Banner (BANR) 10-K 23 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2018	Jun. 30, 2017
Document Information [Line Items]
Entity Registrant Name	Banner Corporation
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Entity Central Index Key	946,673
Current Fiscal Year End Date	--12-31
Entity Public Float			$ 1,847,597,162
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Voting Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		32,626,204
Nonvoting Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		100,029

CONSOLIDATED STATEMENTS OF FINA

CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and due from banks		$ 199,624	$ 177,083
Interest-bearing Deposits in Banks and Other Financial Institutions		61,576	70,636
Cash and Cash Equivalents, at Carrying Value		261,200	247,719
Securities—trading, amortized cost $27,246 and $30,154, respectively		22,318	24,568
Securities—available-for-sale, amortized cost $926,112 and $811,847, respectively		919,485	806,428
Securities—held-to-maturity, fair value $262,188 and $270,528, respectively		260,271	267,873
Federal Home Loan Bank (FHLB) stock		10,334	12,506
Loans Receivable Held-for-sale, Amount		40,725	246,353
Loans receivable		7,598,884	7,451,148
Allowance for loan losses		(89,028)	(85,997)
Total loans, net		7,509,856	7,365,151
Accrued interest receivable		31,259	30,178
Real estate owned (REO), held for sale, net		360	11,081
Property and equipment, net		154,815	166,481
Goodwill		242,659	244,583
Other intangible assets, net		22,655	30,162
Bank-owned life insurance (BOLI)		162,668	158,936
Deferred tax assets, net		71,427	127,694
Other assets		53,177	53,955
Total assets		9,763,209	9,793,668
Deposits:
Non-interest-bearing		3,265,544	3,140,451
Interest-bearing transaction and savings accounts		3,950,950	3,935,630
Interest-bearing certificates	[1]	966,937	1,045,333
Total deposits		8,183,431	8,121,414
Advances from FHLB at fair value		202	54,216
Other borrowings		95,860	105,685
Junior subordinated debentures at fair value (issued in connection with Trust Preferred Securities)		98,707	95,200
Accrued expenses and other liabilities		71,344	71,369
Deferred compensation		41,039	40,074
Total liabilities		8,490,583	8,487,958
COMMITMENTS AND CONTINGENCIES (Note 23)
SHAREHOLDERS’ EQUITY
Preferred stock - $0.01 par value per share, 500,000 shares authorized; no shares issued and outstanding at December 31, 2017 and December 31, 2016		0	0
Retained earnings		90,535	95,328
Accumulated other comprehensive loss		(5,036)	(3,455)
Carrying value of shares held in trust for stock related compensation plans		(7,351)	(7,283)
Liability for common stock issued for stock related compensation plans		7,351	7,283
Shareholders’ equity		1,272,626	1,305,710
Total liabilities and stockholders' equity		9,763,209	9,793,668
Voting Common Stock [Member]
SHAREHOLDERS’ EQUITY
Common stock and paid in capital		1,185,919	1,213,225
Nonvoting Common Stock [Member]
SHAREHOLDERS’ EQUITY
Common stock and paid in capital		$ 1,208	$ 612
[1]	)Certificates of deposit included $11,000 and $426,000 of acquisition premiums at December 31, 2017 and 2016, respectively.

CONSOLIDATED STATEMENTS OF FIN3

CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Securities—trading, amortized cost basis	$ 27,246	$ 30,154
Securities—available-for-sale, amortized cost basis	926,112	811,847
Held-to-maturity Securities, Fair Value	262,188	270,528
Loans Held-for-sale, Fair Value	$ 32,400	$ 9,600
SHAREHOLDERS’ EQUITY
Preferred stock, share par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	500,000	500,000
Preferred stock, shares outstanding	0	0
Voting Common Stock [Member]
SHAREHOLDERS’ EQUITY
Common stock, share par value	$ 0.01	$ 0.01
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	32,626,456	33,108,599
Common stock, shares outstanding	32,626,456	33,108,599
Nonvoting Common Stock [Member]
SHAREHOLDERS’ EQUITY
Common stock, share par value	$ 0.01	$ 0.01
Common stock, shares authorized	5,000,000	5,000,000
Common stock, shares issued	100,029	84,788
Common stock, shares outstanding	100,029	84,788

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INTEREST INCOME:
Loans receivable	$ 374,449	$ 359,612	$ 237,292
Mortgage-backed securities	24,535	19,328	9,049
Securities and cash equivalents	13,300	12,537	8,092
Total interest income	412,284	391,477	254,433
INTEREST EXPENSE:
Deposits	12,273	11,105	8,385
FHLB advances	1,908	953	311
Other borrowings	317	310	211
Junior subordinated debentures	4,752	4,040	3,247
Total interest expense	19,250	16,408	12,154
Net interest income before provision for loan losses	393,034	375,069	242,279
PROVISION FOR LOAN LOSSES	8,000	6,030	0
Net interest income	385,034	369,039	242,279
NON-INTEREST INCOME
Deposit fees and other service charges	51,787	49,156	40,607
Mortgage banking operations	20,880	25,552	17,720
Bank Owned Life Insurance Income	4,618	4,538	2,497
Miscellaneous	8,985	6,001	2,821
Other operating income	86,270	85,247	63,645
Net (loss) gain on sale of securities	(2,080)	843	(540)
Net change in valuation of financial instruments carried at fair value	(2,844)	(2,620)	(813)
Gain on sale of branches, including related loans and deposits	12,189	0	0
Total non-interest income	93,535	83,470	62,292
NON-INTEREST EXPENSE:
Salary and employee benefits	192,096	180,883	127,282
Less capitalized loan origination costs	(17,379)	(18,895)	(14,379)
Occupancy and equipment	47,866	45,000	30,366
Information/computer data services	17,245	19,281	12,110
Payment and card processing expenses	22,665	21,604	16,430
Professional services	17,534	8,120	4,828
Advertising and marketing	8,637	9,709	7,649
Deposit insurance	4,689	4,551	3,189
State/municipal business and use taxes	2,594	3,516	1,889
REO operations	(2,030)	175	397
Amortization of core deposit intangibles	6,246	7,061	3,164
Miscellaneous	27,142	30,131	17,565
Total other operating expense, before acquisition related costs	327,305	311,136	210,490
Acquisition related costs	0	11,733	26,110
Total non-interest expense	327,305	322,869	236,600
Income before provision for income taxes	151,264	129,640	67,971
PROVISION FOR INCOME TAXES	90,488	44,255	22,749
NET INCOME	$ 60,776	$ 85,385	$ 45,222
Earnings per common share
Basic (in dollars per share)	$ 1.85	$ 2.52	$ 1.90
Diluted (in dollars per share)	1.84	2.52	1.89
Cumulative dividends declared per common share (in dollars per share)	$ 2	$ 0.88	$ 0.72
Weighted average number of common shares outstanding:
Basic	32,888,007	33,820,148	23,801,373
Diluted	32,986,707	33,853,511	23,866,621

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
NET INCOME	$ 60,776	$ 85,385	$ 45,222
OTHER COMPREHENSIVE LOSS, NET OF INCOME TAXES:
Unrealized holding loss on securities—available-for-sale arising during the period	(3,318)	(3,940)	(645)
Income tax benefit related to securities—available-for-sale unrealized holding losses	1,182	1,414	249
Reclassification for net (gains) losses on securities—available-for-sale realized in earnings	2,109	(311)	(119)
Income tax (benefit) expense related to securities—available-for-sale realized (gains) losses	(759)	112	43
Other comprehensive loss	(786)	(2,725)	(472)
COMPREHENSIVE INCOME	$ 59,990	$ 82,660	$ 44,750

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Common Stock Including Additional Paid in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, beginning of the period at Dec. 31, 2014	$ 582,888		$ 568,882	$ 14,264	$ (258)
Balance, beginning of the period, shares at Dec. 31, 2014		19,571,548
Net income	45,222			45,222
Other comprehensive income (loss)	(472)				(472)
Accrual of dividends on common stock	(19,871)			(19,871)
Cash paid for repurchase of common stock	0
Stock Issued During Period, Shares, Dividend Reinvestment Plan		810
Proceeds from issuance of common stock for stockholder reinvestment program, net of registration expenses amount	34		34
Amortization of share-based compensation related to restricted stock grants, net of shares surrendered	3,088		3,088
Issuance of unvested restricted common stock, net, shares		120,043
Stock Issued During Period, Value, Acquisitions	688,773
Stock Issued During Period, Shares, Acquisitions		14,549,854
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	397
Balance, end of the period, shares at Dec. 31, 2015		34,242,255
Balance, end of the period at Dec. 31, 2015	1,300,059		1,261,174	39,615	(730)
Net income	85,385			85,385
Other comprehensive income (loss)	(2,725)				(2,725)
Accrual of dividends on common stock	(29,672)			(29,672)
Cash paid for repurchase of common stock	(50,772)		50,772
Repurchase of shares upon termination of ESOP, shares		(1,145,250)
Amortization of share-based compensation related to restricted stock grants, net of shares surrendered	3,401		3,401
Issuance of unvested restricted common stock, net, shares		96,382
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	34
Balance, end of the period, shares at Dec. 31, 2016		33,193,387
Balance, end of the period at Dec. 31, 2016	1,305,710		1,213,837	95,328	(3,455)
Net income	60,776			60,776
Other comprehensive income (loss)	(786)				(786)
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings	0			795	(795)
Accrual of dividends on common stock	(66,364)			66,364
Cash paid for repurchase of common stock	(31,045)		(31,045)
Repurchase of shares upon termination of ESOP, shares		545,166
Amortization of share-based compensation related to restricted stock grants, net of shares surrendered	4,335		4,335
Issuance of unvested restricted common stock, net, shares		78,264
Balance, end of the period, shares at Dec. 31, 2017		32,726,485
Balance, end of the period at Dec. 31, 2017	$ 1,272,626		$ 1,187,127	$ 90,535	$ (5,036)

CONSOLIDATED STATEMENTS OF CHA7

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Accrual of dividends on common share (dollars per share)	$ 0.25	$ 0.25	$ 1.25	$ 0.25	$ 0.23	$ 0.23	$ 0.21	$ 0.21	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 2	$ 0.88	$ 0.72

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES:
Net income	$ 60,776	$ 85,385	$ 45,222
Adjustments to reconcile net income to net cash provided from (used by) operating activities:
Depreciation	14,701	13,464	9,957
Deferred income and expense, net of amortization	1,972	(1,323)	(1,534)
Amortization of core deposit intangibles	6,246	7,061	3,164
Loss (gain) on sale of securities, net	2,080	(843)	540
Net change in valuation of financial instruments carried at fair value	2,844	2,620	813
Purchases of securities—trading	0	(1,725)	(6,338)
Proceeds from sales of securities—trading	1,258	7,839	4,419
Principal repayments and maturities of securities—trading	1,849	3,746	9,535
Gain (Loss) on Sale of Branches, including loans and deposits	12,189	0	0
Decrease (increase) in deferred taxes	56,267	7,883	(3,906)
Decrease in current taxes payable	(2,965)	(2,184)	(1,519)
Equity-based compensation	5,965	4,305	4,334
Increase in cash surrender value of BOLI	(4,057)	(4,507)	(2,481)
Gain on sale of loans, net of capitalized servicing rights	(15,225)	(17,713)	(10,716)
Gain on disposal of real estate held for sale and property and equipment	(4,295)	(1,389)	(391)
PROVISION FOR LOAN LOSSES	8,000	6,030	0
Provision for real estate held for sale	256	876	216
Origination of loans held for sale	(807,137)	(1,063,328)	(709,035)
Proceeds from sales of loans held for sale	1,027,989	880,890	677,166
Net change in:
Other assets	2,546	3,759	(7,319)
Other liabilities	(179)	(6,664)	4,090
Net cash provided from (used by) operating activities	346,702	(75,818)	16,217
INVESTING ACTIVITIES:
Purchases of securities—available-for-sale	(838,247)	(243,115)	(141,989)
Principal repayments and maturities of securities—available-for-sale	187,080	191,534	113,431
Proceeds from sales of securities—available-for-sale	522,564	369,755	232,620
Purchases of securities—held-to-maturity	(6,490)	(60,344)	(13,357)
Principal repayments and maturities of securities—held-to-maturity	11,817	11,009	12,978
Loan originations, net of repayments	(178,609)	(46,042)	(32,675)
Purchases of loans and participating interest in loans	(306,937)	(314,301)	(323,533)
Proceeds from sales of other loans	92,010	233,419	124,407
Proceeds from Divestiture of Businesses	113,222
Net cash received from acquisitions and branch divestitures		0	24,208
Purchases of property and equipment	(12,244)	(16,239)	(12,072)
Proceeds from Sale of Property, Plant, and Equipment	20,121	14,513	4,740
Proceeds from FHLB stock repurchase program	118,304	80,681	48,843
Purchase of FHLB stock	(116,132)	(77,130)	(23,634)
Other	254	2,707	1,092
Net cash (used by) provided from investing activities	(393,287)	146,447	15,059
FINANCING ACTIVITIES:
Increase in deposits, net	222,334	66,346	226,821
Proceeds from Federal Home Loan Bank Advances	150,000	0	0
Repayment of long term FHLB borrowing	(150,009)	(95,009)	(8)
Advances, net of (repayments) of overnight and short-term FHLB borrowings	(54,000)	16,400	(120,400)
(Decrease) increase in other borrowings, net	(9,825)	7,360	16,140
Cash dividends paid	(65,759)	(28,282)	(17,170)
Cash proceeds from issuance of shares for shareholder reinvestment plan	0	0	34
Cash paid for repurchase of common stock	(31,045)	(50,772)	0
Payments Related to Tax Withholding for Share-based Compensation	1,630	870	848
Net cash provided from (used by) financing activities	60,066	(84,827)	104,569
NET CHANGE IN CASH AND CASH EQUIVALENTS	13,481	(14,198)	135,845
CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR	247,719	261,917	126,072
CASH AND CASH EQUIVALENTS, END OF YEAR	261,200	247,719	261,917
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Interest paid in cash	18,875	16,722	12,252
Taxes paid in cash	35,500	36,153	27,256
NON-CASH INVESTING AND FINANCING TRANSACTIONS:
Loans, net of discounts, specific loss allowances and unearned income, transferred to real estate owned and other repossessed assets	10	9,146	4,456
Dividends accrued but not paid until after period end	8,226	7,662	6,271
Assets Disposed	(259,398)
ACQUISITIONS (DISPOSITIONS):
Assets acquired (disposed)		0	4,829,748
Liabilities Transfered	$ (160,465)
Liabilities assumed (transferred)		$ 0	$ 4,249,751

BASIS OF PRESENTATION AND SUMMA

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Business: Banner Corporation (Banner or the Company) is a bank holding company incorporated in the State of Washington. The Company is primarily engaged in the business of planning, directing and coordinating the business activities of two wholly-owned subsidiaries, Banner Bank and Islanders Bank. Banner Bank is a Washington-chartered commercial bank that conducts business from its headquarters in Walla Walla, Washington and, as of December 31, 2017 , its 175 branch offices located in Washington, Oregon, California and Idaho. Banner Bank also has 13 loan production offices located in Washington, Oregon, California, Idaho and Utah. Islanders Bank is also a Washington-chartered commercial bank that conducts business from three locations in San Juan County, Washington. Banner Corporation is subject to regulation by the Board of Governors of the Federal Reserve System (Federal Reserve Board). Banner Bank and Islanders Bank (the Banks) are subject to regulation by the Washington State Department of Financial Institutions, Division of Banks (DFI) and the Federal Deposit Insurance Corporation (the FDIC). The Company’s operating results depend primarily on its net interest income, which is the difference between interest income on interest-earning assets, consisting of loans and investment securities, and interest expense on interest-bearing liabilities, composed primarily of customer deposits, FHLB advances, other borrowings and junior subordinated debentures. Net income also is affected by the level of the Company’s non-interest income, including deposit fees and other service charges, gains and losses on the sale of securities, results of mortgage banking operations, which includes loan origination and servicing fees and gains and losses on the sale of loans, as well as non-interest expense, provisions for loan losses and income tax provisions. In addition, net income is affected by the net change in the value of certain financial instruments carried at fair value. Basis of Presentation and Principles of Consolidation: The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All material intercompany transactions, profits and balances have been eliminated. The consolidated financial statements of the Company have been prepared in accordance with generally accepted accounting principles in the United States (GAAP) and under the rules and regulations of the U.S. Securities and Exchange Commission (the SEC). Subsequent Events: The Company has evaluated events and transactions subsequent to December 31, 2017 for potential recognition or disclosure. Cash and Cash Equivalents: Cash and cash equivalents include cash and due from banks and temporary investments which are federal funds sold and interest bearing balances due from other banks. Cash and cash equivalents generally have maturities of three months or less at the date of purchase. Business Combinations: Business combinations are accounted for using the acquisition method of accounting and, accordingly, assets acquired and liabilities assumed, both tangible and intangible, and consideration exchanged are recorded at acquisition date fair values. The excess purchase consideration over fair value of net assets acquired is recorded as goodwill. In the event that the fair value of net assets acquired exceeds the purchase price, including fair value of liabilities assumed, a bargain purchase gain is recorded on that acquisition. Expenses incurred in connection with a business combination are expensed as incurred. Changes in deferred tax asset valuation allowances related to acquired tax uncertainties are recognized in net income after the measurement period. Use of Estimates: In the opinion of management, the accompanying consolidated statements of financial condition and related consolidated statements of operations, comprehensive income, changes in shareholders’ equity and cash flows reflect all adjustments (which include reclassification and normal recurring adjustments) that are necessary for a fair presentation in conformity with GAAP. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect amounts reported in the financial statements. Various elements of the Company’s accounting policies, by their nature, are inherently subject to estimation techniques, valuation assumptions and other subjective assessments. In particular, management has identified several accounting policies that, due to the judgments, estimates and assumptions inherent in those policies, are critical to an understanding of Banner’s financial statements. These policies relate to (i) the methodology for the recognition of interest income, (ii) determination of the provision and allowance for loan and lease losses, (iii) the valuation of financial assets and liabilities recorded at fair value, including other-than-temporary impairment (OTTI) losses, (iv) the valuation of intangible assets, such as goodwill, core deposit intangibles (CDI) and mortgage servicing rights, (v) the valuation of real estate held for sale, (vi) the valuation or recognition of deferred tax assets and liabilities and (vii) the valuation of assets and liabilities acquired in business combinations and subsequent recognition of related income and expense. These policies and judgments, estimates and assumptions are described in greater detail in subsequent Notes to the Consolidated Financial Statements. Management believes that the judgments, estimates and assumptions used in the preparation of the financial statements are appropriate based on the factual circumstances at the time. However, given the sensitivity of the financial statements to these critical accounting policies, the use of other judgments, estimates and assumptions could result in material differences in the Company’s results of operations or financial condition. Further, subsequent changes in economic or market conditions could have a material impact on these estimates and the Company’s financial condition and operating results in future periods. Securities: Securities are classified as held-to-maturity when the Company has the ability and positive intent to hold them to maturity. Securities classified as available-for-sale are available for future liquidity requirements and may be sold prior to maturity. Securities classified as trading are also available for future liquidity requirements and may be sold prior to maturity. Purchase premiums and discounts are recognized in interest income using the interest method over the terms of the securities. Securities classified as held-to-maturity are carried at cost, adjusted for amortization of premiums and accretion of discounts to maturity and, if appropriate, any other-than-temporary impairment losses. Securities classified as available-for-sale are recorded at fair value. Unrealized holding gains and losses on securities classified as available-for-sale are excluded from earnings and are reported net of tax as accumulated other comprehensive income (AOCI), a component of shareholders’ equity, until realized. Securities classified as trading are also recorded at fair value. Unrealized holding gains and losses on securities classified as trading are included in earnings. (See Note 18 for a more complete discussion of accounting for the fair value of financial instruments.) Declines in the fair value of securities below their cost that are deemed to be other-than-temporary are recognized in earnings as realized losses. Realized gains and losses on sale are computed on the specific identification method and are included in earnings on the trade date sold. The Company reviews investment securities on an ongoing basis for the presence of OTTI or permanent impairment, taking into consideration current market conditions, fair value in relationship to cost, extent and nature of the change in fair value, issuer rating changes and trends, whether the Company intends to sell a security or if it is likely that it will be required to sell the security before recovery of the amortized cost basis of the investment, which may be maturity, and other factors. For debt securities, if the Company intends to sell the security or it is likely that the Company will be required to sell the security before recovering its cost basis, the entire impairment loss would be recognized in earnings as an OTTI. If the Company does not intend to sell the security and it is not likely that the Company will be required to sell the security but the Company does not expect to recover the entire amortized cost basis of the security, only the portion of the impairment loss representing credit losses would be recognized in earnings. The credit loss on a security is measured as the difference between the amortized cost basis and the present value of the cash flows expected to be collected. Projected cash flows are discounted by the original or current effective interest rate depending on the nature of the security being measured for potential OTTI. The remaining impairment related to all other factors, the difference between the present value of the cash flows expected to be collected and fair value, is recognized as a charge to AOCI. Impairment losses related to all other factors are presented as separate categories within AOCI. For investment securities transferred from held-to-maturity to available-for-sale, unrealized gains or losses from the time of transfer are accreted or amortized over the remaining life of the debt security based on the amount and timing of future estimated cash flows. The accretion or amortization of the amount recorded in AOCI increases the carrying value of the investment and does not affect earnings. Investment in FHLB Stock: At December 31, 2017 , the Banks had $10.3 million in FHLB of Des Moines stock (FHLB stock), compared to $12.5 million at December 31, 2016 . The Banks' investments in FHLB stock are generally viewed as a long-term investment and are carried at par value ( $100 per share), which reasonably approximates its fair value. FHLB stock does not have a readily determinable fair value. Ownership of FHLB stock is restricted to the FHLB and member institutions and can only be purchased and redeemed at par. As members of the FHLB system, the Banks are required to maintain a minimum level of investment in FHLB stock based on specific percentages of their outstanding FHLB advances. Management periodically evaluates FHLB stock for impairment. Management's determination of whether these investments are impaired is based on its assessment of the ultimate recoverability of cost rather than by recognizing temporary declines in value. The determination of whether a decline affects the ultimate recoverability of cost is influenced by criteria such as (1) the significance of any decline in net assets of the FHLB as compared to the capital stock amount for the FHLB and the length of time this situation has persisted, (2) commitments by the FHLB to make payments required by law or regulation and the level of such payments in relation to the operating performance of the FHLB, (3) the impact of legislative and regulatory changes on institutions and, accordingly, the customer base of the FHLB, and (4) the liquidity position of the FHLB. The Company has determined there is no impairment on the FHLB stock investment as of December 31, 2017 . Loans Receivable: The Banks originate residential one- to four-family and multifamily mortgage loans for both portfolio investment and sale in the secondary market. The Banks also originate construction and land development, commercial real estate, commercial business, agricultural and consumer loans for portfolio investment. Loans receivable not designated as held for sale are recorded at the principal amount outstanding, net of allowance for loan losses, deferred fees, discounts and premiums. Premiums, discounts and deferred loan fees are amortized to maturity using the level-yield methodology. Some of the Company’s loans are reported as troubled debt restructures (TDRs). Loans are reported as TDRs when the Banks grant a concession(s) to a borrower experiencing financial difficulties that it would not otherwise consider. Examples of such concessions include forgiveness of principal or accrued interest, extending the maturity date(s) or providing a lower interest rate than would be normally available for a transaction of similar risk. As a result of these concessions, loans identified as TDRs are impaired as the Banks will not collect all amounts due, both principal and interest, in accordance with the terms of the original loan agreement. TDRs are accounted for in accordance with the Banks’ impaired loan accounting policies. Loans Held for Sale . Residential one- to four-family and multifamily mortgage loans originated with the intent to be sold in the secondary market are considered held for sale. Residential one- to four-family loans under best effort delivery commitments are carried at the lower of aggregate cost or estimated market value. Residential one- to four-family loans under mandatory delivery commitments are carried at fair value in order to match changes in the value of the loans with the value of the economic hedges on the loans. Fair values for residential mortgage loans held for sale are determined by comparing actual loan rates to current secondary market prices for similar loans. As of December 31, 2016 , multifamily held for sale loans were carried at the lower of aggregate cost or estimated market value. During 2017, the Company elected fair value accounting on newly originated multifamily held for sale loans; as a result, as of December 31, 2017 , multifamily held for sale loans are carried at fair value in order to match changes in the value of the loans with the value of the economic hedges on the loans. Fair values for multifamily loans held for sale are calculated based on discounted cash flows using a discount rate that is a combination of market spreads for similar loan types added to selected index rates. Net unrealized losses on loans held for sale that are carried at lower of cost or market are recognized through the valuation allowance by charges to income. Non-refundable fees and direct loan origination costs related to loans held for sale are recognized as part of the cost basis of the loan. Gains and losses on sales of loans held for sale are determined using the specific identification method and are recorded in the mortgage banking operations component of non-interest income . Acquired Loans: Purchased loans, including loans acquired in business combinations, are recorded at their fair value at the acquisition date. Credit discounts are included in the determination of fair value; therefore, an allowance for loan and lease losses is not recorded at the acquisition date. Acquired loans are evaluated upon acquisition and classified as either purchased credit-impaired or purchased non-credit-impaired. Purchased credit-impaired (PCI) loans reflect credit deterioration since origination such that it is probable at acquisition that the Company will be unable to collect all contractually required payments. The excess of the cash flows expected to be collected over a PCI pool's carrying value is considered to be the accretable yield and is recognized as interest income over the estimated life of the pool using the effective yield method. The excess of the undiscounted contractual balances due over the cash flows expected to be collected is considered to be the nonaccretable difference. The nonaccretable difference represents the Company's estimate of the credit losses expected to occur and was considered in determining the fair value of the loans as of the acquisition date. Subsequent to the acquisition date, any increases in expected cash flows over those expected at the purchase date are adjusted through a change to the accretable yield on a prospective basis. Any subsequent decreases in expected cash flows attributable to credit deterioration are recognized by recording a provision for loan losses. For purchased non-credit-impaired loans, the difference between the fair value and unpaid principal balance of the loan at the acquisition date is amortized or accreted to interest income over the life of the loans. Any subsequent deterioration in credit quality is recognized by recording a provision for loan losses. Income Recognition on Nonaccrual and Impaired Loans and Securities: Interest on loans and securities is accrued as earned unless management doubts the collectability of the asset or the unpaid interest. Interest accruals on loans are generally discontinued when loans become 90 days past due for payment of interest or principal and the loans are then placed on nonaccrual status. All previously accrued but uncollected interest is deducted from interest income upon transfer to nonaccrual status. For any future payments collected, interest income is recognized only upon management’s assessment that there is a strong likelihood that the full amount of a loan will be repaid or recovered. A loan may be put on nonaccrual status sooner than this policy would dictate if, in management’s judgment, the interest may be uncollectable. While less common, similar interest reversal and nonaccrual treatment is applied to investment securities if their ultimate collectability becomes questionable. Provision and Allowance for Loan Losses: The provision for loan losses reflects the amount required to maintain the allowance for loan losses at an appropriate level based upon management’s evaluation of the adequacy of general and specific loss reserves. The Company maintains an allowance for loan losses consistent in all material respects with GAAP. The Company has established systematic methodologies for the determination of the adequacy of the Company’s allowance for loan losses. The methodologies are set forth in a formal policy and take into consideration the need for a general valuation allowance as well as specific allowances that are tied to individual problem loans. The Company increases its allowance for loan losses by charging provisions for probable loan losses against its income and values impaired loans consistent with accounting guidelines. The allowance for loan losses is maintained at a level sufficient to provide for estimated losses based on evaluating known and inherent risks in the loan portfolio and upon the Company’s continuing analysis of the factors underlying the quality of the loan portfolio. These factors include, among others, changes in the size and composition of the loan portfolio, delinquency rates, actual loan loss experience, current economic conditions, detailed analysis of individual loans for which full collectability may not be assured, and determination of the existence and realizable value of the collateral and guarantees securing the loans. Realized losses related to specific assets are applied as a reduction of the carrying value of the assets and charged immediately against the allowance for loan loss reserve. Recoveries on previously charged off loans are credited to the allowance for loan losses. The reserve is based upon factors and trends identified by Banner at the time financial statements are prepared. Although the Company uses the best information available, future adjustments to the allowance for loan losses may be necessary due to economic, operating, regulatory and other conditions beyond the Company’s control. The adequacy of general and specific reserves is based on a continuing evaluation of the pertinent factors underlying the quality of the loan portfolio as well as individual review of certain large balance loans. Large groups of smaller-balance homogeneous loans are collectively evaluated for impairment. Loans that are collectively evaluated for impairment include residential real estate and consumer loans and, as appropriate, smaller balance non-homogeneous loans. Larger balance non-homogeneous residential construction and land, commercial real estate, commercial business loans and unsecured loans are individually evaluated for impairment. Loans are considered impaired when, based on current information and events, the Company determines that it is probable that it will be unable to collect all amounts due according to the contractual terms of the loan agreement. Factors involved in determining impairment include, but are not limited to, the financial condition of the borrower and the value of the underlying collateral. Impaired loans are measured based on the present value of expected future cash flows discounted at the loan’s effective interest rate or, as a practical expedient, at the loan’s observable market price, or if the loan is collateral dependent, at the fair value of collateral less selling costs. Subsequent changes in the value of impaired loans are included within the provision for loan losses in the same manner in which impairment initially was recognized or as a reduction in the provision that would otherwise be reported. The Company’s methodology for assessing the appropriateness of the allowance for loan losses consists of several key elements, which include specific allowances, an allocated formula allowance and an unallocated allowance. Losses on specific loans are provided for when the losses are probable and estimable. General loan loss reserves are established to provide for inherent loan portfolio risks not specifically provided for. The level of general reserves is based on analysis of potential exposures existing in the loan portfolio including evaluation of historical trends, current market conditions and other relevant factors identified by us at the time the financial statements are prepared. The formula allowance is calculated by applying loss factors to outstanding loans, excluding those loans that are subject to individual analysis for specific allowances. Loss factors are based on the Company’s historical loss experience adjusted for significant environmental considerations, including the experience of other banking organizations, which in the judgment of management affects the collectability of the loan portfolio as of the evaluation date. The unallocated allowance is based upon the Company’s evaluation of various factors that are not directly measured in the determination of the formula and specific allowances. While the Company believes the estimates and assumptions used in the determination of the adequacy of the allowance for loan losses are reasonable, there can be no assurance that such estimates and assumptions will not be proved incorrect in the future, or that the actual amount of future provisions will not exceed the amount of past provisions or that any increased provisions that may be required will not adversely impact the financial condition and results of operations of the Company. In addition, the determination of the amount of the allowance for loan losses is subject to review by bank regulators as part of the routine examination process, which may result in the adjustment of reserves based upon their judgment of information available to them at the time of their examination. Loan Origination and Commitment Fees: Loan origination fees, net of certain specifically defined direct loan origination costs, are deferred and recognized as an adjustment of the loans’ interest yield using the level-yield method over the contractual term of each loan adjusted for actual loan prepayment experience. Net deferred fees or costs related to loans held for sale are recognized as part of the cost basis of the loan. Loan commitment fees are deferred until the expiration of the commitment period unless management believes there is a remote likelihood that the underlying commitment will be exercised, in which case the fees are amortized to fee income using the straight-line method over the commitment period. If a loan commitment is exercised, the deferred commitment fee is accounted for in the same manner as a loan origination fee. Deferred commitment fees associated with expired commitments are recognized as fee income. Reserve for Unfunded Commitments: A reserve for unfunded commitments is maintained at a level that, in the opinion of management, is adequate to absorb probable losses associated with the Banks' commitments to lend funds under existing agreements such as letters or lines of credit. Management determines the adequacy of the reserve for unfunded commitments based upon reviews of individual credit facilities, current economic conditions, the risk characteristics of the various categories of commitments and other relevant factors. The reserve is based on estimates and ultimate losses may vary from the current estimates. These estimates are evaluated on a regular basis and, as adjustments become necessary, they are reported in earnings in the periods in which they become known. Draws on unfunded commitments that are considered uncollectible at the time funds are advanced are charged to the allowance for loan losses. Provisions for unfunded commitment losses are recognized in non-interest expense and added to the reserve for unfunded commitments, which is included in other liabilities. Real Estate Owned: Property acquired by foreclosure or deed in lieu of foreclosure is initially recorded at the estimated fair value of the property, less expected selling costs. Development and improvement costs relating to the property are capitalized while direct holding costs are expensed. The carrying value of the property is periodically evaluated by management and, if necessary, allowances are established to reduce the carrying value to net realizable value. Gains or losses at the time the property is sold are charged or credited to operations in the period in which they are realized. The amounts the Banks will ultimately recover from real estate held for sale may differ substantially from the carrying value of the assets because of market factors beyond the Banks’ control or because of changes in the Banks’ strategies for recovering the investment. Property and Equipment: Property and equipment is carried at cost less accumulated depreciation. Depreciation is based upon the straight-line method applied to individual assets and groups of assets acquired in the same year over the lesser of their estimated useful lives or the related lease terms of the assets: Buildings and leased improvements 10–39 years Furniture and equipment 3 – 10 years Routine maintenance, repairs and replacement costs are expensed as incurred. Expenditures which significantly increase values or extend useful lives are capitalized. The Company reviews buildings, leasehold improvements and equipment for impairment whenever events or changes in circumstances indicate that the undiscounted cash flows for the property are less than its carrying value. If identified, an impairment loss is recognized through a charge to earnings based on the fair value of the property. Held for sale property is recorded at the lower of the estimated fair value of the property, less expected selling costs, or the book value at the date the property is transferred to held for sale. Depreciation is not recorded on held for sale property. Goodwill: Goodwill represents the excess of the purchase consideration over the fair value of the assets acquired, net of the fair values of liabilities assumed in a business combination and is not amortized but is reviewed annually, or more frequently as current circumstances and conditions warrant, for impairment. An assessment of qualitative factors is completed to determine if it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If the qualitative analysis concludes that further analysis is required, then a quantitative impairment test would be completed. The quantitative goodwill impairment test is used to identify the existence of impairment and the amount of impairment loss and compares the reporting unit's estimated fair values, including goodwill, to its carrying amount. If the fair value exceeds the carry amount then goodwill is not considered impaired. If the carrying amount exceeds its fair value, an impairment loss would be recognized equal to the amount of excess, limited to the amount of total goodwill allocated to that reporting unit. The impairment loss would be recognized as a charge to earnings. The disposal of a portion of a reporting unit that meets the definition of a business requires goodwill to be allocated for purposes of determining the gain or loss on disposal. Since the sale of the Utah branches met the definition of a business, goodwill was allocated to the sale based on the fair value of the Utah branches compared to the relative fair value of the reporting unit. Other Intangible Assets: Other intangible assets consist primarily of core deposit intangibles (CDI), which are amounts recorded in business combinations or deposit purchase transactions related to the value of transaction-related deposits and the value of the customer relationships associated with the deposits. CDI is being amortized on an accelerated basis over a weighted average estimated useful life of three to ten years. These assets are reviewed at least annually for events or circumstances that could impact their recoverability. These events could include loss of the underlying core deposits, increased competition or adverse changes in the economy. To the extent other identifiable intangible assets are deemed unrecoverable, impairment losses are recorded in other non-interest expense to reduce the carrying amount of the assets. Other intangibles also include favorable leasehold intangibles (LHI). LHI represents the value assigned to leases assumed in an acquisition in which the lease terms are favorable compared to a market lease at the date of acquisition. LHI is amortized over the underlying lease term and is reviewed at least annually for events or circumstances that could impair the value. Mortgage Servicing Rights: Servicing assets are recognized as separate assets when rights are acquired through purchase or sale of loans. Generally, purchased servicing rights are capitalized at the cost to acquire the rights. For sales of mortgage loans, the value of the servicing right is estimated and capitalized. Fair values are estimated based on an independent dealer analysis of discounted cash flows. Capitalized servicing rights are reported in other assets and are amortized into mortgage banking operations in proportion to, and over the period of, the estimated future net servicing income of the underlying financial assets. Servicing assets are evaluated for impairment based upon the fair value of the rights as compared to amortized cost. Impairment is determined by stratifying rights into tranches based on predominant risk characteristics for the underlying loans, such as interest rate, balance outstanding, loan type, age and remaining term, and investor type. Impairment is recognized through a valuation allowance for an individual tranche, to the extent that fair value is less than the capitalized amount for the tranche. If the Company later determines that all or a portion of the impairment no longer exists for a particular tranche, a reduction of the allowance may be recorded as an increase to income. Servicing fee income is recorded for fees earned for servicing loans and is reflected in mortgage banking operations on the Consolidated Statements of Operations. The fees are based on a contractual percentage of the outstanding principal or a fixed amount per loan and are recorded as income when earned. The amortization of mortgage servicing rights is netted against loan servicing fee income. Bank-Owned Life Insurance (BOLI): The Banks have purchased, or acquired through mergers, life insurance policies in connection with the implementation of certain executive supplemental income, salary continuation and deferred compensation retirement plans. These policies provide protection against the adverse financial effects that could result from the death of a key employee and provide tax-exempt income to offset expenses associated with the plans. It is the Banks’ intent to hold these policies as a long-term investment; however, there may be an income tax impact if the Bank chooses to surrender certain policies. Although the lives of individual current or former management-level employees are insured, the Banks are the respective owners and sole or partial beneficiaries. Derivative Instruments: Deriv

