First Interstate BancSystem (FIBK) 10-Q 7 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2018shares
Entity Registrant Name	FIRST INTERSTATE BANCSYSTEM INC
Trading Symbol	FIBK
Entity Central Index Key	860,413
Document Fiscal Year Focus	2,018
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Fiscal Period Focus	Q3
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Class A Common Stock
Entity Common Stock, Shares Outstanding	38,107,555
Class B Common Stock
Entity Common Stock, Shares Outstanding	22,501,994

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 229.8	$ 196.5
Interest bearing deposits in banks	686.8	562.3
Federal Funds Sold	48.4	0.1
Total cash and cash equivalents	965	758.9
Investment securities:
Available-for-sale	2,158.8	2,208.7
Held-to-maturity (estimated fair values of $407.4 and $483.3 at September 30, 2018 and December 31, 2017, respectively)	417.8	484.5
Total investment securities	2,576.6	2,693.2
Loans held for investment	8,480.3	7,567.7
Mortgage loans held for sale	37.7	46.6
Total loans	8,518	7,614.3
Less allowance for loan losses	73.6	72.1
Net loans	8,444.4	7,542.2
Goodwill	546.4	444.7
Company-owned life insurance	273.7	260.6
Premises and equipment, net of accumulated depreciation	244.2	241.9
Accrued interest receivable	48	38
Mortgage servicing rights, net of accumulated amortization and impairment reserve	27	24.8
Core deposit intangibles, net of accumulated amortization	59.3	49.1
Other real estate owned (“OREO”)	17.3	10.1
Deferred tax asset, net	0	4
Other assets	153.9	145.8
Total assets	13,355.8	12,213.3
Deposits:
Non-interest bearing	3,261.2	2,900
Interest bearing	7,584.4	7,034.9
Total deposits	10,845.6	9,934.9
Securities sold under repurchase agreements	635.9	643
Accounts payable and accrued expenses	99.4	86.6
Accrued interest payable	6.7	5.6
Deferred tax liability, net	3	0
Long-term debt	22.4	13.1
Other borrowed funds	1.5	20
Subordinated debentures held by subsidiary trusts	86.9	82.5
Total liabilities	11,701.4	10,785.7
Stockholders’ equity:
Nonvoting noncumulative preferred stock without par value; authorized 100,000 shares; no shares issued and outstanding as of September 30, 2018 or December 31, 2017	0	0
Common stock	865.5	687
Retained earnings	828.3	752.6
Accumulated other comprehensive loss, net	(39.4)	(12)
Total stockholders’ equity	1,654.4	1,427.6
Total liabilities and stockholders’ equity	$ 13,355.8	$ 12,213.3

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investment securities:
Estimated fair value	$ 407,400	$ 483,300
Stockholders' equity:
Nonvoting, noncumulative preferred stock, shares authorized	100,000	100,000
Nonvoting, noncumulative preferred stock, shares issued	0	0
Nonvoting, noncumulative preferred stock, shares outstanding	0	0

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest income:
Interest and fees on loans	$ 103.9	$ 94	$ 292.1	$ 231.6
Interest and dividends on investment securities:
Taxable	13.9	11.7	41	30.2
Exempt from federal taxes	0.6	0.8	1.8	2.5
Interest on deposits in banks	2.8	2.3	6.9	4.8
Total interest income	121.2	108.8	341.8	269.1
Interest expense:
Interest on deposits	8.9	6.2	22.3	15.3
Interest on securities sold under repurchase agreements	0.7	0.4	1.8	0.9
Interest on other borrowed funds	0.1	0.4	0.2	0.4
Interest on other debt	0.4	0.2	0.9	1.2
Interest on subordinated debentures held by subsidiary trusts	1.1	0.8	3	2.3
Total interest expense	11.2	8	28.2	20.1
Net interest income	110	100.8	313.6	249
Provision for loan losses	2	3.4	7	7.5
Net interest income after provision for loan losses	108	97.4	306.6	241.5
Non-interest income:
Gain (Loss) on Termination of Interest Rate Swap	0	(1.1)	0	(1.1)
Mortgage banking revenues	6.7	8.2	19.3	22.5
Investment securities gains (losses), net	0	0.8	0	0.8
Other income	4.5	3	11	10.9
Total non-interest income	36.2	38.3	109	104.6
Non-interest expense:
Salaries and wages	36.8	34.7	105.7	88.4
Employee benefits	11.9	10.2	35.5	29.6
Outsourced technology services	6.8	6.6	20.9	17.9
Occupancy, net	6.5	6.1	18.8	16
Furniture and equipment	3.5	3.1	9.5	8.2
OREO expense, net of income	0.2	0.2	0.3	0.2
Professional fees	1.9	1.9	5.2	4.7
FDIC insurance premiums	1.4	1.7	4.3	3.4
Mortgage servicing rights amortization	0.8	0.8	2.3	2.1
Mortgage servicing rights recovery	0	0	0	(0.1)
Core deposit intangibles amortization	2	1.9	5.5	3.6
Other expenses	15.8	14.5	48.1	40.9
Acquisition related expenses	3.1	13	5.4	23.9
Total non-interest expense	90.7	94.7	261.5	238.8
Income before income tax expense	53.5	41	154.1	107.3
Income tax expense	12.1	13.7	34.3	35
Net income	$ 41.4	$ 27.3	$ 119.8	$ 72.3
Basic earnings per common share (in dollars per share)	$ 0.71	$ 0.49	$ 2.10	$ 1.46
Diluted earnings per common share (in dollars per share)	$ 0.71	$ 0.48	$ 2.09	$ 1.45
Weighted average common shares outstanding for basic earnings per share computation	58,254,575	56,094,401	56,951,029	49,514,818
Weighted Average Number of Shares Outstanding, Diluted	58,640,475	56,530,868	57,330,027	50,000,882
Credit and Debit Card [Member]
Non-interest income:
Payment services revenues	$ 10.1	$ 12.4	$ 33.5	$ 31
Investment Advisory, Management and Administrative Service [Member]
Non-interest income:
Wealth management revenues	5.8	5.5	17.5	15.6
Deposit Account [Member]
Non-interest income:
Payment services revenues	5.7	5.9	16.6	15.3
Financial Service, Other [Member]
Non-interest income:
Payment services revenues	$ 3.4	$ 3.6	$ 11.1	$ 9.6

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 41.4	$ 27.3	$ 119.8	$ 72.3
Other comprehensive income, before tax:
Change in net unrealized (losses) gains during period	(6.3)	(1.8)	(33.9)	15.6
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity	0.5	0.5	1.5	1.4
Defined benefit post-retirement benefits plans:
Change in net actuarial gain	(0.2)	(0.2)	(0.5)	(1.1)
Other comprehensive income (loss), before tax	(6)	(1.8)	(32.9)	15.1
Deferred tax benefit (expense) related to other comprehensive income	1.6	0.8	8.6	(6)
Other comprehensive (loss) income, net of tax	(4.4)	(1)	(24.3)	9.1
Comprehensive income, net of tax	37	26.3	95.5	81.4
Unrealized Gain (Loss) on Derivatives	$ 0	$ (0.6)	$ 0	$ (1.1)

Consolidated Statement of Chang

Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Common stock	Retained earnings	Accumulated other comprehensive income (loss)	ASU 2018-02Retained earnings
Beginning Balance at Dec. 31, 2016	$ 982.6	$ 296.1	$ 694.6	$ (8.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	72.3		72.3
Other comprehensive income, net of tax expense	9.1			9.1
Common stock transactions:
Common shares purchased and retired	(0.9)	(0.9)
Stock Issued During Period, Value, New Issues	385.9	385.9
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	2	2
Stock-based compensation expense	3.4	3.4
Common cash dividend declared	(35)		(35)
Ending Balance at Sep. 30, 2017	1,419.4	686.5	731.9	1
Beginning Balance at Dec. 31, 2017	1,427.6	687	752.6	(12)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	119.8		119.8
Reclassification of the income tax effects of the Tax Cut and Jobs Act from AOCI				(3.1)	$ 3.1
Other comprehensive income, net of tax expense	(24.3)			(24.3)
Common stock transactions:
Common shares purchased and retired	(1)	(1)
Stock Issued During Period, Value, New Issues	173.3	173.3
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	1.9	1.9
Stock-based compensation expense	4.3	4.3
Common cash dividend declared	(47.2)		(47.2)
Ending Balance at Sep. 30, 2018	$ 1,654.4	$ 865.5	$ 828.3	$ (39.4)

Consolidated Statement of Cha_2

Consolidated Statement of Changes in Stockholders' Equity (Parenthetical) - $ / shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Common stock
Common stock transactions:
Common shares purchased and retired	23,960	22,727
Common shares issued	3,848,929	11,267,676
Non-vested common shares issued	210,039	134,044
Non-vested common shares forfeited	40,122	30,070
Stock options exercised (in shares)	148,834	180,789
Shares tendered in payment of option price and income tax withholding amounts	28,194	56,082
Retained earnings
Common stock transactions:
Common dividends (in dollars per share)	$ 0.84	$ 0.72

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Statement of Cash Flows [Abstract]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	$ (0.5)	$ (1.1)
Repayments of Other Long-term Debt	0.4	0.1
Cash flows from operating activities:
Net income	119.8	72.3
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	7	7.5
Depreciation and amortization	19.9	17.9
Net premium amortization on investment securities	7.9	8.6
Gain (Loss) on Sale of Debt Investments	0	0.8
Realized and unrealized net gains on mortgage banking activities	(4.2)	(15.3)
Net gain on sale of OREO	(0.4)	(0.4)
Asset Impairment Charges	0.1	0.3
Proceeds From The Sale Of Health Savings Accounts	0	(3.1)
Mortgage servicing rights recovery	0	0.1
Deferred tax expenses	13.2	19.8
Net increase in cash surrender value of company-owned life insurance	(3.6)	(3.8)
Stock-based compensation expense	4.3	3.4
Originations of mortgage loans held for sale	(738.3)	(719.2)
Proceeds from sales of mortgage loans held for sale	747.1	731.1
Changes in operating assets and liabilities, net of effects of acquisition:
Increase in interest receivable	(6.4)	(3.2)
(Increase) decrease in other assets	(0.7)	(4.8)
Increase in accrued interest payable	0.9	0.2
Decrease in accounts payable and accrued expenses	5.3	(15.7)
Net cash provided by operating activities	171.9	94.7
Cash flows from investing activities:
Purchase of investment securities, Held-to-maturity	(0.3)	(12.8)
Purchase of investment securities, Available-for-sale	(320.6)	(386.5)
Proceeds from maturities and paydowns of held-to-maturity investment securities	66.9	76
Proceeds from maturities and paydowns of available-for-sale investment securities	333.3	319.9
Extensions of credit to customers, net of repayments	(225.5)	(20.9)
Recoveries of loans charged-off	9.6	6.5
Proceeds from sale of OREO	4.3	4.1
Acquisition of intangible assets	0	(28)
Proceeds from the sale of Health Savings Accounts	0	6.1
Acquisition of bank and bank holding company, net of cash and cash equivalents received	28.2	91.8
Capital expenditures, net of sales	(0.5)	(12.2)
Net cash provided by (used in) investing activities	(104.6)	44
Cash flows from financing activities:
Net increase (decrease) in deposits	214.4	(111.6)
Net (decrease) increase in securities sold under repurchase agreements	(7.1)	97.7
Net decrease in other borrowed funds	(24.5)	10
Advances on long-term debt	2.7	0
Proceeds from issuance of common stock	1.9	2
Purchase and retirement of common stock	(1)	(0.9)
Dividends paid to common stockholders	(47.2)	(35)
Net cash provided by (used in) financing activities	138.8	(37.9)
Net increases (decrease) in cash and cash equivalents	206.1	100.8
Cash and cash equivalents at beginning of period	758.9	782
Cash and cash equivalents at end of period	965	882.8
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	15.8	24.3
Cash paid during the period for interest expense	27.1	19.9
Noncash or Part Noncash Acquisition, Value of Assets Acquired [Abstract]
Transfer of loans to loans held for sale	1.4	6.3
Transfer of loans to other real estate owned	10.7	3.2
Capitalization of internally originated mortgage servicing rights	4.5	4.1
Noncash or Part Noncash Acquisition, Investments Acquired	3.1	424.3
Noncash Or Part Noncash Acquisition, HTM Investments Acquired	0	57.3
Noncash Or Part Noncash Acquisition, Loans Held For Sale Acquired	0	10.2
Noncash Or Part Noncash Acquisition, Loans Acquired	713.1	2,080.4
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	14	46.7
Noncash Or Part Noncash Acquisition, Goodwill	100.8	232.2
Noncash or Part Noncash Acquisition, Intangible Assets Acquired	15.7	48
Noncash Or Part Noncash Acquisition, Mortgage Servicing Asset Acquired	0	3.5
Noncash Or Part Noncash Acquisition, Interest Receivable Acquired	3.6	57
Noncash Or Part Noncash Acquisition, Company-Owned Life Insurance Acquired	9.5	26
Noncash Or Part Noncash Acquisition, Deferred Tax Assets Acquired	0	7.6
Noncash Or Part Noncash Acquisition, Other Real Estate Owned Acquired	0.6	1.2
Noncash or Part Noncash Acquisition, Other Assets Acquired	6.5	31.6
Noncash or Part Noncash Acquisition, Value of Assets Acquired	866.9	3,026
Noncash Or Part Noncash Acquisition, Deposits Acquired	696.3	2,669
Noncash or Part Noncash Acquisition, Debt Assumed	7	0
Noncash or Part Noncash Acquisition, Other Liabilities Assumed	6	0
Noncash or Part Noncash Acquisition, Trust Preferred Securities Assumed	4.4	0
Noncash or Part Noncash Acquisition, Deferred Tax Liability	0.4	0
Noncash or Part Noncash Acquisition, Payables Assumed	7.7	62.9
Noncash or Part Noncash Acquisition, Value of Liabilities Assumed	$ 721.8	$ 2,731.9

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation In the opinion of management, the accompanying unaudited consolidated financial statements of First Interstate BancSystem, Inc., First Interstate Bank (“FIB”), Inland Northwest Bank (“INB’), and its other subsidiaries (together, the “Company”) contain all adjustments (all of which are of a normal recurring nature) necessary to present fairly the financial position of the Company at September 30, 2018 and December 31, 2017 , the results of operations for each of the three and nine month periods ended September 30, 2018 and 2017 , and cash flows and changes in stockholders’ equity for each of the nine month periods ended September 30, 2018 and 2017 , in conformity with U.S. generally accepted accounting principles (“GAAP”). The balance sheet information at December 31, 2017 is derived from audited consolidated financial statements. Certain reclassifications, none of which were material, have been made to conform prior year financial statements to the September 30, 2018 presentation. These reclassifications did not change previously reported net income or stockholders’ equity. These unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 . Operating results for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 . Revenue Recognition Accounting Standards Codification (“ASC”) 606, Revenue from Contracts with Customers (“ASC 606”), establishes principles for reporting information about the nature, amount, timing and uncertainty of revenue and cash flows arising from the entity’s contracts to provide goods or services to customers. The core principle requires an entity to recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration that it expects to be entitled to receive in exchange for those goods or services recognized as performance obligations are satisfied. The new revenue recognition standards became effective for the Company on January 1, 2018. The majority of our revenue-generating transactions are not subject to ASC 606, including revenue generated from financial instruments, such as our loans, guarantees, derivatives and investment securities, as well as revenue related to our mortgage servicing activities, as these activities are subject to other GAAP discussed elsewhere within our disclosures. ASC 606 is applicable to non-interest revenue streams such as wealth management and trust fee income, service charges on deposit accounts, interchange and other fees, and annuity and insurance commissions. However, the recognition of these revenue streams did not change significantly upon the adoption of ASC 606. Substantially all of the Company’s revenue is generated from contracts with customers. Descriptions of our revenue-generating activities that are within the scope of ASC 606 are discussed below: • Wealth management and trust fee income - this 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 - these 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 - these 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 - these 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.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 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 Idaho Independent Bank ("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. The Company believes the transaction, if completed on the terms contemplated, will complement the Company's footprint and will provide the Company with an expanded presence in several high-growth markets, including Boise and Coeur d’Alene, Idaho. 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 approval and IIBK shareholder approval. Community 1 st Bank. On October 11, 2018, the Company also entered into a definitive agreement to acquire all of the outstanding stock of Community 1st Bank ("CMYF"), a community bank headquartered in Post Falls, Idaho with three banking offices in North Idaho, in an all-stock transaction valued at approximately $21.5 million in aggregate, or $ 17.20 per share of CMYF stock. The Company believes the transaction, if completed on the terms contemplated, will complement the Company’s footprint and will provide the Company with an expanded presence in North Idaho's high-growth markets. 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 approval and CMYF shareholder approval. 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 will merge 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 $100.8 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 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 Deferred tax assets, net 1.2 (1.6 ) (5) (0.4 ) Other assets 29.3 (9.7 ) (6) 19.6 Total assets acquired 801.9 (5.0 ) 796.9 Liabilities assumed: Deposits 696.1 0.2 (7) 696.3 Accounts payable and accrued expense 8.1 (0.4 ) (8) 7.7 Long term debt 13.0 — 13.0 Trust preferred securities 5.2 (0.8 ) (9) 4.4 Total liabilities assumed 722.4 (1.0 ) 721.4 Net assets acquired $ 79.5 $ (4.0 ) $ 75.5 Consideration paid: Cash $ 3.0 Class A common stock 173.3 Total consideration paid 176.3 Goodwill $ 100.8 Explanation of fair value adjustments and the removal of previously recorded fair value marks recorded by Northwest: (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 the write-off of pre-existing deferred tax assets and purchase accounting adjustments as a result of the acquisition. (6) Adjustment consists of reductions to the fair value of other items, including the removal of Northwest previously recorded goodwill. (7) Increase in book value of time deposits to their estimated fair values based upon interest rates of similar time deposits with similar terms on the date of acquisition based upon valuation from an independent accounting and advisory firm. (8) Decrease due to the write-off of off balance sheet reserves. (9) Write down of the book value of debt to the estimated fair values on the date of acquisition based upon favorable interest rates in the market. 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 ten years. The Company acquired certain loans that are subject to Accounting Standards Codification ("ASC") Topic 310-30 "Loans and Debt Securities Acquired with Deteriorated Credit Quality." ASC Topic 310-30 provides recognition, measurement and disclosure guidance for acquired loans that have evidence of deterioration in credit quality since origination for which it is probable, at acquisition, the Company will be unable to collect all contractual amounts owed. For loans that meet the criteria stipulated in ASC Topic 310-30, the excess of all cash flows expected at acquisition over the initial fair value of the loans acquired ("accretable yield") is amortized to interest income over the expected remaining lives of the underlying loans using the effective interest method. The accretable yield will fluctuate due to changes in (i) estimated lives of underling credit-impaired loans, (ii) assumptions regarding future principal and interest amounts collected, and (iii) indices used to fair value variable rate loans. Information regarding Northwest loans acquired deemed credit-impaired as of the August 16, 2018 acquisition date are as follows: Contractually required principal and interest payments $ 27.5 Contractual cash flows not expected to be collected (“non-accretable discount”) 4.4 Cash flows expected to be collected 23.1 Interest component of cash flows expected to be collected (“accretable discount”) 3.2 Fair value of acquired credit-impaired loans $ 19.9 Information regarding Northwest acquired loans not deemed credit-impaired at the August 16, 2018 acquisition date are as follows: Contractually required principal and interest payments $ 894.8 Contractual cash flows not expected to be collected 26.1 Fair value at acquisition $ 693.2 Unaudited pro forma consolidated revenues and net income as if the Northwest acquisition had occurred as of January 1, 2018, are not presented because the effect of this acquisition was not considered significant. The accompanying consolidated statements of income for the three and nine months ended September 30, 2018 , 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 will continued to operate as INB until November 9, 2018 at which point INB’s operations will be integrated with the Company’s operations, and INB will merge with FIB. 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 loss (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 for the three and nine months ended September 30, 2018 and 2017 , include the results of operations of the acquired entity from the May 30, 2017 acquisition date. 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 was 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. Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Interest income $ 121.2 $ 108.7 $ 341.8 $ 312.1 Non-interest income 36.2 38.3 109.0 116.2 Total revenues $ 157.4 $ 147.0 $ 450.8 $ 428.3 Net income $ 41.4 $ 34.9 $ 119.8 $ 94.0 EPS - basic $ 0.71 $ 0.52 $ 2.10 $ 1.55 EPS - diluted 0.71 0.51 2.09 1.53 The unaudited pro forma net income presented in the table above for 2017 was adjusted to exclude acquisition-related costs, including change in control expenses related to employee benefit plans and legal and professional expenses of $19.7 million, 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 2017 does not capture operating cost savings and other business synergies expected as a result of the acquisition. The Company recorded $3.1 million of Northwest related pre-tax acquisition related expenses for the three months ended September 30, 2018 and $5.4 million of Northwest and Cascade related pre-tax acquisition related expenses for the nine months ended September 30, 2018 . These costs are incorporated in non-interest expenses in the Company’s consolidated statements of income. Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 Legal and Professional Fees $ 2.4 $ 3.0 Employee Expenses — 0.1 Technology Conversion and Contract Termination 0.5 2.0 Other 0.2 0.3 Total Acquisition Related Expenses $ 3.1 $ 5.4

