6 $ 8,783.0 $ 1,914.6 $ —

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)subsidiarysegment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Property, Plant and Equipment
Number of significant subsidiaries \| subsidiary	1
Cash on deposit with Federal Reserve Bank	$ 574,400,000	$ 552,000,000
Compensating balances with Federal Reserve Bank	28,100,000	16,100,000
Mortgage loans held for sale	33,300,000	46,600,000
Deferred compensation plan assets	12,100,000	12,200,000
Deferred compensation plan liabilities	12,100,000	12,200,000
Impairment losses	0	0	$ 200,000
Write-downs of OREO	(100,000)	(400,000)	(600,000)
Carrying value of foreclosed OREO	2,000,000	2,700,000
Federal Reserve Bank stock	37,500,000	10,700,000
Federal Home Loan Bank stock	31,800,000	10,200,000
Income tax examination, penalties	$ 0	0	0
Number of operating segments \| segment	1
Advertising expense	$ 3,200,000	3,500,000	2,800,000
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	5,600,000	3,800,000	4,400,000
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation			2,200,000
Mortgage Loans in Process of Foreclosure, Amount	$ 400,000
Buildings and improvements \| Minimum
Property, Plant and Equipment
Estimated useful lives	5 years
Buildings and improvements \| Maximum
Property, Plant and Equipment
Estimated useful lives	45 years
Furniture and equipment \| Minimum
Property, Plant and Equipment
Estimated useful lives	4 years
Furniture and equipment \| Maximum
Property, Plant and Equipment
Estimated useful lives	15 years
Restricted Stock
Property, Plant and Equipment
Stock compensation expense	$ 5,600,000	3,300,000	3,900,000
Tax benefits from stock-based compensation	200,000	600,000	1,500,000
Common Stock Including Additional Paid in Capital [Member]
Property, Plant and Equipment
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition		3,800,000	4,400,000
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	$ 1,100,000	$ 2,600,000	$ 2,200,000

Acquisitions - Narrative (Deta

Acquisitions - Narrative (Details) $ / shares in Units, $ in Millions	Oct. 11, 2018USD ($)$ / shares	Aug. 16, 2018USD ($)$ / sharesshares	May 30, 2017USD ($)$ / sharesshares	Aug. 12, 2016USD ($)	Jun. 30, 2017USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Oct. 05, 2018$ / sharesshares
Business Acquisition [Line Items]
Cash Paid Related To Cascade Options			$ 9.3
Cash Paid For Cascade Unvested Restricted Stock			$ 2.2
Shares Issued For Cascade Unvested Restricted Stock \| shares			168,000
Expense Related To Restricted Awards Excluded From Consideration Paid			$ 2.4
Restricted Stock Expense Included In Consideration Paid			$ 5.5
Goodwill							$ 546.7	$ 444.7	$ 212.8
Number of operating segments \| segment							1
Acquisition related expenses							$ 12.4	$ 27.2	$ 2.8
Community 1st Bank [Member]
Business Acquisition [Line Items]
Estimate value per share of Acquisition \| $ / shares	$ 17.20
Inland Northwest Bank [Member]
Business Acquisition [Line Items]
Estimate value per share of Acquisition \| $ / shares	$ 22.73
Bank of the Cascades [Member]
Business Acquisition [Line Items]
Number of banking offices			46
Class A Common Stock \| Idaho Independent Bank [Member]
Business Acquisition [Line Items]
Business Acquisition, Conversion Share Rate, Shares \| shares										0.5000
Estimate value per share of Acquisition \| $ / shares										$ 45.45
Class A Common Stock \| Community 1st Bank [Member]
Business Acquisition [Line Items]
Business Acquisition, Conversion Share Rate, Shares \| shares										0.3784
Estimate value per share of Acquisition \| $ / shares										$ 45.45
Core Deposits Intangibles
Business Acquisition [Line Items]
Finite-lived intangible assets acquired			$ 15.7	$ 48
Idaho Independent Bank [Member]
Business Acquisition [Line Items]
Number of banking offices	11
Estimate of Payments to Acquire Businesses, Gross	$ 181.3
Northwest Bank Acquisition, as Recorded by the Company [Member]
Business Acquisition [Line Items]
Core deposit intangible assets		$ 15.7
Cash paid as consideration		$ 3
Cascade Bank
Business Acquisition [Line Items]
Revenue reported by Cascade					$ 12.9
Net income reported by Cascade					$ 3
Cascade Bank \| Class A Common Stock
Business Acquisition [Line Items]
Common stock issued (in shares) \| shares			3,837,540
Cascade Bank Acquisition, as Recorded by the Company
Business Acquisition [Line Items]
Core deposit intangible assets			$ 48
Cash paid as consideration			155
Total consideration paid			541
Goodwill			$ 232.8
Inland Northwest Bank [Member]
Business Acquisition [Line Items]
Number of banking offices		20
Total consideration paid		$ 176.3
Goodwill		$ 101.1
Number of operating segments \| segment							1
Revenue reported by Cascade						$ 5.9
Net income reported by Cascade						$ 2.1
Inland Northwest Bank [Member] \| Class A Common Stock
Business Acquisition [Line Items]
Business Acquisition Conversion Share Rate \| shares		0.516
Business Acquisition, Share Price \| $ / shares		$ 45.15
Inland Northwest Bank [Member] \| Core Deposits Intangibles
Business Acquisition [Line Items]
Estimated useful lives of related deposits		10 years
Bank of the Cascades [Member]
Business Acquisition [Line Items]
Cash received by Cascade shareholders (in dollars per share) \| $ / shares			$ 1.91
Common stock issued (in shares) \| shares			11,300,000
Bank of the Cascades [Member] \| Class A Common Stock
Business Acquisition [Line Items]
Business Acquisition Conversion Share Rate \| shares			0.14864
Business Acquisition, Share Price \| $ / shares			$ 34.30
Bank of the Cascades [Member] \| Core Deposits Intangibles
Business Acquisition [Line Items]
Estimated useful lives of related deposits			10 years
Community 1st Bank [Member]
Business Acquisition [Line Items]
Number of banking offices	3
Estimate of Payments to Acquire Businesses, Gross	$ 21.5
Employee Benefit Plan Expense [Member]
Business Acquisition [Line Items]
Acquisition related expenses							$ 2.3
Legal and Professional Expenses [Member]
Business Acquisition [Line Items]
Acquisition related expenses							$ 21.8

Acquisitions - Schedule of Rec

Acquisitions - Schedule of Recognized Identifiable Assets Acquired and Liabilities Assumed (Details) $ / shares in Units, $ in Millions		Oct. 11, 2018USD ($)	Aug. 16, 2018USD ($)$ / sharesshares	May 30, 2017USD ($)$ / sharesshares	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Cash Paid For Cascade Unvested Restricted Stock				$ 2.2
Shares Issued For Cascade Unvested Restricted Stock \| shares				168,000
Cash Paid Related To Cascade Options				$ 9.3
Goodwill					$ 546.7	$ 444.7	$ 212.8
Number of operating segments \| segment					1
Expense Related To Restricted Awards Excluded From Consideration Paid				2.4
Restricted Stock Expense Included In Consideration Paid				5.5
Idaho Independent Bank [Member]
Business Acquisition [Line Items]
Number of banking offices		11
Estimate of Payments to Acquire Businesses, Gross		$ 181.3
Community 1st Bank [Member]
Business Acquisition [Line Items]
Number of banking offices		3
Estimate of Payments to Acquire Businesses, Gross		$ 21.5
Northwest Bank Acquisition, As Recorded By Inland Northwest Bank [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			$ 31.2
Investment securities			3.1
Business Combinations, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Held for Investment			727.9
Allowance for loan losses			(8)
Premises and equipment			14.5
Other real estate owned (“OREO”)			0.3
Core deposit intangible assets			2.4
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Assets			29.3
Total assets acquired			800.7
Deposits			696.1
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed, Other Liabilities			8.1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt			13
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, 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
Cascade Bank Acquisition, As Recorded By Cascade Bank
Business Acquisition [Line Items]
Cash and cash equivalents				246.8
Investment securities				476.7
Loans held for investment				2,111
Mortgage loans held for sale				10.3
Allowance for loan losses				(24)
Premises and equipment				46.6
Other real estate owned (“OREO”)				1.2
Core deposit intangible assets				0
Deferred tax assets, net				47.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Assets				98.6
Total assets acquired				3,014.8
Deposits				2,669.9
Accounts payable and accrued expense				62.2
Total liabilities assumed				2,732.1
Net assets acquired				282.7
Cascade Bank Acquisition, Fair Value Adjustments
Business Acquisition [Line Items]
Cash and cash equivalents				0
Investment securities				4.9
Loans held for investment				(31.7)
Mortgage loans held for sale				0
Allowance for loan losses				24
Premises and equipment				0.1
Other real estate owned (“OREO”)				0
Core deposit intangible assets				48
Deferred tax assets, net				(20.9)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Assets				2.1
Total assets acquired				26.5
Deposits				(0.9)
Accounts payable and accrued expense				1.9
Total liabilities assumed				1
Net assets acquired				25.5
Cascade Bank Acquisition, as Recorded by the Company
Business Acquisition [Line Items]
Cash and cash equivalents				246.8
Investment securities				481.6
Loans held for investment				2,079.3
Mortgage loans held for sale				10.3
Allowance for loan losses				0
Premises and equipment				46.7
Other real estate owned (“OREO”)				1.2
Core deposit intangible assets				48
Deferred tax assets, net				26.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Assets				100.7
Total assets acquired				3,041.3
Deposits				2,669
Accounts payable and accrued expense				64.1
Total liabilities assumed				2,733.1
Net assets acquired				308.2
Cash				155
Total consideration paid				541
Goodwill				232.8
Cascade Bank Acquisition, as Recorded by the Company \| Class A Common Stock
Business Acquisition [Line Items]
Class A common stock				386
Northwest Bank Acquisition, Fair Value Adjustments [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			0
Investment securities			0
Business Combinations, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Held for Investment	[1]		(14.8)
Allowance for loan losses	[2]		8
Premises and equipment	[3]		(0.5)
Other real estate owned (“OREO”)			0.3
Core deposit intangible assets	[4]		13.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Assets			(10)
Total assets acquired			(3.7)
Deposits			0.2
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed, Other Liabilities			(0.4)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt			0.1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Trust Preferred Securities			(0.8)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Deferred Tax Liability	[5]		1.5
Total liabilities assumed			0.6
Net assets acquired			(4.3)
Northwest Bank Acquisition, as Recorded by the Company [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			31.2
Investment securities			3.1
Business Combinations, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Held for Investment			713.1
Allowance for loan losses			0
Premises and equipment			14
Other real estate owned (“OREO”)			0.6
Core deposit intangible assets			15.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Assets			19.3
Total assets acquired			797
Deposits			696.3
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed, Other Liabilities			7.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt			13.1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Trust Preferred Securities			4.4
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Deferred Tax Liability			0.3
Total liabilities assumed			721.8
Net assets acquired			75.2
Cash			3
Class A common stock			$ 173.3
Inland Northwest Bank [Member]
Business Acquisition [Line Items]
Number of banking offices			20
Total consideration paid			$ 176.3
Goodwill			$ 101.1
Number of operating segments \| segment					1
Inland Northwest Bank [Member] \| Class A Common Stock
Business Acquisition [Line Items]
Business Acquisition Conversion Share Rate \| shares			0.516
Business Acquisition, Share Price \| $ / shares			$ 45.15
Cascade Bank \| Class A Common Stock
Business Acquisition [Line Items]
Class A common stock				$ 173.3
Common stock issued (in shares) \| shares				3,837,540
Bank of the Cascades [Member]
Business Acquisition [Line Items]
Cash received by Cascade shareholders (in dollars per share) \| $ / shares				$ 1.91
Common stock issued (in shares) \| shares				11,300,000
Bank of the Cascades [Member] \| Class A Common Stock
Business Acquisition [Line Items]
Business Acquisition Conversion Share Rate \| shares				0.14864
Business Acquisition, Share Price \| $ / shares				$ 34.30
Bank of the Cascades [Member]
Business Acquisition [Line Items]
Number of banking offices				46
Core Deposits Intangibles \| Inland Northwest Bank [Member]
Business Acquisition [Line Items]
Estimated useful lives of related deposits			10 years
Core Deposits Intangibles \| Bank of the Cascades [Member]
Business Acquisition [Line Items]
Estimated useful lives of related deposits				10 years

[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]	(9) Adjustment consists of the write-off of pre-existing deferred tax assets and purchase accounting adjustments as a result of the acquisition.