ACCOUNTING STANDARDS RECENTLY A

ACCOUNTING STANDARDS RECENTLY ADOPTED OR ISSUED	12 Months Ended
	Dec. 31, 2017
Accounting Changes and Error Corrections [Abstract]
ACCOUNTING STANDARDS RECENTLY ADOPTED OR ISSUED	ACCOUNTING STANDARDS RECENTLY ISSUED OR ADOPTED Revenue from Contracts with Customers In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers , which creates Topic 606 and supersedes Topic 605, Revenue Recognition . The core principle of Topic 606 is that an entity recognizes 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. In general, the new guidance requires companies to use more judgment and make more estimates than under current guidance, including identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. Under the terms of ASU 2015-14 the standard is effective for interim and annual periods beginning after December 15, 2017. For financial reporting purposes, the standard allows for either full retrospective adoption, meaning the standard is applied to all of the periods presented, or modified retrospective adoption, meaning the standard is applied only to the most current period presented in the financial statements with the cumulative effect of initially applying the standard recognized at the date of initial application. Management adopted the new guidance on January 1, 2018. Management has completed its identification of all revenue streams included in the financial statements (excluding interest income, which is outside of the scope of the pronouncement) and identified which revenue streams are within the scope of the pronouncement. Management is finalizing its evaluation on whether the implementation of this ASU will result in any accounting changes for the revenue streams within the scope of this ASU. Management does not expect the adoption of this ASU to have a material impact on the Company’s Consolidated Financial Statements other than reclassification of expenses from non-interest expense to non-interest income and additional disclosure requirements. In April 2016, FASB issued ASU No. 2016-10, Identifying Performance Obligations and Licensing . The amendments in this ASU do not change the core principle of the guidance in Topic 606. Rather, the amendments in this ASU clarify the following two aspects of Topic 606: identifying performance obligations and the licensing implementation guidance, while retaining the related principles for those areas. The amendments in this ASU affect the guidance in ASU 2014-09, discussed above, which is not yet effective. The effective date and transition requirements for the amendments in this ASU are the same as the effective date and transition requirements in Topic 606 ( Revenues from Contracts with Customers ). Refer to Company's status of implementation in the first paragraph of this section. In May 2016, FASB issued ASU No. 2016-12, Narrow-Scope Improvements and Practical Expedients , amending ASC Topic 606 ( Revenue from Contracts with Customers ). The amendments in this ASU do not change the core principle of the guidance in Topic 606. Rather, the amendments in this ASU affect only several narrow aspects of Topic 606. The amendments in this ASU affect the guidance in ASU 2014-09, discussed above, which is not yet effective. The effective date and transition requirements for the amendments in this ASU are the same as the effective date and transition requirements in Topic 606. Refer to Company's status of implementation in the first paragraph of this section. Recognition and Measurement of Financial Assets and Financial Liabilities In January 2016, FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities . The amendments in this ASU require equity securities to be measured at fair value with changes in the fair value recognized through net income. The amendments allow equity investments that do not have readily determinable fair values to be remeasured at fair value under certain circumstances and require enhanced disclosures about those investments. This ASU simplifies the impairment assessment of equity investments without readily determinable fair values. This ASU also eliminates the requirement to disclose the method(s) 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. The amendments in this ASU require separate presentation in other comprehensive income of 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. This ASU excludes from net income gains or losses that the entity may not realize because those financial liabilities are not usually transferred or settled at their fair values before maturity. The amendments in this ASU require separate presentation of financial assets and financial liabilities by measurement category and form of financial asset (that is, securities or loans and receivables) on the balance sheet or in the accompanying notes to the financial statements. The amendments in this ASU are effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. At December 31, 2017 , Banner held $5.6 million of available-for-sale equity investment securities. The provisions of ASU No. 2016-01 require changes in the value of equity securities to be recognized in the income statement which could result in additional volatility in income. Leases (Topic 842) In February 2016, FASB issued ASU No. 2016-02, Leases (Topic 842) . The amendments in this ASU require lessees to recognize the following for all leases (with the exception of short-term) at the commencement date; a lease liability, which is a lessee‘s obligation to make lease payments arising from a lease, measured on a discounted basis; and a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. The amendments in this ASU leave lessor accounting largely unchanged, although certain targeted improvements were made to align lessor accounting with the lessee accounting model. This ASU simplifies the accounting for sale and leaseback transactions primarily because lessees must recognize lease assets and lease liabilities. Lessees will no longer be provided with a source of off-balance sheet financing. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early application is permitted upon issuance. Lessees (for capital and operating leases) and lessors (for sales-type, direct financing, and operating leases) must apply a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The modified retrospective approach would not require any transition accounting for leases that expired before the earliest comparative period presented. Lessees and lessors may not apply a full retrospective transition approach. The Company is currently evaluating the provisions of ASU No. 2016-02 to determine the potential impact the new standard will have on the Company's Consolidated Financial Statements and regulatory capital ratios and has contracted with a third party software solution to meet new requirements of this ASU with implementation to begin later in 2018. The Company leases 108 buildings and offices under non-cancelable operating leases, the majority of which will be subject to this ASU. While the Company has not quantified the impact to its balance sheet, upon the adoption of this ASU the Company expects to report increased assets and increased liabilities on its Consolidated Statements of Financial Condition as a result of recognizing right-of-use assets and lease liabilities related to these leases and certain equipment under non-cancelable operating lease agreements, which currently are not reflected in its Consolidated Statements of Financial Condition. Derivatives and Hedging (Topic 815) In August 2017, FASB issued ASU No. 2017-12, Targeted Improvements to Accounting for Hedging Activities . The amendments in this ASU are intended to provide investors better insight to an entity's risk management hedging strategies by permitting a company to recognize the economic results of its hedging strategies in its financial statements. The amendments in this ASU permit hedge accounting for hedging relationships involving nonfinancial risk and interest rate risk by removing certain limitations in cash flow and fair value hedging relationships. In addition, the ASU requires an entity to present the earnings effect of the hedging instrument in the same income statement line item in which the earnings effect of the hedged item is reported. This ASU is effective for fiscal years beginning after December 15, 2018, and early adoption is permitted. Adoption of ASU 2017-12 is not expected to have a material impact on the Company's Consolidated Financial Statements. Financial Instruments—Credit Losses (Topic 326) In June 2016, FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments . Current GAAP requires an “incurred loss” methodology for recognizing credit losses that delays recognition until it is probable a loss has been incurred. The main objective of this ASU is to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. The ASU affects loans, debt securities, trade receivables, net investments in leases, off-balance-sheet credit exposures, reinsurance receivables, and any other financial asset not excluded from the scope that have the contractual right to receive cash. The ASU replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. This ASU require a financial asset (or group of financial assets) measured at amortized cost basis to be presented at the net amount expected to be collected. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial asset(s) to present the net carrying value at the amount expected to be collected on the financial asset. The measurement of expected credit losses will be based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. This ASU broadens the information that an entity must consider in developing its expected credit loss estimate for assets measured either collectively or individually. The use of forecasted information incorporates more timely information in the estimate of expected credit loss, which will be more decision useful to users of the financial statements. This ASU will be effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. The Company is still evaluating the effects this ASU will have on the Company’s Consolidated Financial Statements. The Company has formed an internal committee to oversee the project, engaged a third-party vendor to assist with the project and is nearing completion of its gap analysis phase of the project. Upon adoption, the Company expects changes in the processes and procedures used to calculate the allowance for loan losses, including changes in assumptions and estimates to consider expected credit losses over the life of the loan versus the current accounting practice that utilizes the incurred loss model. The new guidance may result in an increase in the allowance for loan losses which will also reflect the new requirement to include the nonaccretable principal differences on purchased credit-impaired loans; however, the Company is still in the process of determining the magnitude of the change and its impact on the Consolidated Financial Statements. In addition, the current accounting policy and procedures for other-than-temporary impairment on investment securities available-for-sale will be replaced with an allowance approach. The Company has begun developing and implementing processes to address this ASU. Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20) In March 2017, FASB issued ASU No. 2017-08, Premium Amortization on Purchased Callable Debt Securities . This ASU shortens the amortization period for certain callable debt securities held at a premium. Specifically, the ASU requires the premium to be amortized to the earliest call date. Under current GAAP, premiums and discounts on callable debt securities generally are amortized to the maturity date. The ASU does not require an accounting change for securities held at a discount; the discount continues to be amortized to the maturity date. This ASU more closely align the amortization period of premiums and discounts to expectations incorporated in market pricing on the underlying securities. This ASU is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The Company is still evaluating the effects this ASU will have on the Company’s Consolidated Financial Statements. Application of US GAAP to the Tax Cuts and Jobs Act On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118 (SAB 118) to address the application of US GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the 2017 Tax Act. SAB 118 provides guidance to registrants under three scenarios: (1) Measurement of certain income tax effects is complete, (2) Measurement of certain income tax effects can be reasonably estimated and (3) Measurement of certain income tax effects cannot be reasonably estimated. SAB 118 provides a one year measurement period for the registrant to complete its accounting for certain income tax effects that are considered provisional or for which reasonable estimates cannot be made. The Company recognized the income tax effects of the 2017 Tax Act in its 2017 financial statements in accordance with SAB 118. Income Statement - Reporting Comprehensive Income (Topic 220) In February 2018, FASB Issued ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. This ASU allows a reclassification from AOCI to retained earnings for stranded tax effects resulting from the 2017 Tax Act. The ASU eliminates the stranded tax effects resulting from the 2017 Tax Act and improves the usefulness of information reported to financial statement users. The ASU also requires certain disclosures about the stranded tax effects. This ASU is effective for all entities for fiscal years beginning after December 15, 2018. Early adoption is permitted, including adoption in any interim period, for reporting periods for which financial statements have not yet been issued. The ASU should be applied to either in the period of adoption or retrospectively to each period in which the effect of the change in the federal corporate tax rate is recognized. The Company elected to early adopt this ASU and to reclassify $795,000 of stranded tax effects from AOCI to retained earnings in the fourth quarter of 2017.

BRANCH DIVESTITURE BRANCH DIVES

BRANCH DIVESTITURE BRANCH DIVESTITURE (Notes)	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Schedule of Noncash or Part Noncash Divestitures [Table Text Block]	BRANCH DIVESTITURE On October 6, 2017, Banner Bank completed the sale of its Utah branches and related assets and liabilities to People’s Intermountain Bank, a banking subsidiary of People’s Utah Bancorp (NASDAQ: PUB). Under the terms of the purchase and assumption agreement, the sale included $253.8 million in loans, $160.3 million in deposits and all of Banner Bank’s seven Utah bank branches located in Provo, Orem, Salem, Springville, South Jordan, Salt Lake City and Woods Cross. The sale also included $4.0 million of property and equipment and $581,000 of accrued interest. In addition, Banner allocated an associated $1.9 million of goodwill and $1.1 million of other intangible assets with the divestiture, which constituted the disposal of a business. The deposit premium paid to Banner was $13.8 million based on average daily deposits for a period prior to closing. The net gain recorded on the sale was $12.2 million .

SECURITIES

SECURITIES	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
SECURITIES	SECURITIES The amortized cost, gross unrealized gains and losses and estimated fair value of securities at December 31, 2017 and 2016 are summarized as follows (in thousands): December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Trading: Municipal bonds $ 100 $ 100 Corporate bonds 27,132 22,058 Equity securities 14 160 $ 27,246 $ 22,318 Available-for-Sale: U.S. Government and agency obligations $ 72,829 $ 68 $ (431 ) $ 72,466 Municipal bonds 68,513 665 (445 ) 68,733 Corporate bonds 5,431 6 (44 ) 5,393 Mortgage-backed or related securities 745,956 1,003 (7,402 ) 739,557 Asset-backed securities 27,667 184 (93 ) 27,758 Equity securities 5,716 10 (148 ) 5,578 $ 926,112 $ 1,936 $ (8,563 ) $ 919,485 Held-to-Maturity: U.S. Government and agency obligations $ 1,024 $ 29 $ — $ 1,053 Municipal bonds: 189,860 3,385 (1,252 ) 191,993 Corporate bonds 3,978 7 — 3,985 Mortgage-backed or related securities 65,409 266 (518 ) 65,157 $ 260,271 $ 3,687 $ (1,770 ) $ 262,188 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Trading: U.S. Government and agency obligations $ 1,230 $ 1,326 Municipal bonds 331 335 Corporate bonds 26,959 21,143 Mortgage-backed or related securities 1,620 1,641 Equity securities 14 123 $ 30,154 $ 24,568 Available-for-Sale: U.S. Government and agency obligations $ 57,288 $ 146 $ (456 ) $ 56,978 Municipal bonds 110,487 455 (1,089 ) 109,853 Corporate bonds 10,255 77 (49 ) 10,283 Mortgage-backed or related securities 598,899 2,064 (6,251 ) 594,712 Asset-backed securities 29,319 — (326 ) 28,993 Equity securities 5,599 10 — 5,609 $ 811,847 $ 2,752 $ (8,171 ) $ 806,428 Held-to-Maturity: U.S. Government and agency obligations $ 1,065 $ — $ (18 ) $ 1,047 Municipal bonds: 196,989 4,173 (1,272 ) 199,890 Corporate bonds 3,876 — — 3,876 Mortgage-backed or related securities 65,943 309 (537 ) 65,715 $ 267,873 $ 4,482 $ (1,827 ) $ 270,528 At December 31, 2017 and 2016 , the gross unrealized losses and the fair value for securities available-for-sale and held-to-maturity aggregated by the length of time that individual securities have been in a continuous unrealized loss position was as follows (in thousands): December 31, 2017 Less Than 12 Months 12 Months or More Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Available-for-Sale: U.S. Government and agency obligations $ 31,276 $ (211 ) $ 23,341 $ (220 ) $ 54,617 $ (431 ) Municipal bonds 20,879 (185 ) 13,360 (260 ) 34,239 (445 ) Corporate bonds 296 (4 ) 4,682 (40 ) 4,978 (44 ) Mortgage-backed or related securities 559,916 (5,138 ) 100,662 (2,264 ) 660,578 (7,402 ) Asset-backed securities — — 9,926 (93 ) 9,926 (93 ) Equity securities 5,480 (148 ) — — 5,480 (148 ) $ 617,847 $ (5,686 ) $ 151,971 $ (2,877 ) $ 769,818 $ (8,563 ) Held-to-Maturity: Municipal bonds $ 21,839 $ (171 ) $ 34,314 $ (1,081 ) $ 56,153 $ (1,252 ) Mortgage-backed or related securities 38,023 (378 ) 4,434 (140 ) 42,457 (518 ) $ 59,862 $ (549 ) $ 38,748 $ (1,221 ) $ 98,610 $ (1,770 ) December 31, 2016 Less Than 12 Months 12 Months or More Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Available-for-Sale: U.S. Government and agency obligations $ 39,043 $ (442 ) $ 1,012 $ (14 ) $ 40,055 $ (456 ) Municipal bonds 60,765 (1,087 ) 556 (2 ) 61,321 (1,089 ) Corporate bonds 5,206 (49 ) — — 5,206 (49 ) Mortgage-backed or related securities 403,431 (5,604 ) 47,467 (647 ) 450,898 (6,251 ) Asset-backed securities 9,928 (101 ) 19,064 (225 ) 28,992 (326 ) $ 518,373 $ (7,283 ) $ 68,099 $ (888 ) $ 586,472 $ (8,171 ) Held-to-Maturity: U.S. Government and agency obligations $ 1,047 $ (18 ) $ — $ — $ 1,047 $ (18 ) Municipal bonds $ 64,802 $ (1,267 ) $ 204 $ (5 ) $ 65,006 $ (1,272 ) Mortgage-backed or related securities 42,245 (537 ) — — 42,245 (537 ) $ 108,094 $ (1,822 ) $ 204 $ (5 ) $ 108,298 $ (1,827 ) At December 31, 2017 , there were 226 securities—available-for-sale with unrealized losses, compared to 243 at December 31, 2016 . At December 31, 2017 , there were 66 securities—held-to-maturity with unrealized losses, compared to 73 at December 31, 2016 . Management does not believe that any individual unrealized loss as of December 31, 2017 or 2016 represented OTTI. The decline in fair market value of these securities was generally due to changes in interest rates. Sales of securities—trading totaled $1.3 million with a resulting net gain of $28,000 for the year ended December 31, 2017 and totaled $7.8 million with a resulting net gain of $530,000 for the year ended December 31, 2016 . Sales of securities—trading for the year ended December 31, 2015 totaled $4.4 million with a resulting net loss of $690,000 . The Company did no t recognize any OTTI charges or recoveries on securities—trading during the years ended December 31, 2017 , 2016 or 2015. There were no securities—trading in a nonaccrual status at December 31, 2017 and 2016 . Net unrealized holding gains of $658,000 were recognized in 2017 and losses of $376,000 in 2016 . Sales of securities—available-for-sale totaled $522.6 million with a resulting net loss of $2.1 million for the year ended December 31, 2017 . Sales of securities—available-for-sale totaled $369.8 million with a resulting net gain of $311,000 for the year ended December 31, 2016 . Sales of securities—available-for-sale totaled $232.6 million with a resulting net gain of $126,000 for the year ended December 31, 2015 . There were no securities—available-for-sale in a nonaccrual status at December 31, 2017 and 2016 . There were no sales of securities—held-to-maturity during the years ended December 31, 2017 , 2016 or 2015 . There were no securities—held-to-maturity in a nonaccrual status at December 31, 2017 and 2016 . The amortized cost and estimated fair value of securities at December 31, 2017 , by contractual maturity, are shown below (in thousands). Expected maturities will differ from contractual maturities because some securities may be called or prepaid with or without call or prepayment penalties. December 31, 2017 Trading Available-for-Sale Held-to-Maturity Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Maturing in one year or less $ 100 $ 100 $ 3,241 $ 3,230 $ 1,968 $ 1,967 Maturing after one year through five years — — 39,513 39,070 37,734 37,626 Maturing after five years through ten years — — 215,837 213,923 97,736 98,747 Maturing after ten years through twenty years 17,132 14,543 100,862 101,181 84,352 86,249 Maturing after twenty years 10,000 7,515 560,943 556,503 38,481 37,599 27,232 22,158 920,396 913,907 260,271 262,188 Equity securities 14 160 5,716 5,578 — — $ 27,246 $ 22,318 $ 926,112 $ 919,485 $ 260,271 $ 262,188 The following table presents, as of December 31, 2017 , investment securities which were pledged to secure borrowings, public deposits or other obligations as permitted or required by law (in thousands): Carrying Value Amortized Cost Fair Value Purpose or beneficiary: State and local governments public deposits $ 126,512 $ 126,438 $ 128,984 Interest rate swap counterparties 14,698 14,740 14,703 Repurchase transaction accounts 123,911 124,049 123,936 Other 3,924 3,924 3,835 Total pledged securities $ 269,045 $ 269,151 $ 271,458