Goodwill and Intangibles

Goodwill and Intangibles	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangibles	Goodwill and Core Deposit Intangibles Management analyzes its goodwill for impairment on an annual basis and between annual tests in certain circumstances, such as upon material adverse changes in legal, business, regulatory and economic factors. An impairment loss is recorded to the extent that the carrying amount of goodwill exceeds its implied fair value. The Company performed an impairment assessment as of July 1, 2018 and 2017 and concluded that there was no impairment to goodwill. Goodwill As of September 30, 2018 2017 Net carrying value at beginning of nine month period $ 444.7 $ 212.8 Addition to provisional goodwill from acquisition 100.8 232.2 Measurement period adjustment to previously recorded goodwill 0.9 — Net carrying value at end of period $ 546.4 $ 445.0 Core deposit intangibles (“CDI”) Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 CDI, net, beginning of period $ 45.6 $ 52.8 $ 49.1 $ 9.6 Established through acquisitions or provisional adjustments 15.7 — 15.7 48.0 Reductions due to sale of accounts — — — (3.1 ) CDI current period amortization (2.0 ) (1.9 ) (5.5 ) (3.6 ) Total CDI, net, end of period $ 59.3 $ 50.9 $ 59.3 $ 50.9 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. The following table provides the estimated future CDI amortization expense: Years Ending December 31, 2018 remaining $ 2.4 2019 8.9 2020 8.1 2021 7.5 2022 6.9 Thereafter 25.5 Total $ 59.3

Investment Securities

Investment Securities	9 Months Ended
	Sep. 30, 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: September 30, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale: U.S. Treasury notes $ 3.0 $ — $ — $ 3.0 Obligations of U.S. government agencies 576.2 — (15.3 ) 560.9 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 1,462.0 1.4 (37.8 ) 1,425.6 Private mortgage-backed securities 74.8 — (1.8 ) 73.0 Corporate securities 93.0 0.1 (1.0 ) 92.1 Other investments 4.2 — — 4.2 Total $ 2,213.2 $ 1.5 $ (55.9 ) $ 2,158.8 September 30, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to-Maturity: State, county and municipal securities $ 153.7 $ 1.2 $ (1.7 ) $ 153.2 Obligations of U.S. government agencies 19.7 — (0.3 ) 19.4 U.S agency residential mortgage-backed securities & collateralized mortgage obligations 198.0 7.8 (16.8 ) 189.0 Corporate securities 46.3 — (0.6 ) 45.7 Other investments 0.1 — — 0.1 Total $ 417.8 $ 9.0 $ (19.4 ) $ 407.4 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 & collateralized mortgage obligations 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 realized gains and losses from the disposition of available-for-sale investment securities for the three and nine months ended September 30, 2018 and 2017 . 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 September 30, 2018 and December 31, 2017 : Less than 12 Months 12 Months or More Total September 30, 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 $ 199.9 $ (4.8 ) $ 346.5 $ (10.5 ) $ 546.4 $ (15.3 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 851.8 (19.2 ) 448.2 (18.6 ) 1,300.0 (37.8 ) Private mortgage-backed securities 49.9 (1.2 ) 22.9 (0.6 ) 72.8 (1.8 ) Corporate securities 38.7 (0.9 ) 1.9 (0.1 ) 40.6 (1.0 ) Total $ 1,140.3 $ (26.1 ) $ 819.5 $ (29.8 ) $ 1,959.8 $ (55.9 ) Less than 12 Months 12 Months or More Total September 30, 2018 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity: State, county and municipal securities $ 59.8 $ (1.0 ) $ 26.2 $ (0.7 ) $ 86.0 $ (1.7 ) Obligations of U.S. government agencies 9.6 (0.2 ) 9.8 (0.1 ) 19.4 (0.3 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 85.8 (13.1 ) 44.0 (3.7 ) 129.8 (16.8 ) Corporate securities 30.9 (0.4 ) 8.8 (0.2 ) 39.7 (0.6 ) Total $ 186.1 $ (14.7 ) $ 88.8 $ (4.7 ) $ 274.9 $ (19.4 ) 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 ) Obligations of U.S. government agencies 9.7 — 9.9 (0.2 ) 19.6 (0.2 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 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 ) 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. The Company had 720 and 581 individual investment securities that were in an unrealized loss position as of September 30, 2018 and December 31, 2017 , respectively. As of September 30, 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 the three and nine months ended September 30, 2018 or 2017 . Maturities of investment securities at September 30, 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 September 30, 2018 Amortized Cost Estimated Fair Value Amortized Cost Estimated Fair Value Within one year $ 511.5 $ 501.8 $ 70.6 $ 68.9 After one year but within five years 1,444.9 1,407.9 222.9 216.0 After five years but within ten years 189.3 183.3 100.7 99.9 After ten years 67.5 65.8 23.6 22.6 Total $ 2,213.2 $ 2,158.8 $ 417.8 $ 407.4 As of September 30, 2018 , the Company had investment securities callable within one year with amortized costs and estimated fair values of $107.4 million and $105.1 million , respectively. These investment securities are primarily included in the after one year but within five years category in the table above. As of September 30, 2018 , the Company did not have any structured notes callable within one year.

Loans

Loans	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Loans	Loans The following table presents loans by class as of the dates indicated: September 30, December 31, Real estate loans: Commercial $ 3,213.1 $ 2,822.9 Construction: Land acquisition & development 314.5 348.7 Residential 250.6 240.2 Commercial 219.6 119.4 Total construction loans 784.7 708.3 Residential 1,581.2 1,487.4 Agricultural 217.8 158.2 Total real estate loans 5,796.8 5,176.8 Consumer: Indirect consumer 800.8 784.7 Other consumer 198.1 175.1 Credit card 79.4 74.6 Total consumer loans 1,078.3 1,034.4 Commercial 1,337.2 1,215.4 Agricultural 264.8 136.2 Other, including overdrafts 3.2 4.9 Loans held for investment 8,480.3 7,567.7 Mortgage loans held for sale 37.7 46.6 Total loans $ 8,518.0 $ 7,614.3 The following tables present the Company’s recorded investment and contractual aging of the Company’s recorded investment in loans by class as of the dates indicated. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of September 30, 2018 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 9.6 $ 3.0 $ 0.5 $ 13.1 $ 3,185.0 $ 15.0 $ 3,213.1 Construction: Land acquisition & development 0.7 0.7 0.4 1.8 309.0 3.7 314.5 Residential 3.4 0.4 — 3.8 246.2 0.6 250.6 Commercial 5.3 — — 5.3 210.7 3.6 219.6 Total construction loans 9.4 1.1 0.4 10.9 765.9 7.9 784.7 Residential 3.2 7.3 1.8 12.3 1,562.5 6.4 1,581.2 Agricultural 1.3 — 0.3 1.6 203.6 12.6 217.8 Total real estate loans 23.5 11.4 3.0 37.9 5,717.0 41.9 5,796.8 Consumer: Indirect consumer 5.0 1.2 0.2 6.4 792.6 1.8 800.8 Other consumer 1.1 0.4 0.2 1.7 196.0 0.4 198.1 Credit card 0.6 0.4 0.8 1.8 77.6 — 79.4 Total consumer loans 6.7 2.0 1.2 9.9 1,066.2 2.2 1,078.3 Commercial 4.1 2.0 0.8 6.9 1,315.3 15.0 1,337.2 Agricultural 2.7 0.7 0.2 3.6 259.1 2.1 264.8 Other, including overdrafts — — — — 3.2 — 3.2 Loans held for investment 37.0 16.1 5.2 58.3 8,360.8 61.2 8,480.3 Mortgage loans originated for sale — — — — 37.7 — 37.7 Total loans $ 37.0 $ 16.1 $ 5.2 $ 58.3 $ 8,398.5 $ 61.2 $ 8,518.0 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 Loans from business combinations included in the tables above include certain loans that had evidence of deterioration in credit quality since origination and for which it was probable, at acquisition, that all contractually required payments would not be collected. The following table displays the outstanding unpaid balances and accrual status of loans acquired with credit impairment as of September 30, 2018 and 2017 : As of September 30, 2018 2017 Outstanding balance $ 49.3 $ 46.2 Carrying value Loans on accrual status 35.5 30.8 Total carrying value $ 35.5 $ 30.8 The following table summarizes changes in the accretable yield for loans acquired deemed credit impaired for the three and nine months ended September 30, 2018 and 2017 : Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Beginning balance $ 6.5 $ 7.7 $ 7.3 $ 6.8 Acquisitions 3.2 — 3.2 — Additions — 0.2 0.4 2.1 Accretion income (0.7 ) (0.9 ) (2.4 ) (2.1 ) Reductions due to exit events (0.1 ) (0.1 ) (0.6 ) (1.1 ) Reclassifications from nonaccretable differences 0.6 0.5 1.6 1.7 Ending balance $ 9.5 $ 7.4 $ 9.5 $ 7.4 Acquired loans that met the criteria for nonaccrual of interest prior to acquisition were considered performing upon acquisition. If interest on non-accrual loans had been accrued, such income would have been approximately $0.8 million and $0.9 million for the three months ended September 30, 2018 and 2017 , respectively, and approximately $1.6 million and $1.8 million for the nine months ended September 30, 2018 and 2017 , respectively. The Company considers impaired loans to include all originated loans, except consumer loans, that are risk rated as doubtful, or have been placed on non-accrual status or renegotiated in troubled debt restructurings, and all loans acquired with evidence of deterioration in credit quality and for which it was probable, at acquisition, that the Company would be unable to collect all contractual amounts owed. The following tables present information on the Company’s recorded investment in impaired loans as of dates indicated: As of September 30, 2018 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 29.1 $ 12.5 $ 8.7 $ 21.2 $ 1.7 Construction: Land acquisition & development 10.4 0.7 3.5 4.2 0.2 Residential 0.7 0.2 0.4 0.6 0.1 Commercial 4.4 0.2 3.3 3.5 1.2 Total construction loans 15.5 1.1 7.2 8.3 1.5 Residential 8.8 5.6 2.1 7.7 0.4 Agricultural 12.8 12.6 — 12.6 — Total real estate loans 66.2 31.8 18.0 49.8 3.6 Commercial 24.1 5.2 15.2 20.4 4.4 Agricultural 2.2 1.7 0.5 2.2 0.2 Total $ 92.5 $ 38.7 $ 33.7 $ 72.4 $ 8.2 As of 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 The following table presents the average recorded investment in and income recognized on impaired loans for the periods indicated: Three Months Ended September 30, 2018 2017 Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Real estate $ 54.5 $ — $ 59.9 $ 0.1 Commercial 20.7 — 31.6 — Agricultural 1.9 — 2.3 — Total $ 77.1 $ — $ 93.8 $ 0.1 Nine Months Ended September 30, 2018 2017 Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Real estate $ 54.1 $ 0.1 $ 63.0 $ 0.4 Commercial 22.0 0.1 31.9 0.1 Agricultural 1.6 — 2.6 — Total $ 77.7 $ 0.2 $ 97.5 $ 0.5 The amount of interest income recognized by the Company within the period that the loans were impaired was primarily related to loans modified in a troubled debt restructuring 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 would have been approximately $0.8 million and $0.9 million for the three months ended September 30, 2018 and 2017 , respectively, and approximately $1.6 million and $1.8 million for the nine months ended September 30, 2018 and 2017 , respectively. Collateralized impaired loans are generally recorded at the fair value of the underlying collateral using discounted cash flows, independent appraisals and management estimates based upon current market conditions. For loans measured under the present value of cash flows method, the change in present value attributable to the passage of time, if applicable, is recognized in the provision for loan losses and thus no interest income is recognized. Modifications of performing loans are made in the ordinary course of business and are completed on a case-by-case basis as negotiated with the borrower. Loan modifications typically include interest rate changes, interest only periods of less than twelve months, short-term payment deferrals and extension of amortization periods to provide payment relief. A loan modification is considered a troubled debt restructuring if the borrower is experiencing financial difficulties and the Company, for economic or legal reasons, grants a concession to the borrower that it would not otherwise consider. Certain troubled debt restructurings are on non-accrual status at the time of restructuring and may be returned to accrual status after considering the borrower’s sustained repayment performance in accordance with the restructuring agreement for a period of at least six months and management is reasonably assured of future performance. If the troubled debt restructuring meets these performance criteria and the interest rate granted at the modification is equal to or greater than the rate that the Company was willing to accept at the time of the restructuring for a new loan with comparable risk, then the loan will return to performing status and the accrual of interest will resume, although they continue to be individually evaluated for impairment and disclosed as impaired loans. The Company had loans renegotiated in troubled debt restructurings of $30.3 million as of September 30, 2018 , of which $24.4 million were included in non-accrual loans and $5.9 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 three and nine months ended September 30, 2018 : Number of Notes Type of Concession Principal Balance at Restructure Date Three Months Ended September 30, 2018 Interest only period Extension of term or amortization schedule Interest rate adjustment Other (1) Commercial real estate 3 $ 3.4 $ — $ — $ 0.5 $ 3.9 Total loans restructured during period 3 $ 3.4 $ — $ — $ 0.5 $ 3.9 (1) Other includes concessions that reduce or defer payments for a specified period of time and/or concessions that do not fit into other designated categories. Number of Notes Type of Concession Principal Balance at Restructure Date Nine Months Ended September 30, 2018 Interest only period Extension of term or amortization schedule Interest rate adjustment Other (1) Commercial real estate 5 $ 3.6 $ — $ — $ 0.5 $ 4.1 Total loans restructured during period 5 $ 3.6 $ — $ — $ 0.5 $ 4.1 (1) Other includes concessions that reduce or defer payments for a specified period of time and/or concessions that do not fit into other designated categories. For troubled debt restructurings that were on non-accrual status or otherwise deemed impaired before the modification, a specific reserve may already be recorded. In periods subsequent to modification, the Company continues to evaluate all troubled debt restructurings for possible impairment and recognizes impairment through the allowance. Additionally these loans continue to work their way through the credit cycle through charge-off, pay-off or foreclosure. Financial effects of modifications of troubled debt restructurings may include principal loan forgiveness or other charge-offs directly related to the restructuring. The Company had no charge-offs directly related to modifying troubled debt restructurings during the three and nine months ended September 30, 2018 or 2017 . The Company had no material troubled debt restructurings during the previous 12 months for which there was a payment default during the three and nine months ended September 30, 2018 . The Company considers a payment default to occur on troubled debt restructurings when the loan is 90 days or more past due or was placed on non-accrual status after the modification. At September 30, 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 loan is not currently sufficient, collateral or other sources of repayment are sufficient to satisfy the debt. Continuance of a substandard loan is not warranted unless positive steps are taken to improve the worthiness of the credit. Doubtful — includes loans that exhibit pronounced weaknesses to a point where collection or liquidation in full, on the basis of currently existing facts, conditions and values, is highly questionable and improbable. Doubtful loans are required to be placed on non-accrual status and are assigned specific loss exposure. Company management undertakes the same process for assigning risk ratings to acquired loans as it does for originated loans. Acquired loans rated as substandard or lower or that were on non-accrual status or designated as troubled debt restructurings at the time of acquisition are deemed to be acquired credit impaired loans accounted for under ASC Topic 310-30, regardless of whether they are classified as performing or non-performing loans. The following tables present the Company’s recorded investment in criticized loans by class and credit quality indicator based on the most recent analysis performed as of the dates indicated: As of September 30, 2018 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 108.1 $ 81.4 $ 4.8 $ 194.3 Construction: Land acquisition & development 5.4 7.0 3.3 15.7 Residential 4.1 0.3 0.4 4.8 Commercial 1.5 3.7 3.4 8.6 Total construction loans 11.0 11.0 7.1 29.1 Residential 5.5 11.0 1.1 17.6 Agricultural 8.4 24.6 — 33.0 Total real estate loans 133.0 128.0 13.0 274.0 Consumer: Indirect consumer 0.8 2.2 0.1 3.1 Other consumer 0.4 0.8 0.1 1.3 Total consumer loans 1.2 3.0 0.2 4.4 Commercial 50.6 48.6 11.2 110.4 Agricultural 14.1 21.5 0.5 36.1 Total $ 198.9 $ 201.1 $ 24.9 $ 424.9 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 Other 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	9 Months Ended
	Sep. 30, 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 for the periods indicated: Three Months Ended September 30, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 33.9 $ 7.8 $ 30.6 $ 1.8 $ — $ 74.1 Provision charged to operating expense (0.9 ) 2.4 0.5 — — 2.0 Less loans charged-off (0.7 ) (3.0 ) (1.1 ) — — (4.8 ) Add back recoveries of loans previously charged-off 0.6 1.2 0.5 — — 2.3 Ending balance $ 32.9 $ 8.4 $ 30.5 $ 1.8 $ — $ 73.6 Nine Months Ended September 30, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 31.6 $ 8.7 $ 30.6 $ 1.2 $ — $ 72.1 Provision charged to operating expense 1.4 4.7 0.5 0.4 — 7.0 Less loans charged-off (2.8 ) (8.6 ) (3.7 ) — — (15.1 ) Add back recoveries of loans previously charged-off 2.7 3.6 3.1 0.2 — 9.6 Ending balance $ 32.9 $ 8.4 $ 30.5 $ 1.8 $ — $ 73.6 As of September 30, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Loans individually evaluated for impairment $ 3.6 $ — $ 4.4 $ 0.2 $ — $ 8.2 Loans collectively evaluated for impairment 29.3 8.4 26.1 1.6 — 65.4 Allowance for loan losses $ 32.9 $ 8.4 $ 30.5 $ 1.8 $ — $ 73.6 As of September 30, 2018 Real Estate Consumer Commercial Agriculture Other Total Loans held for investment: Individually evaluated for impairment $ 49.8 $ — $ 20.4 $ 2.2 $ — $ 72.4 Collectively evaluated for impairment 5,747.0 1,078.3 1,316.8 262.6 3.2 8,407.9 Total loans held for investment $ 5,796.8 $ 1,078.3 $ 1,337.2 $ 264.8 $ 3.2 $ 8,480.3 Three Months Ended September 30, 2017 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 33.5 $ 7.6 $ 33.1 $ 1.5 $ — $ 75.7 Provision charged to operating expense (0.7 ) 2.6 1.5 — — 3.4 Less loans charged-off (1.7 ) (3.1 ) (2.6 ) — — (7.4 ) Add back recoveries of loans previously charged-off 0.6 1.0 1.3 — — 2.9 Ending balance $ 31.7 $ 8.1 $ 33.3 $ 1.5 $ — $ 74.6 Nine Months Ended September 30, 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 to operating expense 4.8 5.2 (2.2 ) (0.3 ) — 7.5 Less loans charged-off (3.0 ) (8.1 ) (4.5 ) (0.1 ) — (15.7 ) Add back recoveries of loans previously charged-off 1.3 3.3 1.9 0.1 — 6.6 Ending balance $ 31.7 $ 8.1 $ 33.3 $ 1.5 $ — $ 74.6 As of December 31, 2017 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Loans individually evaluated for impairment $ 6.2 $ — $ 4.4 $ 0.2 $ — $ 10.8 Loans collectively evaluated for impairment 25.4 8.7 26.2 1.0 — 61.3 Allowance for loan losses $ 31.6 $ 8.7 $ 30.6 $ 1.2 $ — $ 72.1 As of December 31, 2017 Real Estate Consumer Commercial Agriculture Other Total Loans held for investment: 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 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 September 30, 2018 and December 31, 2017 , the Company’s allowance for loan losses included $0.6 million and $1.0 million related to loans acquired credit impaired.