Acquisitions - Schedule of Acq

Acquisitions - Schedule of Acquisition Related Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs, Legal Fees	$ 4	$ 9.6	$ 2.1
Business Combination, Acquisition Related Costs, Employee Expense	1.1	5.1	0.2
Business Combination, Acquisition Related Costs, Technology and Contract Termination	6.6	10.2	0.2
Business Combination, Acquisition Related Costs, Other Expenses	0.7	2.3	0.3
Total acquisition related expenses	$ 12.4	$ 27.2	$ 2.8

Acquisitions - Schedules of Lo

Acquisitions - Schedules of Loans Acquired (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended
	Jun. 30, 2017	Sep. 30, 2018	Aug. 16, 2018	May 30, 2017
Business Acquisition [Line Items]
Contractually required principal and interest payments				$ 49.7
Contractual cash flows not expected to be collected (“non-accretable discount”)				24.7
Cash flows expected to be collected				25
Interest component of cash flows expected to be collected (“accretable discount”)				1.9
Fair value of acquired credit-impaired loans				23.1
Contractually required principal and interest payments				2,098.1
Contractual cash flows not expected to be collected				23.3
Fair value at acquisition				$ 2,066.5
Cascade Bank
Business Acquisition [Line Items]
Revenue reported by Cascade	$ 12.9
Net income reported by Cascade	$ 3
Inland Northwest Bank [Member]
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
Contractually required principal and interest payments			894.8
Contractual cash flows not expected to be collected			26.1
Fair value at acquisition			$ 693.2
Revenue reported by Cascade		$ 5.9
Net income reported by Cascade		$ 2.1

Acquisitions - Schedule of Una

Acquisitions - Schedule of Unaudited Pro Forma Revenue and Income (Details) - Cascade Bank - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Interest income	$ 473.4	$ 420.8
Non-interest income	143.3	153.3
Total revenues	616.7	574.1
Net income	$ 162.5	$ 126.4
EPS - basic (in dollars per share)	$ 2.81	$ 2.03
EPS - diluted (in dollars per share)	$ 2.79	$ 2.01

Goodwill and Core Deposit Int_3

Goodwill and Core Deposit Intangibles - Schedule of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Property, Plant and Equipment, Net	$ 245.2	$ 241.9
Goodwill [Roll Forward]
Net carrying value at beginning of period	444.7	212.8
Acquisitions and measurement period adjustments	102	231.9
Net carrying value at end of period	546.7	$ 444.7
Inland Northwest Bank [Member]
Goodwill [Line Items]
Change in goodwill	$ 0.3

Goodwill and Core Deposit Int_4

Goodwill and Core Deposit Intangibles - Goodwill Narrative (Details) - USD ($)	Jul. 01, 2017	Jul. 01, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill			$ 546,700,000	$ 444,700,000	$ 212,800,000
Impairment of goodwill	$ 0	$ 0

Goodwill and Core Deposit Int_5

Goodwill and Core Deposit Intangibles - Schedule of Core Deposit Intangibles Activity (Details) - USD ($) $ in Millions	May 30, 2017	Aug. 12, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-lived Intangible Assets [Roll Forward]
Accumulated amortization			$ 7.9	$ 5.5	$ 3.4
Core Deposits Intangibles
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross				74	$ 29.2
Finite-lived Intangible Assets [Roll Forward]
Gross CDI, beginning of period			49.1
Established through acquisitions	$ 15.7	$ 48
Reductions due to sale of accounts			0	(3.2)
Accumulated amortization			(32.8)	(24.9)
Net CDI, end of period			$ 56.9	$ 49.1

Goodwill and Core Deposit Int_6

Goodwill and Core Deposit Intangibles - Intangible Assets Narrative (Details) - Core Deposits Intangibles - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life (in years)	10 years
Proceeds from sale of custodial rights	$ 6.2
Reductions due to sale of accounts	$ 0	$ (3.2)

Goodwill and Core Deposit Int_7

Goodwill and Core Deposit Intangibles - Schedule of Future Estimated CDI Amortization Expense (Details) - Core Deposits Intangibles - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
2,018	$ 8.9
2,019	8.1
2,020	7.5
2,021	6.9
2,022	6.3
Thereafter	19.2
Total	$ 56.9	$ 49.1

Investment Securities - Amorti

Investment Securities - Amortized Cost and Approximate Fair Values of Investment Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available for Sale and Held-to-Maturity Securities
Available-for-sale Securities, Gross Realized Gains	$ 0	$ 1.1	$ 0.4
Available-for-sale Securities, Gross Realized Losses	(0.1)	(0.4)	$ (0.1)
Available-for-Sale:
Amortized Cost	2,305.2	2,229.3
Gross Unrealized Gains	2.6	3.9
Gross Unrealized Losses	(37.1)	(24.5)
Estimated Fair Value	2,270.7	2,208.7
Held-to-Maturity:
Amortized Cost	406.8	484.5
Gross Unrealized Gains	2.2	11.5
Gross Unrealized Losses	(8.3)	(12.7)
Estimated Fair Value	400.7	483.3
US Treasury notes
Available-for-Sale:
Amortized Cost	2.6	3.2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	2.6	3.2
State, county and municipal securities
Held-to-Maturity:
Amortized Cost	150.9	172.4
Gross Unrealized Gains	1.8	2.6
Gross Unrealized Losses	(0.9)	(0.6)
Estimated Fair Value	151.8	174.4
Available-for-sale securities, amortized cost basis	115.5
Obligations of U.S. government agencies
Available-for-Sale:
Amortized Cost	569.3	569.5
Gross Unrealized Gains	0.1	0
Gross Unrealized Losses	(10.2)	(8)
Estimated Fair Value	559.2	561.5
Held-to-Maturity:
Amortized Cost	19.8	19.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(0.3)	(0.2)
Estimated Fair Value	19.5	19.6
Corporate Debt Securities [Member]
Available-for-Sale:
Amortized Cost	92.9	88
Gross Unrealized Gains	0	0.1
Gross Unrealized Losses	(1)	(0.3)
Estimated Fair Value	91.9	87.8
Held-to-Maturity:
Amortized Cost	46.3	61.6
Gross Unrealized Gains	0.1	0.1
Gross Unrealized Losses	(0.6)	(0.3)
Estimated Fair Value	45.8	61.4
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Amortized Cost	1,566.4	1,474.1
Gross Unrealized Gains	2.5	3.8
Gross Unrealized Losses	(24.1)	(15.4)
Estimated Fair Value	1,544.8	1,462.5
Held-to-Maturity:
Amortized Cost	189.7	230.5
Gross Unrealized Gains	0.3	8.8
Gross Unrealized Losses	(6.5)	(11.6)
Estimated Fair Value	183.5	227.7
Private mortgage-backed securities
Available-for-Sale:
Amortized Cost	72	91.5
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1.8)	(0.8)
Estimated Fair Value	70.2	90.7
Other Investments
Available-for-Sale:
Amortized Cost	2	3
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	2	3
Other Investments
Held-to-Maturity:
Amortized Cost	0.1	0.2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	0.1	$ 0.2
Idaho, Montana, Oregon, South Dakota, Washington, and Wyoming \| State, county and municipal securities
Held-to-Maturity:
Available-for-sale securities, amortized cost basis	$ 66.8

Investment Securities - Realiz

Investment Securities - Realized Gains (Losses) on Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Gross realized gains	$ 0	$ 1.1	$ 0.4
Gross realized losses	0.1	$ 0.4	$ 0.1
State, county and municipal securities
Schedule of Available-for-sale Securities
General obligation securities, amortized cost	115.5
State, county and municipal securities \| Idaho, Montana, Oregon, South Dakota, Washington, and Wyoming
Schedule of Available-for-sale Securities
General obligation securities, amortized cost	$ 66.8

Investment Securities - Gross

Investment Securities - Gross Unrealized Losses and Fair Values of Investment Securities (Details)	12 Months Ended
	Dec. 31, 2018USD ($)Investments	Dec. 31, 2017USD ($)Investments
Fair Value
Less than 12 Months	$ 1,123,200,000	$ 1,080,300,000
12 Months or More	779,000,000	705,300,000
Total	1,902,200,000	1,785,600,000
Gross Unrealized Losses
Less than 12 Months	(22,600,000)	(10,700,000)
12 Months or More	(14,500,000)	(13,800,000)
Total	(37,100,000)	(24,500,000)
Fair Value
Less than 12 Months	90,400,000	180,600,000
12 Months or More	216,900,000	87,700,000
Gross Unrealized Losses
Less than 12 Months	(2,800,000)	(9,700,000)
12 Months or More	(5,500,000)	(3,000,000)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	307,300,000	268,300,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	$ (8,300,000)	$ (12,700,000)
Available-for-Sale and Held-to-Maturity:
Investment securities in an unrealized loss position (number of securities) \| Investments	760	581
Impairment losses	$ 0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Fair Value
Less than 12 Months	735,200,000	$ 670,100,000
12 Months or More	503,700,000	439,200,000
Total	1,238,900,000	1,109,300,000
Gross Unrealized Losses
Less than 12 Months	(14,500,000)	(6,200,000)
12 Months or More	(9,600,000)	(9,200,000)
Total	(24,100,000)	(15,400,000)
Fair Value
Less than 12 Months	0	76,400,000
12 Months or More	39,600,000	60,500,000
Gross Unrealized Losses
Less than 12 Months	0	(9,100,000)
12 Months or More	(600,000)	(2,500,000)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	39,600,000	136,900,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(600,000)	(11,600,000)
Obligations of U.S. government agencies
Fair Value
Less than 12 Months	363,100,000	284,900,000
12 Months or More	154,500,000	266,100,000
Total	517,600,000	551,000,000
Gross Unrealized Losses
Less than 12 Months	(7,900,000)	(3,400,000)
12 Months or More	(2,300,000)	(4,600,000)
Total	(10,200,000)	(8,000,000)
Fair Value
Less than 12 Months	19,500,000	9,700,000
12 Months or More	0	9,900,000
Gross Unrealized Losses
Less than 12 Months	(300,000)	0
12 Months or More	0	(200,000)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	19,500,000	19,600,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(300,000)	(200,000)
Corporate Debt Securities [Member]
Fair Value
Less than 12 Months	24,900,000	51,300,000
12 Months or More	51,400,000	0
Total	76,300,000	51,300,000
Gross Unrealized Losses
Less than 12 Months	(200,000)	(300,000)
12 Months or More	(800,000)	0
Total	(1,000,000)	(300,000)
Fair Value
Less than 12 Months	45,000,000	41,200,000
12 Months or More	120,200,000	5,000,000
Gross Unrealized Losses
Less than 12 Months	(2,200,000)	(200,000)
12 Months or More	(4,300,000)	(100,000)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	165,200,000	46,200,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(6,500,000)	(300,000)
Private mortgage-backed securities
Fair Value
Less than 12 Months	0	74,000,000
12 Months or More	69,400,000	0
Total	69,400,000	74,000,000
Gross Unrealized Losses
Less than 12 Months	0	(800,000)
12 Months or More	(1,800,000)	0
Total	(1,800,000)	(800,000)
State, county and municipal securities
Fair Value
Less than 12 Months	25,900,000	53,300,000
12 Months or More	57,100,000	12,300,000
Gross Unrealized Losses
Less than 12 Months	(300,000)	(400,000)
12 Months or More	(600,000)	(200,000)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	83,000,000	65,600,000
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	$ (900,000)	$ (600,000)

Investment Securities - Maturi

Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity
Available-for-sale amortized cost, within one year	$ 477.8
Available-for-sale amortized cost, after one year but within five years	1,519.2
Available-for-sale amortized cost, after five years but within ten years	154.5
Available-for-sale amortized cost, after ten years	153.7
Amortized Cost	2,305.2	$ 2,229.3
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity
Available-for-sale estimated fair value, within one year	472.3
Available-for-sale estimated fair value, after one year but within five years	1,495
Available-for-sale estimated fair value, after ten years	151.9
Available-for-sale estimated fair value, after five years but within ten years	151.5
Available-for-Sale, Estimated Fair Value	2,270.7	2,208.7
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount
Held-to-maturity amortized cost, within one year	64.1
Held-to-maturity amortized cost, after one year but within five years	221.6
Held-to-maturity amortized cost, after five years but within ten years	94.4
Held-to-maturity amortized cost, after ten years	26.7
Amortized Cost	406.8	484.5
Held-to-maturity Securities, Debt Maturities, Fair Value, Rolling Maturity
Held-to-maturity estimated fair value, within one year	63
Held-to-maturity estimated fair value, after one year but within five years	216.7
Held-to-maturity estimated fair value, after five years but within ten years	94.9
Held-to-maturity estimated fair value, after ten years	26.1
Estimated Fair Value	400.7	483.3
Available-for-sale Securities and Held-to-maturity Securities
Securities sold under agreements to repurchase	1,943.1	2,087.7
Pledged assets separately reported, securities pledged for repurchase agreements, at fair value	1,908.4	2,062.6
Callable within one year
Available-for-sale Securities and Held-to-maturity Securities
Investment securities primarily classified as available-for-sale, amortized costs, after one year but within five years	2
Investment Securities,Callable Structured, Fair Value	2
Investment securities primarily classified as available-for-sale, fair value, after one year but within five years	64.7	64.8
Mortgage Backed Securities, Variable Rate
Available-for-sale Securities and Held-to-maturity Securities
Available-for-sale securities, amortized cost basis	$ 219.5	$ 247.9