LOANS RECEIVABLE AND THE ALLOWA

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES	LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES Loans receivable at December 31, 2017 and 2016 are summarized as follows (dollars in thousands): December 31, 2017 December 31, 2016 Amount Percent of Total Amount Percent of Total Commercial real estate: Owner-occupied $ 1,284,363 16.9 % $ 1,352,999 18.1 % Investment properties 1,937,423 25.5 1,986,336 26.7 Multifamily real estate 314,188 4.1 248,150 3.3 Commercial construction 148,435 2.0 124,068 1.7 Multifamily construction 154,662 2.0 124,126 1.7 One- to four-family construction 415,327 5.5 375,704 5.0 Land and land development: Residential 164,516 2.2 170,004 2.3 Commercial 24,583 0.3 29,184 0.4 Commercial business 1,279,894 16.8 1,207,879 16.2 Agricultural business, including secured by farmland 338,388 4.4 369,156 5.0 One- to four-family residential 848,289 11.2 813,077 10.9 Consumer: Consumer secured by one- to four-family 522,931 6.9 493,211 6.6 Consumer—other 165,885 2.2 157,254 2.1 Total loans outstanding 7,598,884 100.0 % 7,451,148 100.0 % Less allowance for loan losses (89,028 ) (85,997 ) Net loans $ 7,509,856 $ 7,365,151 Loan amounts included net unamortized costs of $158,000 at December 31, 2017 and were net of unearned fees of $5.8 million at December 31, 2016 . Net loans include net discounts on acquired loans of $21.1 million and $31.1 million as of December 31, 2017 and 2016 , respectively. The Company’s loans to directors, executive officers and related entities are on substantially the same terms and underwriting as those prevailing at the time for comparable transactions with unrelated persons and do not involve more than normal risk of collectability. Such loans had balances of $3.5 million and $4.3 million at December 31, 2017 and 2016 , respectively. Purchased credit-impaired loans: The outstanding contractual unpaid principal balance of PCI loans, excluding acquisition accounting adjustments, were $32.5 million at December 31, 2017 and $48.4 million at December 31, 2016 . The carrying balance of PCI loans were $21.3 million at December 31, 2017 and $32.3 million at December 31, 2016 . The following table presents the changes in the accretable yield for PCI loans for the years ended December 31, 2017 and 2016 (in thousands): Years Ended December 31 2017 2016 Balance, beginning of period $ 8,717 $ 10,375 Accretion to interest income (5,929 ) (9,333 ) Disposals and other (564 ) (1,018 ) Reclassifications from non-accretable difference 4,296 8,693 Balance, end of period $ 6,520 $ 8,717 As of December 31, 2017 and December 31, 2016, the non-accretable difference between the contractually required payments and cash flows expected to be collected was $11.3 million and $15.7 million , respectively. Impaired Loans and the Allowance for Loan Losses: A loan is considered impaired when, based on current information and circumstances, the Company determines it is probable that it will be unable to collect all amounts due according to the contractual terms of the loan agreement, including scheduled interest payments. Factors involved in determining impairment include, but are not limited to, the financial condition of the borrower, the value of the underlying collateral and the current status of the economy. Impaired loans are comprised of loans on nonaccrual, TDRs, and loans that are 90 days or more past due, but are still on accrual. Purchased credit-impaired loans are considered performing within the scope of the PCI accounting guidance and are not included in the impaired loan tables. The following tables provide additional information on impaired loans, excluding PCI loans, with and without specific allowance reserves at December 31, 2017 and 2016 . Recorded investment includes the unpaid principal balance or the carrying amount of loans less charge-offs and net deferred loan fees (in thousands): December 31, 2017 Unpaid Principal Balance Recorded Investment Related Allowance Without Allowance (1) With Allowance (2) Commercial real estate: Owner-occupied $ 7,807 $ 6,447 $ 199 $ 18 Investment properties 11,296 4,200 6,884 263 One- to four-family construction 298 298 — — Land and land development: Residential 1,134 798 — — Commercial business 4,441 3,424 555 50 Agricultural business/farmland 9,388 6,230 3,031 264 One- to four-family residential 9,547 3,709 5,775 178 Consumer: Consumer secured by one- to four-family 1,498 1,324 139 7 Consumer—other 134 58 73 2 $ 45,543 $ 26,488 $ 16,656 $ 782 December 31, 2016 Unpaid Principal Balance Recorded Investment Related Allowance Without Allowance (1) With Allowance (2) Commercial real estate: Owner-occupied $ 3,786 $ 3,373 $ 203 $ 20 Investment properties 9,916 5,565 4,304 408 Multifamily real estate 508 147 349 64 One- to four-family construction 1,180 — 1,180 156 Land and land development: Residential 3,012 750 1,106 219 Commercial 1,608 998 — — Commercial business 3,753 3,074 651 69 Agricultural business/farmland 6,438 6,354 — — One- to four-family residential 11,439 3,149 8,026 479 Consumer: Consumer secured by one- to four-family 1,904 1,721 144 1 Consumer—other 391 226 166 4 $ 43,935 $ 25,357 $ 16,129 $ 1,420 (1) Includes loans without an allowance reserve that have been individually evaluated for impairment and that evaluation concluded that no reserve was needed, and $10.6 million and $10.0 million of homogenous and small balance loans as of December 31, 2017 and December 31, 2016 , respectively, that are collectively evaluated for impairment for which a general reserve has been established. (2) Loans with a specific allowance reserve have been individually evaluated for impairment using either a discounted cash flow analysis or, for collateral dependent loans, current appraisals less costs to sell to establish realizable value. The following table summarizes our average recorded investment and interest income recognized on impaired loans by loan class for the years ended December 31, 2017 , 2016 and 2015 (in thousands): Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Commercial real estate: Owner-occupied $ 3,697 $ 11 $ 2,721 $ 2 $ 1,467 $ 9 Investment properties 9,136 195 18,529 242 8,003 303 Multifamily real estate 251 10 513 21 362 18 One- to four-family construction 418 27 1,158 75 1,463 114 Land and land development: Residential 1,396 42 1,948 85 2,406 49 Commercial 867 — 1,003 — 931 — Commercial business 5,996 68 4,290 37 1,667 35 Agricultural business/farmland 6,184 207 5,004 119 1,143 19 One- to four-family residential 9,499 322 11,976 441 17,770 630 Consumer: Consumer secured by one- to four-family 1,635 9 1,778 17 736 11 Consumer—other 184 7 615 17 392 18 $ 39,263 $ 898 $ 49,535 $ 1,056 $ 36,340 $ 1,206 The following table presents TDRs by accrual and nonaccrual status at December 31, 2017 and 2016 (in thousands): December 31, 2017 December 31, 2016 Accrual Status Nonaccrual Status Total TDRs Accrual Nonaccrual Total Commercial real estate: Owner-occupied $ 199 $ 87 $ 286 $ 203 $ 96 $ 299 Investment properties 6,884 — 6,884 4,304 — 4,304 Multifamily real estate — — — 349 — 349 One- to four-family construction — — — 1,180 — 1,180 Land and land development: Residential — — — 1,106 — 1,106 Commercial business 555 — 555 653 — 653 Agricultural business/farmland 3,129 29 3,158 3,125 79 3,204 One- to four-family residential 5,136 801 5,937 7,678 843 8,521 Consumer: Consumer secured by one- to four-family 139 — 139 143 6 149 Consumer—other 73 — 73 166 — 166 $ 16,115 $ 917 $ 17,032 $ 18,907 $ 1,024 $ 19,931 As of December 31, 2017 and 2016 , the Company had commitments to advance funds up to an additional amount of $45,000 and $127,000 , respectively, related to TDRs. The following table presents new TDRs that occurred during the years ended December 31, 2017 , 2016 and 2015 (dollars in thousands): Number of Contracts Pre-modification Outstanding Recorded Investment Post-modification Outstanding Recorded Investment Year Ended December 31, 2017 Recorded Investment (1) (2) Commercial real estate: Investment properties 1 3,714 3,714 Total 1 $ 3,714 $ 3,714 Year Ended December 31, 2016 Recorded Investment (1) (2) Commercial real estate: Owner-occupied 1 $ 194 $ 194 One- to four-family residential 1 $ 78 $ 78 Total 2 $ 272 $ 272 Year Ended December 31, 2015 Recorded Investment (1) (2) Land and land development: Residential 2 $ 1,302 $ 483 Agricultural business/farmland 3 $ 822 $ 822 One- to four-family residential 2 $ 431 $ 431 Total 7 $ 2,555 $ 1,736 (1) Since most loans were already considered classified and/or on non-accrual status prior to restructuring, the modifications did not have a material effect on the Company’s determination of the allowance for loan losses. (2) Generally these modifications do not fit into one separate type, such as rate, term, amount, interest-only or payment, but instead are a combination of multiple types of modifications; therefore, they are disclosed in aggregate. There were no TDRs which incurred a payment default within the year ended December 31, 2017 for which the payment default occurred within twelve months of the restructure date. There were no TDRs that incurred a payment default in the year ended December 31, 2016. A default on a restructured loan results in a transfer to nonaccrual status, a charge-off or a combination of both. Credit Quality Indicators : To appropriately and effectively manage the ongoing credit quality of the Company’s loan portfolio, management has implemented a risk-rating or loan grading system for its loans. The system is a tool to evaluate portfolio asset quality throughout each applicable loan’s life as an asset of the Company. Generally, loans and leases are risk rated on an aggregate borrower/relationship basis with individual loans sharing similar ratings. There are some instances when specific situations relating to individual loans will provide the basis for different risk ratings within the aggregate relationship. Loans are graded on a scale of 1 to 9. A description of the general characteristics of these categories is shown below: Overall Risk Rating Definitions : Risk-ratings contain both qualitative and quantitative measurements and take into account the financial strength of a borrower and the structure of the loan or lease. Consequently, the definitions are to be applied in the context of each lending transaction and judgment must also be used to determine the appropriate risk rating, as it is not unusual for a loan or lease to exhibit characteristics of more than one risk-rating category. Consideration for the final rating is centered in the borrower’s ability to repay, in a timely fashion, both principal and interest. There were no material changes in the risk-rating or loan grading system in 2017 . Risk Rating 1: Exceptional A credit supported by exceptional financial strength, stability, and liquidity. The risk rating of 1 is reserved for the Company’s top quality loans, generally reserved for investment grade credits underwritten to the standards of institutional credit providers. Risk Rating 2: Excellent A credit supported by excellent financial strength, stability and liquidity. The risk rating of 2 is reserved for very strong and highly stable customers with ready access to alternative financing sources. Risk Rating 3: Strong A credit supported by good overall financial strength and stability. Collateral margins are strong, cash flow is stable although susceptible to cyclical market changes. Risk Rating 4: Acceptable A credit supported by the borrower’s adequate financial strength and stability. Assets and cash flow are reasonably sound and provide for orderly debt reduction. Access to alternative financing sources will be more difficult to obtain. Risk Rating 5: Watch A credit with the characteristics of an acceptable credit but one which requires more than the normal level of supervision and warrants formal quarterly management reporting. Credits in this category are not yet criticized or classified, but due to adverse events or aspects of underwriting require closer than normal supervision. Generally, credits should be watch credits in most cases for six months or less as the impact of stress factors are analyzed. Risk Rating 6: Special Mention A credit with potential weaknesses that deserves management’s close attention is risk rated a 6. If left uncorrected, these potential weaknesses will result in deterioration in the capacity to repay debt. A key distinction between Special Mention and Substandard is that in a Special Mention credit, there are identified weaknesses that pose potential risk(s) to the repayment sources, versus well defined weaknesses that pose risk(s) to the repayment sources. Assets in this category are expected to be in this category no more than 9-12 months as the potential weaknesses in the credit are resolved. Risk Rating 7: Substandard A credit with well defined weaknesses that jeopardize the ability to repay in full is risk rated a 7. These credits are inadequately protected by either the sound net worth and payment capacity of the borrower or the value of pledged collateral. These are credits with a distinct possibility of loss. Loans headed for foreclosure and/or legal action due to deterioration are rated 7 or worse. Risk Rating 8: Doubtful A credit with an extremely high probability of loss is risk rated 8. These credits have all the same critical weaknesses that are found in a substandard loan; however, the weaknesses are elevated to the point that based upon current information, collection or liquidation in full is improbable. While some loss on doubtful credits is expected, pending events may strengthen a credit making the amount and timing of any loss indeterminate. In these situations taking the loss is inappropriate until it is clear that the pending event has failed to strengthen the credit and improve the capacity to repay debt. Risk Rating 9: Loss A credit that is considered to be currently uncollectible or of such little value that it is no longer a viable Bank asset is risk rated 9. Losses are taken in the accounting period in which the credit is determined to be uncollectible. Taking a loss does not mean that a credit has absolutely no recovery or salvage value but, rather, it is not practical or desirable to defer writing off the credit, even though partial recovery may occur in the future. The following tables show Banner’s portfolio of risk-rated loans and non-risk-rated loans by grade or other characteristic as of December 31, 2017 and 2016 (in thousands): December 31, 2017 By class: Pass (Risk Ratings 1-5) (1) Special Substandard Doubtful Loss Total Loans Commercial real estate: Owner-occupied $ 1,246,125 $ 12,227 $ 26,011 $ — $ — $ 1,284,363 Investment properties 1,918,940 9,118 9,365 — — 1,937,423 Multifamily real estate 313,432 — 756 — — 314,188 Commercial construction 148,435 — — — — 148,435 Multifamily construction 154,662 — — — — 154,662 One- to four-family construction 411,802 — 3,525 — — 415,327 Land and land development: Residential 153,073 10,554 889 — — 164,516 Commercial 21,665 — 2,918 — — 24,583 Commercial business 1,213,365 12,135 54,282 112 — 1,279,894 Agricultural business, including secured by farmland 321,110 3,852 13,426 — — 338,388 One- to four-family residential 842,304 569 5,416 — — 848,289 Consumer: Consumer secured by one- to four-family 520,675 — 2,256 — — 522,931 Consumer—other 165,594 13 278 — — 165,885 Total $ 7,431,182 $ 48,468 $ 119,122 $ 112 $ — $ 7,598,884 December 31, 2016 By class: Pass (Risk Ratings 1-5) (1) Special Substandard Doubtful Loss Total Loans Commercial real estate: Owner-occupied $ 1,313,142 $ 14,394 $ 25,463 $ — $ — $ 1,352,999 Investment properties 1,948,822 23,846 13,668 — — 1,986,336 Multifamily real estate 247,258 — 892 — — 248,150 Commercial construction 124,068 — — — — 124,068 Multifamily construction 124,126 — — — — 124,126 One- to four-family construction 371,636 — 4,068 — — 375,704 Land and land development: Residential 167,764 — 2,240 — — 170,004 Commercial 25,090 — 4,094 — — 29,184 Commercial business 1,148,585 35,036 24,258 — — 1,207,879 Agricultural business, including secured by farmland 356,656 3,335 9,165 — — 369,156 One- to four-family residential 807,837 967 4,273 — — 813,077 Consumer: Consumer secured by one- to four-family 490,877 5 2,327 2 — 493,211 Consumer—other 156,547 108 594 5 — 157,254 Total $ 7,282,408 $ 77,691 $ 91,042 $ 7 $ — $ 7,451,148 (1) The Pass category includes some performing loans that are part of homogenous pools which are not individually risk-rated. This includes all consumer loans, all one- to four-family residential loans and, as of December 31, 2017 and 2016 , in the commercial business category, $296.8 million and $225.0 million , respectively, of credit-scored small business loans. As loans in these homogeneous pools become non-accrual, they are individually risk-rated. The following tables provide additional detail on the age analysis of Banner’s past due loans as of December 31, 2017 and 2016 (in thousands): December 31, 2017 30 – 59 Days Past Due 60 – 89 Days Past Due 90 Days or More Past Due Total Past Due Purchased Credit-Impaired Current Total Loans Loans 90 Days or More Past Due and Accruing Non-accrual Commercial real estate: Owner-occupied $ 5,323 $ 76 $ 5,490 $ 10,889 $ 7,682 $ 1,265,792 $ 1,284,363 $ — $ 6,447 Investment properties 1,737 — 4,096 5,833 7,166 1,924,424 1,937,423 — 4,199 Multifamily real estate 105 — — 105 169 313,914 314,188 — — Commercial construction — — — — — 148,435 148,435 — — Multifamily construction 3,416 — — 3,416 — 151,246 154,662 — — One- to four-family construction 4,892 725 298 5,915 446 408,966 415,327 298 — Land and land development: Residential — — 798 798 — 163,718 164,516 — 798 Commercial — — — — 2,919 21,664 24,583 — — Commercial business 1,574 404 2,577 4,555 2,159 1,273,180 1,279,894 18 3,406 Agricultural business/farmland 598 533 2,017 3,148 565 334,675 338,388 — 6,132 One- to four-family residential 4,475 1,241 2,715 8,431 136 839,722 848,289 1,085 3,264 Consumer: Consumer secured by one- to four-family 1,355 62 713 2,130 — 520,801 522,931 85 1,239 Consumer—other 609 136 15 760 68 165,057 165,885 — 58 Total $ 24,084 $ 3,177 $ 18,719 $ 45,980 $ 21,310 $ 7,531,594 $ 7,598,884 $ 1,486 $ 25,543 December 31, 2016 30–59 Days Past Due 60–89 Days Past Due 90 Days or More Past Due Total Past Due Purchased Credit-Impaired Current Total Loans Loans 90 Days or More Past Due and Accruing Non-accrual Commercial real estate: Owner-occupied $ 1,938 $ — $ 2,538 $ 4,476 $ 13,281 $ 1,335,242 $ 1,352,999 $ — $ 3,373 Investment properties 117 — 5,447 5,564 10,168 1,970,604 1,986,336 701 4,864 Multifamily real estate — — 147 147 139 247,864 248,150 147 — Commercial construction — — — — — 124,068 124,068 — — Multifamily construction — — — — — 124,126 124,126 — — One- to four-family construction — — — — 862 374,842 375,704 — — Land and land development: Residential 48 — 750 798 — 169,206 170,004 — 750 Commercial — — 998 998 3,016 25,170 29,184 — 998 Commercial business 2,314 647 1,591 4,552 3,821 1,199,506 1,207,879 — 3,074 Agricultural business/farmland 360 1,244 2,768 4,372 684 364,100 369,156 — 3,229 One- to four-family residential 1,793 249 2,110 4,152 274 808,651 813,077 1,233 2,263 Consumer: Consumer secured by one- to four-family 932 160 986 2,078 18 491,115 493,211 61 1,660 Consumer—other 1,421 154 147 1,722 59 155,473 157,254 11 215 Total $ 8,923 $ 2,454 $ 17,482 $ 28,859 $ 32,322 $ 7,389,967 $ 7,451,148 $ 2,153 $ 20,426 The following tables provide additional information on the allowance for loan losses and loan balances individually and collectively evaluated for impairment at or for the year ended December 31, 2017 (in thousands): For the Year Ended December 31, 2017 Commercial Real Estate Multifamily Real Estate Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance for loan losses: Beginning balance $ 20,993 $ 1,360 $ 34,252 $ 16,533 $ 2,967 $ 2,238 $ 4,104 $ 3,550 $ 85,997 Provision for loan losses 2,639 262 (7,921 ) 4,355 3,326 (415 ) 586 5,168 8,000 Recoveries 372 11 1,237 1,226 134 270 481 — 3,731 Charge-offs (1,180 ) — — (3,803 ) (2,374 ) (38 ) (1,305 ) — (8,700 ) Ending balance $ 22,824 $ 1,633 $ 27,568 $ 18,311 $ 4,053 $ 2,055 $ 3,866 $ 8,718 $ 89,028 December 31, 2017 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance individually evaluated for impairment $ 281 $ — $ — $ 50 $ 264 $ 178 $ 9 $ — $ 782 Allowance collectively evaluated for impairment 22,543 1,633 27,567 18,214 3,676 1,877 3,857 8,718 88,085 Allowance for purchased credit-impaired loans — — 1 47 113 — — — 161 Total allowance for loan losses $ 22,824 $ 1,633 $ 27,568 $ 18,311 $ 4,053 $ 2,055 $ 3,866 $ 8,718 $ 89,028 December 31, 2017 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Loan balances: Loans individually evaluated for impairment $ 16,017 $ — $ 750 $ 1,812 $ 8,585 $ 5,136 $ 212 $ — $ 32,512 Loans collectively evaluated for impairment 3,190,921 314,019 903,408 1,275,923 329,238 843,017 688,536 — 7,545,062 Purchased credit-impaired loans 14,848 169 3,365 2,159 565 136 68 — 21,310 Total loans $ 3,221,786 $ 314,188 $ 907,523 $ 1,279,894 $ 338,388 $ 848,289 $ 688,816 $ — $ 7,598,884 The following tables provide additional information on the allowance for loan losses and loan balances individually and collectively evaluated for impairment at or for the year ended December 31, 2016 (in thousands): For the Year Ended December 31, 2016 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance for loan losses: Beginning balance $ 20,716 $ 4,195 $ 27,131 $ 13,856 $ 3,645 $ 4,732 $ 902 $ 2,831 $ 78,008 Provision for loan losses 441 (2,835 ) 5,566 1,632 (170 ) (3,402 ) 4,079 719 6,030 Recoveries 582 — 2,171 1,993 59 1,283 610 — 6,698 Charge-offs (746 ) — (616 ) (948 ) (567 ) (375 ) (1,487 ) — (4,739 ) Ending balance $ 20,993 $ 1,360 $ 34,252 $ 16,533 $ 2,967 $ 2,238 $ 4,104 $ 3,550 $ 85,997 December 31, 2016 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance individually evaluated for impairment $ 428 $ 64 $ 374 $ 69 $ — $ 480 $ 5 $ — $ 1,420 Allowance collectively evaluated for impairment 20,565 1,296 33,845 16,464 2,967 1,758 4,099 3,550 84,544 Allowance for purchased credit-impaired loans — — 33 — — — — — 33 Total allowance for loan losses $ 20,993 $ 1,360 $ 34,252 $ 16,533 $ 2,967 $ 2,238 $ 4,104 $ 3,550 $ 85,997 December 31, 2016 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Loan balances: Loans individually evaluated for impairment $ 10,300 $ 349 $ 4,034 $ 2,946 $ 4,766 $ 7,678 $ 309 $ — $ 30,382 Loans collectively evaluated for impairment 3,305,586 247,662 815,174 1,201,112 363,706 805,125 650,079 — 7,388,444 Purchased credit-impaired loans 23,449 139 3,878 3,821 684 274 77 — 32,322 Total loans $ 3,339,335 $ 248,150 $ 823,086 $ 1,207,879 $ 369,156 $ 813,077 $ 650,465 $ — $ 7,451,148 The following table provides additional information on the allowance for loan losses for the year ended December 31, 2015 (in thousands): For the Year Ended December 31, 2015 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance for loan losses: Beginning balance $ 18,784 $ 4,562 $ 25,545 $ 12,043 $ 3,821 $ 5,447 $ 483 $ 5,222 $ 75,907 Provision for loan losses 1,177 (480 ) 666 1,611 (878 ) (1,068 ) 1,363 (2,391 ) — Recoveries 819 113 1,811 948 1,927 772 570 — 6,960 Charge-offs (64 ) — (891 ) (746 ) (1,225 ) (419 ) (1,514 ) — (4,859 ) Ending balance $ 20,716 $ 4,195 $ 27,131 $ 13,856 $ 3,645 $ 4,732 $ 902 $ 2,831 $ 78,008

REAL ESTATE OWNED, HELD FOR SAL

REAL ESTATE OWNED, HELD FOR SALE, NET	12 Months Ended
	Dec. 31, 2017
Real Estate [Abstract]
REAL ESTATE OWNED, HELD FOR SALE, NET	REAL ESTATE OWNED, HELD FOR SALE, NET The following table presents the changes in REO, net of valuation allowance, for the years ended December 31, 2017 , 2016 and 2015 (in thousands): Years Ended December 31 2017 2016 2015 Balance, beginning of period $ 11,081 $ 11,627 $ 3,352 Additions from loan foreclosures 46 8,909 4,351 Additions from capitalized costs 54 — 298 Additions from acquisitions — 400 8,231 Proceeds from dispositions of REO (13,474 ) (10,812 ) (4,740 ) Gain on sale of REO 2,909 1,833 351 Valuation adjustments in the period (256 ) (876 ) (216 ) Balance, end of period $ 360 $ 11,081 $ 11,627 At December 31, 2017 the Company had no foreclosed residential real estate properties held as REO compared to $917,000 at December 31, 2016. The recorded investment in one- to four-family residential loans in the process of foreclosure was $2.0 million at December 31, 2017 and $715,000 at December 31, 2016.

PROPERTY AND EQUIPMENT, NET

PROPERTY AND EQUIPMENT, NET	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT, NET	PROPERTY AND EQUIPMENT, NET Land, buildings and equipment owned by the Company and its subsidiaries at December 31, 2017 and 2016 are summarized as follows (in thousands): December 31 2017 2016 Land (1) $ 35,080 $ 35,463 Buildings and leasehold improvements (1) 154,374 163,879 Furniture and equipment 105,643 94,999 295,097 294,341 Less accumulated depreciation (140,282 ) (127,860 ) Property and equipment, net $ 154,815 $ 166,481 (1) The Company had $3.8 million and $8.5 million of properties held for sale that were included in land and buildings at December 31, 2017 and 2016 , respectively. The Company’s depreciation expense related to property and equipment was $14.7 million , $13.5 million , and $10.0 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. The Company’s rental expense was $16.4 million , $16.7 million , and $10.2 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. The Company’s obligations under long-term property leases are as follows (in thousands): Year Amount 2018 $ 16,029 2019 13,199 2020 12,080 2021 10,100 2022 6,725 Thereafter 13,926 Total $ 72,059

DEPOSITS

DEPOSITS	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
DEPOSITS	DEPOSITS Deposits consist of the following at December 31, 2017 and 2016 (in thousands): December 31 2017 2016 Non-interest-bearing checking $ 3,265,544 $ 3,140,451 Interest-bearing checking 971,137 914,484 Regular savings accounts 1,557,500 1,523,391 Money market accounts 1,422,313 1,497,755 Total interest-bearing transaction and savings accounts 3,950,950 3,935,630 Certificates of deposit: Certificates of deposit less than or equal to $250,000 813,997 884,403 Certificates of deposit greater than $250,000 152,940 160,930 Total certificates of deposit (1) 966,937 1,045,333 Total deposits $ 8,183,431 $ 8,121,414 Included in total deposits: Public fund transaction accounts $ 198,719 $ 221,765 Public fund interest-bearing certificates 23,685 25,650 Total public deposits $ 222,404 $ 247,415 Total brokered deposits $ 57,228 $ 34,074 (1) Certificates of deposit included $11,000 and $426,000 of acquisition premiums at December 31, 2017 and 2016 , respectively. Deposits at December 31, 2017 and 2016 included deposits from the Company’s directors, executive officers and related entities totaling $10.0 million and $7.2 million , respectively. At December 31, 2017 and 2016, the Company had certificates of deposit of $155.9 million and $165.4 million , respectively, that were equal to or greater than $250,000. Scheduled maturities and weighted average interest rates of certificate accounts at December 31, 2017 are as follows (dollars in thousands): December 31, 2017 Amount Weighted Average Rate Maturing in one year or less $ 685,592 0.49 % Maturing after one year through two years 98,257 0.72 Maturing after two years through three years 141,209 1.30 Maturing after three years through four years 25,902 1.08 Maturing after four years through five years 13,775 1.26 Maturing after five years 2,202 1.05 Total certificates of deposit $ 966,937 0.66 %

ADVANCES FROM FEDERAL HOME LOAN

ADVANCES FROM FEDERAL HOME LOAN BANK OF DES MOINES	12 Months Ended
	Dec. 31, 2017
Advances from Federal Home Loan Banks [Abstract]
ADVANCES FROM FEDERAL HOME LOAN BANK OF DES MOINES	ADVANCES FROM FEDERAL HOME LOAN BANK OF DES MOINES Utilizing a blanket pledge, qualifying loans receivable at December 31, 2017 and 2016 , were pledged as security for FHLB borrowings and there were no securities pledged as collateral as of December 31, 2017 or 2016 . At December 31, 2017 and 2016 , FHLB advances were scheduled to mature as follows (in thousands): December 31 2017 2016 Maturing in one year or less $ — $ 54,000 Maturing after one year through three years — — Maturing after three years through five years — — Maturing after five years 169 179 Total FHLB advances, at par 169 54,179 Fair value adjustment 33 37 Total FHLB advances, carried at fair value $ 202 $ 54,216 The maximum amount outstanding from the FHLB advances at month end for the years ended December 31, 2017 and 2016 was $453.2 million and $300.2 million , respectively. The average FHLB advances balance outstanding for the years ended December 31, 2017 and 2016 was $151.3 million and $141.9 million , respectively. The average contractual interest rate on the FHLB advances for the years ended December 31, 2017 and 2016 was 1.26% and 0.67% , respectively. As of December 31, 2017 , Banner Bank has established a borrowing line with the FHLB to borrow up to 35% of its total assets, contingent on having sufficient qualifying collateral and ownership of FHLB stock. Islanders Bank similarly may borrow up to 35% of its total assets, also contingent on collateral and FHLB stock. At December 31, 2017 , the maximum total FHLB credit line was $3.55 billion and $98.7 million for Banner Bank and Islanders Bank, respectively.

OTHER BORROWINGS

OTHER BORROWINGS	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
OTHER BORROWINGS	OTHER BORROWINGS Other borrowings consist of retail and wholesale repurchase agreements, other term borrowings and Federal Reserve Bank borrowings. Repurchase Agreements: At December 31, 2017 , retail repurchase agreements carry interest rates ranging from 0.15% to 0.40% . In addition to the retail repurchase agreements, Banner Bank had one wholesale repurchase agreement with an interest rate of 2.15% . These repurchase agreements are secured by the pledge of certain mortgage-backed and agency securities with a carrying value of $123.9 million . Banner Bank has the right to pledge or sell these securities, but it must replace them with substantially the same securities. Federal Reserve Bank of San Francisco and Other Borrowings: Banner Bank periodically borrows funds on an overnight basis from the Federal Reserve Bank through the Borrower-In-Custody (BIC) program. Such borrowings are secured by a pledge of eligible loans. At December 31, 2017 , based upon available unencumbered collateral, Banner Bank was eligible to borrow $1.15 billion from the Federal Reserve Bank, although, at that date, as well as at December 31, 2016 , Banner Bank had no funds borrowed under this or other borrowing arrangements. At December 31, 2017 , Banner Bank had uncommitted federal funds lines of credit agreements with other financial institutions totaling $110.0 million , while Islanders Bank had an uncommitted federal funds line of credit agreement with another financial institution totaling $5.0 million . No balances were outstanding under these agreements as of December 31, 2017 and 2016 . Availability of lines is subject to federal funds balances available for loan and continued borrower eligibility. These lines are intended to support short-term liquidity needs and the agreements may restrict consecutive day usage. A summary of all other borrowings at December 31, 2017 and 2016 by the period remaining to maturity is as follows (dollars in thousands): At or for the Years Ended December 31 2017 2016 Amount Weighted Average Rate Amount Weighted Average Rate Repurchase agreements: Maturing in one year or less $ 95,860 0.29 % $ 100,685 0.19 % Maturing after one year through two years — — 5,000 2.15 Maturing after two years — — — — Total year-end outstanding $ 95,860 0.29 $ 105,685 0.28 Average outstanding $ 111,872 0.28 $ 108,427 0.29 Maximum outstanding at any month-end 120,245 n/a 112,309 n/a

JUNIOR SUBORDINATED DEBENTURES

JUNIOR SUBORDINATED DEBENTURES AND MANDATORILY REDEEMABLE TRUST PREFERRED SECURITIES	12 Months Ended
	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
JUNIOR SUBORDINATED DEBENTURES AND MANDATORILY REDEEMABLE TRUST PREFERRED SECURITIES	JUNIOR SUBORDINATED DEBENTURES AND MANDATORILY REDEEMABLE TRUST PREFERRED SECURITIES At December 31, 2017 , the Company had nine wholly-owned subsidiary grantor trusts (the Trusts), which had issued $136.0 million of trust preferred securities to third parties, as well as $4.2 million of common capital securities, carried among other assets, which were issued to the Company. Trust preferred securities and common capital securities accrue and pay distributions periodically at specified annual rates as provided in the indentures. The Trusts used the proceeds from the offerings to purchase a like amount of junior subordinated debentures (the Debentures) of the Company. The Debentures are the sole assets of the Trusts. The Company’s obligations under the debentures and related documents, taken together, constitute a full and unconditional guarantee by the Company of the obligations of the Trusts. The trust preferred securities (TPS) are mandatorily redeemable upon the maturity of the Debentures, or upon earlier redemption as provided in the indentures. The Company has the right to redeem the Debentures in whole on or after specific dates, at a redemption price specified in the indentures plus any accrued but unpaid interest to the redemption date. All of the trust preferred securities issued by the Trusts qualified as Tier 1 capital as of December 31, 2017 . At December 31, 2017 , the Trusts comprised $136.0 million , or 11.2% of the Company’s total risk-based capital. The following table is a summary of trust preferred securities at December 31, 2017 (dollars in thousands): Name of Trust Aggregate Liquidation Amount of Trust Preferred Securities Aggregate Liquidation Amount of Common Capital Securities Aggregate Principal Amount of Junior Subordinated Debentures Stated Maturity (1) Current Interest Rate Reset Period Interest Rate Spread Banner Capital Trust II $ 15,000 $ 464 $ 15,464 2033 4.71 % Quarterly Three-month LIBOR + 3.35% Banner Capital Trust III 15,000 465 15,465 2033 4.26 Quarterly Three-month LIBOR + 2.90% Banner Capital Trust IV 15,000 465 15,465 2034 4.21 Quarterly Three-month LIBOR + 2.85% Banner Capital Trust V 25,000 774 25,774 2035 3.02 Quarterly Three-month LIBOR + 1.57% Banner Capital Trust VI 25,000 774 25,774 2037 3.10 Quarterly Three-month LIBOR + 1.62% Banner Capital Trust VII 25,000 774 25,774 2037 2.72 Quarterly Three-month LIBOR + 1.38% Siuslaw Statutory Trust I 8,000 248 8,248 2034 4.30 Quarterly Three-month LIBOR + 2.70% Greater Sacramento Bancorp Statutory Trust I 4,000 124 4,124 2033 4.71 Quarterly Three-month LIBOR + 3.35% Greater Sacramento Bancorp Statutory Trust II 4,000 124 4,124 2035 3.27 Quarterly Three-month LIBOR + 1.68% Total TPS liability at par $ 136,000 $ 4,212 140,212 3.57 % Fair value adjustment (2) (41,505 ) Total TPS liability at fair value (2) $ 98,707 (1) All of the Company's trust preferred securities are eligible for redemption. (2) The Company has elected to use fair value accounting on its TPS.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The following table presents the components of the provision for income taxes included in the Consolidated Statements of Operations for the years ended December 31, 2017 , 2016 and 2015 (in thousands): Years Ended December 31 2017 2016 2015 Current Federal $ 30,961 $ 29,787 $ 24,683 State 3,085 2,477 1,399 Total Current 34,046 32,264 26,082 Deferred Federal 58,646 9,908 (3,310 ) State (2,204 ) 2,083 (23 ) Total Deferred 56,442 11,991 (3,333 ) Provision for income taxes $ 90,488 $ 44,255 $ 22,749 The following table presents the reconciliation of the federal statutory rate to the actual effective rate for the years ended December 31, 2017 , 2016 and 2015 : Years Ended December 31 2017 2016 2015 Federal income tax statutory rate 35.0 % 35.0 % 35.0 % Increase (decrease) in tax rate due to: Tax-exempt interest (2.6 ) (2.6 ) (3.9 ) Investment in life insurance (1.1 ) (1.2 ) (1.3 ) State income taxes, net of federal tax offset 2.0 2.2 1.1 Tax credits (0.6 ) (0.8 ) (1.6 ) Merger and acquisition costs — — 1.9 Federal law change 28.2 — — Other (1.1 ) 1.5 2.3 Effective income tax rate 59.8 % 34.1 % 33.5 % The following table reflects the effect of temporary differences that gave rise to the components of the net deferred tax asset as of December 31, 2017 and 2016 (in thousands): December 31 2017 2016 Deferred tax assets: Loan loss and REO $ 22,294 $ 36,719 Deferred compensation 13,045 23,189 Net operating loss carryforward 43,721 82,714 Federal and state tax credits 7,614 7,711 State net operating losses 6,706 7,396 Loan discount 4,736 9,696 Other 4,326 6,217 Total deferred tax assets 102,442 173,642 Deferred tax liabilities: Depreciation (1,343 ) (2,218 ) Deferred loan fees, servicing rights and loan origination costs (9,564 ) (13,291 ) Intangibles (5,690 ) (11,178 ) Financial instruments accounted for under fair value accounting (9,702 ) (16,186 ) Other (325 ) (880 ) Total deferred tax liabilities (26,624 ) (43,753 ) Deferred income tax asset 75,818 129,889 Valuation allowance (4,391 ) (2,195 ) Deferred tax asset, net $ 71,427 $ 127,694 Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recognized or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income tax expense in the period of enactment. In December 2017, the federal government enacted the 2017 Tax Act. Among other provisions, the 2017 Tax Act reduced the federal marginal corporate income tax rate from 35% to 21%. As a result of the passage of the 2017 Tax Act, the Company recorded a $42.6 million charge for the revaluation of its net deferred tax asset to account for the future impact of the decrease in the corporate income tax rate and other provisions of the legislation. The charge was recorded as an increase to tax expense and reduction of the net deferred tax asset. The $42.6 million charge recorded by the Company included $4.2 million of provisional income tax expense related to AMT credits that are limited under Section 383 of the Code, which resulted in a reduction in the AMT deferred tax asset. The adjustments to deferred tax assets and receivables related to the refundable nature of AMT credits are provisional amounts estimated based on information available as of December 31, 2017 . As a result, these amounts could be adjusted during the measurement period, which will end in December 2018. The Company did not identify items for which the income tax effects of the 2017 Tax Act have not been completed and a reasonable estimate could not be determined as of December 31, 2017. The utilization of the limited AMT credits under the refundable AMT credit law is uncertain and subject to change as the Company obtains additional guidance on application of the law. The Company will recognize any changes to the provisional amounts as management refines estimates of cumulative temporary differences, and their interpretations of the application of the 2017 Tax Act. The Company expects to complete its analysis of the provisional items during the second half of 2018. At December 31, 2017 , the Company has federal net operating loss carryforwards of approximately $208.2 million . The Company also has $94.6 million state net operating loss carryforwards, which the Company has established a $184,000 valuation reserve against. The federal and state net operating losses will expire, if unused, by the end of 2034 . The Company has federal general business credit carryforwards at December 31, 2017 of $3.4 million , which will expire, if unused, by the end of 2031 . The Company also has federal alternative minimum tax credit carryforwards of $4.2 million , which are available to reduce future federal regular income taxes, if any, over a five-year period under the new tax law. As of December 31, 2017 , the Company had established a $4.2 million valuation reserve against its alternative minimum tax credit carryforwards. Additionally, at December 31, 2017 , the Company has no state credit carryovers. At December 31, 2016 , the Company had federal and state net operating loss carryforwards of approximately $236.3 million and $145.8 million , respectively, and federal general business credits carryforwards of $3.3 million . At that same date, the Company also had federal alternative minimum tax credit carryforwards of approximately $4.2 million . As a consequence of our acquisition of Starbuck Bancshares, Inc., the holding company for AmericanWest Bank (AmericanWest) the Company experienced a change in control within the meaning of Section 382 of the Code. In addition, the underlying Section 382 limitations at Starbuck Bancshares, Inc.'s level continue to apply to the Company. Section 382 limits the ability of a corporate taxpayer to use net operating loss carryforwards, general business credits, and recognized built-in-losses, on an annual basis, incurred prior to the change in control against income earned after the change in control. As a result of the Section 382 limitations, the Company is limited to utilizing $21.5 million on an annual basis (after the application of the Section 382 limitations carried over from Starbuck Bancshares, Inc.) of federal net operating loss carryforwards, general business credits, and recognized built-in losses. The applicable state Section 382 limitations range from $525,000 to $21.5 million . The Company has provided a $184,000 valuation reserve against the portion of its various state net operating loss carryforwards and tax credits that it believes it is more likely than not that it will not realize the benefit because the application of the Section 382 limitations at the state level is based on future apportionment rates. In addition, as a consequence of Banner's capital raise in June 2010, the Company experienced a change in control within the meaning of Section 382 of the Code. As a result of the Section 382 limitations, the Company is limited to utilizing $6.9 million of net operating loss carryforwards which existed prior to the acquisition of Starbuck Bancshares, Inc., on an annual basis. Based on its analysis, the Company believes it is more likely than not that the June 2010 change in control will not impact its ability to utilize all of the related available net operating loss carryforwards, general business credits, and recognized built-in-losses. Retained earnings at December 31, 2017 and 2016 included approximately $5.4 million in tax basis bad debt reserves for which no income tax liability has been recorded. In the future, if this tax bad debt reserve is used for purposes other than to absorb bad debts or the Company no longer qualifies as a bank or is completely liquidated, the Company will incur a federal tax liability at the then-prevailing corporate tax rate, established as $1.9 million at December 31, 2017 . Tax credit investments: The Company invests in low income housing tax credit funds that are designed to generate a return primarily through the realization of federal tax credits. The Company accounts for these investments by amortizing the cost of tax credit investments over the life of the investment using a proportional amortization method and tax credit investment amortization expense is a component of the provision for income taxes. The following table presents the balances of the Company's tax credit investments and related unfunded commitments at December 31, 2017 and 2016 (in thousands): December 31, 2017 December 31, 2016 Tax credit investments $ 7,311 $ 4,654 Unfunded commitments—tax credit investments 4,417 665 The following table presents other information related to the Company's tax credit investments for the years ended December 31, 2017 and 2016 (in thousands): For the year ended December 31, 2017 2016 Tax credits and other tax benefits recognized $ 1,140 $ 1,136 Tax credit amortization expense included in provision for income taxes 1,144 672

EMPLOYEE BENEFIT PLANS

EMPLOYEE BENEFIT PLANS	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
EMPLOYEE BENEFIT PLANS	EMPLOYEE BENEFIT PLANS Employee Retirement Plans: Substantially all of the Company’s and the Banks' employees are eligible to participate in its 401(k)/Profit Sharing Plan, a defined contribution and profit sharing plan sponsored by the Company. Employees may elect to have a portion of their salary contributed to the plan in conformity with Section 401(k) of the Internal Revenue Code. At the discretion of the Company’s Board of Directors, the Company may elect to make matching and/or profit sharing contributions for the employees’ benefit. For the years ended December 31, 2017 , 2016 and 2015 , $4.8 million , $4.6 million and $2.8 million , respectively, was expensed for 401(k) contributions. The Board of Directors has elected to make a 4% of eligible compensation matching contribution for 2018 . Supplemental Retirement and Salary Continuation Plans: Through the Banks, the Company is obligated under various non-qualified deferred compensation plans to help supplement the retirement income of certain executives, including certain retired executives, selected by resolution of the Banks’ Boards of Directors or in certain cases by the former directors of acquired banks. These plans are unfunded, include both defined benefit and defined contribution plans, and provide for payments after the executive’s retirement. In the event of a participant employee’s death prior to or during retirement, the Company is obligated to pay to the designated beneficiary the benefits set forth under the plan. For the years ended December 31, 2017 , 2016 and 2015 , expense recorded for supplemental retirement and salary continuation plan benefits totaled $3.5 million , $2.7 million , and $1.3 million , respectively. At December 31, 2017 and 2016 , liabilities recorded for the various supplemental retirement and salary continuation plan benefits totaled $38.6 million and $38.3 million , respectively, and are recorded in a deferred compensation liability account. Deferred Compensation Plans and Rabbi Trusts: The Company and the Banks also offer non-qualified deferred compensation plans to members of their Boards of Directors and certain employees. The plans permit each participant to defer a portion of director fees, non-qualified retirement contributions, salary or bonuses for future receipt. Compensation is charged to expense in the period earned. In connection with its acquisitions, the Company also assumed liability for certain deferred compensation plans for key employees, retired employees and directors. In order to fund the plans’ future obligations, the Company has purchased life insurance policies or other investments, including Banner Corporation common stock, which in certain instances are held in irrevocable trusts commonly referred to as “Rabbi Trusts.” As the Company is the owner of the investments and the beneficiary of the insurance policies, and in order to reflect the Company’s policy to pay benefits equal to the accumulations, the assets and liabilities are reflected in the Consolidated Statements of Financial Condition. Banner Corporation common stock held for such plans is reported as a contra-equity account and was recorded at an original cost of $7.4 million at December 31, 2017 and $7.3 million at December 31, 2016 . At December 31, 2017 and 2016 , liabilities recorded in connection with deferred compensation plan benefits totaled $9.9 million ( $7.4 million in contra-equity) and $9.0 million ( $7.3 million in contra-equity), respectively, and are recorded in deferred compensation or equity as appropriate. The Banks have purchased, or acquired through mergers, life insurance policies in connection with the implementation of certain executive supplemental retirement, salary continuation and deferred compensation retirement plans, as well as additional policies not related to any specific plan. These policies provide protection against the adverse financial effects that could result from the death of a key employee and provide tax-exempt income to offset expenses associated with the plans. It is the Banks’ intent to hold these policies as a long-term investment. However, there will be an income tax impact if the Banks choose to surrender certain policies. Although the lives of individual current or former management-level employees are insured, the Banks are the owners and sole or partial beneficiaries. At December 31, 2017 and 2016 , the cash surrender value of these policies was $162.7 million and $158.9 million , respectively. The Banks are exposed to credit risk to the extent an insurance company is unable to fulfill its financial obligations under a policy. In order to mitigate this risk, the Banks use a variety of insurance companies and regularly monitor their financial condition.