Other Real Estate Owned

Other Real Estate Owned	9 Months Ended
	Sep. 30, 2018
Repossessed Assets [Abstract]
Other Real Estate Owned	Other Real Estate Owned Information with respect to the Company’s other real estate owned follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Beginning balance $ 14.9 $ 11.3 $ 10.1 $ 10.0 OREO acquired through acquisition 0.6 — 0.6 1.2 Additions 3.2 1.4 10.6 3.2 Valuation adjustments (0.1 ) (0.2 ) (0.1 ) (0.3 ) Dispositions (1.3 ) (2.1 ) (3.9 ) (3.7 ) Ending balance $ 17.3 $ 10.4 $ 17.3 $ 10.4 The carrying values of foreclosed residential real estate properties included in other real estate owned were $2.6 million and $2.7 million as of September 30, 2018 and December 31, 2017 , respectively. The Company had $2.0 million of consumer mortgage loans collateralized by residential real estate property that were in the process of foreclosure as of September 30, 2018 and none as of December 31, 2017 .

Derivatives and Hedging Activit

Derivatives and Hedging Activities	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative and Hedging Activities	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 September 30, 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. 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. September 30, 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 $ 386.8 $ 11.3 $ 344.2 $ 7.5 Interest rate lock commitments 62.9 1.1 60.7 1.3 Total derivative assets $ 449.7 $ 12.4 $ 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 $ 386.8 $ 11.1 $ 344.2 $ 7.8 Forward loan sales contracts 77.4 0.2 88.8 0.1 Total derivative liabilities $ 464.2 $ 11.3 $ 433.0 $ 7.9 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. During the three and nine months ended September 30, 2018 , the Company did not record any hedge ineffectiveness. 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 September 30, 2018 and December 31, 2017 : September 30, 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 $ 11.3 $ — $ 11.3 $ 1.0 $ 1.8 $ 8.5 Mortgage related derivatives 1.1 — 1.1 — — 1.1 Total derivatives 12.4 — 12.4 1.0 1.8 9.6 Total assets $ 12.4 $ — $ 12.4 $ 1.0 $ 1.8 $ 9.6 Financial Liabilities Interest rate swap contracts $ 11.1 $ — $ 11.1 $ 1.0 $ 10.0 $ 0.1 Mortgage related derivatives 0.2 — 0.2 — — 0.2 Total derivatives 11.3 — 11.3 1.0 10.0 0.3 Repurchase agreements 635.9 — 635.9 — 635.9 — Total liabilities $ 647.2 $ — $ 647.2 $ 1.0 $ 645.9 $ 0.3 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 other non-interest income in the Company’s statements of income for the periods indicated: Three Months Ended September 30, Nine Months Ended September 30, 2018 2018 2017 2018 2017 Derivatives designated as hedges: Amount of loss recognized in other comprehensive income (effective portion) $ — $ (0.7 ) $ — $ (1.1 ) Reclassification adjustment for derivatives net (gains) losses included in income — 1.1 — 1.1 Non-hedging interest rate derivatives: Amount of gain recognized in other non-interest income 0.1 — 0.4 — Amount of net fee income recognized in other non-interest income — 0.2 0.9 0.4 Amount of net gains recognized in mortgage banking revenues — 0.4 — 0.5

Capital Stock

Capital Stock	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Capital Stock	Capital Stock The Company had 38,107,555 shares of Class A common stock and 22,501,994 shares of Class B common stock outstanding as of September 30, 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 . 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. In addition, during the nine months ended September 30, 2018 , the Company issued 11,389 shares of its Class A common stock to directors for their annual service on the Company’s board of directors. The aggregate value of the shares issued to directors of $0.5 million is included in stock-based compensation expense in the accompanying consolidated statements of changes in stockholders’ equity. During the nine months ended September 30, 2018 and 2017 , the Company did not repurchase any shares of its Class A common stock other than stock repurchases which were redemptions of vested restricted shares tendered in lieu of cash for payment of income tax withholding amounts by participants in the Company’s equity compensation plans.

Earnings per Common Share

Earnings per Common Share	9 Months Ended
	Sep. 30, 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 share for the three and nine month periods ended September 30, 2018 and 2017 : Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net income $ 41.4 $ 27.3 $ 119.8 $ 72.3 Weighted average common shares outstanding for basic earnings per share computation 58,254,575 56,094,401 56,951,029 49,514,818 Dilutive effects of stock-based compensation 385,900 436,467 378,998 486,064 Weighted average common shares outstanding for diluted earnings per common share computation 58,640,475 56,530,868 57,330,027 50,000,882 Basic earnings per common share $ 0.71 $ 0.49 $ 2.10 $ 1.46 Diluted earnings per common share $ 0.71 $ 0.48 $ 2.09 $ 1.45 Anti-dilutive unvested time restricted stock 4,376 — 120,553 94,210 The Company had 154,176 and 174,696 shares of unvested restricted stock as of September 30, 2018 and 2017 , 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	9 Months Ended
	Sep. 30, 2018
Banking and Thrift [Abstract]
Regulatory Capital	Regulatory Capital On July 2, 2013, the Board of Governors of the Federal Reserve Bank issued a final rule implementing a revised regulatory capital framework for U.S. banks in accordance with the Basel III international accord and satisfying related mandates under the Dodd-Frank Wall Street Reform and Consumer Protection Act. The revised regulatory capital framework (the “Basel III Capital Rules”) substantially revised the risk-based capital requirements applicable to bank holding companies and depository institutions by defining the components of capital and addressing other issues affecting the numerator in banking institutions’ regulatory capital ratios, addressing risk weights and other issues affecting the denominator in banking institutions’ regulatory capital ratios and replacing the existing risk-weighting approach with a more risk-sensitive approach. The Basel III Capital Rules became effective for the Company on January 1, 2015, subject to a phase-in period for certain provisions. The capital conservation buffer required under Basel III began to phase in starting January 1, 2016 and will be fully implemented on January 1, 2019. As of September 30, 2018 and December 31, 2017 , the Company exceeded all capital adequacy requirements to which it is subject. Actual capital amounts and ratios for the Company and its subsidiary Banks, as of September 30, 2018 and December 31, 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) September 30, 2018 Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total risk-based capital: Consolidated $ 1,254.8 12.76 % $ 971.1 9.875 % $ 1,032.6 10.50 % $ 983.4 10.00 % FIB 1,107.7 12.28 890.5 9.875 946.9 10.50 901.8 10.00 INB 77.6 9.86 77.7 9.875 82.7 10.50 78.7 10.00 Tier 1 risk-based capital: Consolidated 1,181.2 12.01 774.5 7.875 835.9 8.50 786.7 8.00 FIB 1,034.0 11.47 710.2 7.875 766.5 8.50 721.5 8.00 INB 77.6 9.86 62.0 7.875 66.9 8.50 63.0 8.00 Common equity tier 1 risk-based capital: Consolidated 1,096.8 11.15 626.9 6.375 688.4 7.00 639.2 6.50 FIB 1,034.0 11.47 574.9 6.375 631.3 7.00 586.2 6.50 INB 77.6 9.86 50.2 6.375 55.1 7.00 51.2 6.50 Leverage capital ratio: Consolidated 1,181.2 9.73 485.6 4.000 485.6 4.00 607.0 5.00 FIB 1,034.0 8.77 471.8 4.000 471.8 4.00 589.7 5.00 INB 77.6 9.81 31.7 4.000 31.7 4.00 39.6 5.00 Actual Adequately Capitalized Basel III Phase-In Schedule Adequately Capitalized Basel III Fully Phased-In Well Capitalized (1) December 31, 2017 Amount Ratio Amount Ratio Amount Ratio Amount Ratio 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 requirements to be deemed “well capitalized” are only applicable to FIB and INB. However, the Company manages its capital position as if the requirements apply to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies In the normal course of business, the Company is involved in various other claims and litigation. In the opinion of management, following consultation with legal counsel, the ultimate liability or disposition thereof of all other claims and litigation is not expected to have a material adverse effect on the consolidated financial condition, results of operations or liquidity of the Company. As of September 30, 2018 , the Company had commitments under construction contracts of $5.4 million . On October 11, 2018, the Company entered into a definitive agreement to acquire all of the outstanding stock of Idaho Independent Bank ("IIBK"), a community bank headquartered in Coeur d' Alene, Idaho with 11 banking offices across Idaho, in an all-stock transaction valued at approximately $181.3 million in aggregate, or $22.73 per share of IIBK stock. The Company believes the transaction, if completed on the terms contemplated, will complement the Company's footprint and will provide the Company with an expanded presence in several high-growth markets, including Boise and Coeur d’Alene, Idaho. 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 approval and IIBK shareholder approval. On October 11, 2018, the Company also entered into a definitive agreement to acquire all of the outstanding stock of Community 1st Bank ("CMYF"), a community bank headquartered in Post Falls, Idaho with three banking offices in North Idaho, in an all-stock transaction valued at approximately $21.5 million in aggregate, or $17.20 per share of CMYF stock. The Company believes the transaction, if completed on the terms contemplated, will complement the Company’s footprint and will provide the Company with an expanded presence in North Idaho's high-growth markets. 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 approval and CMYF shareholder approval. 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 $0.5 million of sold residential mortgage loans with recourse provisions still in effect as of September 30, 2018 .

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk	9 Months Ended
	Sep. 30, 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. Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the commitment contract. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. At September 30, 2018 , commitments to extend credit to existing and new borrowers approximated $2,515.4 million , which included $701.8 million on unused credit card lines and $942.1 million with commitment maturities beyond one year. Standby letters of credit are conditional commitments issued by the Company to guarantee the performance of a customer to a third party. At September 30, 2018 , the Company had outstanding standby letters of credit of $45.0 million . The estimated fair value of the obligation undertaken by the Company in issuing the standby letters of credit is included in other liabilities in the Company’s consolidated balance sheet.

Other Comprehensive Income_Loss

Other Comprehensive Income/Loss	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Other Comprehensive Income/Loss	Other Comprehensive Income/Loss The gross amounts of each component of other comprehensive income and the related tax effects are as follows: Pre-tax Tax Expense (Benefit) Net of Tax Three Months Ended September 30, 2018 2017 2018 2017 2018 2017 Investment securities available-for sale: Change in net unrealized gains during period $ (6.3 ) $ (1.8 ) $ (1.7 ) $ (0.8 ) $ (4.6 ) $ (1.0 ) Reclassification adjustment for net gains included in net income — (0.8 ) — (0.3 ) — (0.5 ) Change in unamortized loss on available- for-sale securities transferred into held-to- maturity 0.5 0.5 0.1 0.2 0.4 0.3 Unrealized (gain) loss on derivatives — (0.6 ) — (0.3 ) — (0.3 ) Reclassification adjustment for derivatives net (gains) losses included in income — 1.1 — 0.5 — 0.6 Defined benefits post-retirement benefit plan: Change in net actuarial (gain) loss (0.2 ) (0.2 ) — (0.1 ) (0.2 ) (0.1 ) Total other comprehensive income (loss) $ (6.0 ) $ (1.8 ) $ (1.6 ) $ (0.8 ) $ (4.4 ) $ (1.0 ) Pre-tax Tax Expense (Benefit) Net of Tax Nine Months Ended September 30, 2018 2017 2018 2017 2018 2017 Investment securities available-for sale: Change in net unrealized gains during period $ (33.9 ) $ 15.6 $ (8.9 ) $ 6.1 $ (25.0 ) $ 9.5 Reclassification adjustment for net gains included in net income — (0.8 ) — (0.3 ) — (0.5 ) Change in unamortized loss on available- for-sale securities transferred into held-to- maturity 1.5 1.4 0.4 0.6 1.1 0.8 Unrealized (gain) loss on derivatives — (1.1 ) — (0.4 ) — (0.7 ) Reclassification adjustment for derivatives net (gains) losses included in income — 1.1 — 0.4 — 0.7 Defined benefits post-retirement benefit plan: Change in net actuarial (gain) loss (0.5 ) (1.1 ) (0.1 ) (0.4 ) (0.4 ) (0.7 ) Total other comprehensive income (loss) $ (32.9 ) $ 15.1 $ (8.6 ) $ 6.0 $ (24.3 ) $ 9.1 The components of accumulated other comprehensive loss, net of related tax effects, are as follows: September 30, December 31, Net unrealized gain (loss) on investment securities available-for-sale $ (40.3 ) $ (13.3 ) Net unrealized gain (loss) on derivatives — 1.3 Net actuarial gain (loss) on defined benefit post-retirement benefit plans 0.9 — Net accumulated other comprehensive gain (loss) $ (39.4 ) $ (12.0 )

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 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. The Company’s policy is to recognize transfers between levels as of the end of the reporting period. There were no transfers between Level 1 and Level 2 during the three and nine months ended September 30, 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. Loans Held for Sale. Fair value measurements for loans held for sale are obtained from an independent pricing service. The fair value measurements consider observable data that may include binding contracts or quotes or bids from third party investors as well as loan level pricing adjustments. Interest Rate Swap Contracts. Fair values for derivative interest rate swap contracts are based upon the estimated amounts to settle the contracts considering current interest rates and are calculated using discounted cash flows that are observable or that can be corroborated by observable market data. The inputs used to determine fair value include the 3 month LIBOR forward curve to estimate variable rate cash inflows and the federal funds effective swap rate to estimate the discount rate. The estimated variable rate cash inflows are compared to the fixed rate outflows and such difference is discounted to a present value to estimate the fair value of the interest rate swaps. The change in the value of derivative assets attributable to basis risk, or the risk that offsetting investments in a hedging strategy will not experience price changes in entirely opposite directions from each other, was not significant in the reported periods. The Company also obtains and compares the reasonableness of the pricing from an independent third party. Interest Rate Lock Commitments. Fair value measurements for interest rate lock commitments are obtained from an independent pricing service. The fair value measurements consider observable data that may include prices available from secondary market investors taking into consideration various characteristics of the loan, including the loan amount, interest rate, value of the servicing and loan to value ratio, among other things. Observable data is then adjusted to reflect changes in interest rates, the Company’s estimated pull-through rate and estimated direct costs necessary to complete the commitment into a closed loan net of origination and processing fees collected from the borrower. Forward Loan Sales Contracts. The fair value measurements for forward loan sales contracts are obtained from an independent pricing service. The fair value measurements consider observable data that includes sales of similar loans. Deferred Compensation Plan Assets and Liabilities. The fair values of deferred compensation plan assets are based primarily on the use of independent, market-based data to reflect a value that would be reasonably expected in an orderly transaction between market participants at the measurement date. These investments are in the same funds and purchased in the same amounts as the participants’ selected investments, which represent the underlying liabilities to plan participants. Deferred compensation plan liabilities are recorded at amounts due to participants, based on the fair value of participants’ selected investments. Financial assets and liabilities measured at fair value on a recurring basis are as follows: Fair Value Measurements at Reporting Date Using As of September 30, 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 $ 3.0 $ — $ 3.0 $ — Obligations of U.S. government agencies 560.9 — 560.9 — U.S. agencies mortgage-backed securities & collateralized mortgage obligations 1,425.6 — 1,425.6 — Private mortgage-backed securities 73.0 — 73.0 — Corporate securities 92.1 — 92.1 — Other investments 4.2 — 4.2 — Loans held for sale 37.7 — 37.7 — Derivative assets: Interest rate swap contracts 11.3 — 11.3 — Interest rate lock commitments 1.1 — 1.1 — Derivative liabilities: Interest rate swap contracts 11.1 — 11.1 — Forward loan sale contracts 0.2 — 0.2 — Deferred compensation plan assets 13.0 — 13.0 — Deferred compensation plan liabilities 13.0 — 13.0 — 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. agencies 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 September 30, 2018 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Impaired loans $ 28.7 $ — $ — $ 28.7 Other real estate owned 0.6 — — 0.6 Long-lived assets to be disposed of by sale 3.5 — — 3.5 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) Impaired loans $ 32.6 $ — $ — $ 32.6 Other real estate owned 1.3 — — 1.3 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 September 30, 2018 , certain impaired loans with a carrying value of $ 43.5 million were reduced by specific valuation allowance allocations of $ 8.2 million and partial loan charge-offs of $ 6.6 million resulting in a reported fair value of $ 28.7 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. The Company had no material write downs on OREO properties during the nine months ended September 30, 2018 and 2017 . 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 September 30, 2018 , the Company had long-lived assets to be disposed of by sale with carrying values aggregating $4.0 million , which was reduced by write-downs of $0.5 million , resulting in a fair value of $3.5 million . As of December 31, 2017 , long-lived assets to be disposed of by sale with carrying values of $0.8 million , had zero write-downs resulting in a 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: Fair Value As of September 30, 2018 December 31, 2017 Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 28.7 $ 32.6 Appraisal Appraisal adjustment 0.0% - 78.1% (26.1%) Other real estate owned 0.6 1.3 Appraisal Appraisal adjustment 8.0% - 96.2% (11.6%) Long-lived assets to be disposed of by sale 3.5 0.8 Appraisal Appraisal adjustment 0.0% - 0.0% 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 September 30, 2018 Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets: Cash and cash equivalents $ 965.0 $ 965.0 $ 965.0 $ — $ — Investment debt securities available-for-sale 2,158.8 2,158.8 — 2,158.8 — Investment debt securities held-to-maturity 417.8 407.4 — 407.4 — Accrued interest receivable 48.0 48.0 — 48.0 — Mortgage servicing rights, net 27.0 41.8 — 41.8 — Loans held for sale 37.7 37.7 — 37.7 — Net loans held for investment 8,480.3 8,406.8 — 8,378.1 28.7 Derivative assets 12.4 12.4 — 12.4 — Deferred compensation plan assets 13.0 13.0 — 13.0 — Total financial assets $ 12,160.0 $ 12,090.9 $ 965.0 $ 11,097.2 $ 28.7 Financial liabilities: Total deposits, excluding time deposits $ 9,560.3 $ 9,560.3 $ 9,560.3 $ — $ — Time deposits 1,285.3 1,269.2 — 1,269.2 — Securities sold under repurchase agreements 635.9 635.9 — 635.9 — Other borrowed funds 1.5 1.5 — 1.5 — Accrued interest payable 6.7 6.7 — 6.7 — Long-term debt 22.4 19.6 — 19.6 — Subordinated debentures held by subsidiary trusts 86.9 82.4 — 82.4 — Derivative liabilities 11.3 11.3 — 11.3 — Deferred compensation plan liabilities 13.0 13.0 — 13.0 — Total financial liabilities $ 11,623.3 $ 11,599.9 $ 9,560.3 $ 2,039.6 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2017 Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets: Cash and cash equivalents $ 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 — Net loans held for investment 7,542.2 7,298.8 — 7,266.2 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 $ —

Recent Authoritative Accounting

Recent Authoritative Accounting Guidance	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Recent Authoritative Accounting Guidance	Recent Authoritative Accounting Guidance ASU 2014-09, “Revenue from Contracts with Customers (Topic 606).” 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 (Subtopic 825-10): 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. The Company has determined the new guidance in ASU 2016-02 will have an immaterial impact on its consolidated financial statements, results of operations or liquidity. ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” The amendments in ASU 2016-13 require a financial asset or group of financial assets measured at amortized cost basis to be presented on a company’s financial statements at the net amount expected to be collected based on historical experience, current conditions and reasonable and supportable forecasts. ASU 2016-13 requires a company’s income statement to reflect the measurement of credit losses for newly recognized financial assets as well as the expected increases or decreases of expected credit losses that have taken place during the period. The amendments in ASU 2016-13 require that the allowance for credit losses for purchased financial assets with a more-than-insignificant amount of credit deterioration since origination be measured at amortized cost basis with the initial allowance for credit losses added to the purchase price rather than being reported as a credit loss expense. ASU 2016-13 also requires that credit losses relating to available-for-sale debt securities be recorded through an allowance for credit losses. The amendments in ASU 2016-13 are effective for the Company for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. The amendments will be applied through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period. A prospective transition approach is required for debt securities for which other-than-temporary impairment was recognized before the effective date. Amounts previously recognized in accumulated other comprehensive income as of the date of adoption that relate to improvement in cash flows expected to be collected will continue to be accreted into income over the remaining life of the asset. Recoveries of amounts previously written off relating to improvements in cash flows after the date of adoption will be recorded in earnings when received. The Company is currently evaluating the new guidance to determine the impact it will have on its consolidated financial statements, results of operations and liquidity. ASU 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 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 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 2017-07, “Compensation – Retirement Benefits (Topic 715): 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 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. The Company plans to adopt ASU 2017-12 on January 1, 2019. 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. 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. 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.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 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 SEC. On October 24, 2018 , the Company declared a quarterly dividend to common shareholders of $0.28 per share, to be paid on November 19, 2018 to shareholders of record as of November 9, 2018 . No other events requiring recognition or disclosure were identified.