Loans - Schedule of Loans by C

Loans - Schedule of Loans by Class (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable
Loans held for investment	$ 8,470.4	$ 7,567.7
Mortgage loans held for sale	33.3	46.6
Total loans	8,503.7	7,614.3
Commercial
Loans and Leases Receivable
Loans held for investment	$ 3,235.4	2,822.9
Loans receivable, maturity	5 years
Land acquisition & development
Loans and Leases Receivable
Loans held for investment	$ 321.6	348.7
Residential
Loans and Leases Receivable
Loans held for investment	242.8	240.2
Commercial
Loans and Leases Receivable
Loans held for investment	274.3	119.4
Total construction loans
Loans and Leases Receivable
Loans held for investment	838.7	708.3
Residential
Loans and Leases Receivable
Loans held for investment	$ 1,542	1,487.4
Loans receivable, maturity	15 years
Agricultural
Loans and Leases Receivable
Loans held for investment	$ 217.4	158.2
Total real estate loans
Loans and Leases Receivable
Loans held for investment	5,833.5	5,176.8
Indirect consumer
Loans and Leases Receivable
Loans held for investment	787.8	784.7
Other consumer
Loans and Leases Receivable
Loans held for investment	200.6	175.1
Credit card consumer
Loans and Leases Receivable
Loans held for investment	81.8	74.6
Total consumer loans
Loans and Leases Receivable
Loans held for investment	1,070.2	1,034.4
Commercial
Loans and Leases Receivable
Loans held for investment	1,310.3	1,215.4
Agricultural
Loans and Leases Receivable
Loans held for investment	254.8	136.2
Other, including overdrafts
Loans and Leases Receivable
Loans held for investment	1.6	4.9
Loans held for investment
Loans and Leases Receivable
Loans held for investment	8,470.4	7,567.7
Total loans
Loans and Leases Receivable
Total loans	8,503.7	7,614.3
Home equity line of credit
Loans and Leases Receivable
Loans held for investment	$ 409.5	$ 397
Loans receivable, loan to value limit	80.00%

Loans - Schedule of Outstandin

Loans - Schedule of Outstanding Unpaid Principal Balance and Accrual Status of Loans Acquired With Credit Impairment (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deteriorated Loans Transferred in [Abstract]
Outstanding principal	$ 43.4	$ 38.2
Loans on accrual status	30.2	24.9
Total carrying value	$ 30.2	$ 24.9

Loans - Schedule of Changes in

Loans - Schedule of Changes in Accretable Yield for Loans Acquired with Credit Impairment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Rollforward [Abstract]
Beginning Balance	$ 7.3	$ 6.8	$ 6.7
Acquisitions	3.2	1.9	1.1
Additions	(3.1)	(2.9)	(2.5)
Accretion income	0.6	0.1	0
Reductions due to exit events	(1.1)	(1.5)	(1.1)
Reclassifications from nonaccretable differences	2	2.9	2.6
Ending Balance	$ 8.9	$ 7.3	$ 6.8

Loans - Schedule of Recorded I

Loans - Schedule of Recorded Investment in Past Due Loans by Class (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Recorded Investment, Past Due
Impaired Loans, interest lost on nonaccrual loans	$ 3.4
Loans held for investment		$ 8,470.4	$ 7,567.7
Mortgage loans held for sale		33.3	46.6
Total loans		8,503.7	7,614.3
Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		12.2	3.7
Current Loans		3,214	2,792.4
Non-accrual Loans		9.2	26.8
Loans held for investment		3,235.4	2,822.9
Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1.9	7.9
Current Loans		316	337.8
Non-accrual Loans		3.7	3
Loans held for investment		321.6	348.7
Residential
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1.4	2.1
Current Loans		240.4	236.4
Non-accrual Loans		1	1.7
Loans held for investment		242.8	240.2
Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.4	0
Current Loans		273.7	115.6
Non-accrual Loans		0.2	3.8
Loans held for investment		274.3	119.4
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		3.7	10
Current Loans		830.1	689.8
Non-accrual Loans		4.9	8.5
Loans held for investment		838.7	708.3
Residential
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		10.1	15.1
Current Loans		1,525.3	1,464.1
Non-accrual Loans		6.6	8.2
Loans held for investment		1,542	1,487.4
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		2.2	0.5
Current Loans		202.6	154.3
Non-accrual Loans		12.6	3.4
Loans held for investment		217.4	158.2
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		28.2	29.3
Current Loans		5,772	5,100.6
Non-accrual Loans		33.3	46.9
Loans held for investment		5,833.5	5,176.8
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		9.3	10.3
Current Loans		776.8	772.6
Non-accrual Loans		1.7	1.8
Loans held for investment		787.8	784.7
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		2	2.2
Current Loans		198.1	172.6
Non-accrual Loans		0.5	0.3
Loans held for investment		200.6	175.1
Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		2.1	2.2
Current Loans		79.7	72.4
Non-accrual Loans		0	0
Loans held for investment		81.8	74.6
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		13.4	14.7
Current Loans		1,054.6	1,017.6
Non-accrual Loans		2.2	2.1
Loans held for investment		1,070.2	1,034.4
Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		10.8	6.3
Current Loans		1,283.7	1,189.5
Non-accrual Loans		15.8	19.6
Loans held for investment		1,310.3	1,215.4
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		2.4	1.9
Current Loans		249.4	133.5
Non-accrual Loans		3	0.8
Loans held for investment		254.8	136.2
Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Current Loans		1.6	4.9
Non-accrual Loans		0	0
Loans held for investment		1.6	4.9
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		54.8	52.2
Current Loans		8,361.3	7,446.1
Non-accrual Loans		54.3	69.4
Loans held for investment		8,470.4	7,567.7
Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Current Loans		33.3	46.6
Non-accrual Loans		0	0
Mortgage loans held for sale		33.3
Total loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		54.8	52.2
Current Loans		8,394.6	7,492.7
Non-accrual Loans		54.3	69.4
Total loans		8,503.7	7,614.3
Financing Receivables, 30 to 59 Days Past Due \| Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		10.4	2.9
Financing Receivables, 30 to 59 Days Past Due \| Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1.6	7.3
Financing Receivables, 30 to 59 Days Past Due \| Residential
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1	2.1
Financing Receivables, 30 to 59 Days Past Due \| Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.4	0
Financing Receivables, 30 to 59 Days Past Due \| Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		3	9.4
Financing Receivables, 30 to 59 Days Past Due \| Residential
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		8.8	13.3
Financing Receivables, 30 to 59 Days Past Due \| Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		2.2	0.3
Financing Receivables, 30 to 59 Days Past Due \| Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		24.4	25.9
Financing Receivables, 30 to 59 Days Past Due \| Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		6.8	7.8
Financing Receivables, 30 to 59 Days Past Due \| Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1.4	1.6
Financing Receivables, 30 to 59 Days Past Due \| Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.9	0.9
Financing Receivables, 30 to 59 Days Past Due \| Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		9.1	10.3
Financing Receivables, 30 to 59 Days Past Due \| Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		8.3	3.9
Financing Receivables, 30 to 59 Days Past Due \| Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		2.1	1.8
Financing Receivables, 30 to 59 Days Past Due \| Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, 30 to 59 Days Past Due \| Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		43.9	41.9
Financing Receivables, 30 to 59 Days Past Due \| Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, 30 to 59 Days Past Due \| Total loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		43.9	41.9
Financing Receivables, 60 to 89 Days Past Due \| Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1	0.5
Financing Receivables, 60 to 89 Days Past Due \| Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.1	0.3
Financing Receivables, 60 to 89 Days Past Due \| Residential
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.4	0
Financing Receivables, 60 to 89 Days Past Due \| Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, 60 to 89 Days Past Due \| Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.5	0.3
Financing Receivables, 60 to 89 Days Past Due \| Residential
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1.1	1.4
Financing Receivables, 60 to 89 Days Past Due \| Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, 60 to 89 Days Past Due \| Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		2.6	2.2
Financing Receivables, 60 to 89 Days Past Due \| Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		2.1	2.1
Financing Receivables, 60 to 89 Days Past Due \| Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.5	0.5
Financing Receivables, 60 to 89 Days Past Due \| Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.4	0.6
Financing Receivables, 60 to 89 Days Past Due \| Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		3	3.2
Financing Receivables, 60 to 89 Days Past Due \| Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1.2	1.7
Financing Receivables, 60 to 89 Days Past Due \| Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.3	0.1
Financing Receivables, 60 to 89 Days Past Due \| Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, 60 to 89 Days Past Due \| Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		7.1	7.2
Financing Receivables, 60 to 89 Days Past Due \| Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, 60 to 89 Days Past Due \| Total loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		7.1	7.2
Financing Receivables, Equal to Greater than 90 Days Past Due \| Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.8	0.3
Financing Receivables, Equal to Greater than 90 Days Past Due \| Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.2	0.3
Financing Receivables, Equal to Greater than 90 Days Past Due \| Residential
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, Equal to Greater than 90 Days Past Due \| Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, Equal to Greater than 90 Days Past Due \| Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.2	0.3
Financing Receivables, Equal to Greater than 90 Days Past Due \| Residential
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.2	0.4
Financing Receivables, Equal to Greater than 90 Days Past Due \| Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0.2
Financing Receivables, Equal to Greater than 90 Days Past Due \| Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1.2	1.2
Financing Receivables, Equal to Greater than 90 Days Past Due \| Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.4	0.4
Financing Receivables, Equal to Greater than 90 Days Past Due \| Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.1	0.1
Financing Receivables, Equal to Greater than 90 Days Past Due \| Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0.8	0.7
Financing Receivables, Equal to Greater than 90 Days Past Due \| Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1.3	1.2
Financing Receivables, Equal to Greater than 90 Days Past Due \| Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		1.3	0.7
Financing Receivables, Equal to Greater than 90 Days Past Due \| Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, Equal to Greater than 90 Days Past Due \| Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, Equal to Greater than 90 Days Past Due \| Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		3.8	3.1
Financing Receivables, Equal to Greater than 90 Days Past Due \| Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		0	0
Financing Receivables, Equal to Greater than 90 Days Past Due \| Total loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due		$ 3.8	$ 3.1

Loans - Schedule of Recorded_2

Loans - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Recorded Investment, Impaired [Line Items]
Loans and Leases Receivable, Impaired, Troubled Debt, Interest Income	$ 3	$ 3.5	$ 4.2
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	83	107.9	132.8
Recorded Investment With No Allowance	36	51.4	57.9
Recorded Investment With Allowance	28.8	31.8	46.8
Total Recorded Investment	64.8	83.2	104.7
Related Allowance	6.8	10.8	14
Average Recorded Investment	74	94	101.1
Income Recognized	0.3	0.5	0.6
Impaired Loans, interest lost on nonaccrual loans			3.4
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	22.2	45.6	57
Recorded Investment With No Allowance	8.6	20.9	24.4
Recorded Investment With Allowance	7.7	14.1	21.4
Total Recorded Investment	16.3	35	45.8
Related Allowance	0.7	3.9	2.8
Land acquisition & development
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	10	10	12.1
Recorded Investment With No Allowance	0.4	3.4	4.3
Recorded Investment With Allowance	3.5	0.5	1.8
Total Recorded Investment	3.9	3.9	6.1
Related Allowance	0.2	0	0.8
Residential
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	1.1	1.8	1.6
Recorded Investment With No Allowance	0.6	1.7	0.2
Recorded Investment With Allowance	0.4	0	0.6
Total Recorded Investment	1	1.7	0.8
Related Allowance	0.1	0	0
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	0.7	4.7	4.8
Recorded Investment With No Allowance	0.2	0.4	3.9
Recorded Investment With Allowance	0	3.5	0.7
Total Recorded Investment	0.2	3.9	4.6
Related Allowance	0	2.2	0.7
Total construction loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	11.8	16.5	18.5
Recorded Investment With No Allowance	1.2	5.5	8.4
Recorded Investment With Allowance	3.9	4	3.1
Total Recorded Investment	5.1	9.5	11.5
Related Allowance	0.3	2.2	1.5
Residential
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	8.8	11.5	8.2
Recorded Investment With No Allowance	5.7	8.2	4.1
Recorded Investment With Allowance	2	2	2.5
Total Recorded Investment	7.7	10.2	6.6
Related Allowance	0.3	0.1	0.3
Agricultural
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	12.9	3.7	5.1
Recorded Investment With No Allowance	12.5	3.6	4.5
Recorded Investment With Allowance	0.2	0	0.2
Total Recorded Investment	12.7	3.6	4.7
Related Allowance	0	0	0
Total real estate loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	55.7	77.3	88.8
Recorded Investment With No Allowance	28	38.2	41.4
Recorded Investment With Allowance	13.8	20.1	27.2
Total Recorded Investment	41.8	58.3	68.6
Related Allowance	1.3	6.2	4.6
Average Recorded Investment	50	63.5	69.2
Income Recognized	0.1	0.3	0.3
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	24.1	29.5	40.3
Recorded Investment With No Allowance	5.5	12.4	13.2
Recorded Investment With Allowance	14.4	11.4	19.2
Total Recorded Investment	19.9	23.8	32.4
Related Allowance	5.2	4.4	9.3
Average Recorded Investment	21.9	28.1	30.1
Income Recognized	0.2	0.2	0.3
Agricultural
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	3.2	1.1	3.7
Recorded Investment With No Allowance	2.5	0.8	3.3
Recorded Investment With Allowance	0.6	0.3	0.4
Total Recorded Investment	3.1	1.1	3.7
Related Allowance	0.3	0.2	0.1
Average Recorded Investment	2.1	2.4	1.8
Income Recognized	$ 0	$ 0	$ 0