STOCK-BASED COMPENSATION PLANS

STOCK-BASED COMPENSATION PLANS	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION PLANS	STOCK-BASED COMPENSATION PLANS The Company operates the following stock-based compensation plans as approved by its shareholders: • 2012 Restricted Stock and Incentive Bonus Plan. • 2014 Omnibus Incentive Plan. The purpose of these plans is to promote the success and enhance the value of the Company by providing a means for attracting and retaining highly skilled employees, officers and directors of Banner Corporation and its affiliates and linking their personal interests with those of the Company's shareholders. Under these plans the Company currently has outstanding restricted stock share grants, restricted stock unit grants, and stock options. 2012 Restricted Stock and Incentive Bonus Plan Under the 2012 Restricted Stock and Incentive Bonus Plan (2012 Restricted Stock Plan), which was approved by shareholders on April 24, 2012 , the Company is authorized to issue up to 300,000 shares of its common stock to provide a means for attracting and retaining highly skilled officers of Banner Corporation and its affiliates. Shares granted under the 2012 Restricted Stock Plan have a minimum vesting period of three years. The 2012 Restricted Stock Plan will continue in effect for a term of ten years, after which no further awards may be granted. The 2012 Restricted Stock Plan was amended on April 23, 2013 to provide for the ability to grant (1) cash-denominated incentive-based awards payable in cash or common stock, including those that are eligible to qualify as qualified performance-based compensation for the purposes of Section 162(m) of the Code and (2) restricted stock awards that qualify as qualified performance-based compensation for the purposes of Section 162(m) of the Code. Vesting requirements may include time-based conditions, performance-based conditions, and/or market-based conditions. As of December 31, 2017 , the Company had granted 270,699 shares of restricted stock from the 2012 Restricted Stock Plan (as amended and restated), of which 263,400 shares had vested and 7,299 shares remain unvested. 2014 Omnibus Incentive Plan The 2014 Omnibus Incentive Plan (the 2014 Plan) was approved by shareholders on April 22, 2014. The 2014 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance units, other stock-based awards and other cash awards, and provides for vesting requirements which may include time-based or performance-based conditions. The Company has reserved 900,000 shares of its common stock for issuance under the 2014 Plan in connection with the exercise of awards. As of December 31, 2017 , 371,342 restricted stock shares and 34,975 restricted stock units have been granted under the 2014 Plan of which 91,117 restricted stock shares and 20,422 restricted stock units have vested. The expense associated with all restricted stock grants was $6.0 million , $4.5 million and $3.5 million respectively, for the years ended December 31, 2017 , 2016 and 2015 . Unrecognized compensation expense for these awards as of December 31, 2017 was $8.0 million and will be amortized over the next 31 months. A summary of the Company's Restricted Stock/Unit award activity during the years ended December 31, 2017, 2016 and 2015 follows: Shares/Units Weighted Average Grant-Date Fair Value Unvested at January 1, 2015 195,106 $ 32.83 Granted (24,931 non-voting) 155,183 45.59 Vested (109,416 ) 30.28 Forfeited (9,311 ) 39.07 Unvested at December 31, 2015 231,562 42.33 Granted (38,934 non-voting) 177,775 41.74 Vested (104,297 ) 41.47 Forfeited (14,321 ) 42.54 Unvested at December 31, 2016 290,719 42.26 Granted (41,318 non-voting) 153,777 55.86 Vested (103,259 ) 43.81 Forfeited (39,160 ) 39.83 Unvested at December 31, 2017 302,077 48.97

PREFERRED STOCK AND RELATED WAR

PREFERRED STOCK AND RELATED WARRANT	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
PREFERRED STOCK AND RELATED WARRANT	PREFERRED STOCK AND RELATED WARRANT On November 21, 2008, as part of the Capital Purchase Program, the Company entered into a Purchase Agreement with U.S. Treasury pursuant to which the Company issued and sold 124,000 shares of Series A Preferred Stock, having a liquidation preference of $1,000 per share ( $124 million liquidation preference in the aggregate) and a ten -year warrant to purchase up to 243,998 shares of the Company’s common stock, par value $0.01 per share, at an initial exercise price of $76.23 per share (post reverse-split), for an aggregate purchase price of $18.6 million in cash. During the year ended December 31, 2012, the Company repurchased or redeemed its Series A Preferred Stock. The related warrants to purchase up to $18.6 million in Banner common stock ( 243,998 shares) were sold by the U.S. Treasury at public auction in June 2013. That sale did not change the Company's capital position and did not have any impact on the financial accounting and reporting for these securities.

REGULATORY CAPITAL REQUIREMENTS

REGULATORY CAPITAL REQUIREMENTS	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
REGULATORY CAPITAL REQUIREMENTS	REGULATORY CAPITAL REQUIREMENTS Banner Corporation is a bank holding company registered with the Federal Reserve. Bank holding companies are subject to capital adequacy requirements of the Federal Reserve under the Bank Holding Company Act of 1956, as amended (BHCA), and the regulations of the Federal Reserve. Banner Bank and Islanders Bank, as state-chartered federally insured commercial banks, are subject to the capital requirements established by the FDIC. The Federal Reserve requires Banner to maintain capital adequacy that generally parallels the FDIC requirements. The following table shows the regulatory capital ratios of the Company and the Banks and the minimum regulatory requirements (dollars in thousands): Actual Minimum for Capital Adequacy Purposes Minimum to be Categorized as “Well-Capitalized” Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio December 31, 2017: The Company—consolidated: Total capital to risk-weighted assets $ 1,214,631 13.81 % $ 703,508 8.00 % $ 879,385 10.00 % Tier 1 capital to risk-weighted assets 1,123,154 12.77 527,631 6.00 527,631 6.00 Tier 1 common equity to risk-weighted assets 994,080 11.30 395,723 4.50 n/a n/a Tier 1 capital to average leverage assets 1,123,154 11.34 396,313 4.00 n/a n/a Banner Bank: Total capital to risk- weighted assets 1,102,195 12.83 687,266 8.00 859,083 10.00 Tier 1 capital to risk- weighted assets 1,013,079 11.79 515,450 6.00 687,266 8.00 Tier 1 common equity to risk-weighted assets 1,013,079 11.79 386,587 4.50 558,404 6.50 Tier 1 capital to average leverage assets 1,013,079 10.53 384,920 4.00 481,150 5.00 Islanders Bank: Total capital to risk- weighted assets 32,122 16.39 15,681 8.00 19,602 10.00 Tier 1 capital to risk- weighted assets 29,761 15.18 11,761 6.00 15,681 8.00 Tier 1 common equity to risk-weighted assets 29,761 15.18 8,821 4.50 12,741 6.50 Tier 1 capital to average leverage assets 29,761 10.65 11,183 4.00 13,979 5.00 December 31, 2016: The Company—consolidated: Total capital to risk-weighted assets $ 1,214,913 13.40 % $ 725,566 8.00 % $ 906,957 10.00 % Tier 1 capital to risk-weighted assets 1,125,267 12.41 544,174 6.00 544,174 6.00 Tier 1 common equity to risk-weighted assets 1,014,994 11.19 408,131 4.50 n/a n/a Tier 1 capital to average leverage assets 1,125,267 11.83 380,519 4.00 n/a n/a Banner Bank: Total capital to risk- weighted assets 1,043,837 11.76 709,882 8.00 887,352 10.00 Tier 1 capital to risk- weighted assets 956,298 10.78 532,411 6.00 709,882 8.00 Tier 1 common equity to risk-weighted assets 956,298 10.78 399,308 4.50 576,779 6.50 Tier 1 capital to average leverage assets 956,298 10.34 369,936 4.00 462,420 5.00 Islanders Bank: Total capital to risk- weighted assets 35,207 18.43 15,281 8.00 19,101 10.00 Tier 1 capital to risk- weighted assets 33,099 17.33 11,461 6.00 15,281 8.00 Tier 1 common equity to risk-weighted assets 33,099 17.33 8,598 4.50 12,416 6.50 Tier 1 capital to average leverage assets 33,099 12.72 10,405 4.00 13,006 5.00 At December 31, 2017 , Banner Corporation and the Banks each exceeded all regulatory capital adequacy requirements. There have been no conditions or events since December 31, 2017 that have materially adversely changed the Tier 1 or Tier 2 capital of the Company or the Banks. However, events beyond the control of the Banks, such as weak or depressed economic conditions in areas where the Banks have most of their loans, could adversely affect future earnings and, consequently, the ability of the Banks to meet their respective capital requirements. The Company may not declare or pay cash dividends on, or repurchase, any of its shares of common stock if the effect thereof would cause equity to be reduced below applicable regulatory capital maintenance requirements or if such declaration and payment would otherwise violate regulatory requirements. Effective January 1, 2015 (with some changes transitioned into full effectiveness over several years), Banner Corporation and the Banks became subject to capital regulations adopted by the Federal Reserve and the FDIC, which established minimum required ratios for common equity Tier 1 (“CET1”) capital, Tier 1 capital, total capital and the leverage ratio; risk-weightings of certain assets and other items for purposes of the risk-based capital ratios, a required capital conservation buffer over the required capital ratios, and defined what qualifies as capital for purposes of meeting the capital requirements. These regulations implement the regulatory capital reforms required by the Dodd-Frank Act and the “Basel III” requirements. Under the capital regulations, the minimum capital ratios applicable to Banner and the Banks are: (i) a CETI capital ratio of 4.5%; (ii) a Tier 1 capital ratio of 6% (increased from 4%); (iii) a total capital ratio of 8% (unchanged from prior rules); and (iv) a Tier 1 leverage ratio of 4% for all institutions. CET1 generally consists of common stock; retained earnings; accumulated other comprehensive income (AOCI), unless an election is made to exclude AOCI from regulatory capital; and certain minority interests; all subject to applicable regulatory adjustments and deductions. Tier 1 capital generally consists of CET1 and noncumulative perpetual preferred stock. Tier 2 capital generally consists of other preferred stock and subordinated debt meeting certain conditions plus an amount of the allowance for loan and lease losses up to 1.25% of assets. Total capital is the sum of Tier 1 and Tier 2 capital. For purposes of determining risk-based capital, assets and certain off-balance sheet items are risk-weighted from 0% to 1,250%, depending on the risk characteristics of the asset or item. The regulations changed certain risk-weightings compared to the earlier capital rules, including a 150% risk weight (up from 100%) for certain high volatility commercial real estate acquisition, development and construction loans and for non-residential mortgage loans that are 90 days past due or otherwise in nonaccrual status; a 20% (up from 0%) credit conversion factor for the unused portion of a commitment with an original maturity of one year or less that is not unconditionally cancellable (up from 0%); and a 250% risk weight (up from 100%) for mortgage servicing and deferred tax assets that are not deducted from capital. In addition to the minimum CET1, Tier 1, total capital and leverage ratios, Banner and each of the Banks now have to maintain a capital conservation buffer consisting of additional CET1 capital above the required minimum levels in order to avoid limitations on paying dividends, engaging in share repurchases, and paying discretionary bonuses based on percentages of eligible retained income that could be utilized for such actions. This new capital conservation buffer requirement began to be phased in starting in January 2016 at 0.625% of risk-weighted assets and will increase each year until fully implemented to an amount greater than 2.5% of risk-weighted assets in January 2019.

GOODWILL, OTHER INTANGIBLE ASSE

GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS	12 Months Ended
	Dec. 31, 2017
Other Intangible Assets and Mortgage Servicing Rights [Abstract]
OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS	GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS Goodwill and Other Intangible Assets: At December 31, 2017 , intangible assets are comprised of goodwill, CDI, and LHI acquired in business combinations. Goodwill represents the excess of the total purchase consideration paid over the fair value of the assets acquired, net of the fair values of liabilities assumed, and is not amortized but is reviewed annually for impairment. Banner has identified one reporting unit for purposes of evaluating goodwill for impairment. At December 31, 2017 , the Company completed a qualitative assessment of goodwill and concluded that it is more likely than not that the fair value of Banner, the reporting unit, exceeds the carrying value. Additions to goodwill during the year ended December 31, 2015 relate to the Starbuck and Siuslaw acquisitions. CDI represents the value of transaction-related deposits and the value of the customer relationships associated with the deposits. LHI represents the value ascribed to leases assumed in an acquisition in which the lease terms are favorable compared to a market lease at the date of acquisition. The Company amortizes CDI and LHI over their estimated useful lives and reviews them at least annually for events or circumstances that could impair their value. The CDI assets shown in the table below represent the value ascribed to the long-term deposit relationships acquired in various bank acquisitions. These intangible assets are being amortized using an accelerated method over estimated useful lives of three to ten years. The CDI and LHI assets are not estimated to have a significant residual value. The following table summarizes the changes in the Company’s goodwill, CDI and LHI for the years ended December 31, 2017, 2016 and 2015 (in thousands): Goodwill CDI LHI Total Balance, January 1, 2015 $ — $ 2,831 $ — $ 2,831 Additions through acquisition 247,738 37,395 776 285,909 Amortization — (3,164 ) (66 ) (3,230 ) Other changes (1) — (300 ) — (300 ) Balance, December 31, 2015 247,738 36,762 710 285,210 Amortization — (7,061 ) (249 ) (7,310 ) Adjustments to goodwill (2) (3,155 ) — — (3,155 ) Balance, December 31, 2016 244,583 29,701 461 274,745 Amortization — (6,247 ) (184 ) (6,431 ) Other changes (1) (1,924 ) (1,076 ) — (3,000 ) Balance, December 31, 2017 $ 242,659 $ 22,378 $ 277 $ 265,314 (1) Acquired Goodwill and CDI were adjusted for the sale of the Utah branches in 2017 and acquired CDI was adjusted for a branch that was subsequently sold during 2015. (2) The adjustments to goodwill in 2016 related to changes in the preliminary goodwill recorded for the Starbuck acquisition including adjustments to loan discount, deferred taxes and REO valuations. Estimated amortization expense in future years with respect to CDI as of December 31, 2017 (in thousands): Year ended: Estimated Amortization 2018 $ 5,372 2019 4,683 2020 3,996 2021 3,307 Thereafter 5,020 Net carrying amount $ 22,378 Mortgage servicing rights are reported in other assets. Mortgage servicing rights are initially recognized at fair value and are amortized in proportion to, and over the period of, the estimated future net servicing income of the underlying financial assets. Mortgage servicing rights are subsequently evaluated for impairment based upon the fair value of the rights compared to the amortized cost (remaining unamortized initial fair value). If the fair value is less than the amortized cost, a valuation allowance is created through an impairment charge to servicing fee income. However, if the fair value is greater than the amortized cost, the amount above the amortized cost is not recognized in the carrying value. In 2017 , 2016 and 2015, the Company did no t record any impairment charges or recoveries against mortgage servicing rights. Unpaid principal balance of loans for which mortgage servicing rights have been recognized totaled $2.19 billion and $2.05 billion at December 31, 2017 and 2016 , respectively. Custodial accounts maintained in connection with this servicing totaled $10.2 million and $10.3 million at December 31, 2017 and 2016 , respectively. An analysis of the mortgage servicing rights for the years ended December 31, 2017 , 2016 and 2015 is presented below (in thousands): Years Ended December 31 2017 2016 2015 Balance, beginning of the year $ 15,249 $ 13,295 $ 9,030 Amounts capitalized 3,361 5,965 5,313 Additions through acquisition — — 2,172 Additions through purchase 94 — — Amortization (1) (3,966 ) (4,011 ) (3,220 ) Balance, end of the year (2) $ 14,738 $ 15,249 $ 13,295 (1) Amortization of mortgage servicing rights is recorded as a reduction of loan servicing income and any unamortized balance is fully written off if the loan repays in full. (2) There was no valuation allowance as of December 31, 2017 and 2016 .

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
FAIR VALUE OF FINANCIAL INSTRUMENTS	FAIR VALUE The following table presents estimated fair values of the Company’s financial instruments as of December 31, 2017 and 2016 , whether or not recognized or recorded in the Consolidated Statements of Financial Condition (in thousands): December 31, 2017 December 31, 2016 Level Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Assets: Cash and due from banks 1 $ 261,200 $ 261,200 $ 247,719 $ 247,719 Securities—trading 2,3 22,318 22,318 24,568 24,568 Securities—available-for-sale 2 919,485 919,485 806,428 806,428 Securities—held-to-maturity 2 256,793 258,710 263,997 266,652 Securities—held-to-maturity 3 3,478 3,478 3,876 3,876 Loans receivable held for sale 2 40,725 40,923 246,353 246,815 Loans receivable 3 7,598,884 7,445,990 7,451,148 7,337,608 FHLB stock 3 10,334 10,334 12,506 12,506 BOLI 1 162,668 162,668 158,936 158,936 Mortgage servicing rights 3 14,738 19,835 15,249 16,740 Derivatives: Interest rate swaps 2 5,083 5,083 8,330 8,330 Interest rate lock and forward sales commitments 2 523 523 482 482 Liabilities: Demand, interest-bearing checking and money market 2 5,658,994 5,658,994 5,552,690 5,552,690 Regular savings 2 1,557,500 1,557,500 1,523,391 1,523,391 Certificates of deposit 2 966,937 947,517 1,045,333 1,028,866 Advances from FHLB at fair value 2 202 202 54,216 54,216 Junior subordinated debentures at fair value 3 98,707 98,707 95,200 95,200 Other borrowings 2 95,860 95,860 105,685 105,685 Derivatives: Interest rate swaps 2 5,083 5,083 8,330 8,330 Interest rate lock and forward sales commitments 2 201 201 289 289 The Company measures and discloses certain assets and liabilities at fair value. 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 (that is, not a forced liquidation or distressed sale). GAAP establishes a consistent framework for measuring fair value and disclosure requirements about fair value measurements. Among other things, the standard requires us to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect the Company’s estimates for market assumptions. These two types of inputs create the following fair value hierarchy: • Level 1 – Quoted prices in active markets for identical instruments. An active market is a market in which transactions occur with sufficient frequency and volume to provide pricing information on an ongoing basis. A quoted price in an active market provides the most reliable evidence of fair value and shall be used to measure fair value whenever available. • Level 2 – Observable inputs other than Level 1 including quoted prices in active markets for similar instruments, quoted prices in less active markets for identical or similar instruments, or other observable inputs that can be corroborated by observable market data. • Level 3 – Unobservable inputs supported by little or no market activity for financial instruments whose value is determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation; also includes observable inputs from non-binding single dealer quotes not corroborated by observable market data. In developing Level 3 measurements, management incorporates whatever market data might be available and uses discounted cash flow models where appropriate. These calculations include projections of future cash flows, including appropriate default and loss assumptions, and market based discount rates. The estimated fair value amounts of financial instruments have been determined by the Company using available market information and appropriate valuation methodologies. However, considerable judgment is required to interpret data to develop the estimates of fair value. Accordingly, the estimates presented herein are not necessarily indicative of the amounts the Company could realize at a future date. The use of different market assumptions and/or estimation methodologies may have a material effect on the estimated fair value amounts. In addition, reasonable comparability between financial institutions may not be likely due to the wide range of permitted valuation techniques and numerous estimates that must be made given the absence of active secondary markets for many of the financial instruments. This lack of uniform valuation methodologies also introduces a greater degree of subjectivity to these estimated fair values. Transfers between levels of the fair value hierarchy are deemed to occur at the end of the reporting period. Items Measured at Fair Value on a Recurring Basis: The following tables present financial assets and liabilities measured at fair value on a recurring basis and the level within the fair value hierarchy of the fair value measurements for those assets and liabilities as of December 31, 2017 and 2016 (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Assets: Securities—trading Municipal bonds $ — $ 100 $ — $ 100 Corporate Bonds (TPS securities) — — 22,058 22,058 Equity securities — 160 — 160 — 260 22,058 22,318 Securities—available-for-sale U.S. Government and agency $ — $ 72,466 $ — $ 72,466 Municipal bonds — 68,733 — 68,733 Corporate bonds — 5,393 — 5,393 Mortgage-backed securities — 739,557 — 739,557 Asset-backed securities — 27,758 — 27,758 Equity securities — 5,578 — 5,578 — 919,485 — 919,485 Loans held for sale — 32,392 — 32,392 Derivatives Interest rate swaps — 5,083 — 5,083 Interest rate lock and forward sales commitments — 523 — 523 $ — $ 957,743 $ 22,058 $ 979,801 Liabilities Advances from FHLB at fair value $ — $ 202 $ — $ 202 Junior subordinated debentures at fair value — — 98,707 98,707 Derivatives Interest rate swaps — 5,083 — 5,083 Interest rate lock and forward sales commitments — 201 — 201 $ — $ 5,486 $ 98,707 $ 104,193 December 31, 2016 Level 1 Level 2 Level 3 Total Assets: Securities—trading U.S. Government and agency $ — $ 1,326 $ — $ 1,326 Municipal bonds — 335 — 335 Corporate Bonds (TPS securities) — — 21,143 21,143 Mortgage-backed securities — 1,641 — 1,641 Equity securities — 123 — 123 — 3,425 21,143 24,568 Securities—available-for-sale U.S. Government and agency $ — $ 56,978 $ — $ 56,978 Municipal bonds — 109,853 — 109,853 Corporate bonds — 10,283 — 10,283 Mortgage-backed securities — 594,712 — 594,712 Asset-backed securities — 28,993 — 28,993 Equity securities — 5,609 — 5,609 — 806,428 — 806,428 Loans held for sale $ — $ 9,600 $ — $ 9,600 Derivatives Interest rate swaps — 8,330 — 8,330 Interest rate lock and forward sales commitments — 482 — 482 $ — $ 828,265 $ 21,143 $ 849,408 Liabilities Advances from FHLB at fair value $ — $ 54,216 $ — $ 54,216 Junior subordinated debentures at fair value — — 95,200 95,200 Derivatives Interest rate swaps — 8,330 — 8,330 Interest rate lock and forward sales commitments — 289 — 289 $ — $ 62,835 $ 95,200 $ 158,035 The following methods were used to estimate the fair value of each class of financial instruments: Cash and Cash Equivalents: The carrying amount of these items is a reasonable estimate of their fair value. Securities: The estimated fair values of investment securities and mortgaged-backed securities are priced using current active market quotes, if available, which are considered Level 1 measurements. For most of the portfolio, matrix pricing based on the securities’ relationship to other benchmark quoted prices is used to establish the fair value. These measurements are considered Level 2. Due to the continued limited activity in the trust preferred markets that have limited the observability of market spreads for some of the Company’s TPS securities, management has classified these securities as a Level 3 fair value measure. Management periodically reviews the pricing information received from third-party pricing services and tests those prices against other sources to validate the reported fair values. Loans Held for Sale: Fair values for residential mortgage loans held for sale are determined by comparing actual loan rates to current secondary market prices for similar loans. Fair values for multifamily loans held for sale are calculated based on discounted cash flows using as a discount rate a combination of market spreads for similar loan types added to selected index rates. Loans Receivable: Fair values are estimated first by stratifying the portfolios of loans with similar financial characteristics. Loans are segregated by type such as multifamily real estate, residential mortgage, nonresidential mortgage, commercial/agricultural, consumer and other. Each loan category is further segmented into fixed- and adjustable-rate interest terms. A preliminary estimate of fair value is then calculated based on discounted cash flows using as a discount rate the current rate offered on similar products, plus an adjustment for liquidity to reflect the non-homogeneous nature of the loans. The preliminary estimate is then further reduced by the amount of the allowance for loan losses to arrive at a final estimate of fair value. Fair value for impaired loans is also based on recent appraisals or estimated cash flows discounted using rates commensurate with risk associated with the estimated cash flows. Assumptions regarding credit risk, cash flows and discount rates are judgmentally determined using available market information and specific borrower information. FHLB Stock: The fair value is based upon the redemption value of the stock which equates to its carrying value. Bank-Owned Life Insurance: The fair value of BOLI policies owned is based on the various insurance contracts' cash surrender value. Mortgage Servicing Rights: Fair values are estimated based on an independent dealer analysis of discounted cash flows. The evaluation utilizes assumptions market participants would use in determining fair value including prepayment speeds, delinquency and foreclosure rates, the discount rate, servicing costs, and the timing of cash flows. The mortgage servicing portfolio is stratified by loan type and fair value estimates are adjusted up or down based on the serviced loan interest rates versus current rates on new loan originations since the most recent independent analysis. Deposits: The carrying amount of deposits with no stated maturity, such as savings and checking accounts, is a reasonable estimate of their fair value. The market value of certificates of deposit is based upon the discounted value of contractual cash flows. The discount rate is determined using the rates currently offered on comparable instruments. FHLB Advances: Fair valuations for Banner’s FHLB advances are estimated using fair market values provided by the lender, the FHLB of Des Moines. The FHLB of Des Moines prices advances by discounting the future contractual cash flows for individual advances, using its current cost of funds curve to provide the discount rate. Junior Subordinated Debentures: The fair value of junior subordinated debentures is estimated using an income approach technique. The significant inputs included in the estimation of fair value are the credit risk adjusted spread and three month LIBOR. The credit risk adjusted spread represents the nonperformance risk of the liability. The Company utilizes an external valuation firm to validate the reasonableness of the credit risk adjusted spread used to determine the fair value. The junior subordinated debentures are carried at fair value which represents the estimated amount that would be paid to transfer these liabilities in an orderly transaction amongst market participants. Due to credit concerns in the capital markets and inactivity in the trust preferred markets that have limited the observability of market spreads, management has classified this as a Level 3 fair value measure. Other Borrowings: Other borrowings include securities sold under agreements to repurchase and occasionally federal funds purchased and their carrying amount is considered a reasonable approximation of their fair value. Derivatives: Derivatives include interest rate swap agreements, interest rate lock commitments to originate loans held for sale and forward sales contracts to sell loans and securities related to mortgage banking activities. Fair values for these instruments, which generally change as a result of changes in the level of market interest rates, are estimated based on dealer quotes and secondary market sources. Off-Balance Sheet Items: Off-balance sheet financial instruments include unfunded commitments to extend credit, including standby letters of credit, and commitments to purchase investment securities. The fair value of these instruments is not considered to be material. Limitations: The fair value estimates presented herein are based on pertinent information available to management as of December 31, 2017 and 2016 . The factors used in the fair value estimates are subject to change subsequent to the dates the fair value estimates are completed, therefore, current estimates of fair value may differ significantly from the amounts presented herein. Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3) The following table provides a description of the valuation technique, unobservable inputs, quantitative and qualitative information about the unobservable inputs for the Company's assets and liabilities classified as Level 3 and measured at fair value on a recurring and nonrecurring basis at December 31, 2017 and 2016 : December 31 2017 2016 Financial Instruments Valuation Technique Unobservable Inputs Weighted Average Rate Weighted Average Rate Corporate Bonds (TPS securities) Discounted cash flows Discount rate 6.69 % 6.00 % Junior subordinated debentures Discounted cash flows Discount rate 6.69 % 6.00 % Impaired loans Collateral Valuations Discount to appraised value 8.5% to 20.0% n/a REO Appraisals Discount to appraised value 42% 0% to 45% TPS Securities : Management believes that the credit risk-adjusted spread used to develop the discount rate utilized in the fair value measurement of TPS securities is indicative of the risk premium a willing market participant would require under current market conditions for instruments with similar contractual rates, terms and conditions and issuers with similar credit risk profiles and with similar expected probability of default. Management attributes the change in fair value of these instruments, compared to their par value, primarily to perceived general market adjustments to the risk premiums for these types of assets subsequent to their issuance. Junior subordinated debentures : Similar to the TPS securities discussed above, management believes that the credit risk-adjusted spread utilized in the fair value measurement of the junior subordinated debentures is indicative of the risk premium a willing market participant would require under current market conditions for an issuer with Banner's credit risk profile. Management attributes the change in fair value of the junior subordinated debentures, compared to their par value, primarily to perceived general market adjustments to the risk premiums for these types of liabilities subsequent to their issuance. Future contractions in the risk adjusted spread relative to the spread currently utilized to measure the Company's junior subordinated debentures at fair value as of December 31, 2017 , or the passage of time, will result in negative fair value adjustments. At December 31, 2017 , the discount rate utilized was based on a credit spread of 500 basis points and three month LIBOR of 169 basis points. The following table provides a reconciliation of the assets and liabilities measured at fair value using significant unobservable inputs (Level 3) on a recurring basis during the years ended December 31, 2017 and 2016 (in thousands): Level 3 Fair Value Inputs TPS Securities Borrowings— Junior Subordinated Debentures Balance at January 1, 2016 $ 18,699 $ 92,480 Total gains or losses recognized Assets gains 719 — Liabilities losses — 2,720 Purchases, issuances and settlements 1,725 — Balance at December 31, 2016 21,143 95,200 Total gains or losses recognized Assets gains 915 — Liabilities losses — 3,507 Balance at December 31, 2017 $ 22,058 $ 98,707 The Company has elected to continue to recognize the interest income and dividends from the securities reclassified to fair value as a component of interest income as was done in prior years when they were classified as available-for-sale. Interest expense related to the FHLB advances and junior subordinated debentures continues to be measured based on contractual interest rates and reported in interest expense. The change in fair value of these financial instruments has been recorded as a component of non-interest income. Items Measured at Fair Value on a Non-recurring Basis The following table presents financial assets and liabilities measured at fair value on a non-recurring basis and the level within the fair value hierarchy of the fair value measurements for those assets at December 31, 2017 and 2016 (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Impaired loans $ — $ — $ 6,535 $ 6,535 REO $ — $ — $ 360 $ 360 December 31, 2016 Level 1 Level 2 Level 3 Total REO — — 11,081 11,081 The following table presents the losses resulting from non-recurring fair value adjustments for the years ended December 31, 2017 and 2016 (in thousands): For the year ended December 31, 2017 2016 Impaired loans $ (2,852 ) $ (182 ) REO (256 ) (876 ) Total loss from nonrecurring measurements $ (3,108 ) $ (1,058 ) Impaired loans : Impaired loans are measured based on the present value of expected future cash flows discounted at the loan's effective interest rate or, as a practical expedient, at the loan's observable market price or the fair value of collateral if the loan is collateral dependent. If this practical expedient is used, the impaired loans are considered to be held at fair value. Subsequent changes in the value of impaired loans are included within the provision for loan losses in the same manner in which impairment initially was recognized or as a reduction in the provision that would otherwise be reported. Impaired loans are periodically evaluated to determine if valuation adjustments, or partial write-downs, should be recorded. The need for valuation adjustments arises when observable market prices or current appraised values of collateral indicate a shortfall in collateral value compared to current carrying values of the related loan. If the Company determines that the value of the impaired loan is less than the carrying value of the loan, the Company either establishes an impairment reserve as a specific component of the allowance for loan losses or charges off the impaired amount. These valuation adjustments are considered non-recurring fair value adjustments. REO : The Company records REO (acquired through a lending relationship) at fair value on a non-recurring basis. Fair value adjustments on REO are based on updated real estate appraisals which are based on current market conditions. All REO properties are recorded at the estimated fair value of the real estate, less expected selling costs. From time to time, non-recurring fair value adjustments to REO are recorded to reflect partial write-downs based on an observable market price or current appraised value of property. Banner considers any valuation inputs related to REO to be Level 3 inputs. The individual carrying values of these assets are reviewed for impairment at least annually and any additional impairment charges are expensed to operations.