Basis of Presentation Basis of

Basis of Presentation Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition Accounting Standards Codification (“ASC”) 606, Revenue from Contracts with Customers (“ASC 606”), establishes principles for reporting information about the nature, amount, timing and uncertainty of revenue and cash flows arising from the entity’s contracts to provide goods or services to customers. The core principle requires an entity to recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration that it expects to be entitled to receive in exchange for those goods or services recognized as performance obligations are satisfied. The new revenue recognition standards became effective for the Company on January 1, 2018. The majority of our revenue-generating transactions are not subject to ASC 606, including revenue generated from financial instruments, such as our loans, guarantees, derivatives and investment securities, as well as revenue related to our mortgage servicing activities, as these activities are subject to other GAAP discussed elsewhere within our disclosures. ASC 606 is applicable to non-interest revenue streams such as wealth management and trust fee income, service charges on deposit accounts, interchange and other fees, and annuity and insurance commissions. However, the recognition of these revenue streams did not change significantly upon the adoption of ASC 606. Substantially all of the Company’s revenue is generated from contracts with customers. Descriptions of our revenue-generating activities that are within the scope of ASC 606 are discussed below: • Wealth management and trust fee income - this 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 - these 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 - these 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 - these 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.

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	Acquisitions Idaho Independent Bank. On October 11, 2018, the Company entered into a definitive agreement to acquire all of the outstanding stock of Idaho Independent Bank ("IIBK"), a community bank headquartered in Coeur d' Alene, Idaho with 11 banking offices across Idaho, in an all-stock transaction valued at approximately $ 181.3 million in aggregate, or $ 22.73 per share of IIBK stock. The Company believes the transaction, if completed on the terms contemplated, will complement the Company's footprint and will provide the Company with an expanded presence in several high-growth markets, including Boise and Coeur d’Alene, Idaho. 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 approval and IIBK shareholder approval. Community 1 st Bank. On October 11, 2018, the Company also entered into a definitive agreement to acquire all of the outstanding stock of Community 1st Bank ("CMYF"), a community bank headquartered in Post Falls, Idaho with three banking offices in North Idaho, in an all-stock transaction valued at approximately $21.5 million in aggregate, or $ 17.20 per share of CMYF stock. The Company believes the transaction, if completed on the terms contemplated, will complement the Company’s footprint and will provide the Company with an expanded presence in North Idaho's high-growth markets. 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 approval and CMYF shareholder approval. 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 will merge 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 $100.8 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 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 Deferred tax assets, net 1.2 (1.6 ) (5) (0.4 ) Other assets 29.3 (9.7 ) (6) 19.6 Total assets acquired 801.9 (5.0 ) 796.9 Liabilities assumed: Deposits 696.1 0.2 (7) 696.3 Accounts payable and accrued expense 8.1 (0.4 ) (8) 7.7 Long term debt 13.0 — 13.0 Trust preferred securities 5.2 (0.8 ) (9) 4.4 Total liabilities assumed 722.4 (1.0 ) 721.4 Net assets acquired $ 79.5 $ (4.0 ) $ 75.5 Consideration paid: Cash $ 3.0 Class A common stock 173.3 Total consideration paid 176.3 Goodwill $ 100.8 Explanation of fair value adjustments and the removal of previously recorded fair value marks recorded by Northwest: (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 the write-off of pre-existing deferred tax assets and purchase accounting adjustments as a result of the acquisition. (6) Adjustment consists of reductions to the fair value of other items, including the removal of Northwest previously recorded goodwill. (7) Increase in book value of time deposits to their estimated fair values based upon interest rates of similar time deposits with similar terms on the date of acquisition based upon valuation from an independent accounting and advisory firm. (8) Decrease due to the write-off of off balance sheet reserves. (9) Write down of the book value of debt to the estimated fair values on the date of acquisition based upon favorable interest rates in the market. 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 ten years. The Company acquired certain loans that are subject to Accounting Standards Codification ("ASC") Topic 310-30 "Loans and Debt Securities Acquired with Deteriorated Credit Quality." ASC Topic 310-30 provides recognition, measurement and disclosure guidance for acquired loans that have evidence of deterioration in credit quality since origination for which it is probable, at acquisition, the Company will be unable to collect all contractual amounts owed. For loans that meet the criteria stipulated in ASC Topic 310-30, the excess of all cash flows expected at acquisition over the initial fair value of the loans acquired ("accretable yield") is amortized to interest income over the expected remaining lives of the underlying loans using the effective interest method. The accretable yield will fluctuate due to changes in (i) estimated lives of underling credit-impaired loans, (ii) assumptions regarding future principal and interest amounts collected, and (iii) indices used to fair value variable rate loans. Information regarding Northwest loans acquired deemed credit-impaired as of the August 16, 2018 acquisition date are as follows: Contractually required principal and interest payments $ 27.5 Contractual cash flows not expected to be collected (“non-accretable discount”) 4.4 Cash flows expected to be collected 23.1 Interest component of cash flows expected to be collected (“accretable discount”) 3.2 Fair value of acquired credit-impaired loans $ 19.9 Information regarding Northwest acquired loans not deemed credit-impaired at the August 16, 2018 acquisition date are as follows: Contractually required principal and interest payments $ 894.8 Contractual cash flows not expected to be collected 26.1 Fair value at acquisition $ 693.2 Unaudited pro forma consolidated revenues and net income as if the Northwest acquisition had occurred as of January 1, 2018, are not presented because the effect of this acquisition was not considered significant. The accompanying consolidated statements of income for the three and nine months ended September 30, 2018 , 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 will continued to operate as INB until November 9, 2018 at which point INB’s operations will be integrated with the Company’s operations, and INB will merge with FIB. 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 loss (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.
Schedule of Acquired Loans with Credit Impairment	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 Contractually required principal and interest payments $ 27.5 Contractual cash flows not expected to be collected (“non-accretable discount”) 4.4 Cash flows expected to be collected 23.1 Interest component of cash flows expected to be collected (“accretable discount”) 3.2 Fair value of acquired credit-impaired loans $ 19.9 The following table displays the outstanding unpaid balances and accrual status of loans acquired with credit impairment as of September 30, 2018 and 2017 : As of September 30, 2018 2017 Outstanding balance $ 49.3 $ 46.2 Carrying value Loans on accrual status 35.5 30.8 Total carrying value $ 35.5 $ 30.8 The following table summarizes changes in the accretable yield for loans acquired deemed credit impaired for the three and nine months ended September 30, 2018 and 2017 : Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Beginning balance $ 6.5 $ 7.7 $ 7.3 $ 6.8 Acquisitions 3.2 — 3.2 — Additions — 0.2 0.4 2.1 Accretion income (0.7 ) (0.9 ) (2.4 ) (2.1 ) Reductions due to exit events (0.1 ) (0.1 ) (0.6 ) (1.1 ) Reclassifications from nonaccretable differences 0.6 0.5 1.6 1.7 Ending balance $ 9.5 $ 7.4 $ 9.5 $ 7.4
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 Information regarding Northwest acquired loans not deemed credit-impaired at the August 16, 2018 acquisition date are as follows: Contractually required principal and interest payments $ 894.8 Contractual cash flows not expected to be collected 26.1 Fair value at acquisition $ 693.2
Summary of 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. Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Interest income $ 121.2 $ 108.7 $ 341.8 $ 312.1 Non-interest income 36.2 38.3 109.0 116.2 Total revenues $ 157.4 $ 147.0 $ 450.8 $ 428.3 Net income $ 41.4 $ 34.9 $ 119.8 $ 94.0 EPS - basic $ 0.71 $ 0.52 $ 2.10 $ 1.55 EPS - diluted 0.71 0.51 2.09 1.53
Summary of Pre-tax Merger Related Expenses	The Company recorded $3.1 million of Northwest related pre-tax acquisition related expenses for the three months ended September 30, 2018 and $5.4 million of Northwest and Cascade related pre-tax acquisition related expenses for the nine months ended September 30, 2018 . These costs are incorporated in non-interest expenses in the Company’s consolidated statements of income. Three Months Ended September 30, 2018 Nine Months Ended September 30, 2018 Legal and Professional Fees $ 2.4 $ 3.0 Employee Expenses — 0.1 Technology Conversion and Contract Termination 0.5 2.0 Other 0.2 0.3 Total Acquisition Related Expenses $ 3.1 $ 5.4

Goodwill and Intangibles (Table

Goodwill and Intangibles (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill [Line Items]
Schedule of Goodwill [Table Text Block]	As of September 30, 2018 2017 Net carrying value at beginning of nine month period $ 444.7 $ 212.8 Addition to provisional goodwill from acquisition 100.8 232.2 Measurement period adjustment to previously recorded goodwill 0.9 — Net carrying value at end of period $ 546.4 $ 445.0
Schedule of Finite-Lived Intangible Assets	Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 CDI, net, beginning of period $ 45.6 $ 52.8 $ 49.1 $ 9.6 Established through acquisitions or provisional adjustments 15.7 — 15.7 48.0 Reductions due to sale of accounts — — — (3.1 ) CDI current period amortization (2.0 ) (1.9 ) (5.5 ) (3.6 ) Total CDI, net, end of period $ 59.3 $ 50.9 $ 59.3 $ 50.9
Schedule of Future Amortization Expense	The following table provides the estimated future CDI amortization expense: Years Ending December 31, 2018 remaining $ 2.4 2019 8.9 2020 8.1 2021 7.5 2022 6.9 Thereafter 25.5 Total $ 59.3

Investment Securities (Tables)

Investment Securities (Tables)	9 Months Ended
	Sep. 30, 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: September 30, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale: U.S. Treasury notes $ 3.0 $ — $ — $ 3.0 Obligations of U.S. government agencies 576.2 — (15.3 ) 560.9 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 1,462.0 1.4 (37.8 ) 1,425.6 Private mortgage-backed securities 74.8 — (1.8 ) 73.0 Corporate securities 93.0 0.1 (1.0 ) 92.1 Other investments 4.2 — — 4.2 Total $ 2,213.2 $ 1.5 $ (55.9 ) $ 2,158.8 September 30, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to-Maturity: State, county and municipal securities $ 153.7 $ 1.2 $ (1.7 ) $ 153.2 Obligations of U.S. government agencies 19.7 — (0.3 ) 19.4 U.S agency residential mortgage-backed securities & collateralized mortgage obligations 198.0 7.8 (16.8 ) 189.0 Corporate securities 46.3 — (0.6 ) 45.7 Other investments 0.1 — — 0.1 Total $ 417.8 $ 9.0 $ (19.4 ) $ 407.4 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 & collateralized mortgage obligations 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 September 30, 2018 and December 31, 2017 : Less than 12 Months 12 Months or More Total September 30, 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 $ 199.9 $ (4.8 ) $ 346.5 $ (10.5 ) $ 546.4 $ (15.3 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 851.8 (19.2 ) 448.2 (18.6 ) 1,300.0 (37.8 ) Private mortgage-backed securities 49.9 (1.2 ) 22.9 (0.6 ) 72.8 (1.8 ) Corporate securities 38.7 (0.9 ) 1.9 (0.1 ) 40.6 (1.0 ) Total $ 1,140.3 $ (26.1 ) $ 819.5 $ (29.8 ) $ 1,959.8 $ (55.9 ) Less than 12 Months 12 Months or More Total September 30, 2018 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity: State, county and municipal securities $ 59.8 $ (1.0 ) $ 26.2 $ (0.7 ) $ 86.0 $ (1.7 ) Obligations of U.S. government agencies 9.6 (0.2 ) 9.8 (0.1 ) 19.4 (0.3 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 85.8 (13.1 ) 44.0 (3.7 ) 129.8 (16.8 ) Corporate securities 30.9 (0.4 ) 8.8 (0.2 ) 39.7 (0.6 ) Total $ 186.1 $ (14.7 ) $ 88.8 $ (4.7 ) $ 274.9 $ (19.4 ) 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 ) Obligations of U.S. government agencies 9.7 — 9.9 (0.2 ) 19.6 (0.2 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 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 ) Total $ 180.6 $ (9.7 ) $ 87.7 $ (3.0 ) $ 268.3 $ (12.7 )
Maturities of Investment Securities	Maturities of investment securities at September 30, 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 September 30, 2018 Amortized Cost Estimated Fair Value Amortized Cost Estimated Fair Value Within one year $ 511.5 $ 501.8 $ 70.6 $ 68.9 After one year but within five years 1,444.9 1,407.9 222.9 216.0 After five years but within ten years 189.3 183.3 100.7 99.9 After ten years 67.5 65.8 23.6 22.6 Total $ 2,213.2 $ 2,158.8 $ 417.8 $ 407.4

Loans (Tables)

Loans (Tables)	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Schedule of Loans by Class	The following table presents loans by class as of the dates indicated: September 30, December 31, Real estate loans: Commercial $ 3,213.1 $ 2,822.9 Construction: Land acquisition & development 314.5 348.7 Residential 250.6 240.2 Commercial 219.6 119.4 Total construction loans 784.7 708.3 Residential 1,581.2 1,487.4 Agricultural 217.8 158.2 Total real estate loans 5,796.8 5,176.8 Consumer: Indirect consumer 800.8 784.7 Other consumer 198.1 175.1 Credit card 79.4 74.6 Total consumer loans 1,078.3 1,034.4 Commercial 1,337.2 1,215.4 Agricultural 264.8 136.2 Other, including overdrafts 3.2 4.9 Loans held for investment 8,480.3 7,567.7 Mortgage loans held for sale 37.7 46.6 Total loans $ 8,518.0 $ 7,614.3
Schedule of Recorded Investment in Past Due Loans by Class	The following tables present the Company’s recorded investment and contractual aging of the Company’s recorded investment in loans by class as of the dates indicated. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of September 30, 2018 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 9.6 $ 3.0 $ 0.5 $ 13.1 $ 3,185.0 $ 15.0 $ 3,213.1 Construction: Land acquisition & development 0.7 0.7 0.4 1.8 309.0 3.7 314.5 Residential 3.4 0.4 — 3.8 246.2 0.6 250.6 Commercial 5.3 — — 5.3 210.7 3.6 219.6 Total construction loans 9.4 1.1 0.4 10.9 765.9 7.9 784.7 Residential 3.2 7.3 1.8 12.3 1,562.5 6.4 1,581.2 Agricultural 1.3 — 0.3 1.6 203.6 12.6 217.8 Total real estate loans 23.5 11.4 3.0 37.9 5,717.0 41.9 5,796.8 Consumer: Indirect consumer 5.0 1.2 0.2 6.4 792.6 1.8 800.8 Other consumer 1.1 0.4 0.2 1.7 196.0 0.4 198.1 Credit card 0.6 0.4 0.8 1.8 77.6 — 79.4 Total consumer loans 6.7 2.0 1.2 9.9 1,066.2 2.2 1,078.3 Commercial 4.1 2.0 0.8 6.9 1,315.3 15.0 1,337.2 Agricultural 2.7 0.7 0.2 3.6 259.1 2.1 264.8 Other, including overdrafts — — — — 3.2 — 3.2 Loans held for investment 37.0 16.1 5.2 58.3 8,360.8 61.2 8,480.3 Mortgage loans originated for sale — — — — 37.7 — 37.7 Total loans $ 37.0 $ 16.1 $ 5.2 $ 58.3 $ 8,398.5 $ 61.2 $ 8,518.0 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 Acquired Loans with Credit Impairment	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 Contractually required principal and interest payments $ 27.5 Contractual cash flows not expected to be collected (“non-accretable discount”) 4.4 Cash flows expected to be collected 23.1 Interest component of cash flows expected to be collected (“accretable discount”) 3.2 Fair value of acquired credit-impaired loans $ 19.9 The following table displays the outstanding unpaid balances and accrual status of loans acquired with credit impairment as of September 30, 2018 and 2017 : As of September 30, 2018 2017 Outstanding balance $ 49.3 $ 46.2 Carrying value Loans on accrual status 35.5 30.8 Total carrying value $ 35.5 $ 30.8 The following table summarizes changes in the accretable yield for loans acquired deemed credit impaired for the three and nine months ended September 30, 2018 and 2017 : Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Beginning balance $ 6.5 $ 7.7 $ 7.3 $ 6.8 Acquisitions 3.2 — 3.2 — Additions — 0.2 0.4 2.1 Accretion income (0.7 ) (0.9 ) (2.4 ) (2.1 ) Reductions due to exit events (0.1 ) (0.1 ) (0.6 ) (1.1 ) Reclassifications from nonaccretable differences 0.6 0.5 1.6 1.7 Ending balance $ 9.5 $ 7.4 $ 9.5 $ 7.4
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: As of September 30, 2018 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 29.1 $ 12.5 $ 8.7 $ 21.2 $ 1.7 Construction: Land acquisition & development 10.4 0.7 3.5 4.2 0.2 Residential 0.7 0.2 0.4 0.6 0.1 Commercial 4.4 0.2 3.3 3.5 1.2 Total construction loans 15.5 1.1 7.2 8.3 1.5 Residential 8.8 5.6 2.1 7.7 0.4 Agricultural 12.8 12.6 — 12.6 — Total real estate loans 66.2 31.8 18.0 49.8 3.6 Commercial 24.1 5.2 15.2 20.4 4.4 Agricultural 2.2 1.7 0.5 2.2 0.2 Total $ 92.5 $ 38.7 $ 33.7 $ 72.4 $ 8.2 As of 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 The following table presents the average recorded investment in and income recognized on impaired loans for the periods indicated: Three Months Ended September 30, 2018 2017 Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Real estate $ 54.5 $ — $ 59.9 $ 0.1 Commercial 20.7 — 31.6 — Agricultural 1.9 — 2.3 — Total $ 77.1 $ — $ 93.8 $ 0.1
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 September 30, 2018 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 108.1 $ 81.4 $ 4.8 $ 194.3 Construction: Land acquisition & development 5.4 7.0 3.3 15.7 Residential 4.1 0.3 0.4 4.8 Commercial 1.5 3.7 3.4 8.6 Total construction loans 11.0 11.0 7.1 29.1 Residential 5.5 11.0 1.1 17.6 Agricultural 8.4 24.6 — 33.0 Total real estate loans 133.0 128.0 13.0 274.0 Consumer: Indirect consumer 0.8 2.2 0.1 3.1 Other consumer 0.4 0.8 0.1 1.3 Total consumer loans 1.2 3.0 0.2 4.4 Commercial 50.6 48.6 11.2 110.4 Agricultural 14.1 21.5 0.5 36.1 Total $ 198.9 $ 201.1 $ 24.9 $ 424.9 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 Other 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)	9 Months Ended
	Sep. 30, 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 for the periods indicated: Three Months Ended September 30, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 33.9 $ 7.8 $ 30.6 $ 1.8 $ — $ 74.1 Provision charged to operating expense (0.9 ) 2.4 0.5 — — 2.0 Less loans charged-off (0.7 ) (3.0 ) (1.1 ) — — (4.8 ) Add back recoveries of loans previously charged-off 0.6 1.2 0.5 — — 2.3 Ending balance $ 32.9 $ 8.4 $ 30.5 $ 1.8 $ — $ 73.6 Nine Months Ended September 30, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 31.6 $ 8.7 $ 30.6 $ 1.2 $ — $ 72.1 Provision charged to operating expense 1.4 4.7 0.5 0.4 — 7.0 Less loans charged-off (2.8 ) (8.6 ) (3.7 ) — — (15.1 ) Add back recoveries of loans previously charged-off 2.7 3.6 3.1 0.2 — 9.6 Ending balance $ 32.9 $ 8.4 $ 30.5 $ 1.8 $ — $ 73.6 As of September 30, 2018 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Loans individually evaluated for impairment $ 3.6 $ — $ 4.4 $ 0.2 $ — $ 8.2 Loans collectively evaluated for impairment 29.3 8.4 26.1 1.6 — 65.4 Allowance for loan losses $ 32.9 $ 8.4 $ 30.5 $ 1.8 $ — $ 73.6 As of September 30, 2018 Real Estate Consumer Commercial Agriculture Other Total Loans held for investment: Individually evaluated for impairment $ 49.8 $ — $ 20.4 $ 2.2 $ — $ 72.4 Collectively evaluated for impairment 5,747.0 1,078.3 1,316.8 262.6 3.2 8,407.9 Total loans held for investment $ 5,796.8 $ 1,078.3 $ 1,337.2 $ 264.8 $ 3.2 $ 8,480.3 Three Months Ended September 30, 2017 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 33.5 $ 7.6 $ 33.1 $ 1.5 $ — $ 75.7 Provision charged to operating expense (0.7 ) 2.6 1.5 — — 3.4 Less loans charged-off (1.7 ) (3.1 ) (2.6 ) — — (7.4 ) Add back recoveries of loans previously charged-off 0.6 1.0 1.3 — — 2.9 Ending balance $ 31.7 $ 8.1 $ 33.3 $ 1.5 $ — $ 74.6 Nine Months Ended September 30, 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 to operating expense 4.8 5.2 (2.2 ) (0.3 ) — 7.5 Less loans charged-off (3.0 ) (8.1 ) (4.5 ) (0.1 ) — (15.7 ) Add back recoveries of loans previously charged-off 1.3 3.3 1.9 0.1 — 6.6 Ending balance $ 31.7 $ 8.1 $ 33.3 $ 1.5 $ — $ 74.6 As of December 31, 2017 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Loans individually evaluated for impairment $ 6.2 $ — $ 4.4 $ 0.2 $ — $ 10.8 Loans collectively evaluated for impairment 25.4 8.7 26.2 1.0 — 61.3 Allowance for loan losses $ 31.6 $ 8.7 $ 30.6 $ 1.2 $ — $ 72.1 As of December 31, 2017 Real Estate Consumer Commercial Agriculture Other Total Loans held for investment: 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