Loans - Schedule of Loans Rene

Loans - Schedule of Loans Renegotiated in Troubled Debt Restructurings (Details)	12 Months Ended
	Dec. 31, 2018USD ($)note	Dec. 31, 2017USD ($)note	Dec. 31, 2016USD ($)note
Loans and Leases Receivable, Troubled Debt Restructuring
Loans and Leases Receivable, Impaired, Commitment to Lend	$ 0	$ 0
Loans renegotiated in troubled debt restructurings	23,400,000	44,500,000
Loans renegotiated in troubled debt restructurings, non-accrual loans	17,800,000	31,900,000
Loans renegotiated in troubled debt restructurings, accrual loans	$ 5,600,000	$ 12,600,000
Number of notes under troubled debt restructurings \| note	5	24	35
Concessions in troubled debt restructurings, amount	$ 4,100,000	$ 12,900,000	$ 20,100,000
Charge-offs directly related to modified loans	$ 0	$ 0	$ 0
Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings \| note	3	5	18
Concessions in troubled debt restructurings, amount	$ 3,600,000	$ 2,800,000	$ 7,900,000
Residential
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings \| note			1
Concessions in troubled debt restructurings, amount			$ 100,000
Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings \| note	1	1
Concessions in troubled debt restructurings, amount	$ 200,000	$ 800,000
Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings \| note	1
Concessions in troubled debt restructurings, amount	$ 300,000
Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings \| note		17	13
Concessions in troubled debt restructurings, amount		$ 9,200,000	$ 8,100,000
Balance of notes for which there was a payment default	1,300,000
Agriculture
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings \| note		1
Concessions in troubled debt restructurings, amount		$ 100,000
Construction Loans [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings \| note			1
Concessions in troubled debt restructurings, amount			$ 3,700,000
Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings \| note			2
Concessions in troubled debt restructurings, amount			$ 300,000
Interest Only Period Concession
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	3,600,000	2,700,000	4,800,000
Interest Only Period Concession \| Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	3,600,000	1,500,000	400,000
Interest Only Period Concession \| Residential
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Interest Only Period Concession \| Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0	0
Interest Only Period Concession \| Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0
Interest Only Period Concession \| Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		1,200,000	4,400,000
Interest Only Period Concession \| Agriculture
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		0
Interest Only Period Concession \| Construction Loans [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Interest Only Period Concession \| Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Extension of terms or maturity
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0	3,300,000	10,000,000
Extension of terms or maturity \| Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0	400,000	5,500,000
Extension of terms or maturity \| Residential
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			100,000
Extension of terms or maturity \| Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0	800,000
Extension of terms or maturity \| Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0
Extension of terms or maturity \| Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		2,000,000	400,000
Extension of terms or maturity \| Agriculture
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		100,000
Extension of terms or maturity \| Construction Loans [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			3,700,000
Extension of terms or maturity \| Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			300,000
Interest rate adjustment
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0	0	200,000
Interest rate adjustment \| Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0	0	200,000
Interest rate adjustment \| Residential
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Interest rate adjustment \| Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0	0
Interest rate adjustment \| Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0
Interest rate adjustment \| Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		0	0
Interest rate adjustment \| Agriculture
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		0
Interest rate adjustment \| Construction Loans [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Interest rate adjustment \| Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Other
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	500,000	6,900,000	5,100,000
Other \| Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	0	900,000	1,800,000
Other \| Residential
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Other \| Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	200,000	0
Other \| Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount	$ 300,000
Other \| Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		6,000,000	3,300,000
Other \| Agriculture
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		$ 0
Other \| Construction Loans [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Other \| Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			$ 0

Loans - Schedule of Recorded_3

Loans - Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	$ 8,470.4	$ 7,567.7
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,235.4	2,822.9
Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	321.6	348.7
Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	242.8	240.2
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	274.3	119.4
Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	838.7	708.3
Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,542	1,487.4
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	217.4	158.2
Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	5,833.5	5,176.8
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	787.8	784.7
Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	200.6	175.1
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,070.2	1,034.4
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,310.3	1,215.4
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	254.8	136.2
Other Assets Especial Mentioned
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	178.8	155.1
Other Assets Especial Mentioned \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	102.5	78
Other Assets Especial Mentioned \| Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	5	3.2
Other Assets Especial Mentioned \| Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2.8	2.3
Other Assets Especial Mentioned \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1.7	2.4
Other Assets Especial Mentioned \| Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	9.5	7.9
Other Assets Especial Mentioned \| Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3	3.9
Other Assets Especial Mentioned \| Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	9	4.3
Other Assets Especial Mentioned \| Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	124	94.1
Other Assets Especial Mentioned \| Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0.7	0.8
Other Assets Especial Mentioned \| Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0.3	0.4
Other Assets Especial Mentioned \| Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1	1.2
Other Assets Especial Mentioned \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	39.4	54.7
Other Assets Especial Mentioned \| Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	14.4	5.1
Substandard
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	201.6	217.2
Substandard \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	87.4	96.4
Substandard \| Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	7	16.4
Substandard \| Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2	1.7
Substandard \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3.9	3.6
Substandard \| Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	12.9	21.7
Substandard \| Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	10.8	12.5
Substandard \| Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	24	19.1
Substandard \| Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	135.1	149.7
Substandard \| Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2.1	2.2
Substandard \| Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0.8	0.7
Substandard \| Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2.9	2.9
Substandard \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	45.8	56.3
Substandard \| Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	17.8	8.3
Doubtful
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	20.9	28.2
Doubtful \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2.9	10.3
Doubtful \| Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3.3	0
Doubtful \| Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0.4	0.5
Doubtful \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0	3.5
Doubtful \| Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3.7	4
Doubtful \| Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0.7	1.9
Doubtful \| Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0.1	0
Doubtful \| Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	7.4	16.2
Doubtful \| Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0.1	0.3
Doubtful \| Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0.1	0.2
Doubtful \| Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0.2	0.5
Doubtful \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	11.8	11.1
Doubtful \| Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1.5	0.4
Total Criticized Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	401.3	400.5
Total Criticized Loans \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	192.8	184.7
Total Criticized Loans \| Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	15.3	19.6
Total Criticized Loans \| Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	5.2	4.5
Total Criticized Loans \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	5.6	9.5
Total Criticized Loans \| Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	26.1	33.6
Total Criticized Loans \| Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	14.5	18.3
Total Criticized Loans \| Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	33.1	23.4
Total Criticized Loans \| Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	266.5	260
Total Criticized Loans \| Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2.9	3.3
Total Criticized Loans \| Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1.2	1.3
Total Criticized Loans \| Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	4.1	4.6
Total Criticized Loans \| Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	97	122.1
Total Criticized Loans \| Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	$ 33.7	$ 13.8

Allowance for Loan Losses - Sc

Allowance for Loan Losses - Schedule of Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 72.1	$ 76.2	$ 76.8
Provision charged (credited) to operating expense	8.6	11	10
Less loans charged-off	(19.7)	(22.8)	(19.8)
Add back recoveries of loans previously charged-off	12	7.7	9.2
Ending balance	73	72.1	76.2
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually evaluated for impairment				$ 6.8	$ 10.8	$ 14
Collectively evaluated for impairment				66.2	61.3	62.2
Ending balance	72.1	76.2	76.8	73	72.1	76.2
Total loans:
Individually evaluated for impairment				64.8	83.2	104.7
Collectively evaluated for impairment				8,405.6	7,484.5	5,312
Total loans held for investment				8,470.4	7,567.7	5,416.7
Allowance for loans losses				0.8	1
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	31.7	28.6	52.3
Provision charged (credited) to operating expense	(0.7)	6	(21.7)
Less loans charged-off	(3.7)	(4.3)	(5.2)
Add back recoveries of loans previously charged-off	3.7	1.4	3.2
Ending balance	31	31.7	28.6
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually evaluated for impairment				1.3	6.2	4.6
Collectively evaluated for impairment				29.7	25.5	24
Ending balance	31.7	28.6	52.3	31	31.7	28.6
Total loans:
Individually evaluated for impairment				41.8	58.3	68.6
Collectively evaluated for impairment				5,791.7	5,118.5	3,445.4
Total loans held for investment				5,833.5	5,176.8	3,514
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	8.7	7.7	5.1
Provision charged (credited) to operating expense	6.8	8.1	8.4
Less loans charged-off	(11.3)	(11.3)	(8.6)
Add back recoveries of loans previously charged-off	4.5	4.2	2.8
Ending balance	8.7	8.7	7.7
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				8.7	8.7	7.7
Ending balance	8.7	7.7	5.1	8.7	8.7	7.7
Total loans:
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				1,070.2	1,034.4	970.3
Total loans held for investment				1,070.2	1,034.4	970.3
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	30.5	38.1	18.8
Provision charged (credited) to operating expense	1.9	(2.9)	21.9
Less loans charged-off	(4.7)	(6.8)	(5.8)
Add back recoveries of loans previously charged-off	3.6	2.1	3.2
Ending balance	31.3	30.5	38.1
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually evaluated for impairment				5.2	4.4	9.3
Collectively evaluated for impairment				26.1	26.1	28.8
Ending balance	30.5	38.1	18.8	31.3	30.5	38.1
Total loans:
Individually evaluated for impairment				19.9	23.8	32.4
Collectively evaluated for impairment				1,290.4	1,191.6	765.5
Total loans held for investment				1,310.3	1,215.4	797.9
Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1.2	1.8	0.6
Provision charged (credited) to operating expense	0.6	(0.2)	1.4
Less loans charged-off	0	(0.4)	(0.2)
Add back recoveries of loans previously charged-off	0.2	0	0
Ending balance	2	1.2	1.8
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually evaluated for impairment				0.3	0.2	0.1
Collectively evaluated for impairment				1.7	1	1.7
Ending balance	1.2	1.8	0.6	2	1.2	1.8
Total loans:
Individually evaluated for impairment				3.1	1.1	3.7
Collectively evaluated for impairment				251.7	135.1	129.2
Total loans held for investment				254.8	136.2	132.9
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0
Provision charged (credited) to operating expense	0	0	0
Less loans charged-off	0	0	0
Add back recoveries of loans previously charged-off	0	0	0
Ending balance	0	0	0
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				0	0	0
Ending balance	$ 0	$ 0	$ 0	0	0	0
Total loans:
Individually evaluated for impairment				0	0	0
Collectively evaluated for impairment				1.6	4.9	1.6
Total loans held for investment				$ 1.6	$ 4.9	$ 1.6

Premises and Equipment (Details

Premises and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment
Premises and equipment, gross	$ 422	$ 404.2
Less accumulated depreciation	(176.8)	(162.3)
Premises and equipment, net	245.2	241.9
Land
Property, Plant and Equipment
Premises and equipment, gross	49.9	49.4
Buildings and improvements
Property, Plant and Equipment
Premises and equipment, gross	268.1	257.1
Furniture and equipment
Property, Plant and Equipment
Premises and equipment, gross	$ 104	$ 97.7

Company-Owned Life Insurance (D

Company-Owned Life Insurance (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Company - Owned Life Insurance, By Type
Total	$ 275.1	$ 260.6
Key executive, principal shareholder
Schedule of Company - Owned Life Insurance, By Type
Cash surrender value of life insurance	4.7	4.2
Key executive split dollar
Schedule of Company - Owned Life Insurance, By Type
Cash surrender value of life insurance	9.4	4.9
FIB \| Group life
Schedule of Company - Owned Life Insurance, By Type
Cash surrender value of life insurance	$ 261	$ 251.5

Other Real Estate Owned (Detail

Other Real Estate Owned (Details) - USD ($) $ in Millions	12 Months Ended
Other Real Estate Owned (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Real Estate Acquired Through Foreclosure [Roll Forward]
Balance at beginning of year	$ 10.1	$ 10	$ 6.3
Acquisitions	0.6	1.2	1.1
Additions	12.1	5.4	7.6
Valuation adjustments	(0.1)	(0.4)	(0.6)
Dispositions	(8.3)	(6.1)	(4.4)
Balance at end of year	14.4	10.1	10
Write-downs of OREO	$ (0.1)	$ (0.4)	$ (0.6)

Derivatives and Hedging Activ_3

Derivatives and Hedging Activities - Notional Amounts and Estimated Fair Values of Derivatives (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Sep. 22, 2015
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 454,300,000	$ 404,900,000
Derivative Assets, Estimated Fair Value	10,100,000	8,800,000
Derivative Liability, Notional Amount	467,900,000	433,000,000	$ 100,000,000
Derivative Liabilities, Estimated Fair Value	9,400,000	7,900,000
Not Designated as Hedging Instrument \| Interest rate swap contracts
Derivative [Line Items]
Derivative Asset, Notional Amount	403,300,000	344,200,000
Derivative Assets, Estimated Fair Value	8,800,000	7,500,000
Derivative Liability, Notional Amount	403,300,000	344,200,000
Derivative Liabilities, Estimated Fair Value	8,800,000	7,800,000
Not Designated as Hedging Instrument \| Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	51,000,000	60,700,000
Derivative Assets, Estimated Fair Value	1,300,000	1,300,000
Not Designated as Hedging Instrument \| Forward loan sales contracts
Derivative [Line Items]
Derivative Liability, Notional Amount	64,600,000	88,800,000
Derivative Liabilities, Estimated Fair Value	$ 600,000	$ 100,000

Derivatives and Hedging Activ_4

Derivatives and Hedging Activities - Narrative (Details) - USD ($)	Sep. 06, 2017	Dec. 31, 2018	Dec. 31, 2017	Sep. 22, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Payment to terminate existing interest rate swap contract	$ 1,100,000
Derivative liability, notional amount		$ 467,900,000	$ 433,000,000	$ 100,000,000
Derivative, fixed interest rate				1.94%
Hedge ineffectiveness		$ 0	$ 0