BANNER CORPORATION (PARENT COMP

BANNER CORPORATION (PARENT COMPANY ONLY)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
BANNER CORPORATION (PARENT COMPANY ONLY)	BANNER CORPORATION (PARENT COMPANY ONLY) Summary financial information is as follows (in thousands): Statements of Financial Condition December 31 2017 2016 ASSETS Cash $ 44,887 $ 86,268 Investment in trust equities 4,212 4,212 Investment in subsidiaries 1,329,165 1,307,475 Other assets 3,072 13,784 Total assets $ 1,381,336 $ 1,411,739 LIABILITIES AND SHAREHOLDERS’ EQUITY Miscellaneous liabilities $ 9,607 $ 8,990 Deferred tax liability 396 1,839 Junior subordinated debentures at fair value 98,707 95,200 Shareholders’ equity 1,272,626 1,305,710 Total liabilities and shareholders' equity $ 1,381,336 $ 1,411,739 Statements of Operations Years Ended December 31 2017 2016 2015 INTEREST INCOME: Interest-bearing deposits $ 62 $ 127 $ 122 OTHER INCOME (EXPENSE): Dividend income from subsidiaries 40,570 50,971 170,260 Equity in undistributed (distributions in excess of) income of subsidiaries 27,477 40,852 (116,120 ) Other income 53 60 69 Net change in valuation of financial instruments carried at fair value (3,507 ) (2,720 ) (2,714 ) Interest on other borrowings (4,752 ) (4,040 ) (3,247 ) Other expenses (3,291 ) (3,450 ) (7,175 ) Net income before taxes 56,612 81,800 41,195 BENEFIT FROM INCOME TAXES (4,164 ) (3,585 ) (4,027 ) NET INCOME $ 60,776 $ 85,385 $ 45,222 Statements of Cash Flows Years Ended December 31 2017 2016 2015 OPERATING ACTIVITIES: Net income $ 60,776 $ 85,385 $ 45,222 Adjustments to reconcile net income to net cash provided by operating activities: Distributions in excess of (equity in undistributed) income of subsidiaries (27,477 ) (40,852 ) 116,120 Decrease in deferred taxes (1,442 ) (702 ) (1,398 ) Net change in valuation of financial instruments carried at fair value 3,507 2,720 2,714 Share-based compensation 5,965 4,305 4,334 Decrease (increase) in other assets 10,684 7,332 (10,655 ) Increase (decrease) in other liabilities 69 (202 ) 433 Net cash provided from operating activities 52,082 57,986 156,770 INVESTING ACTIVITIES: Funds transferred to deferred compensation trust (29 ) (26 ) (26 ) Reduction in investment in subsidiaries 5,000 50,000 — Acquisitions — — (132,652 ) Net cash provided from (used by) investing activities 4,971 49,974 (132,678 ) FINANCING ACTIVITIES: Issuance of stock for shareholder reinvestment program — — 34 Withholding taxes paid on share-based compensation (1,630 ) (870 ) (848 ) Repurchase of common stock (31,045 ) (50,772 ) — Cash dividends paid (65,759 ) (28,282 ) (17,170 ) Net cash used by financing activities (98,434 ) (79,924 ) (17,984 ) NET CHANGE IN CASH (41,381 ) 28,036 6,108 CASH, BEGINNING OF PERIOD 86,268 58,232 52,124 CASH, END OF PERIOD $ 44,887 $ 86,268 $ 58,232

STOCK REPURCHASES

STOCK REPURCHASES	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
STOCK REPURCHASE	STOCK REPURCHASES AND RECHARACTERIZATION On April 4, 2016, the Company announced that its Board of Directors had authorized the repurchase of up to 1,711,540 shares of the Company's common stock, or 5% of the Company's outstanding shares. During the year ended December 31, 2016 , the Company adopted a pre-arranged stock trading plan, pursuant to the Board authorization, in accordance with guidelines specified under Rule 10b5-1 of the Securities Exchange Act of 1934. Repurchases under the Company’s 10b5-1 stock trading plan were administered through an independent broker. The stock trading plan provided for the repurchase of up to 1,300,000 shares of the Company’s stock. The stock trading plan terminated on March 12, 2017. Repurchases were subject to the requirements of the Securities and Exchange Commission, including Rule 10b-18, as well as certain price and other requirements specified in the plan. During the year ended December 31, 2016 , the Company repurchased 1,145,250 common shares under the stock trading plan. In addition to the shares repurchased during 2016 under the plan there were 25,628 shares surrendered during 2016 by employees to satisfy tax withholding obligations upon vesting of restricted stock grants. On March 31, 2017 the Company announced that its Board of Directors had renewed its authorization to repurchase up to 5% of the Company's common stock, or 1,658,245 of the Company's outstanding shares. Under the authorization, shares may be repurchased by the Company in open market purchases. The extent to which the Company repurchases its shares and the timing of such repurchases will depend upon market conditions and other corporate considerations. During the year ended December 31, 2017, the Company repurchased 545,166 common shares under the authorization leaving 1,113,079 shares available for future repurchase. In addition to the shares repurchased under the authorization during 2017, there were 29,579 shares surrendered during 2017 by employees to satisfy tax withholding obligations upon vesting of restricted stock grants. The Company did not repurchase any shares of its common stock during the year ended December 31, 2015 except for shares surrendered by employees to satisfy tax withholding obligations upon the vesting of restricted stock grants and shares redeemed relating to the termination of the ESOP. The ESOP was terminated during the year ended December 31, 2014. During the year ended December 31, 2016 , the 1.3 million shares of non-voting common stock issued in connection with the acquisition of Starbuck and its subsidiary, AmericanWest were sold by the original holder of the shares. These shares contained a provision where they would automatically convert from non-voting to voting upon a permitted transfer of the shares. Therefore, these shares were included in Banner's voting common stock outstanding as of December 31, 2016 .

CALCULATION OF EARNINGS PER COM

CALCULATION OF EARNINGS PER COMMON SHARE	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
CALCULATION OF EARNINGS PER COMMON SHARE	CALCULATION OF EARNINGS PER COMMON SHARE The following tables show the calculation of earnings per common share (in thousands, except per share data): Years Ended December 31 2017 2016 2015 Net income $ 60,776 $ 85,385 $ 45,222 Weighted average number of common shares outstanding Basic 32,888,007 33,820,148 23,801,373 Diluted 32,986,707 33,853,511 23,866,621 Earnings per common share Basic $ 1.85 $ 2.52 $ 1.90 Diluted $ 1.84 $ 2.52 $ 1.89 At December 31, 2017 , 2016 and 2015 there were 302,077 , 290,719 , and 231,562 , respectively, issued but unvested restricted stock shares and units that were included in the computation of diluted earnings per share. At December 31, 2016 and 2015 there were options to purchase an additional 5,000 shares of common stock that were not included in the computation of diluted earnings per share because their exercise price resulted in them being anti-dilutive. At December 31, 2017 , 2016 and 2015 there was a warrant to purchase up to 243,998 shares of common stock and these shares were not included in the computation of diluted earnings per share because their exercise price resulted in them being anti-dilutive.

SELECTED QUARTERLY FINANCIAL DA

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)	12 Months Ended
	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)	SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) Results of operations on a quarterly basis for the years ended December 31, 2017 , 2016 and 2015 were as follows (dollars in thousands except for per share data): Year Ended December 31, 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Interest income $ 99,096 $ 104,436 $ 105,278 $ 103,475 Interest expense 4,242 4,730 5,068 5,211 Net interest income before provision for loan losses 94,854 99,706 100,210 98,264 Provision for loan losses 2,000 2,000 2,000 2,000 Net interest income 92,854 97,706 98,210 96,264 Non-interest income 20,845 22,469 20,339 29,882 Non-interest expense 78,078 81,930 82,589 84,709 Income before provision for income taxes 35,621 38,245 35,960 41,437 Provision for income taxes 11,828 12,791 10,883 54,985 Net income (loss) $ 23,793 $ 25,454 $ 25,077 $ (13,548 ) Basic earnings (loss) per share $ 0.72 $ 0.77 $ 0.76 $ (0.41 ) Diluted earnings (loss) per share 0.72 0.77 0.76 (0.41 ) Dividends declared 0.25 1.25 0.25 0.25 Year Ended December 31, 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Interest income $ 95,301 $ 97,321 $ 97,849 $ 101,007 Interest expense 4,258 4,173 4,141 3,836 Net interest income before provision for loan losses 91,043 93,148 93,708 97,171 Provision for loan losses — 2,000 2,000 2,030 Net interest income 91,043 91,148 91,708 95,141 Non-interest income 19,959 20,537 23,512 19,463 Non-interest expense 84,034 79,887 79,092 79,857 Income before provision for income taxes 26,968 31,798 36,128 34,747 Provision for income taxes 9,194 10,841 12,277 11,943 Net income $ 17,774 $ 20,957 $ 23,851 $ 22,804 Basic earnings per share $ 0.52 $ 0.62 $ 0.70 $ 0.69 Diluted earnings per share 0.52 0.61 0.70 0.69 Dividends declared 0.21 0.21 0.23 0.23 Year Ended December 31, 2015 First Quarter Second Quarter Third Quarter Fourth Quarter Interest income $ 49,069 $ 54,076 $ 54,793 $ 96,495 Interest expense 2,533 2,619 2,605 4,396 Net interest income before provision for loan losses 46,536 51,457 52,188 92,099 Provision for loan losses — — — — Net interest income 46,536 51,457 52,188 92,099 Non-interest income 13,696 16,141 14,098 18,356 Non-interest expense 41,914 47,734 46,697 100,254 Income before provision for income taxes 18,318 19,864 19,589 10,201 Provision for income taxes 6,184 6,615 6,642 3,308 Net income $ 12,134 $ 13,249 $ 12,947 $ 6,893 Basic earnings per share $ 0.61 $ 0.64 $ 0.62 $ 0.20 Diluted earnings per share 0.61 0.64 0.62 0.20 Dividends declared 0.18 0.18 0.18 0.18

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	Lease Commitments—The Company leases 108 buildings and offices under non-cancelable operating leases. The leases contain various provisions for increases in rental rates, based either on changes in the published Consumer Price Index or a predetermined escalation schedule. Substantially all of the leases provide the Company with the option to extend the lease term one or more times following expiration of the initial term. Financial Instruments with Off-Balance Sheet Risk—The Company has financial instruments with off-balance-sheet risk generated in the normal course of business to meet the financing needs of its customers. These financial instruments include commitments to extend credit, commitments related to standby letters of credit, commitments to originate loans, commitments to sell loans, and commitments to buy or sell securities. These instruments involve, to varying degrees, elements of credit and interest rate risk similar to the risk involved in on-balance sheet items recognized in our Consolidated Statements of Financial Condition. Our exposure to credit loss in the event of nonperformance by the other party to the financial instrument from commitments to extend credit and standby letters of credit is represented by the contractual notional amount of those instruments. We use the same credit policies in making commitments and conditional obligations as for on-balance sheet instruments. Outstanding commitments for which no asset or liability for the notional amount has been recorded consisted of the following at the dates indicated (in thousands): Contract or Notional Amount December 31, 2017 December 31, 2016 Commitments to extend credit $ 2,300,593 $ 2,204,795 Standby letters of credit and financial guarantees 14,579 17,694 Commitments to originate loans 56,030 69,833 Risk participation agreement 11,451 7,488 Derivatives also included in Note 24: Commitments to originate loans held for sale 43,502 69,487 Commitments to sell loans secured by one- to four-family residential properties 33,069 36,907 Commitments to sell securities related to mortgage banking activities 57,000 44,000 Commitments to extend credit are agreements to lend to a customer, as long as there is no violation of any condition established in the contract. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. Many of the commitments may expire without being drawn upon; therefore, the total commitment amounts do not necessarily represent future cash requirements. Each customer’s creditworthiness is evaluated on a case-by-case basis. The amount of collateral obtained, if deemed necessary upon extension of credit, is based on management’s credit evaluation of the customer. Collateral held varies, but may include accounts receivable, inventory, property, plant and equipment, and income producing commercial properties. The Company's reserve for unfunded loan commitments was $2.4 million and $3.6 million , at December 31, 2017 and 2016 , respectively. Standby letters of credit are conditional commitments issued to guarantee a customer’s performance or payment to a third party. The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loan facilities to customers. Through the acquisition of Starbuck, Banner Bank assumed a risk participation agreement. Under the risk participation agreement, Banner Bank guarantees the financial performance of a borrower on the participated portion of a interest rate swap on a loan. Interest rates on residential one- to four-family mortgage loan applications are typically rate locked (committed) to customers during the application stage for periods ranging from 30 to 60 days, the most typical period being 45 days. Traditionally, these loan applications with rate lock commitments had the pricing for the sale of these loans locked with various qualified investors under a best-efforts delivery program at or near the time the interest rate is locked with the customer. The Bank then attempts to deliver these loans before their rate locks expired. This arrangement generally required delivery of the loans prior to the expiration of the rate lock. Delays in funding the loans would require a lock extension. The cost of a lock extension at times was borne by the customer and at times by the Bank. These lock extension costs have not had a material impact to our operations. For mandatory delivery commitments the Company enters into forward commitments at specific prices and settlement dates to deliver either: (1) residential mortgage loans for purchase by secondary market investors (i.e., Freddie Mac or Fannie Mae), or (2) mortgage-backed securities to broker/dealers. The purpose of these forward commitments is to offset the movement in interest rates between the execution of its residential mortgage rate lock commitments with borrowers and the sale of those loans to the secondary market investor. There were no counterparty default losses on forward contracts during 2017 or 2016 . Market risk with respect to forward contracts arises principally from changes in the value of contractual positions due to changes in interest rates. The Company limits its exposure to market risk by monitoring differences between commitments to customers and forward contracts with market investors and securities broker/dealers. In the event the Company has forward delivery contract commitments in excess of available mortgage loans, the transaction is completed by either paying or receiving a fee to or from the investor or broker/dealer equal to the increase or decrease in the market value of the forward contract. Changes in the value of rate lock commitments are recorded as assets and liabilities as explained in Note 1: “Derivative Instruments.” In the normal course of business, the Company and/or its subsidiaries have various legal proceedings and other contingent matters outstanding. These proceedings and the associated legal claims are often contested and the outcome of individual matters is not always predictable. These claims and counter-claims typically arise during the course of collection efforts on problem loans or with respect to action to enforce liens on properties in which the Banks hold a security interest. Based upon the information known to management at this time, the Company and the Banks are not a party to any legal proceedings that management believes would have a material adverse effect on the results of operations or consolidated financial position at December 31, 2017 . In connection with certain asset sales, the Banks typically make representations and warranties about the underlying assets conforming to specified guidelines. If the underlying assets do not conform to the specifications, the Bank may have an obligation to repurchase the assets or indemnify the purchaser against any loss. The Banks believe that the potential for material loss under these arrangements is remote. Accordingly, the fair value of such obligations is not material.

DERIVATIVES AND HEDGING DERIVAT

DERIVATIVES AND HEDGING DERIVATIVES AND HEDGING	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVES AND HEDGING	DERIVATIVES AND HEDGING The Company, through its Banner Bank subsidiary, is party to various derivative instruments that are used for asset and liability management and customer financing needs. Derivative instruments are contracts between two or more parties that have a notional amount and an underlying variable, require no net investment and allow for the net settlement of positions. The notional amount serves as the basis for the payment provision of the contract and takes the form of units, such as shares or dollars. The underlying variable represents a specified interest rate, index, or other component. The interaction between the notional amount and the underlying variable determines the number of units to be exchanged between the parties and influences the market value of the derivative contract. The Company obtains dealer quotations to value its derivative contracts. The Company's predominant derivative and hedging activities involve interest rate swaps related to certain term loans and forward sales contracts associated with mortgage banking activities. Generally, these instruments help the Company manage exposure to market risk and meet customer financing needs. Market risk represents the possibility that economic value or net interest income will be adversely affected by fluctuations in external factors such as market-driven interest rates and prices or other economic factors. Derivatives Designated in Hedge Relationships The Company's fixed-rate loans result in exposure to losses in value or net interest income as interest rates change. The risk management objective for hedging fixed-rate loans is to effectively convert the fixed-rate received to a floating rate. The Company has hedged exposure to changes in the fair value of certain fixed-rate loans through the use of interest rate swaps. For a qualifying fair value hedge, changes in the value of the derivatives are recognized in current period earnings along with the corresponding changes in the fair value of the designated hedged item attributable to the risk being hedged. Under a prior program, customers received fixed interest rate commercial loans and Banner Bank subsequently hedged that fixed-rate loan by entering into an interest rate swap with a dealer counterparty. Banner Bank receives fixed-rate payments from the customers on the loans and makes similar fixed-rate payments to the dealer counterparty on the swaps in exchange for variable-rate payments based on the one-month LIBOR index. Some of these interest rate swaps are designated as fair value hedges. Through application of the “short cut method of accounting,” there is an assumption that the hedges are effective. Banner Bank discontinued originating interest rate swaps under this program in 2008. As of December 31, 2017 and December 31, 2016 , the notional values or contractual amounts and fair values of the Company's derivatives designated in hedge relationships were as follows (in thousands): Asset Derivatives Liability Derivatives December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 Notional/ Contract Amount Fair Value (1) Notional/ Contract Amount Fair Value (1) Notional/ Contract Amount Fair Value (2) Notional/ Contract Amount Fair Value (2) Interest rate swaps $ 4,350 $ 447 $ 5,855 $ 660 $ 4,350 $ 447 $ 5,855 $ 660 (1) Included in Loans Receivable on the Consolidated Statements of Financial Condition. (2) Included in Other Liabilities on the Consolidated Statements of Financial Condition. Derivatives Not Designated in Hedge Relationships Interest Rate Swaps: Banner Bank uses an interest rate swap program for commercial loan customers, that provides the client with a variable-rate loan and enters into an interest rate swap in which the client receives a variable-rate payment in exchange for a fixed-rate payment. The Bank offsets its risk exposure by entering into an offsetting interest rate swap with a dealer counterparty for the same notional amount and length of term as the client interest rate swap providing the dealer counterparty with a fixed-rate payment in exchange for a variable-rate payment. These swaps do not qualify as designated hedges; therefore, each swap is accounted for as a free standing derivative. Mortgage Banking: In the normal course of business, the Company sells originated one- to four-family and multifamily mortgage loans into the secondary mortgage loan markets. During the period of loan origination and prior to the sale of the loans in the secondary market, the Company has exposure to movements in interest rates associated with written interest rate lock commitments with potential borrowers to originate one- to four-family loans that are intended to be sold and for closed one- to four-family and multifamily mortgage loans held for sale that are awaiting sale and delivery into the secondary market. The Company economically hedges the risk of changing interest rates associated with these mortgage loan commitments by entering into forward sales contracts to sell one- to four-family and multifamily mortgage loans or mortgage-backed securities to broker/dealers at specific prices and dates. As of December 31, 2017 and December 31, 2016 , the notional values or contractual amounts and fair values of the Company's derivatives not designated in hedge relationships were as follows (in thousands): Asset Derivatives Liability Derivatives December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 Notional/ Contract Amount Fair Value (1) Notional/ Contract Amount Fair Value (1) Notional/ Contract Amount Fair Value (2) Notional/ Contract Amount Fair Value (2) Interest rate swaps $ 285,047 $ 4,636 $ 309,936 $ 7,670 $ 285,047 $ 4,636 $ 309,936 $ 7,670 Mortgage loan commitments 29,739 225 42,296 30 13,763 153 27,191 174 Forward sales contracts 43,069 298 71,192 452 47,000 48 9,715 115 $ 357,855 $ 5,159 $ 423,424 $ 8,152 $ 345,810 $ 4,837 $ 346,842 $ 7,959 (1) Included in Other Assets on the Consolidated Statements of Financial Condition, with the exception of those interest rate swaps from prior to 2009 that were not designated in hedge relationships (with a fair value of $499,000 at December 31, 2017 and $822,000 at December 31, 2016 ), which are included in Loans Receivable. (2) Included in Other Liabilities on the Consolidated Statements of Financial Condition. Gains (losses) recognized in income on non-designated hedging instruments for the years ended December 31, 2017 and 2016 were as follows (in thousands): For the Year Ended December 31, Location on Income Statement 2017 2016 Mortgage loan commitments Mortgage banking operations $ 195 $ (348 ) Forward sales contracts Mortgage banking operations (491 ) 296 $ (296 ) $ (52 ) The Company is exposed to credit-related losses in the event of nonperformance by the counterparty to these agreements. Credit risk of the financial contract is controlled through the credit approval, limits, and monitoring procedures and management does not expect the counterparties to fail their obligations. In connection with the interest rate swaps between Banner Bank and the dealer counterparties, the agreements contain a provision where if Banner Bank fails to maintain its status as a well/adequately capitalized institution, then the counterparty could terminate the derivative positions and Banner Bank would be required to settle its obligations. Similarly, Banner Bank could be required to settle its obligations under certain of its agreements if specific regulatory events occur, such as a publicly issued prompt corrective action directive, cease and desist order, or a capital maintenance agreement that required Banner Bank to maintain a specific capital level. If Banner Bank had breached any of these provisions at December 31, 2017 or December 31, 2016 , it could have been required to settle its obligations under the agreements at the termination value. As of December 31, 2017 and 2016 , the termination value of derivatives in a net liability position related to these agreements was $3.7 million and $7.6 million , respectively. The Company generally posts collateral against derivative liabilities in the form of government agency-issued bonds, mortgage-backed securities, or commercial mortgage-backed securities. Collateral posted against derivative liabilities was $16.9 million and $29.3 million as of December 31, 2017 and 2016 , respectively. Derivative assets and liabilities are recorded at fair value on the balance sheet and do not take into account the effects of master netting agreements. Master netting agreements allow the Company to settle all derivative contracts held with a single counterparty on a net basis and to offset net derivative positions with related collateral where applicable. The following table illustrates the potential effect of the Company's derivative master netting arrangements, by type of financial instrument, on the Company's Consolidated Statements of Financial Condition as of December 31, 2017 and December 31, 2016 (in thousands): December 31, 2017 Gross Amounts of Financial Instruments Not Offset in the Statement of Financial Condition Gross Amounts Recognized Amounts offset in the Statement of Financial Condition Net Amounts in the Statement of Financial Condition Netting Adjustment Per Applicable Master Netting Agreements Fair Value of Financial Collateral in the Statement of Financial Condition Net Amount Derivative assets Interest rate swaps $ 5,083 $ — $ 5,083 $ (656 ) $ — $ 4,427 $ 5,083 $ — $ 5,083 $ (656 ) $ — $ 4,427 Derivative liabilities Interest rate swaps $ 5,083 $ — $ 5,083 $ (656 ) $ (3,467 ) $ 960 $ 5,083 $ — $ 5,083 $ (656 ) $ (3,467 ) $ 960 December 31, 2016 Gross Amounts of Financial Instruments Not Offset in the Statement of Financial Condition Gross Amounts Recognized Amounts offset in the Statement of Financial Condition Net Amounts in the Statement of Financial Condition Netting Adjustment Per Applicable Master Netting Agreements Fair Value of Financial Collateral in the Statement of Financial Condition Net Amount Derivative assets Interest rate swaps $ 8,330 $ — $ 8,330 $ (362 ) $ — $ 7,968 $ 8,330 $ — $ 8,330 $ (362 ) $ — $ 7,968 Derivative liabilities Interest rate swaps $ 8,330 $ — $ 8,330 $ (362 ) $ (7,557 ) $ 411 $ 8,330 $ — $ 8,330 $ (362 ) $ (7,557 ) $ 411