Other Real Estate Owned (Tables

Other Real Estate Owned (Tables)	9 Months Ended
	Sep. 30, 2018
Repossessed Assets [Abstract]
Other Real Estate Owned Roll Forward	Information with respect to the Company’s other real estate owned follows: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Beginning balance $ 14.9 $ 11.3 $ 10.1 $ 10.0 OREO acquired through acquisition 0.6 — 0.6 1.2 Additions 3.2 1.4 10.6 3.2 Valuation adjustments (0.1 ) (0.2 ) (0.1 ) (0.3 ) Dispositions (1.3 ) (2.1 ) (3.9 ) (3.7 ) Ending balance $ 17.3 $ 10.4 $ 17.3 $ 10.4

Derivatives and Hedging Activ_2

Derivatives and Hedging Activities (Tables)	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amounts and Estimated Fair Values of Derivatives	The notional amounts and estimated fair values of the Company’s derivatives are presented in the following table. Fair value estimates are obtained from third parties and are based on pricing models. September 30, 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 $ 386.8 $ 11.3 $ 344.2 $ 7.5 Interest rate lock commitments 62.9 1.1 60.7 1.3 Total derivative assets $ 449.7 $ 12.4 $ 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 $ 386.8 $ 11.1 $ 344.2 $ 7.8 Forward loan sales contracts 77.4 0.2 88.8 0.1 Total derivative liabilities $ 464.2 $ 11.3 $ 433.0 $ 7.9
Offsetting Assets and Liabilities	The following table illustrates the potential effect of the Company’s master netting arrangements, by type of financial instrument, on the Company’s consolidated balance sheets as of September 30, 2018 and December 31, 2017 : September 30, 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 $ 11.3 $ — $ 11.3 $ 1.0 $ 1.8 $ 8.5 Mortgage related derivatives 1.1 — 1.1 — — 1.1 Total derivatives 12.4 — 12.4 1.0 1.8 9.6 Total assets $ 12.4 $ — $ 12.4 $ 1.0 $ 1.8 $ 9.6 Financial Liabilities Interest rate swap contracts $ 11.1 $ — $ 11.1 $ 1.0 $ 10.0 $ 0.1 Mortgage related derivatives 0.2 — 0.2 — — 0.2 Total derivatives 11.3 — 11.3 1.0 10.0 0.3 Repurchase agreements 635.9 — 635.9 — 635.9 — Total liabilities $ 647.2 $ — $ 647.2 $ 1.0 $ 645.9 $ 0.3 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, Effect on Other Comprehensive Income (Loss)	The following table presents the pre-tax gains or losses related to derivative contracts that were recorded in other non-interest income in the Company’s statements of income for the periods indicated: Three Months Ended September 30, Nine Months Ended September 30, 2018 2018 2017 2018 2017 Derivatives designated as hedges: Amount of loss recognized in other comprehensive income (effective portion) $ — $ (0.7 ) $ — $ (1.1 ) Reclassification adjustment for derivatives net (gains) losses included in income — 1.1 — 1.1 Non-hedging interest rate derivatives: Amount of gain recognized in other non-interest income 0.1 — 0.4 — Amount of net fee income recognized in other non-interest income — 0.2 0.9 0.4 Amount of net gains recognized in mortgage banking revenues — 0.4 — 0.5

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	9 Months Ended
	Sep. 30, 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 share for the three and nine month periods ended September 30, 2018 and 2017 : Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Net income $ 41.4 $ 27.3 $ 119.8 $ 72.3 Weighted average common shares outstanding for basic earnings per share computation 58,254,575 56,094,401 56,951,029 49,514,818 Dilutive effects of stock-based compensation 385,900 436,467 378,998 486,064 Weighted average common shares outstanding for diluted earnings per common share computation 58,640,475 56,530,868 57,330,027 50,000,882 Basic earnings per common share $ 0.71 $ 0.49 $ 2.10 $ 1.46 Diluted earnings per common share $ 0.71 $ 0.48 $ 2.09 $ 1.45 Anti-dilutive unvested time restricted stock 4,376 — 120,553 94,210

Regulatory Capital (Tables)

Regulatory Capital (Tables)	9 Months Ended
	Sep. 30, 2018
Banking and Thrift [Abstract]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations	Actual capital amounts and ratios for the Company and its subsidiary Banks, as of September 30, 2018 and December 31, 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) September 30, 2018 Amount Ratio Amount Ratio Amount Ratio Amount Ratio Total risk-based capital: Consolidated $ 1,254.8 12.76 % $ 971.1 9.875 % $ 1,032.6 10.50 % $ 983.4 10.00 % FIB 1,107.7 12.28 890.5 9.875 946.9 10.50 901.8 10.00 INB 77.6 9.86 77.7 9.875 82.7 10.50 78.7 10.00 Tier 1 risk-based capital: Consolidated 1,181.2 12.01 774.5 7.875 835.9 8.50 786.7 8.00 FIB 1,034.0 11.47 710.2 7.875 766.5 8.50 721.5 8.00 INB 77.6 9.86 62.0 7.875 66.9 8.50 63.0 8.00 Common equity tier 1 risk-based capital: Consolidated 1,096.8 11.15 626.9 6.375 688.4 7.00 639.2 6.50 FIB 1,034.0 11.47 574.9 6.375 631.3 7.00 586.2 6.50 INB 77.6 9.86 50.2 6.375 55.1 7.00 51.2 6.50 Leverage capital ratio: Consolidated 1,181.2 9.73 485.6 4.000 485.6 4.00 607.0 5.00 FIB 1,034.0 8.77 471.8 4.000 471.8 4.00 589.7 5.00 INB 77.6 9.81 31.7 4.000 31.7 4.00 39.6 5.00 Actual Adequately Capitalized Basel III Phase-In Schedule Adequately Capitalized Basel III Fully Phased-In Well Capitalized (1) December 31, 2017 Amount Ratio Amount Ratio Amount Ratio Amount Ratio 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 requirements to be deemed “well capitalized” are only applicable to FIB and INB. However, the Company manages its capital position as if the requirements apply to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis.

Other Comprehensive Income_Lo_2

Other Comprehensive Income/Loss (Tables)	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Schedule of Comprehensive Income (Loss)	The gross amounts of each component of other comprehensive income and the related tax effects are as follows: Pre-tax Tax Expense (Benefit) Net of Tax Three Months Ended September 30, 2018 2017 2018 2017 2018 2017 Investment securities available-for sale: Change in net unrealized gains during period $ (6.3 ) $ (1.8 ) $ (1.7 ) $ (0.8 ) $ (4.6 ) $ (1.0 ) Reclassification adjustment for net gains included in net income — (0.8 ) — (0.3 ) — (0.5 ) Change in unamortized loss on available- for-sale securities transferred into held-to- maturity 0.5 0.5 0.1 0.2 0.4 0.3 Unrealized (gain) loss on derivatives — (0.6 ) — (0.3 ) — (0.3 ) Reclassification adjustment for derivatives net (gains) losses included in income — 1.1 — 0.5 — 0.6 Defined benefits post-retirement benefit plan: Change in net actuarial (gain) loss (0.2 ) (0.2 ) — (0.1 ) (0.2 ) (0.1 ) Total other comprehensive income (loss) $ (6.0 ) $ (1.8 ) $ (1.6 ) $ (0.8 ) $ (4.4 ) $ (1.0 ) Pre-tax Tax Expense (Benefit) Net of Tax Nine Months Ended September 30, 2018 2017 2018 2017 2018 2017 Investment securities available-for sale: Change in net unrealized gains during period $ (33.9 ) $ 15.6 $ (8.9 ) $ 6.1 $ (25.0 ) $ 9.5 Reclassification adjustment for net gains included in net income — (0.8 ) — (0.3 ) — (0.5 ) Change in unamortized loss on available- for-sale securities transferred into held-to- maturity 1.5 1.4 0.4 0.6 1.1 0.8 Unrealized (gain) loss on derivatives — (1.1 ) — (0.4 ) — (0.7 ) Reclassification adjustment for derivatives net (gains) losses included in income — 1.1 — 0.4 — 0.7 Defined benefits post-retirement benefit plan: Change in net actuarial (gain) loss (0.5 ) (1.1 ) (0.1 ) (0.4 ) (0.4 ) (0.7 ) Total other comprehensive income (loss) $ (32.9 ) $ 15.1 $ (8.6 ) $ 6.0 $ (24.3 ) $ 9.1
Schedule of Accumulated Other Comprehensive Income (Loss)	The components of accumulated other comprehensive loss, net of related tax effects, are as follows: September 30, December 31, Net unrealized gain (loss) on investment securities available-for-sale $ (40.3 ) $ (13.3 ) Net unrealized gain (loss) on derivatives — 1.3 Net actuarial gain (loss) on defined benefit post-retirement benefit plans 0.9 — Net accumulated other comprehensive gain (loss) $ (39.4 ) $ (12.0 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis	Financial assets and liabilities measured at fair value on a recurring basis are as follows: Fair Value Measurements at Reporting Date Using As of September 30, 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 $ 3.0 $ — $ 3.0 $ — Obligations of U.S. government agencies 560.9 — 560.9 — U.S. agencies mortgage-backed securities & collateralized mortgage obligations 1,425.6 — 1,425.6 — Private mortgage-backed securities 73.0 — 73.0 — Corporate securities 92.1 — 92.1 — Other investments 4.2 — 4.2 — Loans held for sale 37.7 — 37.7 — Derivative assets: Interest rate swap contracts 11.3 — 11.3 — Interest rate lock commitments 1.1 — 1.1 — Derivative liabilities: Interest rate swap contracts 11.1 — 11.1 — Forward loan sale contracts 0.2 — 0.2 — Deferred compensation plan assets 13.0 — 13.0 — Deferred compensation plan liabilities 13.0 — 13.0 — 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. agencies 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 September 30, 2018 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Impaired loans $ 28.7 $ — $ — $ 28.7 Other real estate owned 0.6 — — 0.6 Long-lived assets to be disposed of by sale 3.5 — — 3.5 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) Impaired loans $ 32.6 $ — $ — $ 32.6 Other real estate owned 1.3 — — 1.3 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: Fair Value As of September 30, 2018 December 31, 2017 Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 28.7 $ 32.6 Appraisal Appraisal adjustment 0.0% - 78.1% (26.1%) Other real estate owned 0.6 1.3 Appraisal Appraisal adjustment 8.0% - 96.2% (11.6%) Long-lived assets to be disposed of by sale 3.5 0.8 Appraisal Appraisal adjustment 0.0% - 0.0% 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 September 30, 2018 Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets: Cash and cash equivalents $ 965.0 $ 965.0 $ 965.0 $ — $ — Investment debt securities available-for-sale 2,158.8 2,158.8 — 2,158.8 — Investment debt securities held-to-maturity 417.8 407.4 — 407.4 — Accrued interest receivable 48.0 48.0 — 48.0 — Mortgage servicing rights, net 27.0 41.8 — 41.8 — Loans held for sale 37.7 37.7 — 37.7 — Net loans held for investment 8,480.3 8,406.8 — 8,378.1 28.7 Derivative assets 12.4 12.4 — 12.4 — Deferred compensation plan assets 13.0 13.0 — 13.0 — Total financial assets $ 12,160.0 $ 12,090.9 $ 965.0 $ 11,097.2 $ 28.7 Financial liabilities: Total deposits, excluding time deposits $ 9,560.3 $ 9,560.3 $ 9,560.3 $ — $ — Time deposits 1,285.3 1,269.2 — 1,269.2 — Securities sold under repurchase agreements 635.9 635.9 — 635.9 — Other borrowed funds 1.5 1.5 — 1.5 — Accrued interest payable 6.7 6.7 — 6.7 — Long-term debt 22.4 19.6 — 19.6 — Subordinated debentures held by subsidiary trusts 86.9 82.4 — 82.4 — Derivative liabilities 11.3 11.3 — 11.3 — Deferred compensation plan liabilities 13.0 13.0 — 13.0 — Total financial liabilities $ 11,623.3 $ 11,599.9 $ 9,560.3 $ 2,039.6 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2017 Carrying Amount Estimated Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets: Cash and cash equivalents $ 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 — Net loans held for investment 7,542.2 7,298.8 — 7,266.2 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 $ —

Acquisitions - Business Combin

Acquisitions - Business Combination (Narrative) (Details) $ / shares in Units, $ in Millions	Oct. 11, 2018USD ($)$ / shares	Aug. 16, 2018USD ($)$ / sharesshares	May 30, 2017USD ($)$ / sharesshares	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)segment	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Goodwill				$ 546.4	$ 445	$ 546.4	$ 445	$ 444.7	$ 212.8
Acquisition related expenses				3.1	13	5.4	23.9
Net income				$ 41.4	$ 27.3	$ 119.8	$ 72.3
Bank of the Cascades
Business Acquisition [Line Items]
Number of banking offices acquired			46
Core Deposits
Business Acquisition [Line Items]
Estimated useful lives of related deposits						10 years
Northwest Bank Acquisition, as Recorded by the Company [Member]
Business Acquisition [Line Items]
Core deposit intangible assets		$ 15.7
Cash paid by First Interstate in connection with merger		$ 3
Inland Northwest Bank
Business Acquisition [Line Items]
Number of banking offices acquired		20
Cash Paid For Northwest Warrants		$ 3
Total consideration exchanged in connection with the merger		176.3
Goodwill		$ 100.8
Number of operating segments | segment						1
Inland Northwest Bank | Class A Common Stock
Business Acquisition [Line Items]
Business acquisition conversion share rate | shares		0.516
Number of shares issued in connection with Cascade merger | shares		3,840,000
Price per share of First Interstate Class A common stock (in dollars per share) | $ / shares		$ 45.15
Inland Northwest Bank | Core Deposits
Business Acquisition [Line Items]
Estimated useful lives of related deposits		10 years
Bank of the Cascades
Business Acquisition [Line Items]
Business acquisition cash conversion amount (in dollars per share) | $ / shares			$ 1.91
Number of shares issued in connection with Cascade merger | shares			11,300,000
Cash paid by First Interstate in connection with merger			$ 155
Total consideration exchanged in connection with the merger			541
Cash Paid Related To Cascade Options						$ 9.3
Cash Paid For Cascade Unvested Restricted Stock			2.2
Expense related to restricted awards excluded from consideration			2.4
Restricted stock expense included in consideration						$ 5.5
Goodwill			$ 232.8
Number of operating segments | segment						1
Bank of the Cascades | Class A Common Stock
Business Acquisition [Line Items]
Business acquisition conversion share rate | shares			0.14864
Price per share of First Interstate Class A common stock (in dollars per share) | $ / shares			$ 34.30
Shares Issued For Cascade Unvested Restricted Stock | shares			168
Bank of the Cascades | Core Deposits
Business Acquisition [Line Items]
Estimated useful lives of related deposits			10 years
Subsequent Event | Community 1st Bank [Member]
Business Acquisition [Line Items]
Estimate value per share of Acquisition | $ / shares	$ 17.20
Subsequent Event | Inland Northwest Bank
Business Acquisition [Line Items]
Estimate value per share of Acquisition | $ / shares	$ 22.73
Subsequent Event | Idaho Independent Bank [Member]
Business Acquisition [Line Items]
Number of banking offices acquired	11
Estimate of Payments to Acquire Businesses, Gross	$ 181.3
Subsequent Event | Community 1st Bank [Member]
Business Acquisition [Line Items]
Number of banking offices acquired	3
Estimate of Payments to Acquire Businesses, Gross	$ 21.5