Derivatives and Hedging Activ_5

Derivatives and Hedging Activities - Schedule of Master Netting Arrangements (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financial Assets
Gross Amounts Recognized	$ 10.1	$ 8.8
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	10.1	8.8
Financial Instruments	2.7	2.4
Fair Value of Financial Collateral in the Balance Sheet	2.4	0
Net Amount	5	6.4
Offsetting Derivative Liabilities [Abstract]
Gross Amounts Recognized	9.4	7.9
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	9.4	7.9
Financial Instruments	2.7	2.4
Fair Value of Financial Collateral in the Balance Sheet	4.1	3.3
Net Amount	2.6	2.2
Repurchase agreements
Gross Amounts Recognized	712.4	643
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	712.4	643
Financial Instruments	0	0
Fair Value of Financial Collateral in the Balance Sheet	712.4	643
Net Amount	0	0
Offsetting Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned [Abstract]
Gross Amounts Recognized	721.8	650.9
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	721.8	650.9
Financial Instruments	2.7	2.4
Fair Value of Financial Collateral in the Balance Sheet	716.5	646.3
Net Amount	2.6	2.2
Interest rate swap contracts
Financial Assets
Gross Amounts Recognized	8.8	7.5
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	8.8	7.5
Financial Instruments	2.7	2.4
Fair Value of Financial Collateral in the Balance Sheet	2.4	0
Net Amount	3.7	5.1
Offsetting Derivative Liabilities [Abstract]
Gross Amounts Recognized	8.8	7.8
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	8.8	7.8
Financial Instruments	2.7	2.4
Fair Value of Financial Collateral in the Balance Sheet	4.1	3.3
Net Amount	2	2.1
Mortgage related derivatives
Financial Assets
Gross Amounts Recognized	1.3	1.3
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	1.3	1.3
Financial Instruments	0	0
Fair Value of Financial Collateral in the Balance Sheet	0	0
Net Amount	1.3	1.3
Offsetting Derivative Liabilities [Abstract]
Gross Amounts Recognized	0.6	0.1
Gross Amounts Offset in the Balance Sheet	0	0
Net Amounts in the Balance Sheet	0.6	0.1
Financial Instruments	0	0
Fair Value of Financial Collateral in the Balance Sheet	0	0
Net Amount	$ 0.6	$ 0.1

Derivatives and Hedging Activ_6

Derivatives and Hedging Activities - Pre-tax Gains and Losses on Derivative Contracts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Amount of loss recognized in other comprehensive income (effective portion)		$ 1.1	$ 0.2
Designated as Hedging Instrument
Derivative [Line Items]
Amount of loss recognized in other comprehensive income (effective portion)	$ 0	1.1	0.2
Reclassification adjustment for derivative net (gains) losses included in income	0	1.1	0
Not Designated as Hedging Instrument \| Interest Rate Swap
Derivative [Line Items]
Amount of gain (loss) recognized in other non-interest income	0.3	0	0.1
Amount of net fee income recognized in other non-interest income	1.3	0.8	0.9
Amount of net gains (losses) recognized in mortgage banking revenues	$ (0.5)	$ (1.7)	$ 1.4

Mortgage Servicing Rights - Sc

Mortgage Servicing Rights - Schedule of Mortgage Servicing Rights (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Servicing Asset at Amortized Value, Balance [Roll Forward]
Balance at end of year, net of valuation reserve	$ 27.7	$ 24.8
Mortgage loans
Servicing Asset at Amortized Value, Balance [Roll Forward]
Servicing asset at amortized cost, before valuation reserve, beginning	24.8	18.7	$ 15.9
Acquisitions of mortgage servicing rights	0	3.5	0
Originations of mortgage servicing rights	6	5.6	5.8
Amortization expense	(3.1)	(3)	(3)
Servicing asset at amortized cost, before valuation reserve, ending	27.7	24.8	18.7
Less valuation reserve	0	0	(0.2)
Balance at end of year, net of valuation reserve	27.7	24.8	18.5
Principal balance of serviced loans underlying mortgage servicing rights	$ 3,698.2	$ 3,636.7	$ 3,127.5
Mortgage servicing rights as a percentage of serviced loans	0.0075	0.0068	0.0059

Mortgage Servicing Rights - Na

Mortgage Servicing Rights - Narrative (Details) - Mortgage loans - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Mortgage servicing rights, fair value	$ 42,400,000	$ 40,100,000
Servicing asset at fair value, assumptions used to estimate fair value, weighted average life	8 years	7 years 3 months 19 days
Impairment reversals			$ 0
Permanent impairment charged against carrying value	$ 0	$ 0	$ 0
Minimum
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Servicing assets at fair value, assumptions used to estimate fair value, discount rate	10.40%	9.50%
Servicing assets at fair value, assumptions used to estimate fair value, prepayment speed	0.40%	0.50%
Maximum
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Servicing assets at fair value, assumptions used to estimate fair value, discount rate	12.10%	11.30%
Servicing assets at fair value, assumptions used to estimate fair value, prepayment speed	1.50%	1.80%

Deposits (Details)

Deposits (Details) - USD ($)	12 Months Ended
Deposits (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deposits, by Type [Abstract]
Non-interest bearing demand	$ 3,158,300,000	$ 2,900,000,000
Interest bearing:
Demand	2,957,500,000	2,787,500,000
Savings	3,247,900,000	3,095,400,000
Total	547,600,000	432,000,000
Time, other	769,400,000	720,000,000
Total interest bearing	7,522,400,000	7,034,900,000
Total deposits	10,680,700,000	9,934,900,000
Brokered time deposits	24,100,000	0
Time deposits obtained through Certificate of Deposit Account Registry Service (CDARS)	87,100,000	94,200,000
Time deposits of $250,000 or more	221,000,000	182,000,000
FDIC deposit insurance limit	250,000,000
Time, $100 and Over
Due within 3 months or less	45,000,000
Due after 3 months and within 6 months	49,000,000
Due after 6 months and within 12 months	217,500,000
Due within 2020	159,700,000
Total	547,600,000	432,000,000
Total Time
Due within 3 months or less	253,800,000
Due after 3 months and within 6 months	149,200,000
Due after 6 months and within 12 months	420,400,000
Due within 2020	323,700,000
Total	1,317,000,000
Interest expense, time deposits, $100,000 or more	7,000,000	$ 4,300,000	$ 3,700,000
Contractual Maturities, Time Deposits, $100,000 or More, after 2 years	63,500,000
Time Deposits Maturities, after Next Two Years	128,800,000
Contractual Maturities, Time Deposits, $100,000 or More, after 3 years	9,800,000
Time Deposits Maturities, after Next Three Years	30,300,000
Contractual Maturities, Time Deposits, $100,000 or More, after 5 years and thereafter	3,100,000
Time Deposits Maturities, after Next Five Years and Thereafter	$ 10,800,000

Long-Term Debt and Other Borr_3

Long-Term Debt and Other Borrowed Funds (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument
Long-term debt and capital lease obligations	$ 15,800,000	$ 13,100,000
Fiscal Year Maturities of Long-term Debt
2,018	100,000
2,019	100,000
2,020	100,000
2,021	5,100,000
2,022	100,000
Thereafter	10,300,000
Long-term debt and capital lease obligations	15,800,000	13,100,000
Advances from FHLB	0	0
Other borrowings	$ 0	$ 20,000,000
Subordinated term loan \| Subordinated Term Loan, 6.81% \| Parent Company
Debt Instrument
Stated interest rate		6.81%
Capital lease obligations \| Capital Lease Obligation, 8.00% \| Subsidiaries
Debt Instrument
Stated interest rate	8.00%
Capital Lease Obligations	$ 1,300,000	$ 1,400,000
Notes payable \| Subsidiaries
Fiscal Year Maturities of Long-term Debt
Long Term Debt, Acquired or Assumed	$ 11,700,000	14,400,000
Notes payable \| Note Payable, 6.24% \| Subsidiaries
Debt Instrument
Stated interest rate	6.24%
Long-term debt	$ 1,800,000	1,600,000
Notes payable \| Note Payable, 2.28% \| Subsidiaries
Debt Instrument
Stated interest rate	2.28%
Long-term debt	$ 5,000,000	5,000,000
Notes payable \| Note Payable, 1.00% \| Subsidiaries
Debt Instrument
Stated interest rate	1.00%
Long-term debt	$ 5,100,000	5,100,000
Notes payable \| Note Payable, 1.30%, maturing March 31, 2038 [Member] \| Subsidiaries
Debt Instrument
Long-term debt	2,000,000	0
Notes payable \| Note Payable, 1.30%, Maturing June 1, 2034 [Member] \| Subsidiaries
Debt Instrument
Long-term debt	600,000	$ 0
Federal Home Loan Bank \| Notes Payable to FHLB \| Subsidiaries
Fiscal Year Maturities of Long-term Debt
FHLB, advances, maximum amount available	$ 1,399,000,000
Secured Debt
Fiscal Year Maturities of Long-term Debt
Ownership percentage in subsidiary	99.90%
Line of credit facility, maximum borrowing capacity	$ 461,700,000
Federal Funds Purchased
Fiscal Year Maturities of Long-term Debt
Line of credit facility, maximum borrowing capacity	205,000,000
Unsecured Debt [Member]
Fiscal Year Maturities of Long-term Debt
Line of credit facility, maximum borrowing capacity	$ 50,000,000
Minimum \| Note Payable, 6.24% \| Subsidiaries
Debt Instrument
Stated interest rate	1.00%
Maximum \| Note Payable, 6.24% \| Subsidiaries
Debt Instrument
Stated interest rate	6.24%

Subordinated Debentures Held _3

Subordinated Debentures Held by Subsidiary Trusts (Details) $ in Millions	Aug. 16, 2018USD ($)	Dec. 31, 2007USD ($)	Dec. 31, 2018USD ($)trusts	Dec. 31, 2017USD ($)	Jan. 31, 2008USD ($)	Nov. 30, 2007	Oct. 31, 2007USD ($)
Subordinated Borrowing
Number of company sponsored wholly-owned business trusts \| trusts			7
Subordinated debentures held by subsidiary trusts			$ 86.9	$ 82.5
Debt instrument, interest rate at period end			5.55%
Debt Instrument, Redemption, At Issuance through Year Five [Member]
Subordinated Borrowing
Stated interest rate		6.78%
LIBOR \| Debt Instrument, Redemption, After Period Five
Subordinated Borrowing
Debt instrument, basis spread on variable rate		2.75%
First Interstate Statutory Trust II \| Junior Subordinated Deferrable Interest Debentures Issued by FIST II
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts			$ 10.3	10.3			$ 10.3
Debt instrument, interest rate at period end			5.05%
First Interstate Statutory Trust II \| Junior Subordinated Deferrable Interest Debentures Issued by FIST II \| LIBOR \| Debt Instrument, Redemption, After Period Five
Subordinated Borrowing
Debt instrument, basis spread on variable rate		2.25%
First Interstate Statutory Trust I \| Junior Subordinated Deferrable Interest Debentures Issued by FIST I
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts			$ 15.5	15.5			$ 15.5
Debt instrument, interest rate at period end			5.54%
First Interstate Statutory Trust I \| Junior Subordinated Deferrable Interest Debentures Issued by FIST I \| Debt Instrument, Redemption, At Issuance through Year Five [Member]
Subordinated Borrowing
Stated interest rate						7.50%
First Interstate Statutory Trust I \| Junior Subordinated Deferrable Interest Debentures Issued by FIST I \| LIBOR \| Debt Instrument, Redemption, After Period Five
Subordinated Borrowing
Debt instrument, basis spread on variable rate		2.75%
First Interstate Statutory Trust III \| Junior Subordinated Deferrable Interest Debentures Issued by FIST III
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts		$ 20.6	$ 20.6	20.6
Debt instrument, interest rate at period end			5.19%
First Interstate Statutory Trust III \| Junior Subordinated Deferrable Interest Debentures Issued by FIST III \| Debt Instrument, Redemption, At Issuance through Year Five [Member]
Subordinated Borrowing
Stated interest rate		6.88%
First Interstate Statutory Trust III \| Junior Subordinated Deferrable Interest Debentures Issued by FIST III \| LIBOR \| Debt Instrument, Redemption, After Period Five
Subordinated Borrowing
Debt instrument, basis spread on variable rate		2.40%
First Interstate Statutory Trust IV \| Junior Subordinated Deferrable Interest Debentures Issued by FIST IV
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts			$ 15.5	15.5
First Interstate Statutory Trust V \| Junior Subordinated Deferrable Interest Debentures Issued by FIST V
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts			$ 10.3	10.3	$ 10.3
First Interstate Statutory Trust VI \| Junior Subordinated Deferrable Interest Debentures Issued by FIST IV
Subordinated Borrowing
Debt instrument, basis spread on variable rate			5.50%
Debt instrument, interest rate at period end			2.70%
First Interstate Statutory Trust VI \| Junior Subordinated Deferrable Interest Debentures Issued by FIST VI
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts			$ 10.3	10.3	$ 15.5
Debt instrument, basis spread on variable rate			2.75%
Debt instrument, interest rate at period end			1030000000.00%
Northwest Bancorporation Capital Trust 1 [Member] \| Junior Subordinated Deferrable Interest Debentures Issued by FIST VI
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts			$ 4.4	$ 0
Northwest Bancorporation Capital Trust I [Member] \| Junior Subordinated Deferrable Interest Debentures Issued by NWBC I [Member]
Subordinated Borrowing
Debt instrument, basis spread on variable rate	1.70%
Debt instrument, interest rate at period end	4.50%
Northwest Bancorporation Capital Trust I [Member] \| Junior Subordinated Deferrable Interest Debentures Issued by NWBC I [Member] \| Debt Instrument, Redemption, At Issuance through Year Five [Member]
Subordinated Borrowing
Stated interest rate	5.95%
Trust Preferred Securities Subject to Mandatory Redemption \| Trusts
Subordinated Borrowing
Amount of financial instruments subject to mandatory redemption			$ 84.3
Business trust term (in years)			30 years
Trust Preferred Securities Subject to Mandatory Redemption \| Northwest Bancorporation Capital Trust 1 [Member]
Subordinated Borrowing
Amount of financial instruments subject to mandatory redemption	$ 5
Common Stock Subject to Mandatory Redemption \| Trusts
Subordinated Borrowing
Amount of financial instruments subject to mandatory redemption			$ 2.6
Common Stock Subject to Mandatory Redemption \| Northwest Bancorporation Capital Trust I [Member]
Subordinated Borrowing
Amount of financial instruments subject to mandatory redemption	$ 0.2
Subordinated Debentures Subject to Mandatory Redemption \| Trusts
Subordinated Borrowing
Business trust term (in years)			30 years