BASIS OF PRESENTATION AND SUM33

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation	Principles of Consolidation: The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All material intercompany transactions, profits and balances have been eliminated. The consolidated financial statements of the Company have been prepared in accordance with generally accepted accounting principles in the United States (GAAP) and under the rules and regulations of the U.S. Securities and Exchange Commission (the SEC).
Subsequent Events	Subsequent Events: The Company has evaluated events and transactions subsequent to December 31, 2017 for potential recognition or disclosure.
Cash and Cash Equivalents, Policy	Cash and Cash Equivalents: Cash and cash equivalents include cash and due from banks and temporary investments which are federal funds sold and interest bearing balances due from other banks. Cash and cash equivalents generally have maturities of three months or less at the date of purchase.
Business Combinations	Business Combinations: Business combinations are accounted for using the acquisition method of accounting and, accordingly, assets acquired and liabilities assumed, both tangible and intangible, and consideration exchanged are recorded at acquisition date fair values. The excess purchase consideration over fair value of net assets acquired is recorded as goodwill. In the event that the fair value of net assets acquired exceeds the purchase price, including fair value of liabilities assumed, a bargain purchase gain is recorded on that acquisition. Expenses incurred in connection with a business combination are expensed as incurred. Changes in deferred tax asset valuation allowances related to acquired tax uncertainties are recognized in net income after the measurement period.
Use of Estimates	Use of Estimates: In the opinion of management, the accompanying consolidated statements of financial condition and related consolidated statements of operations, comprehensive income, changes in shareholders’ equity and cash flows reflect all adjustments (which include reclassification and normal recurring adjustments) that are necessary for a fair presentation in conformity with GAAP. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect amounts reported in the financial statements. Various elements of the Company’s accounting policies, by their nature, are inherently subject to estimation techniques, valuation assumptions and other subjective assessments. In particular, management has identified several accounting policies that, due to the judgments, estimates and assumptions inherent in those policies, are critical to an understanding of Banner’s financial statements. These policies relate to (i) the methodology for the recognition of interest income, (ii) determination of the provision and allowance for loan and lease losses, (iii) the valuation of financial assets and liabilities recorded at fair value, including other-than-temporary impairment (OTTI) losses, (iv) the valuation of intangible assets, such as goodwill, core deposit intangibles (CDI) and mortgage servicing rights, (v) the valuation of real estate held for sale, (vi) the valuation or recognition of deferred tax assets and liabilities and (vii) the valuation of assets and liabilities acquired in business combinations and subsequent recognition of related income and expense. These policies and judgments, estimates and assumptions are described in greater detail in subsequent Notes to the Consolidated Financial Statements. Management believes that the judgments, estimates and assumptions used in the preparation of the financial statements are appropriate based on the factual circumstances at the time. However, given the sensitivity of the financial statements to these critical accounting policies, the use of other judgments, estimates and assumptions could result in material differences in the Company’s results of operations or financial condition. Further, subsequent changes in economic or market conditions could have a material impact on these estimates and the Company’s financial condition and operating results in future periods.
Securities	Securities: Securities are classified as held-to-maturity when the Company has the ability and positive intent to hold them to maturity. Securities classified as available-for-sale are available for future liquidity requirements and may be sold prior to maturity. Securities classified as trading are also available for future liquidity requirements and may be sold prior to maturity. Purchase premiums and discounts are recognized in interest income using the interest method over the terms of the securities. Securities classified as held-to-maturity are carried at cost, adjusted for amortization of premiums and accretion of discounts to maturity and, if appropriate, any other-than-temporary impairment losses. Securities classified as available-for-sale are recorded at fair value. Unrealized holding gains and losses on securities classified as available-for-sale are excluded from earnings and are reported net of tax as accumulated other comprehensive income (AOCI), a component of shareholders’ equity, until realized. Securities classified as trading are also recorded at fair value. Unrealized holding gains and losses on securities classified as trading are included in earnings. (See Note 18 for a more complete discussion of accounting for the fair value of financial instruments.) Declines in the fair value of securities below their cost that are deemed to be other-than-temporary are recognized in earnings as realized losses. Realized gains and losses on sale are computed on the specific identification method and are included in earnings on the trade date sold. The Company reviews investment securities on an ongoing basis for the presence of OTTI or permanent impairment, taking into consideration current market conditions, fair value in relationship to cost, extent and nature of the change in fair value, issuer rating changes and trends, whether the Company intends to sell a security or if it is likely that it will be required to sell the security before recovery of the amortized cost basis of the investment, which may be maturity, and other factors. For debt securities, if the Company intends to sell the security or it is likely that the Company will be required to sell the security before recovering its cost basis, the entire impairment loss would be recognized in earnings as an OTTI. If the Company does not intend to sell the security and it is not likely that the Company will be required to sell the security but the Company does not expect to recover the entire amortized cost basis of the security, only the portion of the impairment loss representing credit losses would be recognized in earnings. The credit loss on a security is measured as the difference between the amortized cost basis and the present value of the cash flows expected to be collected. Projected cash flows are discounted by the original or current effective interest rate depending on the nature of the security being measured for potential OTTI. The remaining impairment related to all other factors, the difference between the present value of the cash flows expected to be collected and fair value, is recognized as a charge to AOCI. Impairment losses related to all other factors are presented as separate categories within AOCI. For investment securities transferred from held-to-maturity to available-for-sale, unrealized gains or losses from the time of transfer are accreted or amortized over the remaining life of the debt security based on the amount and timing of future estimated cash flows. The accretion or amortization of the amount recorded in AOCI increases the carrying value of the investment and does not affect earnings.
Investment in FHLB Stock	Investment in FHLB Stock: At December 31, 2017 , the Banks had $10.3 million in FHLB of Des Moines stock (FHLB stock), compared to $12.5 million at December 31, 2016 . The Banks' investments in FHLB stock are generally viewed as a long-term investment and are carried at par value ( $100 per share), which reasonably approximates its fair value. FHLB stock does not have a readily determinable fair value. Ownership of FHLB stock is restricted to the FHLB and member institutions and can only be purchased and redeemed at par. As members of the FHLB system, the Banks are required to maintain a minimum level of investment in FHLB stock based on specific percentages of their outstanding FHLB advances. Management periodically evaluates FHLB stock for impairment. Management's determination of whether these investments are impaired is based on its assessment of the ultimate recoverability of cost rather than by recognizing temporary declines in value. The determination of whether a decline affects the ultimate recoverability of cost is influenced by criteria such as (1) the significance of any decline in net assets of the FHLB as compared to the capital stock amount for the FHLB and the length of time this situation has persisted, (2) commitments by the FHLB to make payments required by law or regulation and the level of such payments in relation to the operating performance of the FHLB, (3) the impact of legislative and regulatory changes on institutions and, accordingly, the customer base of the FHLB, and (4) the liquidity position of the FHLB. The Company has determined there is no impairment on the FHLB stock investment as of December 31, 2017 .
Loans Receivable	Loans Receivable: The Banks originate residential one- to four-family and multifamily mortgage loans for both portfolio investment and sale in the secondary market. The Banks also originate construction and land development, commercial real estate, commercial business, agricultural and consumer loans for portfolio investment. Loans receivable not designated as held for sale are recorded at the principal amount outstanding, net of allowance for loan losses, deferred fees, discounts and premiums. Premiums, discounts and deferred loan fees are amortized to maturity using the level-yield methodology. Some of the Company’s loans are reported as troubled debt restructures (TDRs). Loans are reported as TDRs when the Banks grant a concession(s) to a borrower experiencing financial difficulties that it would not otherwise consider. Examples of such concessions include forgiveness of principal or accrued interest, extending the maturity date(s) or providing a lower interest rate than would be normally available for a transaction of similar risk. As a result of these concessions, loans identified as TDRs are impaired as the Banks will not collect all amounts due, both principal and interest, in accordance with the terms of the original loan agreement. TDRs are accounted for in accordance with the Banks’ impaired loan accounting policies.
Finance, Loan and Lease Receivables, Held-for-sale	Loans Held for Sale . Residential one- to four-family and multifamily mortgage loans originated with the intent to be sold in the secondary market are considered held for sale. Residential one- to four-family loans under best effort delivery commitments are carried at the lower of aggregate cost or estimated market value. Residential one- to four-family loans under mandatory delivery commitments are carried at fair value in order to match changes in the value of the loans with the value of the economic hedges on the loans. Fair values for residential mortgage loans held for sale are determined by comparing actual loan rates to current secondary market prices for similar loans. As of December 31, 2016 , multifamily held for sale loans were carried at the lower of aggregate cost or estimated market value. During 2017, the Company elected fair value accounting on newly originated multifamily held for sale loans; as a result, as of December 31, 2017 , multifamily held for sale loans are carried at fair value in order to match changes in the value of the loans with the value of the economic hedges on the loans. Fair values for multifamily loans held for sale are calculated based on discounted cash flows using a discount rate that is a combination of market spreads for similar loan types added to selected index rates. Net unrealized losses on loans held for sale that are carried at lower of cost or market are recognized through the valuation allowance by charges to income. Non-refundable fees and direct loan origination costs related to loans held for sale are recognized as part of the cost basis of the loan. Gains and losses on sales of loans held for sale are determined using the specific identification method and are recorded in the mortgage banking operations component of non-interest income .
Acquired Loans Policy	Acquired Loans: Purchased loans, including loans acquired in business combinations, are recorded at their fair value at the acquisition date. Credit discounts are included in the determination of fair value; therefore, an allowance for loan and lease losses is not recorded at the acquisition date. Acquired loans are evaluated upon acquisition and classified as either purchased credit-impaired or purchased non-credit-impaired. Purchased credit-impaired (PCI) loans reflect credit deterioration since origination such that it is probable at acquisition that the Company will be unable to collect all contractually required payments. The excess of the cash flows expected to be collected over a PCI pool's carrying value is considered to be the accretable yield and is recognized as interest income over the estimated life of the pool using the effective yield method. The excess of the undiscounted contractual balances due over the cash flows expected to be collected is considered to be the nonaccretable difference. The nonaccretable difference represents the Company's estimate of the credit losses expected to occur and was considered in determining the fair value of the loans as of the acquisition date. Subsequent to the acquisition date, any increases in expected cash flows over those expected at the purchase date are adjusted through a change to the accretable yield on a prospective basis. Any subsequent decreases in expected cash flows attributable to credit deterioration are recognized by recording a provision for loan losses. For purchased non-credit-impaired loans, the difference between the fair value and unpaid principal balance of the loan at the acquisition date is amortized or accreted to interest income over the life of the loans. Any subsequent deterioration in credit quality is recognized by recording a provision for loan losses.
Income Recognition on Nonaccrual and Impaired Loans	Income Recognition on Nonaccrual and Impaired Loans and Securities: Interest on loans and securities is accrued as earned unless management doubts the collectability of the asset or the unpaid interest. Interest accruals on loans are generally discontinued when loans become 90 days past due for payment of interest or principal and the loans are then placed on nonaccrual status. All previously accrued but uncollected interest is deducted from interest income upon transfer to nonaccrual status. For any future payments collected, interest income is recognized only upon management’s assessment that there is a strong likelihood that the full amount of a loan will be repaid or recovered. A loan may be put on nonaccrual status sooner than this policy would dictate if, in management’s judgment, the interest may be uncollectable. While less common, similar interest reversal and nonaccrual treatment is applied to investment securities if their ultimate collectability becomes questionable.
Provision and Allowance for Loan Losses	Provision and Allowance for Loan Losses: The provision for loan losses reflects the amount required to maintain the allowance for loan losses at an appropriate level based upon management’s evaluation of the adequacy of general and specific loss reserves. The Company maintains an allowance for loan losses consistent in all material respects with GAAP. The Company has established systematic methodologies for the determination of the adequacy of the Company’s allowance for loan losses. The methodologies are set forth in a formal policy and take into consideration the need for a general valuation allowance as well as specific allowances that are tied to individual problem loans. The Company increases its allowance for loan losses by charging provisions for probable loan losses against its income and values impaired loans consistent with accounting guidelines. The allowance for loan losses is maintained at a level sufficient to provide for estimated losses based on evaluating known and inherent risks in the loan portfolio and upon the Company’s continuing analysis of the factors underlying the quality of the loan portfolio. These factors include, among others, changes in the size and composition of the loan portfolio, delinquency rates, actual loan loss experience, current economic conditions, detailed analysis of individual loans for which full collectability may not be assured, and determination of the existence and realizable value of the collateral and guarantees securing the loans. Realized losses related to specific assets are applied as a reduction of the carrying value of the assets and charged immediately against the allowance for loan loss reserve. Recoveries on previously charged off loans are credited to the allowance for loan losses. The reserve is based upon factors and trends identified by Banner at the time financial statements are prepared. Although the Company uses the best information available, future adjustments to the allowance for loan losses may be necessary due to economic, operating, regulatory and other conditions beyond the Company’s control. The adequacy of general and specific reserves is based on a continuing evaluation of the pertinent factors underlying the quality of the loan portfolio as well as individual review of certain large balance loans. Large groups of smaller-balance homogeneous loans are collectively evaluated for impairment. Loans that are collectively evaluated for impairment include residential real estate and consumer loans and, as appropriate, smaller balance non-homogeneous loans. Larger balance non-homogeneous residential construction and land, commercial real estate, commercial business loans and unsecured loans are individually evaluated for impairment. Loans are considered impaired when, based on current information and events, the Company determines that it is probable that it will be unable to collect all amounts due according to the contractual terms of the loan agreement. Factors involved in determining impairment include, but are not limited to, the financial condition of the borrower and the value of the underlying collateral. Impaired loans are measured based on the present value of expected future cash flows discounted at the loan’s effective interest rate or, as a practical expedient, at the loan’s observable market price, or if the loan is collateral dependent, at the fair value of collateral less selling costs. Subsequent changes in the value of impaired loans are included within the provision for loan losses in the same manner in which impairment initially was recognized or as a reduction in the provision that would otherwise be reported. The Company’s methodology for assessing the appropriateness of the allowance for loan losses consists of several key elements, which include specific allowances, an allocated formula allowance and an unallocated allowance. Losses on specific loans are provided for when the losses are probable and estimable. General loan loss reserves are established to provide for inherent loan portfolio risks not specifically provided for. The level of general reserves is based on analysis of potential exposures existing in the loan portfolio including evaluation of historical trends, current market conditions and other relevant factors identified by us at the time the financial statements are prepared. The formula allowance is calculated by applying loss factors to outstanding loans, excluding those loans that are subject to individual analysis for specific allowances. Loss factors are based on the Company’s historical loss experience adjusted for significant environmental considerations, including the experience of other banking organizations, which in the judgment of management affects the collectability of the loan portfolio as of the evaluation date. The unallocated allowance is based upon the Company’s evaluation of various factors that are not directly measured in the determination of the formula and specific allowances. While the Company believes the estimates and assumptions used in the determination of the adequacy of the allowance for loan losses are reasonable, there can be no assurance that such estimates and assumptions will not be proved incorrect in the future, or that the actual amount of future provisions will not exceed the amount of past provisions or that any increased provisions that may be required will not adversely impact the financial condition and results of operations of the Company. In addition, the determination of the amount of the allowance for loan losses is subject to review by bank regulators as part of the routine examination process, which may result in the adjustment of reserves based upon their judgment of information available to them at the time of their examination.
Loan Origination and Commitment Fees	Loan Origination and Commitment Fees: Loan origination fees, net of certain specifically defined direct loan origination costs, are deferred and recognized as an adjustment of the loans’ interest yield using the level-yield method over the contractual term of each loan adjusted for actual loan prepayment experience. Net deferred fees or costs related to loans held for sale are recognized as part of the cost basis of the loan. Loan commitment fees are deferred until the expiration of the commitment period unless management believes there is a remote likelihood that the underlying commitment will be exercised, in which case the fees are amortized to fee income using the straight-line method over the commitment period. If a loan commitment is exercised, the deferred commitment fee is accounted for in the same manner as a loan origination fee. Deferred commitment fees associated with expired commitments are recognized as fee income.
Reserve for Unfunded Commitments, Policy	Reserve for Unfunded Commitments: A reserve for unfunded commitments is maintained at a level that, in the opinion of management, is adequate to absorb probable losses associated with the Banks' commitments to lend funds under existing agreements such as letters or lines of credit. Management determines the adequacy of the reserve for unfunded commitments based upon reviews of individual credit facilities, current economic conditions, the risk characteristics of the various categories of commitments and other relevant factors. The reserve is based on estimates and ultimate losses may vary from the current estimates. These estimates are evaluated on a regular basis and, as adjustments become necessary, they are reported in earnings in the periods in which they become known. Draws on unfunded commitments that are considered uncollectible at the time funds are advanced are charged to the allowance for loan losses. Provisions for unfunded commitment losses are recognized in non-interest expense and added to the reserve for unfunded commitments, which is included in other liabilities.
Real Estate Held for Sale	Real Estate Owned: Property acquired by foreclosure or deed in lieu of foreclosure is initially recorded at the estimated fair value of the property, less expected selling costs. Development and improvement costs relating to the property are capitalized while direct holding costs are expensed. The carrying value of the property is periodically evaluated by management and, if necessary, allowances are established to reduce the carrying value to net realizable value. Gains or losses at the time the property is sold are charged or credited to operations in the period in which they are realized. The amounts the Banks will ultimately recover from real estate held for sale may differ substantially from the carrying value of the assets because of market factors beyond the Banks’ control or because of changes in the Banks’ strategies for recovering the investment.
Schedule of Property and Equipment Useful Lives	epreciation is based upon the straight-line method applied to individual assets and groups of assets acquired in the same year over the lesser of their estimated useful lives or the related lease terms of the assets: Buildings and leased improvements 10–39 years Furniture and equipment 3 – 10 years
Property and Equipment	Property and Equipment: Property and equipment is carried at cost less accumulated depreciation. Depreciation is based upon the straight-line method applied to individual assets and groups of assets acquired in the same year over the lesser of their estimated useful lives or the related lease terms of the assets: Buildings and leased improvements 10–39 years Furniture and equipment 3 – 10 years Routine maintenance, repairs and replacement costs are expensed as incurred. Expenditures which significantly increase values or extend useful lives are capitalized. The Company reviews buildings, leasehold improvements and equipment for impairment whenever events or changes in circumstances indicate that the undiscounted cash flows for the property are less than its carrying value. If identified, an impairment loss is recognized through a charge to earnings based on the fair value of the property.
Goodwill, Policy	Goodwill: Goodwill represents the excess of the purchase consideration over the fair value of the assets acquired, net of the fair values of liabilities assumed in a business combination and is not amortized but is reviewed annually, or more frequently as current circumstances and conditions warrant, for impairment. An assessment of qualitative factors is completed to determine if it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If the qualitative analysis concludes that further analysis is required, then a quantitative impairment test would be completed. The quantitative goodwill impairment test is used to identify the existence of impairment and the amount of impairment loss and compares the reporting unit's estimated fair values, including goodwill, to its carrying amount. If the fair value exceeds the carry amount then goodwill is not considered impaired. If the carrying amount exceeds its fair value, an impairment loss would be recognized equal to the amount of excess, limited to the amount of total goodwill allocated to that reporting unit. The impairment loss would be recognized as a charge to earnings. The disposal of a portion of a reporting unit that meets the definition of a business requires goodwill to be allocated for purposes of determining the gain or loss on disposal. Since the sale of the Utah branches met the definition of a business, goodwill was allocated to the sale based on the fair value of the Utah branches compared to the relative fair value of the reporting unit.
Other Intangible Assets	Other Intangible Assets: Other intangible assets consist primarily of core deposit intangibles (CDI), which are amounts recorded in business combinations or deposit purchase transactions related to the value of transaction-related deposits and the value of the customer relationships associated with the deposits. CDI is being amortized on an accelerated basis over a weighted average estimated useful life of three to ten years. These assets are reviewed at least annually for events or circumstances that could impact their recoverability. These events could include loss of the underlying core deposits, increased competition or adverse changes in the economy. To the extent other identifiable intangible assets are deemed unrecoverable, impairment losses are recorded in other non-interest expense to reduce the carrying amount of the assets. Other intangibles also include favorable leasehold intangibles (LHI). LHI represents the value assigned to leases assumed in an acquisition in which the lease terms are favorable compared to a market lease at the date of acquisition. LHI is amortized over the underlying lease term and is reviewed at least annually for events or circumstances that could impair the value.
Mortgage Servicing Rights	Mortgage Servicing Rights: Servicing assets are recognized as separate assets when rights are acquired through purchase or sale of loans. Generally, purchased servicing rights are capitalized at the cost to acquire the rights. For sales of mortgage loans, the value of the servicing right is estimated and capitalized. Fair values are estimated based on an independent dealer analysis of discounted cash flows. Capitalized servicing rights are reported in other assets and are amortized into mortgage banking operations in proportion to, and over the period of, the estimated future net servicing income of the underlying financial assets. Servicing assets are evaluated for impairment based upon the fair value of the rights as compared to amortized cost. Impairment is determined by stratifying rights into tranches based on predominant risk characteristics for the underlying loans, such as interest rate, balance outstanding, loan type, age and remaining term, and investor type. Impairment is recognized through a valuation allowance for an individual tranche, to the extent that fair value is less than the capitalized amount for the tranche. If the Company later determines that all or a portion of the impairment no longer exists for a particular tranche, a reduction of the allowance may be recorded as an increase to income. Servicing fee income is recorded for fees earned for servicing loans and is reflected in mortgage banking operations on the Consolidated Statements of Operations. The fees are based on a contractual percentage of the outstanding principal or a fixed amount per loan and are recorded as income when earned. The amortization of mortgage servicing rights is netted against loan servicing fee income.
Bank-Owned Life Insurance (BOLI)	Bank-Owned Life Insurance (BOLI): The Banks have purchased, or acquired through mergers, life insurance policies in connection with the implementation of certain executive supplemental income, salary continuation and deferred compensation retirement plans. These policies provide protection against the adverse financial effects that could result from the death of a key employee and provide tax-exempt income to offset expenses associated with the plans. It is the Banks’ intent to hold these policies as a long-term investment; however, there may be an income tax impact if the Bank chooses to surrender certain policies. Although the lives of individual current or former management-level employees are insured, the Banks are the respective owners and sole or partial beneficiaries.
Derivative Instruments	Derivative Instruments: Derivatives include “off-balance-sheet” financial products, the value of which is dependent on the value of underlying financial assets, such as stock, bonds, foreign currency, or a reference rate or index. Such derivatives include “forwards,” “futures,” “options” or “swaps.” Banner Bank is a party to $7.1 million ($4.4 million designated in a hedge relationship) in notional amounts of interest rate swaps at December 31, 2017 . Some of these swaps serve as hedges to an equal amount of fixed rate loans which include market value prepayment penalties that mirror the provision of the specifically matched interest rate swaps. In addition, Banner Bank uses an interest rate swap program for commercial loan customers that provides the client with a variable rate loan and enters into an interest rate swap allowing them to effectively fix their loan interest rates. These customer swaps are matched with third party swaps with qualified broker/dealer or banks to offset the risk. At December 31, 2017 , Banner Bank had $282.3 million in notional amounts of these customer interest rate swaps outstanding, with an equal amount of offsetting third party swaps also in place. The fair value adjustments for these swaps are reflected in other assets or other liabilities as appropriate. Further, as a part of its mortgage banking activities, the Company issues “rate lock” commitments to one- to four-family loan borrowers and obtains offsetting “best efforts” delivery commitments from purchasers of loans. The Company uses forward contracts for the sale of mortgage-backed securities and mandatory delivery commitments for the sale of loans to hedge one- to four-family loan "rate lock" commitments and one- to four-family loans held for sale. The Company also uses forward contracts for the sale of mortgage backed securities to hedge multifamily held for sale loans. The commitments to originate mortgage loans held for sale and the related delivery contracts are considered derivatives. The Company recognizes all derivatives as either assets or liabilities in the balance sheet and requires measurement of those instruments at fair value through adjustments to current earnings. None of these residential mortgage loan related derivatives are designated as hedging instruments for accounting purposes. Rather, they are accounted for as free-standing derivatives, or economic hedges, and the Company reports changes in fair values of its derivatives in current period net income. The fair values for these instruments, which generally change as a result of changes in the level of market interest rates, are estimated based on dealer quotes and secondary market sources. Assumptions used include rate assumptions based on historical information, current mortgage interest rates, the stage of completion of the underlying application and underwriting process, the time remaining until the expiration of the derivative loan commitment, and the expected net future cash flows related to the associated servicing of the loan (see Note 24 for a more complete discussion of derivatives and hedging).
Transfers of Financial Assets	Transfers of Financial Assets: Transfers of financial assets are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when (1) the assets have been isolated from the Banks, (2) the transferee obtains the right (free of conditions that constrain it from taking advantage of that right) to pledge or exchange the transferred assets, and (3) the Banks do not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
Advertising Expenses	Advertising Expenses: Advertising costs are expensed as incurred. Costs related to production of advertising are considered incurred when the advertising is first used.
Income Taxes	Income Taxes: The Company files a consolidated income tax return including all of its wholly-owned subsidiaries on a calendar year basis. Income taxes are accounted for using the asset and liability method. Under this method, a deferred tax asset or liability is determined based on the enacted tax rates which will be in effect when the differences between the financial statement carrying amounts and tax basis of existing assets and liabilities are expected to be reported in the Company’s income tax returns. The effect on deferred taxes of a change in tax rates is recognized in income in the period of change. A valuation allowance is recognized as a reduction to deferred tax assets when management determines it is more likely than not that deferred tax assets will not be available to offset future income tax liabilities. In December 2017, the federal government enacted the Tax Cuts and Jobs Act (the 2017 Tax Act). Among other provisions, the 2017 Tax Act reduced the federal marginal corporate income tax rate from 35% to 21%. As a result of the passage of the 2017 Tax Act, the Company recorded a $42.6 million charge for the revaluation of its net deferred tax asset to account for the future impact of the decrease in the corporate income tax rate and other provisions of the legislation. The charge was recorded as an increase to tax expense and reduction of the net deferred asset. The Company’s financial results reflect the income tax effects of the 2017 Tax Act for which the accounting is complete and provisional amounts for those specific income tax effects of the 2017 Tax Act for which the accounting is incomplete but a reasonable estimate could be determined. As a result, these amounts could be adjusted during the measurement period, which will end in December 2018. The Company did not identify items for which the income tax effects of the 2017 Tax Act have not been completed and a reasonable estimate could not be determined as of December 31, 2017. The $42.6 million charge recorded by the Company includes $4.2 million of provisional income tax expense related to Alternative Minimum Tax (AMT) credits that are limited under Section 383 of the Internal Revenue Code of 1986 (Code), which resulted in a reduction in the AMT deferred tax asset. The utilization of the limited AMT credits under the refundable AMT credit law is uncertain and will require further analysis as guidance is released by the Internal Revenue Service during 2018. Accounting standards for income taxes prescribe a recognition threshold and measurement process for financial statement recognition and measurement of uncertain tax positions taken or expected to be taken in a tax return, and also provides guidance on the de-recognition of previously recorded benefits and their classification, as well as the proper recording of interest and penalties, accounting in interim periods, disclosures and transition. The Company periodically reviews its income tax positions based on tax laws and regulations and financial reporting considerations, and records adjustments as appropriate. This review takes into consideration the status of current taxing authorities’ examinations of the Company’s tax returns, recent positions taken by the taxing authorities on similar transactions, if any, and the overall tax environment. As of December 31, 2017 , the Company had an insignificant amount of unrecognized tax benefits for uncertain tax positions, none of which if recognized would materially affect the effective tax rate if recognized. The Company does not anticipate that the amount of unrecognized tax benefits will significantly increase or decrease in the next twelve months. The Company’s policy is to recognize interest and penalties on unrecognized tax benefits in income tax expense. The amount of interest and penalties accrued for the years ended December 31, 2017 , 2016 and 2015 is immaterial. The Company files consolidated income tax returns in Oregon, California, Utah and Idaho and for federal purposes. The Company has tax years 2014–2016 open for tax examination under the statute of limitation provisions of the Code.
Share-Based Compensation	Stock-Based Compensation: The Company compensates employees and directors with time-based restricted stock and restricted stock unit grants. Some restricted stock awards include performance-based and market-based goals that impact the number of shares that ultimately vest based on the level of goal achievement. The Company measures the cost of employee or director services received in exchange for an award of equity instruments based on the fair value of the award, which is the intrinsic value on the grant date. This cost is recognized as expense in the Consolidated Statements of Operations ratably over the vesting period of the award. Any tax benefit or deficiency is recorded as income tax benefit or expense in the period the shares vest. Excess tax benefits are classified along with other income tax cash flows as an operating activity. The Company issues restricted stock and restricted stock unit awards which vest over a one or three year period during which time the employee or director accrues or receives dividends and may have full voting rights depending on the terms of the grant.
Earnings Per Share, Policy	Earnings Per Share: Earnings per common share is computed under the two-class method. Pursuant to the two-class method, nonvested stock-based payment awards that contain nonforfeitable rights to dividends or dividend equivalents are participating securities and are included in the computation of EPS. The two-class method is an earnings allocation formula that determines earnings per share for each class of common stock and participating security according to dividends declared (or accumulated) and participation rights in undistributed earnings. Application of the two-class method resulted in the equivalent earnings per share to the treasury method. Basic earnings per common share is computed by dividing net earnings allocated to common shareholders by the weighted-average number of common shares outstanding during the applicable period, excluding outstanding participating securities. Diluted earnings per common share is computed using the weighted-average number of shares determined for the basic earnings per common share computation plus the dilutive effect of stock compensation and warrants for common stock using the treasury stock method.
Comprehensive Income	Comprehensive Income: Accounting principles generally require that recognized revenue, expenses, gains and losses be included in net income. In addition, certain changes in assets and liabilities, such as unrealized gains and losses on available-for-sale securities, are reported as a separate component of the equity section of the Consolidated Statements of Financial Condition, and such items, along with net income, are components of comprehensive income which is reported in the Consolidated Statements of Comprehensive Income.
Business Segments	Business Segments: The Company is managed by legal entity and not by lines of business. Each of the Banks is a community oriented commercial bank chartered in the State of Washington. The Banks’ primary business is that of a traditional banking institution, gathering deposits and originating loans for portfolio in its respective primary market areas. The Banks offer a wide variety of deposit products to their consumer and commercial customers. Lending activities include the origination of real estate, commercial/agriculture business and consumer loans. Banner Bank is also an active participant in the secondary market, originating residential loans for sale on both a servicing released and servicing retained basis. In addition to interest income on loans and investment securities, the Banks receive other income from deposit service charges, loan servicing fees and from the sale of loans and investments. The performance of the Banks is reviewed by the Company’s executive management and Board of Directors on a monthly basis. All of the executive officers of the Company are members of Banner Bank’s management team. Generally Accepted Accounting Principles establish standards to report information about operating segments in annual financial statements and require reporting of selected information about operating segments in interim reports to shareholders. The Company has determined that its current business and operations consist of a single business segment and a single reporting unit.
Reclassification	Reclassification: Certain reclassifications have been made to the prior years’ consolidated financial statements and/or schedules to conform to the current year’s presentation. These reclassifications may have affected certain reported amounts and ratios for the prior periods. These reclassifications had no effect on retained earnings or net income as previously presented and the effect of these reclassifications is considered immaterial.

SECURITIES (Tables)

SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Schedule of Securities	The amortized cost, gross unrealized gains and losses and estimated fair value of securities at December 31, 2017 and 2016 are summarized as follows (in thousands): December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Trading: Municipal bonds $ 100 $ 100 Corporate bonds 27,132 22,058 Equity securities 14 160 $ 27,246 $ 22,318 Available-for-Sale: U.S. Government and agency obligations $ 72,829 $ 68 $ (431 ) $ 72,466 Municipal bonds 68,513 665 (445 ) 68,733 Corporate bonds 5,431 6 (44 ) 5,393 Mortgage-backed or related securities 745,956 1,003 (7,402 ) 739,557 Asset-backed securities 27,667 184 (93 ) 27,758 Equity securities 5,716 10 (148 ) 5,578 $ 926,112 $ 1,936 $ (8,563 ) $ 919,485 Held-to-Maturity: U.S. Government and agency obligations $ 1,024 $ 29 $ — $ 1,053 Municipal bonds: 189,860 3,385 (1,252 ) 191,993 Corporate bonds 3,978 7 — 3,985 Mortgage-backed or related securities 65,409 266 (518 ) 65,157 $ 260,271 $ 3,687 $ (1,770 ) $ 262,188 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Trading: U.S. Government and agency obligations $ 1,230 $ 1,326 Municipal bonds 331 335 Corporate bonds 26,959 21,143 Mortgage-backed or related securities 1,620 1,641 Equity securities 14 123 $ 30,154 $ 24,568 Available-for-Sale: U.S. Government and agency obligations $ 57,288 $ 146 $ (456 ) $ 56,978 Municipal bonds 110,487 455 (1,089 ) 109,853 Corporate bonds 10,255 77 (49 ) 10,283 Mortgage-backed or related securities 598,899 2,064 (6,251 ) 594,712 Asset-backed securities 29,319 — (326 ) 28,993 Equity securities 5,599 10 — 5,609 $ 811,847 $ 2,752 $ (8,171 ) $ 806,428 Held-to-Maturity: U.S. Government and agency obligations $ 1,065 $ — $ (18 ) $ 1,047 Municipal bonds: 196,989 4,173 (1,272 ) 199,890 Corporate bonds 3,876 — — 3,876 Mortgage-backed or related securities 65,943 309 (537 ) 65,715 $ 267,873 $ 4,482 $ (1,827 ) $ 270,528
Schedule of Securities with Continuous Loss Position	At December 31, 2017 and 2016 , the gross unrealized losses and the fair value for securities available-for-sale and held-to-maturity aggregated by the length of time that individual securities have been in a continuous unrealized loss position was as follows (in thousands): December 31, 2017 Less Than 12 Months 12 Months or More Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Available-for-Sale: U.S. Government and agency obligations $ 31,276 $ (211 ) $ 23,341 $ (220 ) $ 54,617 $ (431 ) Municipal bonds 20,879 (185 ) 13,360 (260 ) 34,239 (445 ) Corporate bonds 296 (4 ) 4,682 (40 ) 4,978 (44 ) Mortgage-backed or related securities 559,916 (5,138 ) 100,662 (2,264 ) 660,578 (7,402 ) Asset-backed securities — — 9,926 (93 ) 9,926 (93 ) Equity securities 5,480 (148 ) — — 5,480 (148 ) $ 617,847 $ (5,686 ) $ 151,971 $ (2,877 ) $ 769,818 $ (8,563 ) Held-to-Maturity: Municipal bonds $ 21,839 $ (171 ) $ 34,314 $ (1,081 ) $ 56,153 $ (1,252 ) Mortgage-backed or related securities 38,023 (378 ) 4,434 (140 ) 42,457 (518 ) $ 59,862 $ (549 ) $ 38,748 $ (1,221 ) $ 98,610 $ (1,770 ) December 31, 2016 Less Than 12 Months 12 Months or More Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Available-for-Sale: U.S. Government and agency obligations $ 39,043 $ (442 ) $ 1,012 $ (14 ) $ 40,055 $ (456 ) Municipal bonds 60,765 (1,087 ) 556 (2 ) 61,321 (1,089 ) Corporate bonds 5,206 (49 ) — — 5,206 (49 ) Mortgage-backed or related securities 403,431 (5,604 ) 47,467 (647 ) 450,898 (6,251 ) Asset-backed securities 9,928 (101 ) 19,064 (225 ) 28,992 (326 ) $ 518,373 $ (7,283 ) $ 68,099 $ (888 ) $ 586,472 $ (8,171 ) Held-to-Maturity: U.S. Government and agency obligations $ 1,047 $ (18 ) $ — $ — $ 1,047 $ (18 ) Municipal bonds $ 64,802 $ (1,267 ) $ 204 $ (5 ) $ 65,006 $ (1,272 ) Mortgage-backed or related securities 42,245 (537 ) — — 42,245 (537 ) $ 108,094 $ (1,822 ) $ 204 $ (5 ) $ 108,298 $ (1,827 )
Schedule of Securities by Contractual Maturity Date	The amortized cost and estimated fair value of securities at December 31, 2017 , by contractual maturity, are shown below (in thousands). Expected maturities will differ from contractual maturities because some securities may be called or prepaid with or without call or prepayment penalties. December 31, 2017 Trading Available-for-Sale Held-to-Maturity Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Maturing in one year or less $ 100 $ 100 $ 3,241 $ 3,230 $ 1,968 $ 1,967 Maturing after one year through five years — — 39,513 39,070 37,734 37,626 Maturing after five years through ten years — — 215,837 213,923 97,736 98,747 Maturing after ten years through twenty years 17,132 14,543 100,862 101,181 84,352 86,249 Maturing after twenty years 10,000 7,515 560,943 556,503 38,481 37,599 27,232 22,158 920,396 913,907 260,271 262,188 Equity securities 14 160 5,716 5,578 — — $ 27,246 $ 22,318 $ 926,112 $ 919,485 $ 260,271 $ 262,188
Schedule of Pledged Securities	The following table presents, as of December 31, 2017 , investment securities which were pledged to secure borrowings, public deposits or other obligations as permitted or required by law (in thousands): Carrying Value Amortized Cost Fair Value Purpose or beneficiary: State and local governments public deposits $ 126,512 $ 126,438 $ 128,984 Interest rate swap counterparties 14,698 14,740 14,703 Repurchase transaction accounts 123,911 124,049 123,936 Other 3,924 3,924 3,835 Total pledged securities $ 269,045 $ 269,151 $ 271,458