Acquisitions - Schedule of Rec

Acquisitions - Schedule of Recognized Identifiable Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions		Aug. 16, 2018	May 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Class A common stock		$ 173.3
Goodwill				$ 546.4	$ 445	$ 546.4	$ 444.7	$ 212.8
Net increase to goodwill				$ 0.9	$ 0
Northwest Bank Acquisition, As Recorded By Inland Northwest Bank [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		31.2
Investment securities		3.1
Loans held for investment		727.9
Allowance for loan loss		(8)
Premises and equipment		14.5
Other real estate owned (“OREO”)		0.3
Core deposit intangible assets		2.4
Deferred tax assets, net		1.2
Other assets		29.3
Total assets acquired		801.9
Deposits		696.1
Accounts Payable and Accrued Expense		8.1
Long term debt		13
Trust preferred securities		5.2
Total liabilities assumed		722.4
Net assets acquired		79.5
Northwest Bank Acquisition, Fair Value Adjustments [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		0
Investment securities		0
Loans held for investment	[1]	(14.8)
Allowance for loan loss	[2]	8
Premises and equipment	[3]	(0.5)
Other real estate owned (“OREO”)		0.3
Core deposit intangible assets	[4]	13.3
Deferred tax assets, net	[5]	(1.6)
Other assets	[6]	(9.7)
Total assets acquired		(5)
Deposits	[7]	0.2
Accounts Payable and Accrued Expense	[8]	(0.4)
Long term debt	[9]	0
Trust preferred securities	[10]	(0.8)
Total liabilities assumed		(1)
Net assets acquired		(4)
Northwest Bank Acquisition, as Recorded by the Company [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		31.2
Investment securities		3.1
Loans held for investment		713.1
Allowance for loan loss		0
Premises and equipment		14
Other real estate owned (“OREO”)		0.6
Core deposit intangible assets		15.7
Deferred tax assets, net		(0.4)
Other assets		19.6
Total assets acquired		796.9
Deposits	[9]	696.3
Accounts Payable and Accrued Expense	[9]	7.7
Long term debt	[9]	13
Trust preferred securities	[9]	4.4
Total liabilities assumed		721.4
Net assets acquired		75.5
Cash		3
Class A common stock		173.3
Inland Northwest Bank
Business Acquisition [Line Items]
Total consideration paid		176.3
Goodwill		$ 100.8
Cascade Bank Acquisition, As Recorded By Cascade Bank [Member]
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 loss			(24)
Premises and equipment			46.6
Other real estate owned (“OREO”)			1.2
Core deposit intangible assets			0
Deferred tax assets, net			47.6
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 [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			0
Investment securities	[11]		4.9
Loans held for investment	[12]		(31.7)
Mortgage loans held for sale			0
Allowance for loan loss	[13]		24
Premises and equipment	[14]		0.1
Other real estate owned (“OREO”)			0
Core deposit intangible assets	[15]		48
Deferred tax assets, net	[16]		(20.9)
Other assets			2.1
Total assets acquired			26.5
Deposits	[9]		(0.9)
Accounts Payable and Accrued Expense	[17]		1.9
Total liabilities assumed			1
Net assets acquired			25.5
Bank of the Cascades
Business Acquisition [Line Items]
Cash			155
Total consideration paid			541
Goodwill			232.8
Cascade Bank Acquisition, as Recorded by the Company [Member]
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 loss			0
Premises and equipment			46.7
Other real estate owned (“OREO”)			1.2
Core deposit intangible assets			48
Deferred tax assets, net			26.7
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
Class A common stock			386
Total consideration paid			$ 541
Net increase to goodwill						$ 0.9
[1]	(1) Write down of the book value of loans to their estimated fair values. The fair value of the loans was estimated using cash flow projections based on the remaining maturity and repricing terms, adjusted for estimated future credit losses and prepayments and discounted to present value using a risk-adjusted market rate for similar loans. The fair value of collateral dependent loans acquired with deteriorated credit quality was estimated based on the Company’s analysis of the fair value of each loan’s underlying collateral, discounted using market-derived rates of return with consideration given to the period of time and costs associated with foreclosure and disposition of the collateral.
[2]	(2) Adjustment to remove the Northwest allowance for loan losses at acquisition date, as the credit risk is included in the fair value adjustment for loans receivable described in (1) above.
[3]	(3) Write down of the book value of premises and equipment to their estimated fair values on the date of acquisition based upon broker’s opinion of value.
[4]	(4) Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm.
[5]	(5) Adjustment consists of the write-off of pre-existing deferred tax assets and purchase accounting adjustments as a result of the acquisition.
[6]	(6) Adjustment consists of reductions to the fair value of other items, including the removal of Northwest previously recorded goodwill.
[7]	(7) Increase in book value of time deposits to their estimated fair values based upon interest rates of similar time deposits with similar terms on the date of acquisition based upon valuation from an independent accounting and advisory firm.
[8]	(8) Decrease due to the write-off of off balance sheet reserves.
[9]	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.
[10]	(9) Write down of the book value of debt to the estimated fair values on the date of acquisition based upon favorable interest rates in the market.
[11]	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.
[12]	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.
[13]	Adjustment to remove the Cascade allowance for loan losses at acquisition date, as the credit risk is accounted for in the fair value adjustment for loans receivable described in (2) above.
[14]	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.
[15]	Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm.
[16]	Adjustment consists of the write-off of pre-existing deferred tax assets as a result of the acquisition.
[17]	Increase in fair value due to credit card incentive program, unfavorable leases, write-off of balance sheet reserve, and swap liability offset.

Acquisitions - Schedule of Acq

Acquisitions - Schedule of Acquired loans with credit impairment (Details) - USD ($) $ in Millions	Aug. 16, 2018	May 30, 2017
Bank of the Cascades
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
Inland Northwest Bank
Business Acquisition [Line Items]
Contractually required principal and interest payments	$ 27.5
Contractual cash flows not expected to be collected (“non-accretable discount”)	4.4
Cash flows expected to be collected	23.1
Interest component of cash flows expected to be collected (“accretable discount”)	3.2
Fair value of acquired credit-impaired loans	$ 19.9

Acquisitions - Schedule of A_2

Acquisitions - Schedule of Acquired Loans not Deemed to Have Credit Impairment (Details) - USD ($) $ in Millions	Aug. 16, 2018	May 30, 2017
Inland Northwest Bank
Business Acquisition [Line Items]
Contractually required principal and interest payments	$ 894.8
Contractual cash flows not expected to be collected	26.1
Fair value at acquisition	$ 693.2
Bank of the Cascades
Business Acquisition [Line Items]
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

Acquisitions - Business Acquis

Acquisitions - Business Acquisition, Pro Forma Information (Details) - Bank of the Cascades - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Interest income	$ 121.2	$ 108.7	$ 341.8	$ 312.1
Non-interest income	36.2	38.3	109	116.2
Total revenues	157.4	147	450.8	428.3
Net income	$ 41.4	$ 34.9	$ 119.8	$ 94
EPS - basic (in dollars per share)	$ 0.71	$ 0.52	$ 2.10	$ 1.55
EPS - diluted (in dollars per share)	$ 0.71	$ 0.51	$ 2.09	$ 1.53

Acquisitions - Summary of Pre-

Acquisitions - Summary of Pre-tax Merger Related Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs, Legal Fees	$ 2.4		$ 3
Business Combination, Acquisition Related Costs, Employee Expense	0		0.1
Business Combination, Acquisition Related Costs, Technology and Contract Termination	0.5		2
Business Combination, Acquisition Related Costs, Other Expenses	0.2		0.3
Acquisition related expenses	$ 3.1	$ 13	$ 5.4	$ 23.9

Goodwill and Intangibles - Narr

Goodwill and Intangibles - Narrative (Details) - USD ($)	May 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill		$ 546,400,000	$ 445,000,000	$ 546,400,000	$ 444,700,000	$ 212,800,000
Addition to provisional goodwill from acquisition		100,800,000	232,200,000
Measurement period adjustment to previously recorded goodwill		$ 900,000	$ 0
Impairment of goodwill				$ 0
Bank of the Cascades
Goodwill [Line Items]
Goodwill	$ 232,800,000
Core Deposits
Goodwill [Line Items]
Weighted average useful lives of related deposits				10 years
Core Deposits | Bank of the Cascades
Goodwill [Line Items]
Weighted average useful lives of related deposits	10 years

Goodwill and Intangibles - Sche

Goodwill and Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Finite-lived Intangible Assets Acquired	$ 15.7	$ 0	$ 15.7	$ 48
Finite-Lived Intangible Assets, Period Increase (Decrease)	0	0	0	(3.1)
Goodwill [Roll Forward]
CDI, net, beginning of period	45.6	52.8	49.1	9.6
CDI current period amortization	(2)	(1.9)	(5.5)	(3.6)
Total CDI, net, at September 30	$ 59.3	$ 50.9	$ 59.3	$ 50.9

Goodwill and Intangibles - Sc_2

Goodwill and Intangibles - Schedule of Future Amortization Expense (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
2018 remaining	$ 2.4
2,018	8.9
2,019	8.1
2,020	7.5
2,021	6.9
Thereafter	25.5
Finite-Lived Intangible Assets, Net	$ 59.3	$ 45.6	$ 49.1	$ 50.9	$ 52.8	$ 9.6

Investment Securities - Amorti

Investment Securities - Amortized Cost and Approximate Fair Values of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Available-for-Sale:
Amortized Cost	$ 2,213,200	$ 2,229,300
Gross Unrealized Gains	1,500	3,900
Gross Unrealized Losses	(55,900)	(24,500)
Estimated Fair Value	2,158,800	2,208,700
Held-to-Maturity:
Amortized Cost	417,800	484,500
Gross Unrealized Gains	9,000	11,500
Gross Unrealized Losses	(19,400)	(12,700)
Estimated Fair Value	407,400	483,300
U.S. Treasury notes
Available-for-Sale:
Amortized Cost	3,000	3,200
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	3,000	3,200
Obligations of U.S. government agencies
Available-for-Sale:
Amortized Cost	576,200	569,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(15,300)	(8,000)
Estimated Fair Value	560,900	561,500
Held-to-Maturity:
Amortized Cost	19,700	19,800
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(300)	(200)
Estimated Fair Value	19,400	19,600
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Amortized Cost	1,462,000	1,474,100
Gross Unrealized Gains	1,400	3,800
Gross Unrealized Losses	(37,800)	(15,400)
Estimated Fair Value	1,425,600	1,462,500
Held-to-Maturity:
Amortized Cost	198,000	230,500
Gross Unrealized Gains	7,800	8,800
Gross Unrealized Losses	(16,800)	(11,600)
Estimated Fair Value	189,000	227,700
Private mortgage-backed securities
Available-for-Sale:
Amortized Cost	74,800	91,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,800)	(800)
Estimated Fair Value	73,000	90,700
State, county and municipal securities
Held-to-Maturity:
Amortized Cost	153,700	172,400
Gross Unrealized Gains	1,200	2,600
Gross Unrealized Losses	(1,700)	(600)
Estimated Fair Value	153,200	174,400
Corporate securities
Available-for-Sale:
Amortized Cost	93,000	88,000
Gross Unrealized Gains	100	100
Gross Unrealized Losses	(1,000)	(300)
Estimated Fair Value	92,100	87,800
Held-to-Maturity:
Amortized Cost	46,300	61,600
Gross Unrealized Gains	0	100
Gross Unrealized Losses	(600)	(300)
Estimated Fair Value	45,700	61,400
Other investments
Available-for-Sale:
Amortized Cost	4,200	3,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	4,200	3,000
Other Investments
Held-to-Maturity:
Amortized Cost	100	200
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 100	$ 200

Investment Securities - Gross

Investment Securities - Gross Unrealized Losses and Fair Values of Investment Securities (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)security	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)security	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)security
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	$ 1,140,300,000		$ 1,140,300,000		$ 1,080,300,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	(26,100,000)		(26,100,000)		(10,700,000)
Available-for-Sale, 12 Months or More, Fair Value	819,500,000		819,500,000		705,300,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(29,800,000)		(29,800,000)		(13,800,000)
Available-for-Sale, Total Fair Value	1,959,800,000		1,959,800,000		1,785,600,000
Available-for-Sale, Total Gross Unrealized Losses	(55,900,000)		(55,900,000)		(24,500,000)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value	186,100,000		186,100,000		180,600,000
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses	(14,700,000)		(14,700,000)		(9,700,000)
Held-to-Maturity, 12 Months or More, Fair Value	88,800,000		88,800,000		87,700,000
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses	(4,700,000)		(4,700,000)		(3,000,000)
Held-to-Maturity, Total Fair Value	274,900,000		274,900,000		268,300,000
Held-to-Maturity, Total Gross Unrealized Losses	$ (19,400,000)		$ (19,400,000)		$ (12,700,000)
Investment securities in an unrealized loss position (securities) | security	720		720		581
Impairment loss	$ 0	$ 0	$ 0	$ 0
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	199,900,000		199,900,000		$ 284,900,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	(4,800,000)		(4,800,000)		(3,400,000)
Available-for-Sale, 12 Months or More, Fair Value	346,500,000		346,500,000		266,100,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(10,500,000)		(10,500,000)		(4,600,000)
Available-for-Sale, Total Fair Value	546,400,000		546,400,000		551,000,000
Available-for-Sale, Total Gross Unrealized Losses	(15,300,000)		(15,300,000)		(8,000,000)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value	30,900,000		30,900,000		76,400,000
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses	(400,000)		(400,000)		(9,100,000)
Held-to-Maturity, 12 Months or More, Fair Value	8,800,000		8,800,000		60,500,000
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses	(200,000)		(200,000)		(2,500,000)
Held-to-Maturity, Total Fair Value	39,700,000		39,700,000		136,900,000
Held-to-Maturity, Total Gross Unrealized Losses	(600,000)		(600,000)		(11,600,000)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	851,800,000		851,800,000		670,100,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	(19,200,000)		(19,200,000)		(6,200,000)
Available-for-Sale, 12 Months or More, Fair Value	448,200,000		448,200,000		439,200,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(18,600,000)		(18,600,000)		(9,200,000)
Available-for-Sale, Total Fair Value	1,300,000,000		1,300,000,000		1,109,300,000
Available-for-Sale, Total Gross Unrealized Losses	(37,800,000)		(37,800,000)		(15,400,000)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value	85,800,000		85,800,000		41,200,000
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses	(13,100,000)		(13,100,000)		(200,000)
Held-to-Maturity, 12 Months or More, Fair Value	44,000,000		44,000,000		5,000,000
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses	(3,700,000)		(3,700,000)		(100,000)
Held-to-Maturity, Total Fair Value	129,800,000		129,800,000		46,200,000
Held-to-Maturity, Total Gross Unrealized Losses	(16,800,000)		(16,800,000)		(300,000)
Private mortgage-backed securities
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	49,900,000		49,900,000		74,000,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	(1,200,000)		(1,200,000)		(800,000)
Available-for-Sale, 12 Months or More, Fair Value	22,900,000		22,900,000		0
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(600,000)		(600,000)		0
Available-for-Sale, Total Fair Value	72,800,000		72,800,000		74,000,000
Available-for-Sale, Total Gross Unrealized Losses	(1,800,000)		(1,800,000)		(800,000)
State, county and municipal securities
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value	59,800,000		59,800,000		53,300,000
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses	(1,000,000)		(1,000,000)		(400,000)
Held-to-Maturity, 12 Months or More, Fair Value	26,200,000		26,200,000		12,300,000
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses	(700,000)		(700,000)		(200,000)
Held-to-Maturity, Total Fair Value	86,000,000		86,000,000		65,600,000
Held-to-Maturity, Total Gross Unrealized Losses	(1,700,000)		(1,700,000)		(600,000)
Corporate securities
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value	38,700,000		38,700,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses	(900,000)		(900,000)
Available-for-Sale, 12 Months or More, Fair Value	1,900,000		1,900,000
Available-for-Sale, 12 Months or More, Gross Unrealized Losses	(100,000)		(100,000)
Available-for-Sale, Total Fair Value	40,600,000		40,600,000
Available-for-Sale, Total Gross Unrealized Losses	(1,000,000)		(1,000,000)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months, Fair Value	9,600,000		9,600,000		9,700,000
Held-to-Maturity, Less Than 12 Months, Gross Unrealized Losses	(200,000)		(200,000)		0
Held-to-Maturity, 12 Months or More, Fair Value	9,800,000		9,800,000		9,900,000
Held-to-Maturity, 12 Months or More, Gross Unrealized Losses	(100,000)		(100,000)		(200,000)
Held-to-Maturity, Total Fair Value	19,400,000		19,400,000		19,600,000
Held-to-Maturity, Total Gross Unrealized Losses	$ (300,000)		$ (300,000)		(200,000)
Other Investments
Available-for-Sale:
Available-for-Sale, Less than 12 Months, Fair Value					51,300,000
Available-for-sale, Less than 12 Months, Gross Unrealized Losses					(300,000)
Available-for-Sale, 12 Months or More, Fair Value					0
Available-for-Sale, 12 Months or More, Gross Unrealized Losses					0
Available-for-Sale, Total Fair Value					51,300,000
Available-for-Sale, Total Gross Unrealized Losses					$ (300,000)

Investment Securities - Maturi

Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity
Available-for-Sale Amortized Cost, Within One Year	$ 511,500
Available-for-Sale Amortized Cost, After One Year but Within Five Years	1,444,900
Available-for-Sale Amortized Cost, After Five Years but Within Ten Years	189,300
Available-for-Sale Amortized Cost, After Ten Years	67,500
Amortized Cost	2,213,200	$ 2,229,300
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity
Available-for-Sale Estimated Fair Value, Within One Year	501,800
Available-for-Sale Estimated Fair Value, After One Year but Within Five Years	1,407,900
Available-for-Sale Estimated Fair Value, After Five Years but Within Ten Years	183,300
Available-for-Sale Estimated Fair Value, After Ten Years	65,800
Available-for-Sale, Estimated Fair Value	2,158,800	2,208,700
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount
Held-to-Maturity Amortized Cost, Within One Year	70,600
Held-to-Maturity Amortized Cost, After One Year but Within Five Years	222,900
Held-to-Maturity Amortized Cost, After Five Years but Within Ten Years	100,700
Held-to-Maturity Amortized Cost, After Ten Years	23,600
Amortized Cost	417,800	484,500
Held-to-maturity Securities, Debt Maturities, Fair Value, Rolling Maturity
Held-to-Maturity Estimated Fair Value, Within One Year	68,900
Held-to-Maturity Estimated Fair Value, After One Year but Within Five Years	216,000
Held-to-Maturity Estimated Fair Value, After Five Years but Within Ten Years	99,900
Held-to-Maturity Estimated Fair Value, After Ten Years	22,600
Held-to-Maturity, Estimated Fair Value	407,400	$ 483,300
Callable Within One Year
Available-for-sale Securities and Held-to-maturity Securities
Amortized cost of investment securities callable after one year but within five years	107,400
Fair value of investment securities callable after one year but within five years	$ 105,100

Loans - Schedule of Recorded I

Loans - Schedule of Recorded Investment in Past Due Loans by Class (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans	$ 8,480.3	$ 7,567.7
Mortgage loans held for sale	37.7	46.6
Total loans	8,518	7,614.3
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	13.1	3.7
Current Loans	3,185	2,792.4
Non-accrual Loans	15	26.8
Total Loans	3,213.1	2,822.9
Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.8	7.9
Current Loans	309	337.8
Non-accrual Loans	3.7	3
Total Loans	314.5	348.7
Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	3.8	2.1
Current Loans	246.2	236.4
Non-accrual Loans	0.6	1.7
Total Loans	250.6	240.2
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	5.3	0
Current Loans	210.7	115.6
Non-accrual Loans	3.6	3.8
Total Loans	219.6	119.4
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	10.9	10
Current Loans	765.9	689.8
Non-accrual Loans	7.9	8.5
Total Loans	784.7	708.3
Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	12.3	15.1
Current Loans	1,562.5	1,464.1
Non-accrual Loans	6.4	8.2
Total Loans	1,581.2	1,487.4
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.6	0.5
Current Loans	203.6	154.3
Non-accrual Loans	12.6	3.4
Total Loans	217.8	158.2
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	37.9	29.3
Current Loans	5,717	5,100.6
Non-accrual Loans	41.9	46.9
Total Loans	5,796.8	5,176.8
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	6.4	10.3
Current Loans	792.6	772.6
Non-accrual Loans	1.8	1.8
Total Loans	800.8	784.7
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.7	2.2
Current Loans	196	172.6
Non-accrual Loans	0.4	0.3
Total Loans	198.1	175.1
Credit card
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.8	2.2
Current Loans	77.6	72.4
Non-accrual Loans	0	0
Total Loans	79.4	74.6
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	9.9	14.7
Current Loans	1,066.2	1,017.6
Non-accrual Loans	2.2	2.1
Total Loans	1,078.3	1,034.4
Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	6.9	6.3
Current Loans	1,315.3	1,189.5
Non-accrual Loans	15	19.6
Total Loans	1,337.2	1,215.4
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	3.6	1.9
Current Loans	259.1	133.5
Non-accrual Loans	2.1	0.8
Total Loans	264.8	136.2
Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Current Loans	3.2	4.9
Non-accrual Loans	0	0
Total Loans	3.2	4.9
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	58.3	52.2
Current Loans	8,360.8	7,446.1
Non-accrual Loans	61.2	69.4
Total Loans	8,480.3	7,567.7
Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Current Loans	37.7	46.6
Non-accrual Loans	0	0
Mortgage loans held for sale	37.7	46.6
Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	58.3	52.2
Current Loans	8,398.5	7,492.7
Non-accrual Loans	61.2	69.4
Total loans	8,518	7,614.3
30 to 59 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	9.6	2.9
30 to 59 Days Past Due | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.7	7.3
30 to 59 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	3.4	2.1
30 to 59 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	5.3	0
30 to 59 Days Past Due | Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	9.4	9.4
30 to 59 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	3.2	13.3
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.3	0.3
30 to 59 Days Past Due | Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	23.5	25.9
30 to 59 Days Past Due | Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	5	7.8
30 to 59 Days Past Due | Other consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.1	1.6
30 to 59 Days Past Due | Credit card
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.6	0.9
30 to 59 Days Past Due | Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	6.7	10.3
30 to 59 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	4.1	3.9
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	2.7	1.8
30 to 59 Days Past Due | Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
30 to 59 Days Past Due | Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	37	41.9
30 to 59 Days Past Due | Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
30 to 59 Days Past Due | Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	37	41.9
60 to 89 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	3	0.5
60 to 89 Days Past Due | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.7	0.3
60 to 89 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.4	0
60 to 89 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
60 to 89 Days Past Due | Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.1	0.3
60 to 89 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	7.3	1.4
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
60 to 89 Days Past Due | Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	11.4	2.2
60 to 89 Days Past Due | Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.2	2.1
60 to 89 Days Past Due | Other consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.4	0.5
60 to 89 Days Past Due | Credit card
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.4	0.6
60 to 89 Days Past Due | Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	2	3.2
60 to 89 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	2	1.7
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.7	0.1
60 to 89 Days Past Due | Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
60 to 89 Days Past Due | Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	16.1	7.2
60 to 89 Days Past Due | Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
60 to 89 Days Past Due | Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	16.1	7.2
Equal to Greater than 90 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.5	0.3
Equal to Greater than 90 Days Past Due | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.4	0.3
Equal to Greater than 90 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Equal to Greater than 90 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Equal to Greater than 90 Days Past Due | Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.4	0.3
Equal to Greater than 90 Days Past Due | Residential
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.8	0.4
Equal to Greater than 90 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.3	0.2
Equal to Greater than 90 Days Past Due | Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	3	1.2
Equal to Greater than 90 Days Past Due | Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.2	0.4
Equal to Greater than 90 Days Past Due | Other consumer
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.2	0.1
Equal to Greater than 90 Days Past Due | Credit card
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.8	0.7
Equal to Greater than 90 Days Past Due | Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	1.2	1.2
Equal to Greater than 90 Days Past Due | Commercial
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.8	0.7
Equal to Greater than 90 Days Past Due | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0.2	0
Equal to Greater than 90 Days Past Due | Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Equal to Greater than 90 Days Past Due | Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	5.2	3.1
Equal to Greater than 90 Days Past Due | Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	0	0
Equal to Greater than 90 Days Past Due | Total loans
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]
Total Loans 30 or More Days Past Due	$ 5.2	$ 3.1