Capital Stock and Dividend Re_2

Capital Stock and Dividend Restrictions (Details) $ in Millions	May 30, 2017USD ($)shares	Dec. 31, 2018USD ($)votesshares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)	Nov. 28, 2018shares	Jun. 08, 2018shares	Sep. 25, 2017USD ($)
Class of Stock
Common stock, shares authorized		200,000,000
Aggregate purchase price of shares repurchased and retired \| $		$ 1	$ 1.3	$ 26.9
Class A Common Stock
Class of Stock
Common stock, shares authorized		100,000,000
Common stock, voting rights per share (vote per share) \| votes		1
Common stock, shares, outstanding		38,169,575	33,560,202
Common shares purchased and retired		0	0
Class B Common Stock
Class of Stock
Common stock, shares authorized		100,000,000
Common stock, voting rights per share (vote per share) \| votes		5
Common stock, shares, outstanding		22,453,672	22,905,357
Community 1st Bank [Member] \| Class A Common Stock
Class of Stock
Common stock, shares authorized					492,069
Idaho Independent Bank [Member] \| Class A Common Stock
Class of Stock
Common stock, shares authorized					4,045,302
Inland Northwest Bank [Member] \| Class A Common Stock
Class of Stock
Common stock, shares authorized						3,982,842
Cascade Bank \| Class A Common Stock
Class of Stock
Common stock issued (in shares)	3,837,540
Class A common stock \| $	$ 173.3
Board of Directors
Class of Stock
Aggregate value of shares issued to directors \| $		$ 0.5	$ 0.5
Board of Directors \| Class A Common Stock
Class of Stock
Shares issued to directors during period		11,389	14,926
Secondary Public Offering \| Class A Common Stock
Class of Stock
Common stock, value authorized \| $							$ 250

Earnings per Common Share Compu

Earnings per Common Share Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income, basic and diluted	$ 160.2	$ 106.5	$ 95.7
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Weighted average common shares outstanding for basic earnings per share computation	57,778,857	51,429,366	44,511,774
Dilutive effect of stock-based compensation (in shares)	438,266	473,843	398,622
Weighted average common shares outstanding for diluted earnings per common share computation	58,217,123	51,903,209	44,910,396
Earnings Per Share, Basic and Diluted [Abstract]
Basic earnings per common share (in dollars per share)	$ 2.77	$ 2.07	$ 2.15
Diluted earnings per common share (in dollars per share)	$ 2.75	$ 2.05	$ 2.13
Restricted Stock
Earnings Per Share, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	448	113,874	155,637
Performance Shares
Earnings Per Share, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	83,475	83,635	7,215

Regulatory Capital - Schedule

Regulatory Capital - Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) - USD ($) $ in Millions	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2016
Total risk-based capital:
Actual amount		$ 1,285	$ 1,112.5
Actual ratio (percent)		12.99%	12.76%
Adequately capitalized Basel III phase-in schedule, amount		$ 976.6	$ 806.5
Adequately capitalized Basel III phase-in schedule, ratio (percent)		9.875%	9.25%
Adequately capitalized Basel III fully phased-in, amount		$ 1,038.4	$ 915.5
Adequately capitalized Basel III fully phased-in, ratio (percent)		10.50%	10.50%
Well capitalized, amount		$ 989	$ 871.9
Well capitalized, ratio (percent)		10.00%	10.00%
Tier 1 risk-based capital:
Actual amount		$ 1,212	$ 1,040.3
Actual ratio (percent)		12.26%	11.93%
Adequately capitalized Basel III phase-in schedule, amount		$ 778.8	$ 632.1
Adequately capitalized Basel III phase-in schedule, ratio (percent)		7.875%	7.25%
Adequately capitalized Basel III fully phased-in, amount		$ 840.6	$ 741.1
Adequately capitalized Basel III fully phased-in, ratio (percent)		8.50%	8.50%
Well capitalized, amount		$ 791.2	$ 697.5
Well capitalized, ratio (percent)		8.00%	8.00%
Common Equity Tier One Capital [Abstract]
Actual amount		$ 1,127.8	$ 962.4
Actual ratio (percent)		11.40%	11.04%
Adequately capitalized Basel III phase-in schedule, amount		$ 630.5	$ 501.3
Adequately capitalized Basel III phase-in schedule, ratio (percent)		6.375%	5.75%
Adequately capitalized Basel III fully phased-in, amount		$ 692.3	$ 610.3
Adequately capitalized Basel III fully phased-in, ratio (percent)		7.00%	7.00%
Well capitalized, amount		$ 642.8	$ 566.7
Well capitalized, ratio (percent)		6.50%	6.50%
Leverage capital ratio:
Actual amount		$ 1,212	$ 1,040.3
Actual ratio (percent)		9.47%	8.86%
Adequately capitalized, amount		$ 511.9	$ 469.9
Adequately capitalized, ratio (percent)		4.00%	4.00%
Well capitalized, amount		$ 639.9	$ 587.4
Well capitalized, ratio (percent)		5.00%	5.00%
Required Capital Conservation Buffer, phase in amount				0.625%
Capital Conservation Buffer		4.99%
FIB
Total risk-based capital:
Actual amount		$ 1,184.5	$ 1,066.6
Actual ratio (percent)		12.01%	12.29%
Adequately capitalized Basel III phase-in schedule, amount		$ 973.7	$ 802.7
Adequately capitalized Basel III phase-in schedule, ratio (percent)		9.875%	9.25%
Adequately capitalized Basel III fully phased-in, amount		$ 1,035.3	$ 911.2
Adequately capitalized Basel III fully phased-in, ratio (percent)		10.50%	10.50%
Well capitalized, amount		$ 986	$ 867.8
Well capitalized, ratio (percent)		10.00%	10.00%
Tier 1 risk-based capital:
Actual amount		$ 1,111.6	$ 994.4
Actual ratio (percent)		11.27%	11.46%
Adequately capitalized Basel III phase-in schedule, amount		$ 776.5	$ 629.1
Adequately capitalized Basel III phase-in schedule, ratio (percent)		7.875%	7.25%
Adequately capitalized Basel III fully phased-in, amount		$ 838.1	$ 737.6
Adequately capitalized Basel III fully phased-in, ratio (percent)		8.50%	8.50%
Well capitalized, amount		$ 788.8	$ 694.2
Well capitalized, ratio (percent)		8.00%	8.00%
Common Equity Tier One Capital [Abstract]
Actual amount		$ 1,111.6	$ 994.4
Actual ratio (percent)		11.27%	11.46%
Adequately capitalized Basel III phase-in schedule, amount		$ 628.6	$ 499
Adequately capitalized Basel III phase-in schedule, ratio (percent)		6.375%	5.75%
Adequately capitalized Basel III fully phased-in, amount		$ 690.2	$ 607.4
Adequately capitalized Basel III fully phased-in, ratio (percent)		7.00%	7.00%
Well capitalized, amount		$ 640.9	$ 564.1
Well capitalized, ratio (percent)		6.50%	6.50%
Leverage capital ratio:
Actual amount		$ 1,111.6	$ 994.4
Actual ratio (percent)		8.97%	8.48%
Adequately capitalized, amount		$ 495.9	$ 469.1
Adequately capitalized, ratio (percent)		4.00%	4.00%
Well capitalized, amount		$ 619.8	$ 586.3
Well capitalized, ratio (percent)		5.00%	5.00%
Capital Conservation Buffer			4.01%
Subsequent Event
Compliance with Regulatory Capital Requirements under Banking Regulations
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets, excluding buffer	4.50%
Required Capital Conservation Buffer	2.50%
Total risk-based capital:
Adequately capitalized Basel III fully phased-in, ratio (percent)	10.50%
Tier 1 risk-based capital:
Adequately capitalized Basel III fully phased-in, ratio (percent)	8.50%
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets, excluding buffer	8.00%
Common Equity Tier One Capital [Abstract]
Adequately capitalized Basel III fully phased-in, ratio (percent)	7.00%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets, excluding buffer	6.00%
Leverage capital ratio:
Adequately capitalized, ratio (percent)	4.00%

Commitments and Contingencies

Commitments and Contingencies - Narrative (Details) $ / shares in Units, $ in Millions	Oct. 11, 2018USD ($)$ / shares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Oct. 05, 2018$ / sharesshares
Unrecorded Unconditional Purchase Obligation
Operating leases, rent expense		$ 3.2	$ 2.5	$ 1.9
Construction Contracts
Unrecorded Unconditional Purchase Obligation
Commitments under construction contracts		$ 2.7
Related Entity
Unrecorded Unconditional Purchase Obligation
Ownership percentage in partnership		50.00%
Idaho Independent Bank [Member]
Unrecorded Unconditional Purchase Obligation
Number of banking offices	11
Estimate of Payments to Acquire Businesses, Gross	$ 181.3
Community 1st Bank [Member]
Unrecorded Unconditional Purchase Obligation
Number of banking offices	3
Estimate of Payments to Acquire Businesses, Gross	$ 21.5
Inland Northwest Bank [Member]
Unrecorded Unconditional Purchase Obligation
Estimate value per share of Acquisition \| $ / shares	$ 22.73
Community 1st Bank [Member]
Unrecorded Unconditional Purchase Obligation
Estimate value per share of Acquisition \| $ / shares	$ 17.20
Class A Common Stock \| Community 1st Bank [Member]
Unrecorded Unconditional Purchase Obligation
Estimate value per share of Acquisition \| $ / shares					$ 45.45
Business Acquisition, Conversion Share Rate, Shares \| shares					0.3784
Class A Common Stock \| Idaho Independent Bank [Member]
Unrecorded Unconditional Purchase Obligation
Estimate value per share of Acquisition \| $ / shares					$ 45.45
Business Acquisition, Conversion Share Rate, Shares \| shares					0.5000
Mortgage loans originated for sale
Unrecorded Unconditional Purchase Obligation
Guarantor Obligations, Current Carrying Value		$ 1.5	$ 1.9

Commitments and Contingencies_2

Commitments and Contingencies - Operating Lease Commitments (Details) $ in Millions	Dec. 31, 2018USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,018	$ 6
2,019	5.7
2,020	5.5
2,021	5.3
2,022	5.1
Thereafter	18.1
Operating leases, future minimum payments due	45.7
Third Parties
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,018	4.4
2,019	4.2
2,020	4.1
2,021	4.1
2,022	3.9
Thereafter	15.3
Operating leases, future minimum payments due	36
Related Entity
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,018	1.6
2,019	1.5
2,020	1.4
2,021	1.2
2,022	1.2
Thereafter	2.8
Operating leases, future minimum payments due	$ 9.7

Financial Instruments with Of_2

Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Entity Information
Credit extension commitments	$ 2,620.4	$ 2,179.5
Unused credit card lines	1,058.5	775
Unused Credit Card Lines
Entity Information
Credit extension commitments	726.7	635.3
Standby Letters of Credit
Entity Information
Credit extension commitments	$ 46.7	$ 50.5

Income Taxes - Schedule of Inc

Income Taxes - Schedule of Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 23.1	$ 24.3	$ 40.3
State	7.2	5	5.9
Total current	30.3	29.3	46.2
Deferred:
Federal	12.3	18.4	2.9
State	3.5	2.5	0.5
Total deferred	15.8	20.9	3.4
Total income tax expense	$ 46.1	$ 50.2	$ 49.6