LOANS RECEIVABLE AND THE ALLO35

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Impaired loans excluding purchased credit impaired loans [Table Text Block]	The following tables provide additional information on impaired loans, excluding PCI loans, with and without specific allowance reserves at December 31, 2017 and 2016 . Recorded investment includes the unpaid principal balance or the carrying amount of loans less charge-offs and net deferred loan fees (in thousands): December 31, 2017 Unpaid Principal Balance Recorded Investment Related Allowance Without Allowance (1) With Allowance (2) Commercial real estate: Owner-occupied $ 7,807 $ 6,447 $ 199 $ 18 Investment properties 11,296 4,200 6,884 263 One- to four-family construction 298 298 — — Land and land development: Residential 1,134 798 — — Commercial business 4,441 3,424 555 50 Agricultural business/farmland 9,388 6,230 3,031 264 One- to four-family residential 9,547 3,709 5,775 178 Consumer: Consumer secured by one- to four-family 1,498 1,324 139 7 Consumer—other 134 58 73 2 $ 45,543 $ 26,488 $ 16,656 $ 782 December 31, 2016 Unpaid Principal Balance Recorded Investment Related Allowance Without Allowance (1) With Allowance (2) Commercial real estate: Owner-occupied $ 3,786 $ 3,373 $ 203 $ 20 Investment properties 9,916 5,565 4,304 408 Multifamily real estate 508 147 349 64 One- to four-family construction 1,180 — 1,180 156 Land and land development: Residential 3,012 750 1,106 219 Commercial 1,608 998 — — Commercial business 3,753 3,074 651 69 Agricultural business/farmland 6,438 6,354 — — One- to four-family residential 11,439 3,149 8,026 479 Consumer: Consumer secured by one- to four-family 1,904 1,721 144 1 Consumer—other 391 226 166 4 $ 43,935 $ 25,357 $ 16,129 $ 1,420 (1) Includes loans without an allowance reserve that have been individually evaluated for impairment and that evaluation concluded that no reserve was needed, and $10.6 million and $10.0 million of homogenous and small balance loans as of December 31, 2017 and December 31, 2016 , respectively, that are collectively evaluated for impairment for which a general reserve has been established. (2) Loans with a specific allowance reserve have been individually evaluated for impairment using either a discounted cash flow analysis or, for collateral dependent loans, current appraisals less costs to sell to establish realizable value.
Allowance for Credit Losses on Financing Receivables [Table Text Block]	The following tables provide additional information on the allowance for loan losses and loan balances individually and collectively evaluated for impairment at or for the year ended December 31, 2017 (in thousands): For the Year Ended December 31, 2017 Commercial Real Estate Multifamily Real Estate Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance for loan losses: Beginning balance $ 20,993 $ 1,360 $ 34,252 $ 16,533 $ 2,967 $ 2,238 $ 4,104 $ 3,550 $ 85,997 Provision for loan losses 2,639 262 (7,921 ) 4,355 3,326 (415 ) 586 5,168 8,000 Recoveries 372 11 1,237 1,226 134 270 481 — 3,731 Charge-offs (1,180 ) — — (3,803 ) (2,374 ) (38 ) (1,305 ) — (8,700 ) Ending balance $ 22,824 $ 1,633 $ 27,568 $ 18,311 $ 4,053 $ 2,055 $ 3,866 $ 8,718 $ 89,028 December 31, 2017 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance individually evaluated for impairment $ 281 $ — $ — $ 50 $ 264 $ 178 $ 9 $ — $ 782 Allowance collectively evaluated for impairment 22,543 1,633 27,567 18,214 3,676 1,877 3,857 8,718 88,085 Allowance for purchased credit-impaired loans — — 1 47 113 — — — 161 Total allowance for loan losses $ 22,824 $ 1,633 $ 27,568 $ 18,311 $ 4,053 $ 2,055 $ 3,866 $ 8,718 $ 89,028 December 31, 2017 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Loan balances: Loans individually evaluated for impairment $ 16,017 $ — $ 750 $ 1,812 $ 8,585 $ 5,136 $ 212 $ — $ 32,512 Loans collectively evaluated for impairment 3,190,921 314,019 903,408 1,275,923 329,238 843,017 688,536 — 7,545,062 Purchased credit-impaired loans 14,848 169 3,365 2,159 565 136 68 — 21,310 Total loans $ 3,221,786 $ 314,188 $ 907,523 $ 1,279,894 $ 338,388 $ 848,289 $ 688,816 $ — $ 7,598,884 The following tables provide additional information on the allowance for loan losses and loan balances individually and collectively evaluated for impairment at or for the year ended December 31, 2016 (in thousands): For the Year Ended December 31, 2016 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance for loan losses: Beginning balance $ 20,716 $ 4,195 $ 27,131 $ 13,856 $ 3,645 $ 4,732 $ 902 $ 2,831 $ 78,008 Provision for loan losses 441 (2,835 ) 5,566 1,632 (170 ) (3,402 ) 4,079 719 6,030 Recoveries 582 — 2,171 1,993 59 1,283 610 — 6,698 Charge-offs (746 ) — (616 ) (948 ) (567 ) (375 ) (1,487 ) — (4,739 ) Ending balance $ 20,993 $ 1,360 $ 34,252 $ 16,533 $ 2,967 $ 2,238 $ 4,104 $ 3,550 $ 85,997 December 31, 2016 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance individually evaluated for impairment $ 428 $ 64 $ 374 $ 69 $ — $ 480 $ 5 $ — $ 1,420 Allowance collectively evaluated for impairment 20,565 1,296 33,845 16,464 2,967 1,758 4,099 3,550 84,544 Allowance for purchased credit-impaired loans — — 33 — — — — — 33 Total allowance for loan losses $ 20,993 $ 1,360 $ 34,252 $ 16,533 $ 2,967 $ 2,238 $ 4,104 $ 3,550 $ 85,997 December 31, 2016 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Loan balances: Loans individually evaluated for impairment $ 10,300 $ 349 $ 4,034 $ 2,946 $ 4,766 $ 7,678 $ 309 $ — $ 30,382 Loans collectively evaluated for impairment 3,305,586 247,662 815,174 1,201,112 363,706 805,125 650,079 — 7,388,444 Purchased credit-impaired loans 23,449 139 3,878 3,821 684 274 77 — 32,322 Total loans $ 3,339,335 $ 248,150 $ 823,086 $ 1,207,879 $ 369,156 $ 813,077 $ 650,465 $ — $ 7,451,148 The following table provides additional information on the allowance for loan losses for the year ended December 31, 2015 (in thousands): For the Year Ended December 31, 2015 Commercial Real Estate Multifamily Construction and Land Commercial Business Agricultural Business One- to Four-Family Residential Consumer Unallocated Total Allowance for loan losses: Beginning balance $ 18,784 $ 4,562 $ 25,545 $ 12,043 $ 3,821 $ 5,447 $ 483 $ 5,222 $ 75,907 Provision for loan losses 1,177 (480 ) 666 1,611 (878 ) (1,068 ) 1,363 (2,391 ) — Recoveries 819 113 1,811 948 1,927 772 570 — 6,960 Charge-offs (64 ) — (891 ) (746 ) (1,225 ) (419 ) (1,514 ) — (4,859 ) Ending balance $ 20,716 $ 4,195 $ 27,131 $ 13,856 $ 3,645 $ 4,732 $ 902 $ 2,831 $ 78,008
Past Due Financing Receivables [Table Text Block]	The following tables provide additional detail on the age analysis of Banner’s past due loans as of December 31, 2017 and 2016 (in thousands): December 31, 2017 30 – 59 Days Past Due 60 – 89 Days Past Due 90 Days or More Past Due Total Past Due Purchased Credit-Impaired Current Total Loans Loans 90 Days or More Past Due and Accruing Non-accrual Commercial real estate: Owner-occupied $ 5,323 $ 76 $ 5,490 $ 10,889 $ 7,682 $ 1,265,792 $ 1,284,363 $ — $ 6,447 Investment properties 1,737 — 4,096 5,833 7,166 1,924,424 1,937,423 — 4,199 Multifamily real estate 105 — — 105 169 313,914 314,188 — — Commercial construction — — — — — 148,435 148,435 — — Multifamily construction 3,416 — — 3,416 — 151,246 154,662 — — One- to four-family construction 4,892 725 298 5,915 446 408,966 415,327 298 — Land and land development: Residential — — 798 798 — 163,718 164,516 — 798 Commercial — — — — 2,919 21,664 24,583 — — Commercial business 1,574 404 2,577 4,555 2,159 1,273,180 1,279,894 18 3,406 Agricultural business/farmland 598 533 2,017 3,148 565 334,675 338,388 — 6,132 One- to four-family residential 4,475 1,241 2,715 8,431 136 839,722 848,289 1,085 3,264 Consumer: Consumer secured by one- to four-family 1,355 62 713 2,130 — 520,801 522,931 85 1,239 Consumer—other 609 136 15 760 68 165,057 165,885 — 58 Total $ 24,084 $ 3,177 $ 18,719 $ 45,980 $ 21,310 $ 7,531,594 $ 7,598,884 $ 1,486 $ 25,543 December 31, 2016 30–59 Days Past Due 60–89 Days Past Due 90 Days or More Past Due Total Past Due Purchased Credit-Impaired Current Total Loans Loans 90 Days or More Past Due and Accruing Non-accrual Commercial real estate: Owner-occupied $ 1,938 $ — $ 2,538 $ 4,476 $ 13,281 $ 1,335,242 $ 1,352,999 $ — $ 3,373 Investment properties 117 — 5,447 5,564 10,168 1,970,604 1,986,336 701 4,864 Multifamily real estate — — 147 147 139 247,864 248,150 147 — Commercial construction — — — — — 124,068 124,068 — — Multifamily construction — — — — — 124,126 124,126 — — One- to four-family construction — — — — 862 374,842 375,704 — — Land and land development: Residential 48 — 750 798 — 169,206 170,004 — 750 Commercial — — 998 998 3,016 25,170 29,184 — 998 Commercial business 2,314 647 1,591 4,552 3,821 1,199,506 1,207,879 — 3,074 Agricultural business/farmland 360 1,244 2,768 4,372 684 364,100 369,156 — 3,229 One- to four-family residential 1,793 249 2,110 4,152 274 808,651 813,077 1,233 2,263 Consumer: Consumer secured by one- to four-family 932 160 986 2,078 18 491,115 493,211 61 1,660 Consumer—other 1,421 154 147 1,722 59 155,473 157,254 11 215 Total $ 8,923 $ 2,454 $ 17,482 $ 28,859 $ 32,322 $ 7,389,967 $ 7,451,148 $ 2,153 $ 20,426
Schedule of Loans Receivable, Including Loans Held for Sale	Loans receivable at December 31, 2017 and 2016 are summarized as follows (dollars in thousands): December 31, 2017 December 31, 2016 Amount Percent of Total Amount Percent of Total Commercial real estate: Owner-occupied $ 1,284,363 16.9 % $ 1,352,999 18.1 % Investment properties 1,937,423 25.5 1,986,336 26.7 Multifamily real estate 314,188 4.1 248,150 3.3 Commercial construction 148,435 2.0 124,068 1.7 Multifamily construction 154,662 2.0 124,126 1.7 One- to four-family construction 415,327 5.5 375,704 5.0 Land and land development: Residential 164,516 2.2 170,004 2.3 Commercial 24,583 0.3 29,184 0.4 Commercial business 1,279,894 16.8 1,207,879 16.2 Agricultural business, including secured by farmland 338,388 4.4 369,156 5.0 One- to four-family residential 848,289 11.2 813,077 10.9 Consumer: Consumer secured by one- to four-family 522,931 6.9 493,211 6.6 Consumer—other 165,885 2.2 157,254 2.1 Total loans outstanding 7,598,884 100.0 % 7,451,148 100.0 % Less allowance for loan losses (89,028 ) (85,997 ) Net loans $ 7,509,856 $ 7,365,151 Loan amounts included net unamortized costs of $158,000 at December 31, 2017 and were net of unearned fees of $5.8 million at December 31, 2016 . Net loans include net discounts on acquired loans of $21.1 million and $31.1 million as of December 31, 2017 and 2016 , respectively.
Schedule of Purchased Credit-Impaired Loans, Changes in Accretable Yield	The following table presents the changes in the accretable yield for PCI loans for the years ended December 31, 2017 and 2016 (in thousands): Years Ended December 31 2017 2016 Balance, beginning of period $ 8,717 $ 10,375 Accretion to interest income (5,929 ) (9,333 ) Disposals and other (564 ) (1,018 ) Reclassifications from non-accretable difference 4,296 8,693 Balance, end of period $ 6,520 $ 8,717
Schedule of Impaired Loans With and Without Specific Reserves	The following tables provide additional information on impaired loans, excluding PCI loans, with and without specific allowance reserves at December 31, 2017 and 2016 . Recorded investment includes the unpaid principal balance or the carrying amount of loans less charge-offs and net deferred loan fees (in thousands): December 31, 2017 Unpaid Principal Balance Recorded Investment Related Allowance Without Allowance (1) With Allowance (2) Commercial real estate: Owner-occupied $ 7,807 $ 6,447 $ 199 $ 18 Investment properties 11,296 4,200 6,884 263 One- to four-family construction 298 298 — — Land and land development: Residential 1,134 798 — — Commercial business 4,441 3,424 555 50 Agricultural business/farmland 9,388 6,230 3,031 264 One- to four-family residential 9,547 3,709 5,775 178 Consumer: Consumer secured by one- to four-family 1,498 1,324 139 7 Consumer—other 134 58 73 2 $ 45,543 $ 26,488 $ 16,656 $ 782 December 31, 2016 Unpaid Principal Balance Recorded Investment Related Allowance Without Allowance (1) With Allowance (2) Commercial real estate: Owner-occupied $ 3,786 $ 3,373 $ 203 $ 20 Investment properties 9,916 5,565 4,304 408 Multifamily real estate 508 147 349 64 One- to four-family construction 1,180 — 1,180 156 Land and land development: Residential 3,012 750 1,106 219 Commercial 1,608 998 — — Commercial business 3,753 3,074 651 69 Agricultural business/farmland 6,438 6,354 — — One- to four-family residential 11,439 3,149 8,026 479 Consumer: Consumer secured by one- to four-family 1,904 1,721 144 1 Consumer—other 391 226 166 4 $ 43,935 $ 25,357 $ 16,129 $ 1,420 (1) Includes loans without an allowance reserve that have been individually evaluated for impairment and that evaluation concluded that no reserve was needed, and $10.6 million and $10.0 million of homogenous and small balance loans as of December 31, 2017 and December 31, 2016 , respectively, that are collectively evaluated for impairment for which a general reserve has been established. (2) Loans with a specific allowance reserve have been individually evaluated for impairment using either a discounted cash flow analysis or, for collateral dependent loans, current appraisals less costs to sell to establish realizable value. The following table summarizes our average recorded investment and interest income recognized on impaired loans by loan class for the years ended December 31, 2017 , 2016 and 2015 (in thousands): Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized Commercial real estate: Owner-occupied $ 3,697 $ 11 $ 2,721 $ 2 $ 1,467 $ 9 Investment properties 9,136 195 18,529 242 8,003 303 Multifamily real estate 251 10 513 21 362 18 One- to four-family construction 418 27 1,158 75 1,463 114 Land and land development: Residential 1,396 42 1,948 85 2,406 49 Commercial 867 — 1,003 — 931 — Commercial business 5,996 68 4,290 37 1,667 35 Agricultural business/farmland 6,184 207 5,004 119 1,143 19 One- to four-family residential 9,499 322 11,976 441 17,770 630 Consumer: Consumer secured by one- to four-family 1,635 9 1,778 17 736 11 Consumer—other 184 7 615 17 392 18 $ 39,263 $ 898 $ 49,535 $ 1,056 $ 36,340 $ 1,206
Schedule of Troubled Debt Restructurings	The following table presents TDRs by accrual and nonaccrual status at December 31, 2017 and 2016 (in thousands): December 31, 2017 December 31, 2016 Accrual Status Nonaccrual Status Total TDRs Accrual Nonaccrual Total Commercial real estate: Owner-occupied $ 199 $ 87 $ 286 $ 203 $ 96 $ 299 Investment properties 6,884 — 6,884 4,304 — 4,304 Multifamily real estate — — — 349 — 349 One- to four-family construction — — — 1,180 — 1,180 Land and land development: Residential — — — 1,106 — 1,106 Commercial business 555 — 555 653 — 653 Agricultural business/farmland 3,129 29 3,158 3,125 79 3,204 One- to four-family residential 5,136 801 5,937 7,678 843 8,521 Consumer: Consumer secured by one- to four-family 139 — 139 143 6 149 Consumer—other 73 — 73 166 — 166 $ 16,115 $ 917 $ 17,032 $ 18,907 $ 1,024 $ 19,931 As of December 31, 2017 and 2016 , the Company had commitments to advance funds up to an additional amount of $45,000 and $127,000 , respectively, related to TDRs.
Schedule of Newly Restructured Loans	The following table presents new TDRs that occurred during the years ended December 31, 2017 , 2016 and 2015 (dollars in thousands): Number of Contracts Pre-modification Outstanding Recorded Investment Post-modification Outstanding Recorded Investment Year Ended December 31, 2017 Recorded Investment (1) (2) Commercial real estate: Investment properties 1 3,714 3,714 Total 1 $ 3,714 $ 3,714 Year Ended December 31, 2016 Recorded Investment (1) (2) Commercial real estate: Owner-occupied 1 $ 194 $ 194 One- to four-family residential 1 $ 78 $ 78 Total 2 $ 272 $ 272 Year Ended December 31, 2015 Recorded Investment (1) (2) Land and land development: Residential 2 $ 1,302 $ 483 Agricultural business/farmland 3 $ 822 $ 822 One- to four-family residential 2 $ 431 $ 431 Total 7 $ 2,555 $ 1,736 (1) Since most loans were already considered classified and/or on non-accrual status prior to restructuring, the modifications did not have a material effect on the Company’s determination of the allowance for loan losses. (2) Generally these modifications do not fit into one separate type, such as rate, term, amount, interest-only or payment, but instead are a combination of multiple types of modifications; therefore, they are disclosed in aggregate.
Schedule of Troubled Debt Restructurings Which Incurred A Payment Default	TDRs which incurred a payment default within the year ended December 31, 2017 for which the payment default occurred within twelve months of the restructure date. There were no TDRs that incurred a payment default in the year ended December 31, 2016. A default on a restructured loan results in a transfer to nonaccrual status, a charge-off or a combination of both.
Financing Receivable Credit Quality Indicators [Table Text Block]	The following tables show Banner’s portfolio of risk-rated loans and non-risk-rated loans by grade or other characteristic as of December 31, 2017 and 2016 (in thousands): December 31, 2017 By class: Pass (Risk Ratings 1-5) (1) Special Substandard Doubtful Loss Total Loans Commercial real estate: Owner-occupied $ 1,246,125 $ 12,227 $ 26,011 $ — $ — $ 1,284,363 Investment properties 1,918,940 9,118 9,365 — — 1,937,423 Multifamily real estate 313,432 — 756 — — 314,188 Commercial construction 148,435 — — — — 148,435 Multifamily construction 154,662 — — — — 154,662 One- to four-family construction 411,802 — 3,525 — — 415,327 Land and land development: Residential 153,073 10,554 889 — — 164,516 Commercial 21,665 — 2,918 — — 24,583 Commercial business 1,213,365 12,135 54,282 112 — 1,279,894 Agricultural business, including secured by farmland 321,110 3,852 13,426 — — 338,388 One- to four-family residential 842,304 569 5,416 — — 848,289 Consumer: Consumer secured by one- to four-family 520,675 — 2,256 — — 522,931 Consumer—other 165,594 13 278 — — 165,885 Total $ 7,431,182 $ 48,468 $ 119,122 $ 112 $ — $ 7,598,884 December 31, 2016 By class: Pass (Risk Ratings 1-5) (1) Special Substandard Doubtful Loss Total Loans Commercial real estate: Owner-occupied $ 1,313,142 $ 14,394 $ 25,463 $ — $ — $ 1,352,999 Investment properties 1,948,822 23,846 13,668 — — 1,986,336 Multifamily real estate 247,258 — 892 — — 248,150 Commercial construction 124,068 — — — — 124,068 Multifamily construction 124,126 — — — — 124,126 One- to four-family construction 371,636 — 4,068 — — 375,704 Land and land development: Residential 167,764 — 2,240 — — 170,004 Commercial 25,090 — 4,094 — — 29,184 Commercial business 1,148,585 35,036 24,258 — — 1,207,879 Agricultural business, including secured by farmland 356,656 3,335 9,165 — — 369,156 One- to four-family residential 807,837 967 4,273 — — 813,077 Consumer: Consumer secured by one- to four-family 490,877 5 2,327 2 — 493,211 Consumer—other 156,547 108 594 5 — 157,254 Total $ 7,282,408 $ 77,691 $ 91,042 $ 7 $ — $ 7,451,148 (1) The Pass category includes some performing loans that are part of homogenous pools which are not individually risk-rated. This includes all consumer loans, all one- to four-family residential loans and, as of December 31, 2017 and 2016 , in the commercial business category, $296.8 million and $225.0 million , respectively, of credit-scored small business loans. As loans in these homogeneous pools become non-accrual, they are individually risk-rated.

REAL ESTATE OWNED, HELD FOR S36

REAL ESTATE OWNED, HELD FOR SALE, NET (Tables)	12 Months Ended
	Dec. 31, 2017
Real Estate [Abstract]
Schedule of Changes in Real Estate Owned, Net of Valuation Allowance	The following table presents the changes in REO, net of valuation allowance, for the years ended December 31, 2017 , 2016 and 2015 (in thousands): Years Ended December 31 2017 2016 2015 Balance, beginning of period $ 11,081 $ 11,627 $ 3,352 Additions from loan foreclosures 46 8,909 4,351 Additions from capitalized costs 54 — 298 Additions from acquisitions — 400 8,231 Proceeds from dispositions of REO (13,474 ) (10,812 ) (4,740 ) Gain on sale of REO 2,909 1,833 351 Valuation adjustments in the period (256 ) (876 ) (216 ) Balance, end of period $ 360 $ 11,081 $ 11,627

PROPERTY AND EQUIPMENT, NET (Ta

PROPERTY AND EQUIPMENT, NET (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Land, buildings and equipment owned by the Company and its subsidiaries at December 31, 2017 and 2016 are summarized as follows (in thousands): December 31 2017 2016 Land (1) $ 35,080 $ 35,463 Buildings and leasehold improvements (1) 154,374 163,879 Furniture and equipment 105,643 94,999 295,097 294,341 Less accumulated depreciation (140,282 ) (127,860 ) Property and equipment, net $ 154,815 $ 166,481 (1) The Company had $3.8 million and $8.5 million of properties held for sale that were included in land and buildings at December 31, 2017 and 2016 , respectively.
Schedule of Future Minimum Rental Payments for Operating Leases	The Company’s obligations under long-term property leases are as follows (in thousands): Year Amount 2018 $ 16,029 2019 13,199 2020 12,080 2021 10,100 2022 6,725 Thereafter 13,926 Total $ 72,059

DEPOSITS (Tables)

DEPOSITS (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Schedule of Deposit Liabilities	Deposits consist of the following at December 31, 2017 and 2016 (in thousands): December 31 2017 2016 Non-interest-bearing checking $ 3,265,544 $ 3,140,451 Interest-bearing checking 971,137 914,484 Regular savings accounts 1,557,500 1,523,391 Money market accounts 1,422,313 1,497,755 Total interest-bearing transaction and savings accounts 3,950,950 3,935,630 Certificates of deposit: Certificates of deposit less than or equal to $250,000 813,997 884,403 Certificates of deposit greater than $250,000 152,940 160,930 Total certificates of deposit (1) 966,937 1,045,333 Total deposits $ 8,183,431 $ 8,121,414 Included in total deposits: Public fund transaction accounts $ 198,719 $ 221,765 Public fund interest-bearing certificates 23,685 25,650 Total public deposits $ 222,404 $ 247,415 Total brokered deposits $ 57,228 $ 34,074 (1) Certificates of deposit included $11,000 and $426,000 of acquisition premiums at December 31, 2017 and 2016 , respectively. Deposits at December 31, 2017 and 2016 included deposits from the Company’s directors, executive officers and related entities totaling $10.0 million and $7.2 million , respectively.
Schedule Maturities and Weighted Average Interest Rates of Certificates of Deposit	Scheduled maturities and weighted average interest rates of certificate accounts at December 31, 2017 are as follows (dollars in thousands): December 31, 2017 Amount Weighted Average Rate Maturing in one year or less $ 685,592 0.49 % Maturing after one year through two years 98,257 0.72 Maturing after two years through three years 141,209 1.30 Maturing after three years through four years 25,902 1.08 Maturing after four years through five years 13,775 1.26 Maturing after five years 2,202 1.05 Total certificates of deposit $ 966,937 0.66 %

ADVANCES FROM FEDERAL HOME LO39

ADVANCES FROM FEDERAL HOME LOAN BANK OF DES MOINES (Tables)	12 Months Ended
	Dec. 31, 2017
Advances from Federal Home Loan Banks [Abstract]
Schedule of Federal Home Loan Bank Advances, Fiscal Year Maturity	At December 31, 2017 and 2016 , FHLB advances were scheduled to mature as follows (in thousands): December 31 2017 2016 Maturing in one year or less $ — $ 54,000 Maturing after one year through three years — — Maturing after three years through five years — — Maturing after five years 169 179 Total FHLB advances, at par 169 54,179 Fair value adjustment 33 37 Total FHLB advances, carried at fair value $ 202 $ 54,216

OTHER BORROWINGS (Tables)

OTHER BORROWINGS (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Other Borrowings, Maturity	A summary of all other borrowings at December 31, 2017 and 2016 by the period remaining to maturity is as follows (dollars in thousands): At or for the Years Ended December 31 2017 2016 Amount Weighted Average Rate Amount Weighted Average Rate Repurchase agreements: Maturing in one year or less $ 95,860 0.29 % $ 100,685 0.19 % Maturing after one year through two years — — 5,000 2.15 Maturing after two years — — — — Total year-end outstanding $ 95,860 0.29 $ 105,685 0.28 Average outstanding $ 111,872 0.28 $ 108,427 0.29 Maximum outstanding at any month-end 120,245 n/a 112,309 n/a

JUNIOR SUBORDINATED DEBENTURE41

JUNIOR SUBORDINATED DEBENTURES AND MANDATORILY REDEEMABLE TRUST PREFERRED SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Schedule of Trust Preferred Securities	The following table is a summary of trust preferred securities at December 31, 2017 (dollars in thousands): Name of Trust Aggregate Liquidation Amount of Trust Preferred Securities Aggregate Liquidation Amount of Common Capital Securities Aggregate Principal Amount of Junior Subordinated Debentures Stated Maturity (1) Current Interest Rate Reset Period Interest Rate Spread Banner Capital Trust II $ 15,000 $ 464 $ 15,464 2033 4.71 % Quarterly Three-month LIBOR + 3.35% Banner Capital Trust III 15,000 465 15,465 2033 4.26 Quarterly Three-month LIBOR + 2.90% Banner Capital Trust IV 15,000 465 15,465 2034 4.21 Quarterly Three-month LIBOR + 2.85% Banner Capital Trust V 25,000 774 25,774 2035 3.02 Quarterly Three-month LIBOR + 1.57% Banner Capital Trust VI 25,000 774 25,774 2037 3.10 Quarterly Three-month LIBOR + 1.62% Banner Capital Trust VII 25,000 774 25,774 2037 2.72 Quarterly Three-month LIBOR + 1.38% Siuslaw Statutory Trust I 8,000 248 8,248 2034 4.30 Quarterly Three-month LIBOR + 2.70% Greater Sacramento Bancorp Statutory Trust I 4,000 124 4,124 2033 4.71 Quarterly Three-month LIBOR + 3.35% Greater Sacramento Bancorp Statutory Trust II 4,000 124 4,124 2035 3.27 Quarterly Three-month LIBOR + 1.68% Total TPS liability at par $ 136,000 $ 4,212 140,212 3.57 % Fair value adjustment (2) (41,505 ) Total TPS liability at fair value (2) $ 98,707 (1) All of the Company's trust preferred securities are eligible for redemption. (2) The Company has elected to use fair value accounting on its TPS.

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The following table presents the components of the provision for income taxes included in the Consolidated Statements of Operations for the years ended December 31, 2017 , 2016 and 2015 (in thousands): Years Ended December 31 2017 2016 2015 Current Federal $ 30,961 $ 29,787 $ 24,683 State 3,085 2,477 1,399 Total Current 34,046 32,264 26,082 Deferred Federal 58,646 9,908 (3,310 ) State (2,204 ) 2,083 (23 ) Total Deferred 56,442 11,991 (3,333 ) Provision for income taxes $ 90,488 $ 44,255 $ 22,749
Schedule of Effective Income Tax Rate Reconciliation	The following table presents the reconciliation of the federal statutory rate to the actual effective rate for the years ended December 31, 2017 , 2016 and 2015 : Years Ended December 31 2017 2016 2015 Federal income tax statutory rate 35.0 % 35.0 % 35.0 % Increase (decrease) in tax rate due to: Tax-exempt interest (2.6 ) (2.6 ) (3.9 ) Investment in life insurance (1.1 ) (1.2 ) (1.3 ) State income taxes, net of federal tax offset 2.0 2.2 1.1 Tax credits (0.6 ) (0.8 ) (1.6 ) Merger and acquisition costs — — 1.9 Federal law change 28.2 — — Other (1.1 ) 1.5 2.3 Effective income tax rate 59.8 % 34.1 % 33.5 %
Schedule of Net Deferred Tax Asset	The following table reflects the effect of temporary differences that gave rise to the components of the net deferred tax asset as of December 31, 2017 and 2016 (in thousands): December 31 2017 2016 Deferred tax assets: Loan loss and REO $ 22,294 $ 36,719 Deferred compensation 13,045 23,189 Net operating loss carryforward 43,721 82,714 Federal and state tax credits 7,614 7,711 State net operating losses 6,706 7,396 Loan discount 4,736 9,696 Other 4,326 6,217 Total deferred tax assets 102,442 173,642 Deferred tax liabilities: Depreciation (1,343 ) (2,218 ) Deferred loan fees, servicing rights and loan origination costs (9,564 ) (13,291 ) Intangibles (5,690 ) (11,178 ) Financial instruments accounted for under fair value accounting (9,702 ) (16,186 ) Other (325 ) (880 ) Total deferred tax liabilities (26,624 ) (43,753 ) Deferred income tax asset 75,818 129,889 Valuation allowance (4,391 ) (2,195 ) Deferred tax asset, net $ 71,427 $ 127,694
Schedule of Affordable Housing Tax Credit Information	The following table presents the balances of the Company's tax credit investments and related unfunded commitments at December 31, 2017 and 2016 (in thousands): December 31, 2017 December 31, 2016 Tax credit investments $ 7,311 $ 4,654 Unfunded commitments—tax credit investments 4,417 665 The following table presents other information related to the Company's tax credit investments for the years ended December 31, 2017 and 2016 (in thousands): For the year ended December 31, 2017 2016 Tax credits and other tax benefits recognized $ 1,140 $ 1,136 Tax credit amortization expense included in provision for income taxes 1,144 672

STOCK-BASED COMPENSATION PLANS

STOCK-BASED COMPENSATION PLANS (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity	A summary of the Company's Restricted Stock/Unit award activity during the years ended December 31, 2017, 2016 and 2015 follows: Shares/Units Weighted Average Grant-Date Fair Value Unvested at January 1, 2015 195,106 $ 32.83 Granted (24,931 non-voting) 155,183 45.59 Vested (109,416 ) 30.28 Forfeited (9,311 ) 39.07 Unvested at December 31, 2015 231,562 42.33 Granted (38,934 non-voting) 177,775 41.74 Vested (104,297 ) 41.47 Forfeited (14,321 ) 42.54 Unvested at December 31, 2016 290,719 42.26 Granted (41,318 non-voting) 153,777 55.86 Vested (103,259 ) 43.81 Forfeited (39,160 ) 39.83 Unvested at December 31, 2017 302,077 48.97

REGULATORY CAPITAL REQUIREMEN44

REGULATORY CAPITAL REQUIREMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Regulatory Capital Requirements [Abstract]
Schedule of the Regulatory Capital Ratios and Minimum Regulatory Requirements	The following table shows the regulatory capital ratios of the Company and the Banks and the minimum regulatory requirements (dollars in thousands): Actual Minimum for Capital Adequacy Purposes Minimum to be Categorized as “Well-Capitalized” Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio December 31, 2017: The Company—consolidated: Total capital to risk-weighted assets $ 1,214,631 13.81 % $ 703,508 8.00 % $ 879,385 10.00 % Tier 1 capital to risk-weighted assets 1,123,154 12.77 527,631 6.00 527,631 6.00 Tier 1 common equity to risk-weighted assets 994,080 11.30 395,723 4.50 n/a n/a Tier 1 capital to average leverage assets 1,123,154 11.34 396,313 4.00 n/a n/a Banner Bank: Total capital to risk- weighted assets 1,102,195 12.83 687,266 8.00 859,083 10.00 Tier 1 capital to risk- weighted assets 1,013,079 11.79 515,450 6.00 687,266 8.00 Tier 1 common equity to risk-weighted assets 1,013,079 11.79 386,587 4.50 558,404 6.50 Tier 1 capital to average leverage assets 1,013,079 10.53 384,920 4.00 481,150 5.00 Islanders Bank: Total capital to risk- weighted assets 32,122 16.39 15,681 8.00 19,602 10.00 Tier 1 capital to risk- weighted assets 29,761 15.18 11,761 6.00 15,681 8.00 Tier 1 common equity to risk-weighted assets 29,761 15.18 8,821 4.50 12,741 6.50 Tier 1 capital to average leverage assets 29,761 10.65 11,183 4.00 13,979 5.00 December 31, 2016: The Company—consolidated: Total capital to risk-weighted assets $ 1,214,913 13.40 % $ 725,566 8.00 % $ 906,957 10.00 % Tier 1 capital to risk-weighted assets 1,125,267 12.41 544,174 6.00 544,174 6.00 Tier 1 common equity to risk-weighted assets 1,014,994 11.19 408,131 4.50 n/a n/a Tier 1 capital to average leverage assets 1,125,267 11.83 380,519 4.00 n/a n/a Banner Bank: Total capital to risk- weighted assets 1,043,837 11.76 709,882 8.00 887,352 10.00 Tier 1 capital to risk- weighted assets 956,298 10.78 532,411 6.00 709,882 8.00 Tier 1 common equity to risk-weighted assets 956,298 10.78 399,308 4.50 576,779 6.50 Tier 1 capital to average leverage assets 956,298 10.34 369,936 4.00 462,420 5.00 Islanders Bank: Total capital to risk- weighted assets 35,207 18.43 15,281 8.00 19,101 10.00 Tier 1 capital to risk- weighted assets 33,099 17.33 11,461 6.00 15,281 8.00 Tier 1 common equity to risk-weighted assets 33,099 17.33 8,598 4.50 12,416 6.50 Tier 1 capital to average leverage assets 33,099 12.72 10,405 4.00 13,006 5.00

GOODWILL, OTHER INTANGIBLE AS45

GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS (Tables)	12 Months Ended
	Dec. 31, 2017
Other Intangible Assets and Mortgage Servicing Rights [Abstract]
Schedule of Changes in Goodwill and Intangible Assets	The following table summarizes the changes in the Company’s goodwill, CDI and LHI for the years ended December 31, 2017, 2016 and 2015 (in thousands): Goodwill CDI LHI Total Balance, January 1, 2015 $ — $ 2,831 $ — $ 2,831 Additions through acquisition 247,738 37,395 776 285,909 Amortization — (3,164 ) (66 ) (3,230 ) Other changes (1) — (300 ) — (300 ) Balance, December 31, 2015 247,738 36,762 710 285,210 Amortization — (7,061 ) (249 ) (7,310 ) Adjustments to goodwill (2) (3,155 ) — — (3,155 ) Balance, December 31, 2016 244,583 29,701 461 274,745 Amortization — (6,247 ) (184 ) (6,431 ) Other changes (1) (1,924 ) (1,076 ) — (3,000 ) Balance, December 31, 2017 $ 242,659 $ 22,378 $ 277 $ 265,314 (1) Acquired Goodwill and CDI were adjusted for the sale of the Utah branches in 2017 and acquired CDI was adjusted for a branch that was subsequently sold during 2015. (2) The adjustments to goodwill in 2016 related to changes in the preliminary goodwill recorded for the Starbuck acquisition including adjustments to loan discount, deferred taxes and REO valuations.
Schedule of Estimated Annual Amortization Expense	Estimated amortization expense in future years with respect to CDI as of December 31, 2017 (in thousands): Year ended: Estimated Amortization 2018 $ 5,372 2019 4,683 2020 3,996 2021 3,307 Thereafter 5,020 Net carrying amount $ 22,378
Schedule of Mortgage Servicing Rights at Amortized Value	An analysis of the mortgage servicing rights for the years ended December 31, 2017 , 2016 and 2015 is presented below (in thousands): Years Ended December 31 2017 2016 2015 Balance, beginning of the year $ 15,249 $ 13,295 $ 9,030 Amounts capitalized 3,361 5,965 5,313 Additions through acquisition — — 2,172 Additions through purchase 94 — — Amortization (1) (3,966 ) (4,011 ) (3,220 ) Balance, end of the year (2) $ 14,738 $ 15,249 $ 13,295 (1) Amortization of mortgage servicing rights is recorded as a reduction of loan servicing income and any unamortized balance is fully written off if the loan repays in full. (2) There was no valuation allowance as of December 31, 2017 and 2016 .