Loans - Schedule of Outstandin

Loans - Schedule of Outstanding Unpaid Balances and Accrual Status of Loans Acquired with Credit Impairment (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities [Abstract]
Outstanding balance	$ 49.3	$ 46.2
Loans on accrual status	35.5	30.8
Total carrying value	$ 35.5	$ 30.8

Loans - Schedule of Changes in

Loans - Schedule of Changes in the Accretable Yield for Loans Acquired (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Receivables [Abstract]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Acquired	$ 3.2	$ 0	$ 3.2	$ 0
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Additions	0	0.2	0.4	2.1
Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning Balance	6.5	7.7	7.3	6.8
Accretion income	(0.7)	(0.9)	(2.4)	(2.1)
Reductions due to exit events	(0.1)	(0.1)	(0.6)	(1.1)
Reclassifications from nonaccretable differences	0.6	0.5	1.6	1.7
Ending Balance	9.5	7.4	9.5	7.4
Interest Income on Non-Accrual Loans if Accrued	$ 0.8	$ 0.9	$ 1.6	$ 1.8

Loans - Narrative (Details)

Loans - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Receivables [Abstract]
Interest Income on Non-Accrual Loans if Accrued	$ 800,000	$ 900,000	$ 1,600,000	$ 1,800,000
Loans renegotiated in troubled debt restructurings	30,300,000		30,300,000		$ 44,500,000
Charge-offs directly related to modifying troubled debt restructurings	$ 0	$ 0	0	$ 0
Balance of defaulted loans under trouble debt restructurings			$ 0

Loans - Schedule of Recorded_2

Loans - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	$ 92.5		$ 92.5		$ 107.9
Recorded Investment With No Allowance	38.7		38.7		51.4
Recorded Investment With Allowance	33.7		33.7		31.8
Total Recorded Investment	72.4		72.4		83.2
Related Allowance	8.2		8.2		10.8
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income
Average Recorded Investment	77.1	$ 93.8	77.7	$ 97.5
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Income Recognized	0	0.1	0.2	0.5
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	29.1		29.1		45.6
Recorded Investment With No Allowance	12.5		12.5		20.9
Recorded Investment With Allowance	8.7		8.7		14.1
Total Recorded Investment	21.2		21.2		35
Related Allowance	1.7		1.7		3.9
Land acquisition & development
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	10.4		10.4		10
Recorded Investment With No Allowance	0.7		0.7		3.4
Recorded Investment With Allowance	3.5		3.5		0.5
Total Recorded Investment	4.2		4.2		3.9
Related Allowance	0.2		0.2		0
Residential
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	0.7		0.7		1.8
Recorded Investment With No Allowance	0.2		0.2		1.7
Recorded Investment With Allowance	0.4		0.4		0
Total Recorded Investment	0.6		0.6		1.7
Related Allowance	0.1		0.1		0
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	4.4		4.4		4.7
Recorded Investment With No Allowance	0.2		0.2		0.4
Recorded Investment With Allowance	3.3		3.3		3.5
Total Recorded Investment	3.5		3.5		3.9
Related Allowance	1.2		1.2		2.2
Total construction loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	15.5		15.5		16.5
Recorded Investment With No Allowance	1.1		1.1		5.5
Recorded Investment With Allowance	7.2		7.2		4
Total Recorded Investment	8.3		8.3		9.5
Related Allowance	1.5		1.5		2.2
Residential
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	8.8		8.8		11.5
Recorded Investment With No Allowance	5.6		5.6		8.2
Recorded Investment With Allowance	2.1		2.1		2
Total Recorded Investment	7.7		7.7		10.2
Related Allowance	0.4		0.4		0.1
Agricultural
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	12.8		12.8		3.7
Recorded Investment With No Allowance	12.6		12.6		3.6
Recorded Investment With Allowance	0		0		0
Total Recorded Investment	12.6		12.6		3.6
Related Allowance	0		0		0
Total real estate loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	66.2		66.2		77.3
Recorded Investment With No Allowance	31.8		31.8		38.2
Recorded Investment With Allowance	18		18		20.1
Total Recorded Investment	49.8		49.8		58.3
Related Allowance	3.6		3.6		6.2
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income
Average Recorded Investment	54.5	59.9	54.1	63
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Income Recognized	0	0.1	0.1	0.4
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	24.1		24.1		29.5
Recorded Investment With No Allowance	5.2		5.2		12.4
Recorded Investment With Allowance	15.2		15.2		11.4
Total Recorded Investment	20.4		20.4		23.8
Related Allowance	4.4		4.4		4.4
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income
Average Recorded Investment	20.7	31.6	22	31.9
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Income Recognized	0	0	0.1	0.1
Agricultural
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	2.2		2.2		1.1
Recorded Investment With No Allowance	1.7		1.7		0.8
Recorded Investment With Allowance	0.5		0.5		0.3
Total Recorded Investment	2.2		2.2		1.1
Related Allowance	0.2		0.2		$ 0.2
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income
Average Recorded Investment	1.9	2.3	1.6	2.6
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Income Recognized	$ 0	$ 0	$ 0	$ 0

Loans - Schedule of Loans Rene

Loans - Schedule of Loans Renegotiated in Troubled Debt Restructurings (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)note	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)note	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | note	3		5
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 3,900,000		$ 4,100,000
Loans renegotiated in troubled debt restructurings	30,300,000		30,300,000		$ 44,500,000
Loans renegotiated in troubled debt restructurings, non-accrual loans	24,400,000		24,400,000		31,900,000
Loans renegotiated in troubled debt restructurings, accrual loans	5,900,000		5,900,000		$ 12,600,000
Charge-offs directly related to modifying troubled debt restructurings	0	$ 0	0	$ 0
Balance of defaulted loans under trouble debt restructurings			0
Commitments to lend additional funds	$ 0		$ 0
Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | note	3		5
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 3,900,000		$ 4,100,000
Interest Only Period Concession [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	3,400,000		3,600,000
Interest Only Period Concession [Member] | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	3,400,000		3,600,000
Extended Maturity [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	0		0
Extended Maturity [Member] | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	0		0
Contractual Interest Rate Reduction [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	0		0
Contractual Interest Rate Reduction [Member] | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	0		0
Other Concession [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	500,000		500,000
Other Concession [Member] | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 500,000		$ 500,000

Loans - Schedule of Recorded_3

Loans - Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 8,480.3	$ 7,567.7
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,213.1	2,822.9
Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	314.5	348.7
Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	250.6	240.2
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	219.6	119.4
Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	784.7	708.3
Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,581.2	1,487.4
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	217.8	158.2
Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	5,796.8	5,176.8
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	800.8	784.7
Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	198.1	175.1
Credit card
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	79.4	74.6
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,078.3	1,034.4
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,337.2	1,215.4
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	264.8	136.2
Other Assets Especially Mentioned
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	198.9	155.1
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	108.1	78
Other Assets Especially Mentioned | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	5.4	3.2
Other Assets Especially Mentioned | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4.1	2.3
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1.5	2.4
Other Assets Especially Mentioned | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	11	7.9
Other Assets Especially Mentioned | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	5.5	3.9
Other Assets Especially Mentioned | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	8.4	4.3
Other Assets Especially Mentioned | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	133	94.1
Other Assets Especially Mentioned | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.8	0.8
Other Assets Especially Mentioned | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.4	0.4
Other Assets Especially Mentioned | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1.2	1.2
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	50.6	54.7
Other Assets Especially Mentioned | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	14.1	5.1
Substandard
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	201.1	217.2
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	81.4	96.4
Substandard | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	7	16.4
Substandard | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.3	1.7
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3.7	3.6
Substandard | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	11	21.7
Substandard | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	11	12.5
Substandard | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	24.6	19.1
Substandard | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	128	149.7
Substandard | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2.2	2.2
Substandard | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.8	0.7
Substandard | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3	2.9
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	48.6	56.3
Substandard | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	21.5	8.3
Doubtful
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	24.9	28.2
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4.8	10.3
Doubtful | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3.3	0
Doubtful | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.4	0.5
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3.4	3.5
Doubtful | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	7.1	4
Doubtful | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1.1	1.9
Doubtful | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	0
Doubtful | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	13	16.2
Doubtful | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.1	0.3
Doubtful | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.1	0.2
Doubtful | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.2	0.5
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	11.2	11.1
Doubtful | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0.5	0.4
Total Criticized Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	424.9	400.5
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	194.3	184.7
Total Criticized Loans | Land acquisition & development
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	15.7	19.6
Total Criticized Loans | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4.8	4.5
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	8.6	9.5
Total Criticized Loans | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	29.1	33.6
Total Criticized Loans | Residential
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	17.6	18.3
Total Criticized Loans | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	33	23.4
Total Criticized Loans | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	274	260
Total Criticized Loans | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3.1	3.3
Total Criticized Loans | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1.3	1.3
Total Criticized Loans | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4.4	4.6
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	110.4	122.1
Total Criticized Loans | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 36.1	$ 13.8

Loans Schedule of Loans by Clas

Loans Schedule of Loans by Class (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	$ 8,480.3	$ 7,567.7
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group, Mortgage	37.7	46.6
Loans and Leases Receivable, Gross	8,518	7,614.3
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	3,213.1	2,822.9
Land acquisition & development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	314.5	348.7
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	250.6	240.2
Commercial Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	219.6	119.4
Total construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	784.7	708.3
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	1,581.2	1,487.4
Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	217.8	158.2
Total real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	5,796.8	5,176.8
Indirect consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	800.8	784.7
Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	198.1	175.1
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	79.4	74.6
Total consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	1,078.3	1,034.4
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	1,337.2	1,215.4
Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	264.8	136.2
Other, including overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	3.2	4.9
Loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans And Leases Receivable Held For Investment	8,480.3	7,567.7
Mortgage loans originated for sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group, Mortgage	37.7	46.6
Total loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 8,518	$ 7,614.3

Allowance for Loan Losses - Sc

Allowance for Loan Losses - Schedule of Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 74.1	$ 75.7	$ 72.1	$ 76.2
Provision charged to operating expense	2	3.4	7	7.5
Less loans charged-off	(4.8)	(7.4)	(15.1)	(15.7)
Add back recoveries of loans previously charged-off	2.3	2.9	9.6	6.6
Ending balance	73.6	74.6	73.6	74.6
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					$ 8.2	$ 10.8
Loans collectively evaluated for impairment					65.4	61.3
Allowance for loan losses	74.1	75.7	72.1	76.2	73.6	72.1
Loans held for investment:
Individually evaluated for impairment					72.4	83.2
Individually evaluated for impairment					8,407.9	7,484.5
Total loans					8,480.3	7,567.7
Allowance for credit losses due to subsequent impairment					0.6	1
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	33.9	33.5	31.6	28.6
Provision charged to operating expense	(0.9)	(0.7)	1.4	4.8
Less loans charged-off	(0.7)	(1.7)	(2.8)	(3)
Add back recoveries of loans previously charged-off	0.6	0.6	2.7	1.3
Ending balance	32.9	31.7	32.9	31.7
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					3.6	6.2
Loans collectively evaluated for impairment					29.3	25.4
Allowance for loan losses	33.9	33.5	31.6	28.6	32.9	31.6
Loans held for investment:
Individually evaluated for impairment					49.8	58.3
Individually evaluated for impairment					5,747	5,118.5
Total loans					5,796.8	5,176.8
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	7.8	7.6	8.7	7.7
Provision charged to operating expense	2.4	2.6	4.7	5.2
Less loans charged-off	(3)	(3.1)	(8.6)	(8.1)
Add back recoveries of loans previously charged-off	1.2	1	3.6	3.3
Ending balance	8.4	8.1	8.4	8.1
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					0	0
Loans collectively evaluated for impairment					8.4	8.7
Allowance for loan losses	7.8	7.6	8.7	7.7	8.4	8.7
Loans held for investment:
Individually evaluated for impairment					0	0
Individually evaluated for impairment					1,078.3	1,034.4
Total loans					1,078.3	1,034.4
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	30.6	33.1	30.6	38.1
Provision charged to operating expense	0.5	1.5	0.5	(2.2)
Less loans charged-off	(1.1)	(2.6)	(3.7)	(4.5)
Add back recoveries of loans previously charged-off	0.5	1.3	3.1	1.9
Ending balance	30.5	33.3	30.5	33.3
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					4.4	4.4
Loans collectively evaluated for impairment					26.1	26.2
Allowance for loan losses	30.6	33.1	30.6	38.1	30.5	30.6
Loans held for investment:
Individually evaluated for impairment					20.4	23.8
Individually evaluated for impairment					1,316.8	1,191.6
Total loans					1,337.2	1,215.4
Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1.8	1.5	1.2	1.8
Provision charged to operating expense	0	0	0.4	(0.3)
Less loans charged-off	0	0	0	(0.1)
Add back recoveries of loans previously charged-off	0	0	0.2	0.1
Ending balance	1.8	1.5	1.8	1.5
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					0.2	0.2
Loans collectively evaluated for impairment					1.6	1
Allowance for loan losses	1.8	1.5	1.2	1.8	1.8	1.2
Loans held for investment:
Individually evaluated for impairment					2.2	1.1
Individually evaluated for impairment					262.6	135.1
Total loans					264.8	136.2
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0	0
Provision charged to operating expense	0	0	0	0
Less loans charged-off	0	0	0	0
Add back recoveries of loans previously charged-off	0	0	0	0
Ending balance	0	0	0	0
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Loans individually evaluated for impairment					0	0
Loans collectively evaluated for impairment					0	0
Allowance for loan losses	$ 0	$ 0	$ 0	$ 0	0	0
Loans held for investment:
Individually evaluated for impairment					0	0
Individually evaluated for impairment					3.2	4.9
Total loans					$ 3.2	$ 4.9

Other Real Estate Owned (Detail

Other Real Estate Owned (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Real Estate Acquired Through Foreclosure, Acquired Through Acquisition	$ 0.6	$ 0	$ 0.6	$ 1.2
Real Estate Acquired Through Foreclosure [Roll Forward]
Beginning balance	14.9	11.3	10.1	10
Additions	3.2	1.4	10.6	3.2
Valuation adjustments	(0.1)	(0.2)	(0.1)	(0.3)
Dispositions	(1.3)	(2.1)	(3.9)	(3.7)
Ending balance	17.3	$ 10.4	17.3	$ 10.4
Consumer mortgage loans collateralized by residential real estate property in the process of foreclosure	2		2		$ 0
Residential real estate
Real Estate Acquired Through Foreclosure [Roll Forward]
Beginning balance			2.7
Ending balance	$ 2.6		$ 2.6

Derivatives and Hedging Activ_3

Derivatives and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	$ 10	$ 3.3
Derivative Asset, Notional Amount	449.7	404.9
Derivative Asset, Estimated Fair Value	12.4	8.8
Notional amount of terminated commitment	464.2	433
Derivative Liabilities, Estimated Fair Value	11.3	7.9
Interest rate swap contracts
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	10	3.3
Mortgage Related Derivatives
Derivative [Line Items]
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	0	0
Not Designated as Hedging Instrument | Interest rate swap contracts
Derivative [Line Items]
Derivative Asset, Notional Amount	386.8	344.2
Derivative Asset, Estimated Fair Value	11.3	7.5
Notional amount of terminated commitment	386.8	344.2
Derivative Liabilities, Estimated Fair Value	11.1	7.8
Not Designated as Hedging Instrument | Interest rate lock commitments
Derivative [Line Items]
Derivative Asset, Notional Amount	62.9	60.7
Derivative Asset, Estimated Fair Value	1.1	1.3
Not Designated as Hedging Instrument | Forward loan sales contracts
Derivative [Line Items]
Notional amount of terminated commitment	77.4	88.8
Derivative Liabilities, Estimated Fair Value	$ 0.2	$ 0.1

Derivatives and Hedging Activ_4

Derivatives and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Asset, Gross Amounts Recognized	$ 12.4	$ 8.8
Derivative Asset, Gross Amounts Offset in the Balance Sheet	0	0
Derivative Asset, Net Amounts in the Balance Sheet	12.4	8.8
Derivative Asset, Financial Instruments	1	2.4
Derivative Asset, Fair Value of Financial Collateral in the Balance Sheet	1.8	0
Derivative Asset, Net Amount	9.6	6.4
Total assets, Gross Amounts Recognized	12.4	8.8
Total assets, Gross Amounts Offset in the Balance Sheet	0	0
Total assets, Net Amounts in the Balance Sheet	12.4	8.8
Total assets, Financial Instruments	1	2.4
Total assets, Fair Value of Financial Collateral in the Balance Sheet	1.8	0
Total assets, Net Amount	9.6	6.4
Derivative liability, Gross Amounts Recognized	11.3	7.9
Derivative liability, Gross Amounts Offset in the Balance Sheet	0	0
Derivative liability, Net Amounts in the Balance Sheet	11.3	7.9
Derivative liability, Financial Instruments	1	2.4
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	10	3.3
Derivative liability, Net Amount	0.3	2.2
Repurchase agreements, Gross Amounts Recognized	635.9	643
Repurchase agreements, Gross Amounts Offset in the Balance Sheet	0	0
Repurchase agreements, Net Amounts in the Balance Sheet	635.9	643
Repurchase agreements, Financial Instruments	0	0
Repurchase agreements, Fair Value of Financial Collateral in the Balance Sheet	635.9	643
Repurchase agreements, Net Amount	0	0
Total liabilities, Gross Amounts Recognized	647.2	650.9
Total liabilities, Gross Amounts Offset in the Balance Sheet	0	0
Total liabilities, Net Amounts in the Balance Sheet	647.2	650.9
Total liabilities, Financial Instruments	1	2.4
Total liabilities, Fair Value of Financial Collateral in the Balance Sheet	645.9	646.3
Total liabilities, Net Amount	0.3	2.2
Interest Rate Swap
Derivative [Line Items]
Derivative Asset, Gross Amounts Recognized	11.3	7.5
Derivative Asset, Gross Amounts Offset in the Balance Sheet	0	0
Derivative Asset, Net Amounts in the Balance Sheet	11.3	7.5
Derivative Asset, Financial Instruments	1	2.4
Derivative Asset, Fair Value of Financial Collateral in the Balance Sheet	1.8	0
Derivative Asset, Net Amount	8.5	5.1
Derivative liability, Gross Amounts Recognized	11.1	7.8
Derivative liability, Gross Amounts Offset in the Balance Sheet	0	0
Derivative liability, Net Amounts in the Balance Sheet	11.1	7.8
Derivative liability, Financial Instruments	1	2.4
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	10	3.3
Derivative liability, Net Amount	0.1	2.1
Mortgage Related Derivatives
Derivative [Line Items]
Derivative Asset, Gross Amounts Recognized	1.1	1.3
Derivative Asset, Gross Amounts Offset in the Balance Sheet	0	0
Derivative Asset, Net Amounts in the Balance Sheet	1.1	1.3
Derivative Asset, Financial Instruments	0	0
Derivative Asset, Fair Value of Financial Collateral in the Balance Sheet	0	0
Derivative Asset, Net Amount	1.1	1.3
Derivative liability, Gross Amounts Recognized	0.2	0.1
Derivative liability, Gross Amounts Offset in the Balance Sheet	0	0
Derivative liability, Net Amounts in the Balance Sheet	0.2	0.1
Derivative liability, Financial Instruments	0	0
Derivative liability, Fair Value of Financial Collateral in the Balance Sheet	0	0
Derivative liability, Net Amount	$ 0.2	$ 0.1