Income Taxes - Reconciliation

Income Taxes - Reconciliation of Tax Expense at Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense, Continuing Operations Income Tax Reconciliation [Abstract]
Tax expense at the statutory tax rate	$ 43.3	$ 54.9	$ 50.8
Increase (decrease) in tax resulting from:
Tax-exempt income	(2.8)	(4.5)	(4.4)
State income tax, net of federal income tax benefit	8.5	4.9	4.3
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation			(2.2)
Benefit of stock-based compensation plans			0
Federal tax credits	(2.6)	(2.5)	(2.1)
Benefit due to enactment of federal tax reform	0	(2.2)	0
Other, net	0.8	2.2	1
Total income tax expense	$ 46.1	$ 50.2	$ 49.6

Income Taxes - Deferred Tax As

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Loans, principally due to allowance for loan losses	$ 18.4	$ 18
Loan discount	8.3	6.7
Investment securities, unrealized losses	8.9	5.6
Deferred compensation	17	13.1
Non-performing loan interest	1.2	1.1
Other real estate owned write-downs and carrying costs	0.3	0.6
Tax credit carryforwards	0.1	3.7
Net operating loss carryforwards	3.9	8.7
Other	0.1	3.1
Deferred tax assets	58.2	60.6
Deferred tax liabilities:
Fixed assets, principally differences in bases and depreciation	(6.9)	(6.7)
Deferred loan costs	(2.6)	(1.7)
Investment in joint venture partnership, principally due to differences in depreciation of partnership assets	(0.8)	(0.8)
Prepaid amounts	(0.6)	(0.6)
Government agency stock dividends	(1.5)	(1.6)
Goodwill and core deposit intangibles	(44.2)	(38.1)
Mortgage servicing rights	(6.4)	(5.7)
Other	(3.8)	(1.4)
Deferred tax liabilities	(66.8)	(56.6)
Net deferred tax assets (liabilities)		$ 4
Net deferred tax assets (liabilities)	(8.6)
Federal
Operating Loss Carryforwards [Line Items]
Federal tax credit carryforwards	0.1
Net operating loss carryforwards	$ 5.4

Income Taxes - Narrative (Deta

Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation, at federal statutory income tax rate	35.00%	21.00%	35.00%
Current net income tax receivable	$ 2	$ 5.7
Benefit due to enactment of federal tax reform	$ 0	$ 2.2	$ 0

Stock-Based Compensation - Nar

Stock-Based Compensation - Narrative (Details)	12 Months Ended
Stock-Based Compensation - Narrative (Details)	Dec. 31, 2018USD ($)planshares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock-based compensation plans \| plan	2
Options expiration period	10 years
Stock option awards granted \| shares	0	0
Intrinsic value of fully-vested stock options outstanding	$ 9,000,000
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	0
Tax benefits from stock-based compensation	0
Total intrinsic value of options exercised	4,900,000	$ 6,300,000	$ 5,600,000
Proceeds from Stock Options Exercised	1,800,000	2,400,000	4,700,000
Common Stock Redeemed For Payment of Stock Option Exercises, Aggregate Value	1,600,000	2,800,000	3,100,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	5,600,000	3,300,000	3,900,000
Tax benefits from stock-based compensation	$ 200,000	$ 600,000	$ 1,500,000
Stock issued during period, shares, restricted stock award \| shares	214,893
Unrecognized compensation cost related to nonvested restricted stock awards	$ 7,900,000
Unrecognized compensation cost related to nonvested restricted stock to be recognized over weighted average period (in years)	1 year 10 months 28 days
Restricted Stock \| Upon Achievement of Performance Goals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares, restricted stock award \| shares	59,464
Restricted Stock \| Upon Achievement of Defined Return on Equity Performance Goals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares, restricted stock award \| shares	29,732
Restricted Stock \| Upon Achievement of Defined Total Return to Shareholder Goals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares, restricted stock award \| shares	29,732
Restricted Stock \| Upon One-Third Annual Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares, restricted stock award \| shares	155,429
Restricted Stock \| First Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage	33.33%
Restricted Stock \| Second Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage	33.33%
Restricted Stock \| Third Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage	33.33%
2006 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant \| shares	1,727,765

Stock-Based Compensation - Sch

Stock-Based Compensation - Schedule of Stock Options Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option awards granted	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price	$ 0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding options, beginning of year, number of shares	642,255
Exercised, number of shares	(199,667)
Forfeited, number of shares	(14,412)
Outstanding options, end of year, number of shares	428,176	642,255
Outstanding options exercisable, end of year, number of shares	428,176
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding options, beginning of year, weighted average exercise price (in dollars per share)	$ 16.13
Exercised, weighted average exercise price (in dollars per share)	17.12
Forfeited, weighted average exercise price (in dollars per share)	20.87
Outstanding options, end of year, weighted average exercise price (in dollars per share)	15.61	$ 16.13
Outstanding options exercisable, end of year, weighted average exercise price (in dollars per share)	$ 15.61
Outstanding options, end of year weighted average remaining contractual term (in years)	1 year 6 months 21 days
Outstanding options exercisable, end of year, weighted average remaining contractual term (in years)	1 year 6 months 21 days
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of options exercised	$ 4.9	$ 6.3	$ 5.6
Proceeds from Stock Options Exercised	1.8	2.4	4.7
Common Stock Redeemed For Payment of Stock Option Exercises, Aggregate Value	$ 1.6	$ 2.8	$ 3.1

Stock-Based Compensation - S_2

Stock-Based Compensation - Schedule of Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Ending Balance	$ 1,693.9	$ 1,427.6	$ 982.6
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares, restricted stock award	214,893
Stock compensation expense	$ 5.6	$ 3.3	3.9
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Restricted stock, beginning of year, number of shares	292,506
Granted, number of shares	214,893
Vested, number of shares	(83,736)
Forfeited, number of shares	(43,079)
Canceled, number of shares	0
Restricted stock, end of year, number of shares	380,584	292,506
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Restricted stock, beginning of year, weighted-average measurement date fair value (in dollars per share)	$ 33.24
Granted, weighted average grant date fair value (in dollars per share)	40.97
Vested, weighted average grant date fair value (in dollars per share)	32.42
Forfeited, weighted average grant date fair value (in dollars per share)	36.64
Canceled, weighted average grant date fair value (in dollars per share)	0
Restricted stock, end of year, weighted-average measurement date fair value (in dollars per share)	$ 37.46	$ 33.24
Tax benefits from stock-based compensation	$ 0.2	$ 0.6	1.5
Unrecognized compensation cost related to nonvested restricted stock awards	$ 7.9
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 10 months 28 days
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Ending Balance	$ 866.7	$ 687	$ 296.1
Upon Achievement of Defined Total Return to Shareholder Goals \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares, restricted stock award	29,732

Employee Benefit Plans - Profi

Employee Benefit Plans - Profit Sharing and Savings Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Eligibility requirement, service hours to be completed	20 hours
Deferred Profit Sharing
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Eligibility requirement, requisite service period	2 years
Compensation expense	$ 2,400,000	$ 1,600,000	$ 2,700,000
Savings Plan, Employee Elected
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Compensation expense	6,300,000	$ 5,500,000	$ 4,800,000
Maximum annual contribution per employee, amount per dollar of employee contribution	$ 1.25
Maximum annual contribution per employee, percent	4.00%

Employee Benefit Plans - Postr

Employee Benefit Plans - Postretirement Healthcare Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure
Amortization of gain, weighted average remaining service period (in years)		4 years
Stockholders’ equity	$ 1,693,900	$ 1,427,600	$ 982,600	$ 950,500
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
Defined Benefit Plan, Amortization of Transition Asset (Obligation)	$ 700
Postretirement Healthcare Plan
Defined Benefit Plan Disclosure
Minimum age requirement	55 years
Requisite service period	15 years
Accumulated other comprehensive income (loss), before tax, related to the Plan	$ 1,200
Reduction in accumulated post-retirement benefit obligation due to curtailment			2,800
Reduction in net periodic benefit cost due to curtailment	(2,800)	(300)
Unfunded benefit obligation	(500)	(700)
Net periodic benefit cost	800	$ 400	$ 200
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2,019	120
2,020	90
2,021	60
2,022	50
2023 through 2027	100
Estimated amount amortized from accumulated other comprehensive loss into net periodic benefit costs	$ 140
Minimum
Defined Benefit Plan Disclosure
Assumptions used calculating net periodic benefit cost, discount rate	3.60%	2.40%
Maximum
Defined Benefit Plan Disclosure
Assumptions used calculating net periodic benefit cost, discount rate	6.00%	6.00%

Other Comprehensive Income - C

Other Comprehensive Income - Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Before Tax Amount
Change in net unrealized loss during period	$ (13.9)	$ (6.5)	$ (19.4)
Reclassification adjustment for net loss included in net income	0.1	(0.7)	(0.3)
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity	1.6	1.9	1.9
Change in net unrealized loss on derivatives		(1.1)	(0.2)
Reclassification adjustment for derivative net (gains) losses included in net income	0	1.1	0
Change in net actuarial loss (gain)	(0.6)	(1.3)	3.9
Total other comprehensive loss	(12.8)	(6.6)	(14.1)
Tax Expense (Benefit)
Change in net unrealized loss during period	(3.6)	(2.7)	(7.6)
Reclassification adjustment for net gains included in net income	0	(0.3)	(0.1)
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity	0.4	0.7	0.7
Change in net unrealized loss on derivatives		(0.4)	(0.1)
Reclassification adjustment for derivative net (gains) losses included in net income		0.4
Change in net actuarial loss (gain)	(0.1)	(0.5)	1.6
Total other comprehensive income (loss)	(3.3)	(2.8)	(5.5)
Net of Tax Amount
Change in net unrealized loss during period	(10.3)	(3.8)	(11.8)
Reclassification adjustment for net gains included in net income	0.1	(0.4)	(0.2)
Change in unamortized gain on available-for-sale securities transferred into held-to-maturity	1.2	1.2	1.2
Change in net unrealized loss on derivatives		(0.7)	(0.1)
Reclassification adjustment for derivative net (gains) losses included in net income		0.7
Change in net actuarial loss (gain)	(0.5)	(0.8)	2.3
Other comprehensive income (loss), net of tax	$ (9.5)	$ (3.8)	$ (8.6)

Other Comprehensive Income - A

Other Comprehensive Income - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in net unrealized loss during period	$ (13.9)	$ (6.5)	$ (19.4)
Reclassification adjustment for net loss included in net income	0.1	(0.7)	(0.3)
Accumulated other comprehensive income (loss)	1,693.9	1,427.6	982.6	$ 950.5
Net unrealized gain (loss) on investment securities available-for-sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss)	(25.5)	(13.3)
Net actuarial gain (loss) on defined benefit post-retirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss)		1.3
Total other comprehensive income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss)	(24.6)	$ (12)	$ (8.2)	$ 0.4
Postretirement Healthcare Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before tax, related to the Plan	1.2
Postretirement Healthcare Plan \| Net actuarial gain (loss) on defined benefit post-retirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), before tax, related to the Plan	$ 0.9

Condensed Financial Informati_3

Condensed Financial Information (Parent Company Only) - Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed balance sheets:
Cash and cash equivalents	$ 822	$ 758.9
Investment in subsidiaries, at equity:
Other assets	159.1	145.8
Total assets	13,300.2	12,213.3
Subordinated debentures held by subsidiary trusts	86.9	82.5
Total liabilities	11,606.3	10,785.7
Stockholders’ equity	1,693.9	1,427.6	$ 982.6	$ 950.5
Total liabilities and stockholders’ equity	13,300.2	12,213.3
Parent Company
Condensed balance sheets:
Cash and cash equivalents	72.9	42.3
Investment in subsidiaries, at equity:
Equity method investments	1,648.9	1,432.3
Advances from subsidiaries, net	46	25.7
Other assets	59	61.7
Total assets	1,826.8	1,562
Other liabilities	46	51.9
Subordinated debentures held by subsidiary trusts	86.9	82.5
Total liabilities	132.9	134.4
Stockholders’ equity	1,693.9	1,427.6
Total liabilities and stockholders’ equity	$ 1,826.8	$ 1,562

Condensed Financial Informati_4

Condensed Financial Information (Parent Company Only) - Condensed Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions
Salaries and benefits	$ 146.4	$ 122.7	$ 108.7
Interest expense	40.9	28	17.6
Acquisition related expenses	12.4	27.2	2.8
Earnings before income tax benefit	206.3	156.7	145.3
Income tax benefit	46.1	50.2	49.6
Net income	160.2	106.5	95.7
Parent Company
Condensed Financial Statements, Captions
Dividends from subsidiaries	148.5	150	140
Other interest income	0.1	0.1	0
Other income, primarily management fees from subsidiaries	17	18	15.1
Total income	165.6	168.1	155.1
Salaries and benefits	25.3	21.8	18.8
Interest expense	4.5	4.7	4.1
Acquisition related expenses	8.1	25.3	1.5
Other operating expenses, net	14.5	13	10.4
Total expenses	52.4	64.8	34.8
Earnings before income tax benefit	113.2	103.3	120.3
Income tax benefit	(9.3)	(14.2)	(7.7)
Income before undistributed earnings of subsidiaries	122.5	117.5	128
Undistributed earnings of subsidiaries	37.7	(11)	(32.4)
Net income	$ 160.2	$ 106.5	$ 95.6