Derivatives and Hedging Activ_5

Derivatives and Hedging Activities - Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	$ 0	$ (0.6)	$ 0	$ (1.1)
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	0	0.7	0	1.1
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	(1.1)	0	(1.1)
Not Designated as Hedging Instrument
Derivative [Line Items]
Amount of gain recognized in other non-interest income	0.1	0	0.4	0
Amount of net fee income recognized in other non-interest income	0	0.2	0.9	0.4
Amount of net gains recognized in mortgage banking revenues	$ 0	$ 0.4	$ 0	$ 0.5

Capital Stock (Details)

Capital Stock (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Aug. 16, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Class A common stock		$ 173.3
Share-based Compensation Arrangement by Share-based Payment Award, Aggregate Value of Shares Issued	$ 0.5
Class A Common Stock
Class of Stock [Line Items]
Common stock outstanding (in shares)	38,107,555		33,560,202
Stock repurchased and retired (in shares)	0
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	11,389
Class B Common Stock
Class of Stock [Line Items]
Common stock outstanding (in shares)	22,501,994		22,905,357

Earnings per Common Share - Co

Earnings per Common Share - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Basic and Diluted [Line Items]
Net income	$ 41.4	$ 27.3	$ 119.8	$ 72.3
Weighted average common shares outstanding for basic earnings per share computation	58,254,575	56,094,401	56,951,029	49,514,818
Dilutive effects of stock-based compensation	385,900	436,467	378,998	486,064
Weighted average common shares outstanding for diluted earnings per common share computation	58,640,475	56,530,868	57,330,027	50,000,882
Basic earnings per common share (in dollars per share)	$ 0.71	$ 0.49	$ 2.10	$ 1.46
Diluted earnings per common share (in dollars per share)	$ 0.71	$ 0.48	$ 2.09	$ 1.45
Unvested Restricted Stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock	4,376	0	120,553	94,210
Restricted stock
Earnings Per Share, Basic and Diluted [Line Items]
Anti-dilutive unvested time restricted stock			154,176	174,696

Regulatory Capital - Schedule

Regulatory Capital - Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Total risk-based capital:
Actual Amount	$ 1,254.8	$ 1,112.5
Actual Ratio	12.75978%	12.75962%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 971.1	$ 806.5
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	9.875%	9.25%
Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 1,032.6	$ 915.5
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	10.50%	10.50%
Well Capitalized Amount	$ 983.4	$ 871.9
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 1,181.2	$ 1,040.3
Actual Ratio	12.01132%	11.93154%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 774.5	$ 632.1
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	7.875%	7.25%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 835.9	$ 741.1
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	8.50%	8.50%
Well Capitalized Amount	$ 786.7	$ 697.5
Well Capitalized Ratio	8.00%	8.00%
Common equity tier one risk-based capital:
Actual Amount	$ 1,096.8	$ 962.4
Actual Ratio	11.15322%	11.03808%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 626.9	$ 501.3
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	6.375%	5.75%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 688.4	$ 610.3
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%	7.00%
Well Capitalized Amount	$ 639.2	$ 566.7
Well Capitalized Ratio	6.50%	6.50%
Leverage capital ratio:
Actual Amount	$ 1,181.2	$ 1,040.3
Actual Ratio	9.72992%	8.85532%
Adequately Capitalized Amount	$ 485.6	$ 469.9
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 607	$ 587.4
Well Capitalized Ratio	5.00%	5.00%
FIB
Total risk-based capital:
Actual Amount	$ 1,107.7	$ 1,066.6
Actual Ratio	12.28251%	12.29128%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 890.5	$ 802.7
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	9.875%	9.25%
Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 946.9	$ 911.2
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	10.50%	10.50%
Well Capitalized Amount	$ 901.8	$ 867.8
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 1,034	$ 994.4
Actual Ratio	11.46631%	11.45926%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 710.2	$ 629.1
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	7.875%	7.25%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 766.5	$ 737.6
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	8.50%	8.50%
Well Capitalized Amount	$ 721.5	$ 694.2
Well Capitalized Ratio	8.00%	8.00%
Common equity tier one risk-based capital:
Actual Amount	$ 1,034	$ 994.4
Actual Ratio	11.46631%	11.45926%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 574.9	$ 499
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	6.375%	5.75%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 631.3	$ 607.4
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%	7.00%
Well Capitalized Amount	$ 586.2	$ 564.1
Well Capitalized Ratio	6.50%	6.50%
Leverage capital ratio:
Actual Amount	$ 1,034	$ 994.4
Actual Ratio	8.76766%	8.48004%
Adequately Capitalized Amount	$ 471.8	$ 469.1
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 589.7	$ 586.3
Well Capitalized Ratio	5.00%	5.00%
Inland Northwest Bank
Total risk-based capital:
Actual Amount	$ 77.6
Actual Ratio	9.86329%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 77.7
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	9.875%
Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 82.7
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	10.50%
Well Capitalized Amount	$ 78.7
Well Capitalized Ratio	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 77.6
Actual Ratio	9.86329%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 62
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	7.875%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 66.9
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	8.50%
Well Capitalized Amount	$ 63
Well Capitalized Ratio	8.00%
Common equity tier one risk-based capital:
Actual Amount	$ 77.6
Actual Ratio	9.86329%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 50.2
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	6.375%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 55.1
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%
Well Capitalized Amount	$ 51.2
Well Capitalized Ratio	6.50%
Leverage capital ratio:
Actual Amount	$ 77.6
Actual Ratio	9.80699%
Adequately Capitalized Amount	$ 31.7
Adequately Capitalized Ratio	4.00%
Well Capitalized Amount	$ 39.6
Well Capitalized Ratio	5.00%

Commitments and Contingencies (

Commitments and Contingencies (Details) $ / shares in Units, $ in Millions	Oct. 11, 2018USD ($)$ / shares	Sep. 30, 2018USD ($)	Aug. 16, 2018	Dec. 31, 2017USD ($)
Loss Contingencies [Line Items]
Notional amount of terminated commitment		$ 464.2		$ 433
Mortgage Loans Held for Sale
Loss Contingencies [Line Items]
Mortgage loans with recourse provision in effect		0.5
Construction Contracts
Loss Contingencies [Line Items]
Commitments under construction contracts		$ 5.4
Inland Northwest Bank
Loss Contingencies [Line Items]
Number of banking offices acquired			20
Subsequent Event | Idaho Independent Bank [Member]
Loss Contingencies [Line Items]
Number of banking offices acquired	11
Estimate of Payments to Acquire Businesses, Gross	$ 181.3
Subsequent Event | Community 1st Bank [Member]
Loss Contingencies [Line Items]
Number of banking offices acquired	3
Estimate of Payments to Acquire Businesses, Gross	$ 21.5
Community 1st Bank [Member] | Subsequent Event
Loss Contingencies [Line Items]
Estimate value per share of Acquisition | $ / shares	$ 17.20
Inland Northwest Bank | Subsequent Event
Loss Contingencies [Line Items]
Estimate value per share of Acquisition | $ / shares	$ 22.73

Financial Instruments with Of_2

Financial Instruments with Off-Balance Sheet Risk (Details) $ in Millions	Sep. 30, 2018USD ($)
Entity Information [Line Items]
Credit extension commitments	$ 2,515.4
Credit extension commitments beyond one year	942.1
Unused Credit Card Lines
Entity Information [Line Items]
Credit extension commitments	701.8
Standby Letters of Credit
Entity Information [Line Items]
Credit extension commitments	$ 45

Other Comprehensive Income_Lo_3

Other Comprehensive Income/Loss - Schedule of Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Investment securities available-for sale:
Change in net unrealized gain during period, pre-tax	$ (6,300)	$ (1,800)	$ (33,900)	$ 15,600
Change in net unrealized gain during period, tax expense (benefit)	(1,700)	(800)	(8,900)	6,100
Change in net unrealized gain during period, net of tax	(4,600)	(1,000)	(25,000)	9,500
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity, pre-tax	500	500	1,500	1,400
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity, tax expense (benefit)	100	200	400	600
Change in unamortized loss on available-for-sale securities transferred into held-to-maturity, net of tax	400	300	1,100	800
Defined benefits post-retirement benefit plan:
Change in net actuarial (gain) loss, pre-tax	(200)	(200)	(500)	(1,100)
Change in net actuarial (gain) loss, tax expense (benefit)	0	(100)	(100)	(400)
Change in net actuarial (gain) loss, net of tax amount	(200)	(100)	(400)	(700)
Other comprehensive income (loss), before tax	(6,000)	(1,800)	(32,900)	15,100
Total other comprehensive income, tax expense (benefit)	(1,600)	(800)	(8,600)	6,000
Total other comprehensive income, net of tax amount	(4,400)	(1,000)	(24,300)	9,100
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	0	(600)	0	(1,100)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	0	(300)	0	(400)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	0	(300)	0	(700)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	0	(1,100)	0	(1,100)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	0	(500)	0	(400)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	(600)	0	(700)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	0	800	0	800
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	0	300	0	300
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	$ 0	$ 500	$ 0	$ 500

Other Comprehensive Income_Lo_4

Other Comprehensive Income/Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Net accumulated other comprehensive income:
Net unrealized gain (loss) on investment securities available-for-sale	$ (40.3)	$ (13.3)
Net unrealized gain (loss) on derivatives	0	1.3
Net actuarial gain (loss) on defined benefit post-retirement benefit plans	0.9	0
Net accumulated other comprehensive gain (loss)	$ (39.4)	$ (12)

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	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related allowance	$ 8.2	$ 10.8
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	0	0
Deferred compensation plan assets	0	0
Deferred compensation plan liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Other real estate owned	0	0
Long-lived assets to be disposed of by sale	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	37.7	46.6
Deferred compensation plan assets	13	12.2
Deferred compensation plan liabilities	13	12.2
Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Other real estate owned	0	0
Long-lived assets to be disposed of by sale	0	0
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	0	0
Deferred compensation plan assets	0	0
Deferred compensation plan liabilities	0	0
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans		32.6
Other real estate owned	0.6	1.3
Long-lived assets to be disposed of by sale	3.5	0.8
Related allowance	8.2	10.8
Partial loan charge-offs	6.6	11.4
U.S. Treasury notes | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0	0
U.S. Treasury notes | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	3	3.2
U.S. Treasury notes | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0	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:	560.9	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:	1,425.6	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:	73	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:	92.1	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:	4.2	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:	2,158.8	2,208.7
Loans held for sale	37.7
Derivative assets:	12.4	8.8
Derivative liabilities:	11.3	7.9
Deferred compensation plan assets	13	12.2
Deferred compensation plan liabilities	13	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	37.7	46.6
Deferred compensation plan assets	13	12.2
Deferred compensation plan liabilities	13	12.2
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	28.7	32.6
Other real estate owned	0.6	1.3
Long-lived assets to be disposed of by sale	3.5	0.8
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	0	0
Loans held for sale	0
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:	2,158.8	2,208.7
Loans held for sale	37.7
Derivative assets:	12.4	8.8
Derivative liabilities:	11.3	7.9
Deferred compensation plan assets	13	12.2
Deferred compensation plan liabilities	13	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
Loans held for sale	0
Derivative assets:	0	0
Derivative liabilities:	0	0
Deferred compensation plan assets	0	0
Deferred compensation plan liabilities	0	0
Impaired loans	28.7
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	28.7	32.6
Estimated Fair Value | U.S. Treasury notes | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	3	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:	560.9	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:	1,425.6	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:	73	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:	92.1	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:	4.2	3
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment debt securities available-for-sale:	2,158.8	2,208.7
Loans held for sale	37.7
Derivative assets:	12.4	8.8
Derivative liabilities:	11.3	7.9
Deferred compensation plan assets	13	12.2
Deferred compensation plan liabilities	13	12.2
Carrying Amount | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	43.5	54.8
Long-lived assets to be disposed of by sale	4	0.8
Change During Period | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets to be disposed of by sale	0.5	0
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:	11.3	7.5
Derivative liabilities:	11.1	7.8
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:	11.3	7.5
Derivative liabilities:	11.1	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:	1.1	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:	1.1	1.3
Forward Contracts | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities:	0	0
Forward Contracts | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities:	0.2	0.1
Forward Contracts | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities:	0	0
Forward Contracts | Estimated Fair Value | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities:	$ 0.2	$ 0.1

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Inputs, Quantitative Information (Details) - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Write downs on OREO properties	$ 0	$ 0
Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Level 3 Fair Value Disclosure	0.00%
Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Assets HFS Level 3 Fair Value	0.00%
Discount Rate for OREO Level 3 Fair Value	96.20%
Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Assets HFS Level 3 Fair Value	0.00%
Discount Rate for OREO Level 3 Fair Value	11.60%
Discount Rate for Level 3 Fair Value Disclosure	26.10%
Carrying Amount
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Net loans held for investment	$ 8,480,300,000		$ 7,542,200,000
Change During Period | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value of long-lived assets to be disposed of by sale	500,000		0
Estimated Fair Value
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Net loans held for investment	8,406,800,000		7,298,800,000
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	28,700,000		32,600,000
Other real estate owned	600,000		1,300,000
Fair Value of long-lived assets to be disposed of by sale	3,500,000		800,000
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans			32,600,000
Other real estate owned	600,000		1,300,000
Fair Value of long-lived assets to be disposed of by sale	3,500,000		800,000
Significant Unobservable Inputs (Level 3) | Carrying Amount | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	43,500,000		54,800,000
Fair Value of long-lived assets to be disposed of by sale	4,000,000		800,000
Significant Unobservable Inputs (Level 3) | Estimated Fair Value
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Net loans held for investment			32,600,000
Impaired loans	28,700,000
Significant Unobservable Inputs (Level 3) | Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Impaired loans	$ 28,700,000		$ 32,600,000
Measurement Input, Discount Rate [Member] | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Assets HFS Level 3 Fair Value	0.00%
Discount Rate for OREO Level 3 Fair Value	8.00%
Measurement Input, Discount Rate [Member] | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount Rate for Level 3 Fair Value Disclosure	78.10%

Fair Value Measurements - Sc_2

Fair Value Measurements - Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial assets:
Investment debt securities held-to-maturity	$ 407,400	$ 483,300
Carrying Amount
Financial assets:
Cash and cash equivalents	965,000	759,000
Investment debt securities available-for-sale:	2,158,800	2,208,700
Investment debt securities held-to-maturity	417,800	484,500
Accrued interest receivable	48,000	38,000
Mortgage servicing rights, net	27,000	24,800
Loans held for sale	37,700
Net loans held for investment	8,480,300	7,542,200
Derivative assets	12,400	8,800
Deferred compensation plan assets	13,000	12,200
Total financial assets	12,160,000	11,078,200
Financial liabilities:
Total deposits, excluding time deposits	9,560,300	8,783,000
Time deposits	1,285,300	1,151,900
Securities sold under repurchase agreements	635,900	643,000
Other borrowed funds	1,500	20,000
Accrued interest payable	6,700	5,600
Long-term debt	22,400	13,100
Subordinated debentures held by subsidiary trusts	86,900	82,500
Derivative liabilities	11,300	7,900
Deferred compensation plan liabilities	13,000	12,200
Total financial liabilities	11,623,300	10,719,200
Estimated Fair Value
Financial assets:
Cash and cash equivalents	965,000	759,000
Investment debt securities available-for-sale:	2,158,800	2,208,700
Investment debt securities held-to-maturity	407,400	483,300
Accrued interest receivable	48,000	38,000
Mortgage servicing rights, net	41,800	40,100
Loans held for sale	37,700
Net loans held for investment	8,406,800	7,298,800
Derivative assets	12,400	8,800
Deferred compensation plan assets	13,000	12,200
Total financial assets	12,090,900	10,848,900
Financial liabilities:
Total deposits, excluding time deposits	9,560,300	8,783,000
Time deposits	1,269,200	1,137,900
Securities sold under repurchase agreements	635,900	643,000
Other borrowed funds	1,500	20,000
Accrued interest payable	6,700	5,600
Long-term debt	19,600	11,300
Subordinated debentures held by subsidiary trusts	82,400	76,700
Derivative liabilities	11,300	7,900
Deferred compensation plan liabilities	13,000	12,200
Total financial liabilities	11,599,900	10,697,600
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	965,000	759,000
Investment debt securities available-for-sale:	0	0
Investment debt securities held-to-maturity	0	0
Accrued interest receivable	0	0
Mortgage servicing rights, net	0	0
Loans held for sale	0
Net loans held for investment	0	0
Derivative assets	0	0
Deferred compensation plan assets	0	0
Total financial assets	965,000	759,000
Financial liabilities:
Total deposits, excluding time deposits	9,560,300	8,783,000
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Other borrowed funds	0	0
Accrued interest payable	0	0
Long-term debt	0	0
Subordinated debentures held by subsidiary trusts	0	0
Derivative liabilities	0	0
Deferred compensation plan liabilities	0	0
Total financial liabilities	9,560,300	8,783,000
Significant Other Observable Inputs (Level 2) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment debt securities available-for-sale:	2,158,800	2,208,700
Investment debt securities held-to-maturity	407,400	483,300
Accrued interest receivable	48,000	38,000
Mortgage servicing rights, net	41,800	40,100
Loans held for sale	37,700
Net loans held for investment	8,378,100	7,266,200
Derivative assets	12,400	8,800
Deferred compensation plan assets	13,000	12,200
Total financial assets	11,097,200	10,057,300
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	1,269,200	1,137,900
Securities sold under repurchase agreements	635,900	643,000
Other borrowed funds	1,500	20,000
Accrued interest payable	6,700	5,600
Long-term debt	19,600	11,300
Subordinated debentures held by subsidiary trusts	82,400	76,700
Derivative liabilities	11,300	7,900
Deferred compensation plan liabilities	13,000	12,200
Total financial liabilities	2,039,600	1,914,600
Significant Unobservable Inputs (Level 3) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment debt securities available-for-sale:	0	0
Investment debt securities held-to-maturity	0	0
Accrued interest receivable	0	0
Mortgage servicing rights, net	0	0
Loans held for sale	0
Net loans held for investment		32,600
Impaired loans	28,700
Derivative assets	0	0
Deferred compensation plan assets	0	0
Total financial assets	28,700	32,600
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Other borrowed funds	0	0
Accrued interest payable	0	0
Long-term debt	0	0
Subordinated debentures held by subsidiary trusts	0	0
Derivative liabilities	0	0
Deferred compensation plan liabilities	0	0
Total financial liabilities	$ 0	$ 0

Recent Authoritative Accounti_2

Recent Authoritative Accounting Guidance (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Retained earnings | ASU 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of the income tax effects of the Tax Cut and Jobs Act from AOCI	$ 3.1

Subsequent Events (Details)

Subsequent Events (Details)	Nov. 19, 2018$ / shares
Class A Common Stock | Subsequent Event
Subsequent Event [Line Items]
Dividend amount per share (in dollars)	$ 0.28