Condensed Financial Informati_5

Condensed Financial Information (Parent Company Only) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 160.2	$ 106.5	$ 95.7
Adjustments to reconcile net income to cash provided by operating activities:
Stock-based compensation expense	5.6	3.9	4.4
Tax benefits from stock-based compensation	0	0	2.1
Excess tax benefits from stock-based compensation	0	0	(1.6)
Net cash provided by operating activities	220.2	154.6	118
Cash flows from investing activities:
Acquisition of intangible assets	0	(28)	0
Acquisition of bank and bank holding company, net of cash and cash equivalents received	28.1	91.8	18.6
Net cash provided by (used in) investing activities	(182.3)	(130.6)	(143.1)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of stock issuance costs	1.8	2.4	4.7
Excess tax benefits from stock-based compensation	0	0	1.6
Purchase and retirement of common stock	(1)	(1.3)	(26.9)
Dividends paid to common stockholders	(64.1)	(48.6)	(39.4)
Net cash used in financing activities	25.2	(47.1)	26.6
Net change in cash and cash equivalents	63.1	(23.1)	1.5
Cash and cash equivalents at beginning of period	758.9	782	780.5
Cash and cash equivalents at end of period	822	758.9	782
Parent Company
Cash flows from operating activities:
Net income	160.2	106.5	95.6
Adjustments to reconcile net income to cash provided by operating activities:
Undistributed earnings of subsidiaries	(37.7)	11	32.4
Stock-based compensation expense	5.6	3.9	4.4
Tax benefits from stock-based compensation	0	0	2.1
Excess tax benefits from stock-based compensation	0	0	(1.6)
Other, net	16.4	14.7	(0.8)
Net cash provided by operating activities	144.5	136.1	132.1
Cash flows from investing activities:
Capital distributions from nonbank subsidiaries	0	18	2
Acquisition of intangible assets	0	(28)	0
Acquisition of bank and bank holding company, net of cash and cash equivalents received	(14.7)	(128.3)	0
Investment in subsidiary	0	(18)	0
Net cash provided by (used in) investing activities	(14.7)	(156.3)	2
Cash flows from financing activities:
Net (decrease) increase in advances from subsidiaries	(9.9)	(28.4)	9.1
Repayment of long-term debt	(26)	0	0
Proceeds from issuance of common stock, net of stock issuance costs	1.8	2.4	4.7
Excess tax benefits from stock-based compensation	0	0	1.6
Purchase and retirement of common stock	(1)	(1.3)	(26.9)
Dividends paid to common stockholders	(64.1)	(48.6)	(39.4)
Net cash used in financing activities	(99.2)	(75.9)	(50.9)
Net change in cash and cash equivalents	30.6	(96.1)	83.2
Cash and cash equivalents at beginning of period	42.3	138.4	55.2
Cash and cash equivalents at end of period	72.9	$ 42.3	$ 138.4
Inland Northwest Bank [Member]
Cash flows from financing activities:
Stock Issued	173.3
BOTC Acquisition
Cash flows from financing activities:
Stock Issued	$ 386

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	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	$ 10.1	$ 8.8
Derivative liabilities	9.4	7.9
Deferred compensation plan assets	12.1	12.2
Deferred compensation plan liabilities	12.1	12.2
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 held for sale	0	0
Deferred compensation plan assets	0	0
Deferred compensation plan liabilities	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 held for sale	33.3	46.6
Derivative assets		7.5
Derivative liabilities	8.8	7.8
Deferred compensation plan assets	12.1	12.2
Deferred compensation plan liabilities	12.1	12.2
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 held for sale	0	0
Deferred compensation plan assets	0	0
Deferred compensation plan liabilities	0	0
US 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	0
US 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	2.6	3.2
US 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	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	559.2	561.5
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	1,544.8	1,462.5
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	70.2	90.7
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	91.9	87.9
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	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	3
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	0
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale	2,270.7	2,208.7
Derivative assets	10.1	8.8
Derivative liabilities	9.4	7.9
Deferred compensation plan assets	12.1	12.2
Deferred compensation plan liabilities	12.1	12.2
Estimated Fair Value \| Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	33.3	46.6
Deferred compensation plan assets	12.1	12.2
Deferred compensation plan liabilities	12.1	12.2
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
Derivative assets	0	0
Derivative liabilities	0	0
Deferred compensation plan assets	0	0
Deferred compensation plan liabilities	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	2,270.7	2,208.7
Derivative assets	10.1	8.8
Derivative liabilities	9.4	7.9
Deferred compensation plan assets	12.1	12.2
Deferred compensation plan liabilities	12.1	12.2
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
Derivative assets	0	0
Derivative liabilities	0	0
Deferred compensation plan assets	0	0
Deferred compensation plan liabilities	0	0
Estimated Fair Value \| US 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	2.6	3.2
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	559.2	561.5
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	1,544.8	1,462.5
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	70.2	90.7
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	91.9	87.9
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	2	3
Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	8.8	7.5
Derivative liabilities	8.8	7.8
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	8.8
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	8.8	7.5
Derivative liabilities	8.8	7.8
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	1.3	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	1.3	1.3
Forward loan sales 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 loan sales 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	0.6	0.1
Forward loan sales 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 loan sales 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	$ 0.6	$ 0.1

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Inputs, Quantitative Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
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%)	(0.00%)
Maximum \| Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for OREO Level 3 Fair Value	(96.00%)	(96.00%)
Discount Rate for Assets HFS Level 3 Fair Value	43.00%	0.00%
Weighted Average \| Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Level 3 Fair Value Disclosure	(13.00%)	(26.00%)
Discount Rate for OREO Level 3 Fair Value	(39.00%)	(12.00%)
Discount Rate for Assets HFS Level 3 Fair Value	10.00%	0.00%
Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	$ (12.2)	$ (22.2)
Other real estate owned	(0.6)	(1.6)
Long-lived assets to be disposed of by sale	(0.5)	0
Estimated Fair Value \| Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	24.1
Other real estate owned	0.6
Long-lived assets to be disposed of by sale	4.9
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	0	0
Other real estate owned	0	0
Long-lived assets to be disposed of by sale	0	0
Significant Other Observable Inputs (Level 2) \| Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	0	0
Other real estate owned	0	0
Long-lived assets to be disposed of by sale	0	0
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)
Impaired loans	24.1	32.6
Other real estate owned	0.6	1.3
Long-lived assets to be disposed of by sale	4.9	0.8
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)
Impaired loans	$ 24.1	$ 32.6
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 OREO Level 3 Fair Value	(8.00%)	(8.00%)
Discount Rate for Assets HFS Level 3 Fair Value	0.00%	0.00%
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%)	(78.00%)

Fair Value Measurements - Narr

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related allowance	$ 6.8	$ 10.8	$ 14
Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	(12.2)	(22.2)
Fair Value Measured on a Non-recurring Basis \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	24.1	32.6
Related allowance	6.8	10.8
Partial loan charge-off	5.4	11.4
Carrying Amount \| Fair Value Measured on a Non-recurring Basis \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	36.3	54.8
Assets Held-for-sale, Long Lived, Fair Value Disclosure	5.4	0.8
Changes Measurement [Member] \| Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Held-for-sale, Long Lived, Fair Value Disclosure	0.5	0
Estimated Fair Value \| 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
Assets Held-for-sale, Long Lived, Fair Value Disclosure	4.9	0.8
Estimated Fair Value \| Fair Value Measured on a Non-recurring Basis \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 24.1	$ 32.6

Fair Value Measurements - Sc_2

Fair Value Measurements - Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financial assets:
Held-to-maturity investment securities, estimated fair value	$ 400.7	$ 483.3
Derivative assets	10.1	8.8
Deferred compensation plan assets	12.1	12.2
Financial liabilities:
Derivative liabilities	9.4	7.9
Deferred compensation plan liabilities	12.1	12.2
Carrying Amount
Financial assets:
Cash and cash equivalents	822	759
Investment debt securities available-for-sale	2,270.7	2,208.7
Held-to-maturity investment securities, estimated fair value	406.8	484.5
Accrued interest receivable	44.9	38
Mortgage servicing rights, net	27.7	24.8
Loans Held-for-sale, Fair Value Disclosure	33.3	46.6
Net loans held for investment	8,397.4	7,495.6
Derivative assets	10.1	8.8
Deferred compensation plan assets	12.1	12.2
Total financial assets	12,025	11,078.2
Financial liabilities:
Total deposits, excluding time deposits	9,363.7	8,783
Time deposits	1,317	1,151.9
Securities sold under repurchase agreements	712.4	643
Other borrowed funds		20
Accrued interest payable	7.8	5.6
Long-term debt	15.8	13.1
Subordinated debentures held by subsidiary trusts	86.9	82.5
Derivative liabilities	9.4	7.9
Deferred compensation plan liabilities	12.1	12.2
Total financial liabilities	11,525.1	10,719.2
Estimated Fair Value
Financial assets:
Cash and cash equivalents	822	759
Investment debt securities available-for-sale	2,270.7	2,208.7
Held-to-maturity investment securities, estimated fair value	400.7	483.3
Accrued interest receivable	44.9	38
Mortgage servicing rights, net	42.4	40.1
Loans Held-for-sale, Fair Value Disclosure	33.3	46.6
Net loans held for investment	8,439.7	7,252.2
Derivative assets	10.1	8.8
Deferred compensation plan assets	12.1	12.2
Total financial assets	12,075.9	10,848.9
Financial liabilities:
Total deposits, excluding time deposits	9,363.7	8,783
Time deposits	1,299	1,137.9
Securities sold under repurchase agreements	712.4	643
Other borrowed funds		20
Accrued interest payable	7.8	5.6
Long-term debt	13	11.3
Subordinated debentures held by subsidiary trusts	84.9	76.7
Derivative liabilities	9.4	7.9
Deferred compensation plan liabilities	12.1	12.2
Total financial liabilities	11,502.3	10,697.6
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Estimated Fair Value
Financial assets:
Cash and cash equivalents	822	759
Investment debt securities available-for-sale	0	0
Held-to-maturity investment securities, estimated fair value	0	0
Accrued interest receivable	0	0
Mortgage servicing rights, net	0	0
Loans Held-for-sale, Fair Value Disclosure	0	0
Net loans held for investment	0	0
Derivative assets	0	0
Deferred compensation plan assets	0	0
Total financial assets	822	759
Financial liabilities:
Total deposits, excluding time deposits	9,363.7	8,783
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Other borrowed funds		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 plan liabilities	0	0
Total financial liabilities	9,363.7	8,783
Significant Other Observable Inputs (Level 2) \| Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment debt securities available-for-sale	2,270.7	2,208.7
Held-to-maturity investment securities, estimated fair value	400.7	483.3
Accrued interest receivable	44.9	38
Mortgage servicing rights, net	42.4	40.1
Loans Held-for-sale, Fair Value Disclosure	33.3	46.6
Net loans held for investment	8,415.6	7,219.6
Derivative assets	10.1	8.8
Deferred compensation plan assets	12.1	12.2
Total financial assets	11,229.8	10,057.3
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	1,299	1,137.9
Securities sold under repurchase agreements	712.4	643
Other borrowed funds		20
Accrued interest payable	7.8	5.6
Long-term debt	13	11.3
Subordinated debentures held by subsidiary trusts	84.9	76.7
Derivative liabilities	9.4	7.9
Deferred compensation plan liabilities	12.1	12.2
Total financial liabilities	2,138.6	1,914.6
Significant Unobservable Inputs (Level 3) \| Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment debt securities available-for-sale	0	0
Held-to-maturity investment securities, estimated fair value	0	0
Accrued interest receivable	0	0
Mortgage servicing rights, net	0	0
Loans Held-for-sale, Fair Value Disclosure	0	0
Net loans held for investment	24.1	32.6
Derivative assets	0	0
Deferred compensation plan assets	0	0
Total financial assets	24.1	32.6
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Other borrowed funds		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 plan liabilities	0	0
Total financial liabilities	$ 0	$ 0

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Loan repayments	$ 17,400
Amount of loans removed due to changes in related parties	1,600
Airplane Usage by Company
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Related party transaction, expenses from transactions with related party	53	$ 45	$ 121
Executive Officers, Directors, Shareholders Greater than Five Percent, and Related Entities and Individuals to Such Persons [Member]
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Loans and leases receivable, related parties	43,200	54,600
New loans and advances on existing loans	7,600
Board of Directors Chairman \| Airplane Usage by Company
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Related party transactions, other revenues	25	17	19
Entity Majority Owned by Shareholders and Directors [Member] \| Education, Communication, Strategic Enterprise Planning and Corporate Governance Consultation [Member]
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Related party transaction, expenses from transactions with related party	$ 80	$ 73	$ 100

Recent Authoritative Accounting

Recent Authoritative Accounting Guidance - New Accounting Pronouncements and Changes in Accounting Principles (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction in income tax expense		$ 0
Accounting Standards Update 2016-02 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Operating Lease, Right-of-Use Asset	$ 54.6
Operating Lease, Liability	54.6
Accounting Standards Update 2018-02 \| Adjustments for New Accounting Principle, Early Adoption
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Tax Cuts And Jobs Act Of 2017, Reclassification From AOCI To Retained Earnings	$ 3.1

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events (Details)	Jan. 29, 2019$ / shares
Class A Common Stock \| Subsequent Event
Subsequent Event [Line Items]
Dividends (in dollars per share)	$ 0.31