FAIR VALUE OF FINANCIAL INSTR46

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Fair Value of Financial Instruments, by Balance Sheet Grouping	The following table presents estimated fair values of the Company’s financial instruments as of December 31, 2017 and 2016 , whether or not recognized or recorded in the Consolidated Statements of Financial Condition (in thousands): December 31, 2017 December 31, 2016 Level Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Assets: Cash and due from banks 1 $ 261,200 $ 261,200 $ 247,719 $ 247,719 Securities—trading 2,3 22,318 22,318 24,568 24,568 Securities—available-for-sale 2 919,485 919,485 806,428 806,428 Securities—held-to-maturity 2 256,793 258,710 263,997 266,652 Securities—held-to-maturity 3 3,478 3,478 3,876 3,876 Loans receivable held for sale 2 40,725 40,923 246,353 246,815 Loans receivable 3 7,598,884 7,445,990 7,451,148 7,337,608 FHLB stock 3 10,334 10,334 12,506 12,506 BOLI 1 162,668 162,668 158,936 158,936 Mortgage servicing rights 3 14,738 19,835 15,249 16,740 Derivatives: Interest rate swaps 2 5,083 5,083 8,330 8,330 Interest rate lock and forward sales commitments 2 523 523 482 482 Liabilities: Demand, interest-bearing checking and money market 2 5,658,994 5,658,994 5,552,690 5,552,690 Regular savings 2 1,557,500 1,557,500 1,523,391 1,523,391 Certificates of deposit 2 966,937 947,517 1,045,333 1,028,866 Advances from FHLB at fair value 2 202 202 54,216 54,216 Junior subordinated debentures at fair value 3 98,707 98,707 95,200 95,200 Other borrowings 2 95,860 95,860 105,685 105,685 Derivatives: Interest rate swaps 2 5,083 5,083 8,330 8,330 Interest rate lock and forward sales commitments 2 201 201 289 289
Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables present financial assets and liabilities measured at fair value on a recurring basis and the level within the fair value hierarchy of the fair value measurements for those assets and liabilities as of December 31, 2017 and 2016 (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Assets: Securities—trading Municipal bonds $ — $ 100 $ — $ 100 Corporate Bonds (TPS securities) — — 22,058 22,058 Equity securities — 160 — 160 — 260 22,058 22,318 Securities—available-for-sale U.S. Government and agency $ — $ 72,466 $ — $ 72,466 Municipal bonds — 68,733 — 68,733 Corporate bonds — 5,393 — 5,393 Mortgage-backed securities — 739,557 — 739,557 Asset-backed securities — 27,758 — 27,758 Equity securities — 5,578 — 5,578 — 919,485 — 919,485 Loans held for sale — 32,392 — 32,392 Derivatives Interest rate swaps — 5,083 — 5,083 Interest rate lock and forward sales commitments — 523 — 523 $ — $ 957,743 $ 22,058 $ 979,801 Liabilities Advances from FHLB at fair value $ — $ 202 $ — $ 202 Junior subordinated debentures at fair value — — 98,707 98,707 Derivatives Interest rate swaps — 5,083 — 5,083 Interest rate lock and forward sales commitments — 201 — 201 $ — $ 5,486 $ 98,707 $ 104,193 December 31, 2016 Level 1 Level 2 Level 3 Total Assets: Securities—trading U.S. Government and agency $ — $ 1,326 $ — $ 1,326 Municipal bonds — 335 — 335 Corporate Bonds (TPS securities) — — 21,143 21,143 Mortgage-backed securities — 1,641 — 1,641 Equity securities — 123 — 123 — 3,425 21,143 24,568 Securities—available-for-sale U.S. Government and agency $ — $ 56,978 $ — $ 56,978 Municipal bonds — 109,853 — 109,853 Corporate bonds — 10,283 — 10,283 Mortgage-backed securities — 594,712 — 594,712 Asset-backed securities — 28,993 — 28,993 Equity securities — 5,609 — 5,609 — 806,428 — 806,428 Loans held for sale $ — $ 9,600 $ — $ 9,600 Derivatives Interest rate swaps — 8,330 — 8,330 Interest rate lock and forward sales commitments — 482 — 482 $ — $ 828,265 $ 21,143 $ 849,408 Liabilities Advances from FHLB at fair value $ — $ 54,216 $ — $ 54,216 Junior subordinated debentures at fair value — — 95,200 95,200 Derivatives Interest rate swaps — 8,330 — 8,330 Interest rate lock and forward sales commitments — 289 — 289 $ — $ 62,835 $ 95,200 $ 158,035
Schedule of Valuation Technique, Unobservable Input, and Qualitative Information for Unobservable Inputs	The following table provides a description of the valuation technique, unobservable inputs, quantitative and qualitative information about the unobservable inputs for the Company's assets and liabilities classified as Level 3 and measured at fair value on a recurring and nonrecurring basis at December 31, 2017 and 2016 : December 31 2017 2016 Financial Instruments Valuation Technique Unobservable Inputs Weighted Average Rate Weighted Average Rate Corporate Bonds (TPS securities) Discounted cash flows Discount rate 6.69 % 6.00 % Junior subordinated debentures Discounted cash flows Discount rate 6.69 % 6.00 % Impaired loans Collateral Valuations Discount to appraised value 8.5% to 20.0% n/a REO Appraisals Discount to appraised value 42% 0% to 45%
Schedule of Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	The following table provides a reconciliation of the assets and liabilities measured at fair value using significant unobservable inputs (Level 3) on a recurring basis during the years ended December 31, 2017 and 2016 (in thousands): Level 3 Fair Value Inputs TPS Securities Borrowings— Junior Subordinated Debentures Balance at January 1, 2016 $ 18,699 $ 92,480 Total gains or losses recognized Assets gains 719 — Liabilities losses — 2,720 Purchases, issuances and settlements 1,725 — Balance at December 31, 2016 21,143 95,200 Total gains or losses recognized Assets gains 915 — Liabilities losses — 3,507 Balance at December 31, 2017 $ 22,058 $ 98,707
Schedule of Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis	The following table presents financial assets and liabilities measured at fair value on a non-recurring basis and the level within the fair value hierarchy of the fair value measurements for those assets at December 31, 2017 and 2016 (in thousands): December 31, 2017 Level 1 Level 2 Level 3 Total Impaired loans $ — $ — $ 6,535 $ 6,535 REO $ — $ — $ 360 $ 360 December 31, 2016 Level 1 Level 2 Level 3 Total REO — — 11,081 11,081 The following table presents the losses resulting from non-recurring fair value adjustments for the years ended December 31, 2017 and 2016 (in thousands): For the year ended December 31, 2017 2016 Impaired loans $ (2,852 ) $ (182 ) REO (256 ) (876 ) Total loss from nonrecurring measurements $ (3,108 ) $ (1,058 )

BANNER CORPORATION (PARENT CO47

BANNER CORPORATION (PARENT COMPANY ONLY) (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule of Condensed Financial Condition	Summary financial information is as follows (in thousands): Statements of Financial Condition December 31 2017 2016 ASSETS Cash $ 44,887 $ 86,268 Investment in trust equities 4,212 4,212 Investment in subsidiaries 1,329,165 1,307,475 Other assets 3,072 13,784 Total assets $ 1,381,336 $ 1,411,739 LIABILITIES AND SHAREHOLDERS’ EQUITY Miscellaneous liabilities $ 9,607 $ 8,990 Deferred tax liability 396 1,839 Junior subordinated debentures at fair value 98,707 95,200 Shareholders’ equity 1,272,626 1,305,710 Total liabilities and shareholders' equity $ 1,381,336 $ 1,411,739
Schedule of Condensed Statement of Operations	Statements of Operations Years Ended December 31 2017 2016 2015 INTEREST INCOME: Interest-bearing deposits $ 62 $ 127 $ 122 OTHER INCOME (EXPENSE): Dividend income from subsidiaries 40,570 50,971 170,260 Equity in undistributed (distributions in excess of) income of subsidiaries 27,477 40,852 (116,120 ) Other income 53 60 69 Net change in valuation of financial instruments carried at fair value (3,507 ) (2,720 ) (2,714 ) Interest on other borrowings (4,752 ) (4,040 ) (3,247 ) Other expenses (3,291 ) (3,450 ) (7,175 ) Net income before taxes 56,612 81,800 41,195 BENEFIT FROM INCOME TAXES (4,164 ) (3,585 ) (4,027 ) NET INCOME $ 60,776 $ 85,385 $ 45,222
Schedule of Condensed Statement of Cash Flows	Statements of Cash Flows Years Ended December 31 2017 2016 2015 OPERATING ACTIVITIES: Net income $ 60,776 $ 85,385 $ 45,222 Adjustments to reconcile net income to net cash provided by operating activities: Distributions in excess of (equity in undistributed) income of subsidiaries (27,477 ) (40,852 ) 116,120 Decrease in deferred taxes (1,442 ) (702 ) (1,398 ) Net change in valuation of financial instruments carried at fair value 3,507 2,720 2,714 Share-based compensation 5,965 4,305 4,334 Decrease (increase) in other assets 10,684 7,332 (10,655 ) Increase (decrease) in other liabilities 69 (202 ) 433 Net cash provided from operating activities 52,082 57,986 156,770 INVESTING ACTIVITIES: Funds transferred to deferred compensation trust (29 ) (26 ) (26 ) Reduction in investment in subsidiaries 5,000 50,000 — Acquisitions — — (132,652 ) Net cash provided from (used by) investing activities 4,971 49,974 (132,678 ) FINANCING ACTIVITIES: Issuance of stock for shareholder reinvestment program — — 34 Withholding taxes paid on share-based compensation (1,630 ) (870 ) (848 ) Repurchase of common stock (31,045 ) (50,772 ) — Cash dividends paid (65,759 ) (28,282 ) (17,170 ) Net cash used by financing activities (98,434 ) (79,924 ) (17,984 ) NET CHANGE IN CASH (41,381 ) 28,036 6,108 CASH, BEGINNING OF PERIOD 86,268 58,232 52,124 CASH, END OF PERIOD $ 44,887 $ 86,268 $ 58,232

CALCULATION OF EARNINGS PER C48

CALCULATION OF EARNINGS PER COMMON SHARE (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Weighted Shares Outstanding	The following tables show the calculation of earnings per common share (in thousands, except per share data): Years Ended December 31 2017 2016 2015 Net income $ 60,776 $ 85,385 $ 45,222 Weighted average number of common shares outstanding Basic 32,888,007 33,820,148 23,801,373 Diluted 32,986,707 33,853,511 23,866,621 Earnings per common share Basic $ 1.85 $ 2.52 $ 1.90 Diluted $ 1.84 $ 2.52 $ 1.89

SELECTED QUARTERLY FINANCIAL 49

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2017
Selected Quarterly Financial Information [Abstract]
Schedule of Quarterly Financial Information	Results of operations on a quarterly basis for the years ended December 31, 2017 , 2016 and 2015 were as follows (dollars in thousands except for per share data): Year Ended December 31, 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Interest income $ 99,096 $ 104,436 $ 105,278 $ 103,475 Interest expense 4,242 4,730 5,068 5,211 Net interest income before provision for loan losses 94,854 99,706 100,210 98,264 Provision for loan losses 2,000 2,000 2,000 2,000 Net interest income 92,854 97,706 98,210 96,264 Non-interest income 20,845 22,469 20,339 29,882 Non-interest expense 78,078 81,930 82,589 84,709 Income before provision for income taxes 35,621 38,245 35,960 41,437 Provision for income taxes 11,828 12,791 10,883 54,985 Net income (loss) $ 23,793 $ 25,454 $ 25,077 $ (13,548 ) Basic earnings (loss) per share $ 0.72 $ 0.77 $ 0.76 $ (0.41 ) Diluted earnings (loss) per share 0.72 0.77 0.76 (0.41 ) Dividends declared 0.25 1.25 0.25 0.25 Year Ended December 31, 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Interest income $ 95,301 $ 97,321 $ 97,849 $ 101,007 Interest expense 4,258 4,173 4,141 3,836 Net interest income before provision for loan losses 91,043 93,148 93,708 97,171 Provision for loan losses — 2,000 2,000 2,030 Net interest income 91,043 91,148 91,708 95,141 Non-interest income 19,959 20,537 23,512 19,463 Non-interest expense 84,034 79,887 79,092 79,857 Income before provision for income taxes 26,968 31,798 36,128 34,747 Provision for income taxes 9,194 10,841 12,277 11,943 Net income $ 17,774 $ 20,957 $ 23,851 $ 22,804 Basic earnings per share $ 0.52 $ 0.62 $ 0.70 $ 0.69 Diluted earnings per share 0.52 0.61 0.70 0.69 Dividends declared 0.21 0.21 0.23 0.23 Year Ended December 31, 2015 First Quarter Second Quarter Third Quarter Fourth Quarter Interest income $ 49,069 $ 54,076 $ 54,793 $ 96,495 Interest expense 2,533 2,619 2,605 4,396 Net interest income before provision for loan losses 46,536 51,457 52,188 92,099 Provision for loan losses — — — — Net interest income 46,536 51,457 52,188 92,099 Non-interest income 13,696 16,141 14,098 18,356 Non-interest expense 41,914 47,734 46,697 100,254 Income before provision for income taxes 18,318 19,864 19,589 10,201 Provision for income taxes 6,184 6,615 6,642 3,308 Net income $ 12,134 $ 13,249 $ 12,947 $ 6,893 Basic earnings per share $ 0.61 $ 0.64 $ 0.62 $ 0.20 Diluted earnings per share 0.61 0.64 0.62 0.20 Dividends declared 0.18 0.18 0.18 0.18

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Fair Value, Off-balance Sheet Risks [Table Text Block]	Outstanding commitments for which no asset or liability for the notional amount has been recorded consisted of the following at the dates indicated (in thousands): Contract or Notional Amount December 31, 2017 December 31, 2016 Commitments to extend credit $ 2,300,593 $ 2,204,795 Standby letters of credit and financial guarantees 14,579 17,694 Commitments to originate loans 56,030 69,833 Risk participation agreement 11,451 7,488 Derivatives also included in Note 24: Commitments to originate loans held for sale 43,502 69,487 Commitments to sell loans secured by one- to four-family residential properties 33,069 36,907 Commitments to sell securities related to mortgage banking activities 57,000 44,000

DERIVATIVES AND HEDGING DERIV51

DERIVATIVES AND HEDGING DERIVATIVES AND HEDGING (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	As of December 31, 2017 and December 31, 2016 , the notional values or contractual amounts and fair values of the Company's derivatives designated in hedge relationships were as follows (in thousands): Asset Derivatives Liability Derivatives December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 Notional/ Contract Amount Fair Value (1) Notional/ Contract Amount Fair Value (1) Notional/ Contract Amount Fair Value (2) Notional/ Contract Amount Fair Value (2) Interest rate swaps $ 4,350 $ 447 $ 5,855 $ 660 $ 4,350 $ 447 $ 5,855 $ 660 (1) Included in Loans Receivable on the Consolidated Statements of Financial Condition. (2) Included in Other Liabilities on the Consolidated Statements of Financial Condition.
Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location	As of December 31, 2017 and December 31, 2016 , the notional values or contractual amounts and fair values of the Company's derivatives not designated in hedge relationships were as follows (in thousands): Asset Derivatives Liability Derivatives December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 Notional/ Contract Amount Fair Value (1) Notional/ Contract Amount Fair Value (1) Notional/ Contract Amount Fair Value (2) Notional/ Contract Amount Fair Value (2) Interest rate swaps $ 285,047 $ 4,636 $ 309,936 $ 7,670 $ 285,047 $ 4,636 $ 309,936 $ 7,670 Mortgage loan commitments 29,739 225 42,296 30 13,763 153 27,191 174 Forward sales contracts 43,069 298 71,192 452 47,000 48 9,715 115 $ 357,855 $ 5,159 $ 423,424 $ 8,152 $ 345,810 $ 4,837 $ 346,842 $ 7,959 (1) Included in Other Assets on the Consolidated Statements of Financial Condition, with the exception of those interest rate swaps from prior to 2009 that were not designated in hedge relationships (with a fair value of $499,000 at December 31, 2017 and $822,000 at December 31, 2016 ), which are included in Loans Receivable. (2) Included in Other Liabilities on the Consolidated Statements of Financial Condition. Gains (losses) recognized in income on non-designated hedging instruments for the years ended December 31, 2017 and 2016 were as follows (in thousands): For the Year Ended December 31, Location on Income Statement 2017 2016 Mortgage loan commitments Mortgage banking operations $ 195 $ (348 ) Forward sales contracts Mortgage banking operations (491 ) 296 $ (296 ) $ (52 )
Offsetting Assets and Liabilities	The following table illustrates the potential effect of the Company's derivative master netting arrangements, by type of financial instrument, on the Company's Consolidated Statements of Financial Condition as of December 31, 2017 and December 31, 2016 (in thousands): December 31, 2017 Gross Amounts of Financial Instruments Not Offset in the Statement of Financial Condition Gross Amounts Recognized Amounts offset in the Statement of Financial Condition Net Amounts in the Statement of Financial Condition Netting Adjustment Per Applicable Master Netting Agreements Fair Value of Financial Collateral in the Statement of Financial Condition Net Amount Derivative assets Interest rate swaps $ 5,083 $ — $ 5,083 $ (656 ) $ — $ 4,427 $ 5,083 $ — $ 5,083 $ (656 ) $ — $ 4,427 Derivative liabilities Interest rate swaps $ 5,083 $ — $ 5,083 $ (656 ) $ (3,467 ) $ 960 $ 5,083 $ — $ 5,083 $ (656 ) $ (3,467 ) $ 960 December 31, 2016 Gross Amounts of Financial Instruments Not Offset in the Statement of Financial Condition Gross Amounts Recognized Amounts offset in the Statement of Financial Condition Net Amounts in the Statement of Financial Condition Netting Adjustment Per Applicable Master Netting Agreements Fair Value of Financial Collateral in the Statement of Financial Condition Net Amount Derivative assets Interest rate swaps $ 8,330 $ — $ 8,330 $ (362 ) $ — $ 7,968 $ 8,330 $ — $ 8,330 $ (362 ) $ — $ 7,968 Derivative liabilities Interest rate swaps $ 8,330 $ — $ 8,330 $ (362 ) $ (7,557 ) $ 411 $ 8,330 $ — $ 8,330 $ (362 ) $ (7,557 ) $ 411

BASIS OF PRESENTATION AND SUM52

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Investment in FHLB Stock) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Investments [Line Items]
Federal Home Loan Bank (FHLB) stock	$ 10,334	$ 12,506
Federal Home Loan Bank Stock, Par Value Per Share	$ 100
Investment in Federal Home Loan Bank Stock [Member]
Gain (Loss) on Investments [Line Items]
Other than Temporary Impairment Losses, Investments	$ 0

BASIS OF PRESENTATION AND SUM53

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Property, Plant and Equipment Useful Lives) (Details)	12 Months Ended
	Dec. 31, 2017
Buildings and leased improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	10 years
Buildings and leased improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	39 years
Furniture and equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Furniture and equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	10 years

BASIS OF PRESENTATION AND SUM54

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Textuals) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)subsidiaryofficelocation
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Number of wholly-owned subsidiaries | subsidiary	2
Subsidiary, Banner Bank [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Number of offices | office	175
Number of production offices | office	13
Subsidiary, Islanders Bank [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Number of locations | location	3
Minimum [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Intangible asset, useful life	3 years
Minimum [Member] | Core Deposit Intangibles [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Intangible asset, useful life	3 years
Maximum [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Intangible asset, useful life	10 years
Maximum [Member] | Core Deposit Intangibles [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Intangible asset, useful life	10 years
Loans Receivable [Member] | Interest Rate Swap [Member] | F&M Bank [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Derivative Asset, Notional Amount | $	$ 7.1
Other assets [Member] | Interest Rate Swap [Member]
Basis of Presentation and Summary of Significant Accounting Policies [Abstract]
Derivative Asset, Notional Amount | $	$ 282.3

BRANCH DIVESTITURE Statement

BRANCH DIVESTITURE Statement	Oct. 06, 2017USD ($)
Other Income and Expenses [Abstract]
Loans included in purchase and sale agreement	$ 254,000,000
Deposits included in purchase and sale agreement	160,000,000
Property and equipment included in sale of branches	4,000,000
Accrued interest included in sale of branches	581,000
Goodwill included in sale of branches	1,900,000
Other intangibles included in sale of branches	1,100,000
Deposit premium from sale of branches	13,800,000
Net gain from sale of branches	$ 12,000,000

SECURITIES (Schedule of Securit

SECURITIES (Schedule of Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Trading:
Trading Securities, Amortized Cost	$ 27,246	$ 30,154
Trading Securities, Fair Value	22,318	24,568
Available-for-Sale:
Available-for-sale Securities, Amortized Cost	926,112	811,847
Gross Unrealized Gains	1,936	2,752
Gross Unrealized Losses	(8,563)	(8,171)
Securities—available-for-sale	919,485	806,428
Held-to-Maturity:
Held-to-maturity Securities, Amortized Cost	260,271	267,873
Gross Unrealized Gains	3,687	4,482
Gross Unrealized Losses	(1,770)	(1,827)
Held-to-maturity Securities, Fair Value	262,188	270,528
U.S. Government and agency obligations
Trading:
Trading Securities, Amortized Cost		1,230
Trading Securities, Fair Value		1,326
Available-for-Sale:
Available-for-sale Securities, Amortized Cost	72,829	57,288
Gross Unrealized Gains	68	146
Gross Unrealized Losses	(431)	(456)
Securities—available-for-sale	72,466	56,978
Held-to-Maturity:
Held-to-maturity Securities, Amortized Cost	1,024	1,065
Gross Unrealized Gains	29	0
Gross Unrealized Losses	0	(18)
Held-to-maturity Securities, Fair Value	1,053	1,047
Municipal bonds
Trading:
Trading Securities, Amortized Cost	100	331
Trading Securities, Fair Value	100	335
Available-for-Sale:
Available-for-sale Securities, Amortized Cost	68,513	110,487
Gross Unrealized Gains	665	455
Gross Unrealized Losses	(445)	(1,089)
Securities—available-for-sale	68,733	109,853
Held-to-Maturity:
Held-to-maturity Securities, Amortized Cost	189,860	196,989
Gross Unrealized Gains	3,385	4,173
Gross Unrealized Losses	(1,252)	(1,272)
Held-to-maturity Securities, Fair Value	191,993	199,890
Corporate bonds
Trading:
Trading Securities, Amortized Cost	27,132	26,959
Trading Securities, Fair Value	22,058	21,143
Available-for-Sale:
Available-for-sale Securities, Amortized Cost	5,431	10,255
Gross Unrealized Gains	6	77
Gross Unrealized Losses	(44)	(49)
Securities—available-for-sale	5,393	10,283
Held-to-Maturity:
Held-to-maturity Securities, Amortized Cost	3,978	3,876
Gross Unrealized Gains	7	0
Gross Unrealized Losses	0	0
Held-to-maturity Securities, Fair Value	3,985	3,876
Mortgage-backed or related securities
Trading:
Trading Securities, Amortized Cost		1,620
Trading Securities, Fair Value		1,641
Available-for-Sale:
Available-for-sale Securities, Amortized Cost	745,956	598,899
Gross Unrealized Gains	1,003	2,064
Gross Unrealized Losses	(7,402)	(6,251)
Securities—available-for-sale	739,557	594,712
Held-to-Maturity:
Held-to-maturity Securities, Amortized Cost	65,409	65,943
Gross Unrealized Gains	266	309
Gross Unrealized Losses	(518)	(537)
Held-to-maturity Securities, Fair Value	65,157	65,715
Asset-backed securities
Available-for-Sale:
Available-for-sale Securities, Amortized Cost	27,667	29,319
Gross Unrealized Gains	184	0
Gross Unrealized Losses	(93)	(326)
Securities—available-for-sale	27,758	28,993
Equity securities
Trading:
Trading Securities, Amortized Cost	14	14
Trading Securities, Fair Value	160	123
Available-for-Sale:
Available-for-sale Securities, Amortized Cost	5,716	5,599
Gross Unrealized Gains	10	10
Gross Unrealized Losses	(148)	0
Securities—available-for-sale	$ 5,578	$ 5,609

SECURITIES (Securities with Con

SECURITIES (Securities with Continuous Loss Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available-for-Sale:
Less than 12 Months, Fair Value	$ 617,847	$ 518,373
Less than 12 Months, Unrealized Losses	(5,686)	(7,283)
12 Months or More, Fair Value	151,971	68,099
12 Months or More, Unrealized Losses	(2,877)	(888)
Total Fair Value	769,818	586,472
Total Unrealized Losses	(8,563)	(8,171)
Held-to-Maturity:
Less Than 12 Months, Fair Value	59,862	108,094
Less Than 12 Months, Unrealized Losses	(549)	(1,822)
12 Months or More, Fair Value	38,748	204
12 Months or More, Unrealized Losses	(1,221)	(5)
Total Fair Value	98,610	108,298
Total Unrealized Losses	(1,770)	(1,827)
U.S. Government and agency obligations
Available-for-Sale:
Less than 12 Months, Fair Value	31,276	39,043
Less than 12 Months, Unrealized Losses	(211)	(442)
12 Months or More, Fair Value	23,341	1,012
12 Months or More, Unrealized Losses	(220)	(14)
Total Fair Value	54,617	40,055
Total Unrealized Losses	(431)	(456)
Held-to-Maturity:
Less Than 12 Months, Fair Value		1,047
Less Than 12 Months, Unrealized Losses		(18)
12 Months or More, Fair Value		0
12 Months or More, Unrealized Losses		0
Total Fair Value		1,047
Total Unrealized Losses		(18)
Municipal bonds
Available-for-Sale:
Less than 12 Months, Fair Value	20,879	60,765
Less than 12 Months, Unrealized Losses	(185)	(1,087)
12 Months or More, Fair Value	13,360	556
12 Months or More, Unrealized Losses	(260)	(2)
Total Fair Value	34,239	61,321
Total Unrealized Losses	(445)	(1,089)
Held-to-Maturity:
Less Than 12 Months, Fair Value	21,839	64,802
Less Than 12 Months, Unrealized Losses	(171)	(1,267)
12 Months or More, Fair Value	34,314	204
12 Months or More, Unrealized Losses	(1,081)	(5)
Total Fair Value	56,153	65,006
Total Unrealized Losses	(1,252)	(1,272)
Corporate bonds
Available-for-Sale:
Less than 12 Months, Fair Value	296	5,206
Less than 12 Months, Unrealized Losses	(4)	(49)
12 Months or More, Fair Value	4,682	0
12 Months or More, Unrealized Losses	(40)	0
Total Fair Value	4,978	5,206
Total Unrealized Losses	(44)	(49)
Mortgage-backed or related securities
Available-for-Sale:
Less than 12 Months, Fair Value	559,916	403,431
Less than 12 Months, Unrealized Losses	(5,138)	(5,604)
12 Months or More, Fair Value	100,662	47,467
12 Months or More, Unrealized Losses	(2,264)	(647)
Total Fair Value	660,578	450,898
Total Unrealized Losses	(7,402)	(6,251)
Held-to-Maturity:
Less Than 12 Months, Fair Value	38,023	42,245
Less Than 12 Months, Unrealized Losses	(378)	(537)
12 Months or More, Fair Value	4,434	0
12 Months or More, Unrealized Losses	(140)	0
Total Fair Value	42,457	42,245
Total Unrealized Losses	(518)	(537)
Asset-backed securities
Available-for-Sale:
Less than 12 Months, Fair Value	0	9,928
Less than 12 Months, Unrealized Losses	0	(101)
12 Months or More, Fair Value	9,926	19,064
12 Months or More, Unrealized Losses	(93)	(225)
Total Fair Value	9,926	28,992
Total Unrealized Losses	(93)	$ (326)
Equity Securities
Available-for-Sale:
Less than 12 Months, Fair Value	5,480
Less than 12 Months, Unrealized Losses	(148)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Total Fair Value	5,480
Total Unrealized Losses	$ (148)

SECURITIES (Securities Debt Mat

SECURITIES (Securities Debt Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized Cost
Maturing in one year or less	$ 100
Maturing after one year through five years	0
Maturing after five years through ten years	0
Maturing after ten years through twenty years	17,132
Maturing after twenty years	10,000
Total with Maturity Date	27,232
Equity securities	14
Trading Securities, Cost	27,246	$ 30,154
Fair Value
Maturing in one year or less	100
Maturing after one year through five years	0
Maturing after five years through ten years	0
Maturing after ten years through twenty years	14,543
Maturing after twenty years	7,515
Total with Maturity Date	22,158
Equity securities	160
Trading Securities, Fair Value	22,318	24,568
Amortized Cost
Maturing in one year or less	3,241
Maturing after one year through five years	39,513
Maturing after five years through ten years	215,837
Maturing after ten years through twenty years	100,862
Maturing after twenty years	560,943
Total with Maturity Date	920,396
Equity securities	5,716
Available-for-sale Securities, Amortized Cost	926,112	811,847
Fair Value
Maturing in one year or less	3,230
Maturing after one year through five years	39,070
Maturing after five years through ten years	213,923
Maturing after ten years through twenty years	101,181
Maturing after twenty years	556,503
Total with Maturity Date	913,907
Equity securities	5,578
Fair Value	919,485	806,428
Amortized Cost
Maturing in one year or less	1,968
Maturing after one year through five years	37,734
Maturing after five years through ten years	97,736
Maturing after ten years through twenty years	84,352
Maturing after twenty years	38,481
Held-to-maturity Securities	260,271	267,873
Fair Value
Maturing in one year or less	1,967
Maturing after one year through five years	37,626
Maturing after five years through ten years	98,747
Maturing after ten years through twenty years	86,249
Maturing after twenty years	37,599
Held-to-maturity Securities, Fair Value	$ 262,188	$ 270,528

SECURITIES (Securities Pledged)

SECURITIES (Securities Pledged) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Pledged Financial Instruments, Not Separately Reported, Securities [Abstract]
State and local governments public deposits, carrying value	$ 126,512
Interest rate swap counterparties, carrying value	14,698
Repurchase transaction accounts, carrying value	123,911
Other, carrying value	3,924
Total pledged securities, carrying value	269,045
State and local governments public deposits, amortized cost	126,438
Interest rate swap counterparties, amortized cost	14,740
Repurchase transaction accounts, amortized cost	124,049
Other, amortized cost	3,924
Total pledged securities, amortized cost	269,151
State and local governments public deposits, fair value	128,984
Interest rate swap counterparties, fair value	14,703
Repurchase transaction accounts, fair value	123,936
Other, fair value	3,835
Total pledged securities, fair value	$ 271,458

SECURITIES (Textuals) (Details)

SECURITIES (Textuals) (Details)	12 Months Ended
	Dec. 31, 2017USD ($)security	Dec. 31, 2016USD ($)security	Dec. 31, 2015USD ($)security
Trading:
Trading securites, proceeds from sale	$ 1,258,000	$ 7,839,000	$ 4,419,000
Trading Securities, Realized Gain (Loss)	28,000	(530,000)	690,000
Trading securities, OTTI charges	$ 0	$ 0	$ 0
Trading securities, number of securities in nonaccrual status | security	0	0	0
Trading securities, unrealized holding gain	$ 658,000	$ 400,000
Available-for-Sale:
Available-for-sale securities, unrealized loss position, number of securities | security	226	243
Available-for-sale securities, proceeds from sale	$ 522,600,000	$ 369,800,000	$ 232,600,000
Available-for-sale securities, Realized Gain (Loss)	(2,109,000)	311,000	126,000
Available-for-sale securities, OTTI charges	$ 0	$ 0	$ 0
Available-for-sale Securities, Number of Securities in Nonaccrual Status | security	0	0	0
Held-to-Maturity:
Held-to-maturity Securities, unrealized loss position, number of securities | security	66	73
Held-to-maturity Securities, proceeds from sale	$ 0	$ 0	$ 0
Held-to-maturity securities, number of securities in nonaccrual status | security	0	0	0

LOANS RECEIVABLE AND THE ALLO61

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Type) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 7,598,884	$ 7,451,148
Allowance for loan losses	89,028	85,997	$ 78,008	$ 75,907
Total loans, net	$ 7,509,856	$ 7,365,151
Percent of total loans	100.00%	100.00%
Unearned loan fees in excess of unamortized costs	$ 158	$ (5,800)
Discount on acquired loans, net	21,100	31,100
Related party loans	3,500	4,300
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 1,284,363	$ 1,352,999
Percent of total loans	16.90%	18.10%
Commercial real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 1,937,423	$ 1,986,336
Percent of total loans	25.50%	26.70%
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 314,188	$ 248,150
Allowance for loan losses	$ 1,633	$ 1,360	4,195	4,562
Percent of total loans	4.10%	3.30%
Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 148,435	$ 124,068
Percent of total loans	2.00%	1.70%
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 154,662	$ 124,126
Percent of total loans	2.00%	1.70%
One-to four-family construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 415,327	$ 375,704
Percent of total loans	5.50%	5.00%
Land and land development - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 164,516	$ 170,004
Percent of total loans	2.20%	2.30%
Land and land development - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 24,583	$ 29,184
Percent of total loans	0.30%	0.40%
Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 1,279,894	$ 1,207,879
Allowance for loan losses	$ 18,311	$ 16,533	13,856	12,043
Percent of total loans	16.80%	16.20%
Agricultural business, including secured by farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 338,388	$ 369,156
Allowance for loan losses	$ 4,053	$ 2,967	3,645	3,821
Percent of total loans	4.40%	5.00%
One- to four-family residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 848,289	$ 813,077
Allowance for loan losses	$ 2,055	$ 2,238	$ 4,732	$ 5,447
Percent of total loans	11.20%	10.90%
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 522,931	$ 493,211
Percent of total loans	6.90%	6.60%
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 165,885	$ 157,254
Percent of total loans	2.20%	2.10%

LOANS RECEIVABLE AND THE ALLO62

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Purchased Credit-Impaired Loans, Changes in Accretable Yield) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Outstanding contractual unpaid balance of purchased credit-impaired loans	$ 32,500	$ 48,400
Carrying balance of purchased credit-impaired loans	21,310	32,322
Accretable Yield Movement Schedule [Roll Forward]
Balance, beginning of period	8,717	10,375
Accretion to interest income	5,929	9,333
Disposals	564	1,018
Reclassifications from non-accretable difference	4,296	8,693
Balance, end of period	6,520	8,717
Certain Loans Acquired in Transfer, Nonaccretable Difference	$ 11,300	$ 15,700

LOANS RECEIVABLE AND THE ALLO63

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Impaired Loans With and Without Specific Reserves) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	$ 45,543	$ 43,935
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	26,488	25,357
Recorded Investment	16,656	16,129
Related Allowance	782	1,420
Impaired Financing Receivable, Average Recorded Investment	39,263	49,535	$ 36,340
Interest Income Recognized	898	1,056	1,206
Commerical real estate - owner-occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	7,807	3,786
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	6,447	3,373
Recorded Investment	199	203
Related Allowance	18	20
Impaired Financing Receivable, Average Recorded Investment	3,697	2,721	1,467
Interest Income Recognized	11	2	9
Commercial real estate - investment properties [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	11,296	9,916
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	4,200	5,565
Recorded Investment	6,884	4,304
Related Allowance	263	408
Impaired Financing Receivable, Average Recorded Investment	9,136	18,529	8,003
Interest Income Recognized	195	242	303
Multifamily real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance		508
Impaired Financing Receivable, with No Related Allowance, Recorded Investment		147
Recorded Investment		349
Related Allowance		64
Impaired Financing Receivable, Average Recorded Investment	251	513	362
Interest Income Recognized	10	21	18
One-to four-family construction [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	298	1,180
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	298	0
Recorded Investment	0	1,180
Related Allowance	0	156
Impaired Financing Receivable, Average Recorded Investment	418	1,158	1,463
Interest Income Recognized	27	75	114
Land and land development - residential [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	1,134	3,012
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	798	750
Recorded Investment	0	1,106
Related Allowance	0	219
Impaired Financing Receivable, Average Recorded Investment	1,396	1,948	2,406
Interest Income Recognized	42	85	49
Land and land development - commercial [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance		1,608
Impaired Financing Receivable, with No Related Allowance, Recorded Investment		998
Recorded Investment		0
Related Allowance		0
Impaired Financing Receivable, Average Recorded Investment	867	1,003	931
Interest Income Recognized	0	0	0
Commercial business [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	4,441	3,753
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	3,424	3,074
Recorded Investment	555	651
Related Allowance	50	69
Impaired Financing Receivable, Average Recorded Investment	5,996	4,290	1,667
Interest Income Recognized	68	37	35
Agricultural business, including secured by farmland [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	9,388	6,438
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	6,230	6,354
Recorded Investment	3,031	0
Related Allowance	264	0
Impaired Financing Receivable, Average Recorded Investment	6,184	5,004	1,143
Interest Income Recognized	207	119	19
One- to four-family residential [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	9,547	11,439
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	3,709	3,149
Recorded Investment	5,775	8,026
Related Allowance	178	479
Impaired Financing Receivable, Average Recorded Investment	9,499	11,976	17,770
Interest Income Recognized	322	441	630
Consumer secured by one- to four-family [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	1,498	1,904
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,324	1,721
Recorded Investment	139	144
Related Allowance	7	1
Impaired Financing Receivable, Average Recorded Investment	1,635	1,778	736
Interest Income Recognized	9	17	11
Consumer Loan [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	134	391
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	58	226
Recorded Investment	73	166
Related Allowance	2	4
Impaired Financing Receivable, Average Recorded Investment	184	615	392
Interest Income Recognized	$ 7	$ 17	$ 18

LOANS RECEIVABLE AND THE ALLO64

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Troubled Debt Restructuring) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	$ 16,115	$ 18,907
Nonaccrual Status	917	1,024
Total TDRs	17,032	19,931
Financing Receivable, Modifications, Commitments to Advance Funds	45	127
Commerical real estate - owner-occupied [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	199	203
Nonaccrual Status	87	96
Total TDRs	286	299
Commercial real estate - investment properties [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	6,884	4,304
Nonaccrual Status	0	0
Total TDRs	6,884	4,304
Multifamily real estate [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	0	349
Nonaccrual Status	0	0
Total TDRs	0	349
One-to four-family construction [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	0	1,180
Nonaccrual Status	0	0
Total TDRs	0	1,180
Land and land development - residential [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	0	1,106
Nonaccrual Status	0	0
Total TDRs	0	1,106
Commercial business [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	555	653
Nonaccrual Status	0	0
Total TDRs	555	653
Agricultural business, including secured by farmland [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	3,129	3,125
Nonaccrual Status	29	79
Total TDRs	3,158	3,204
One- to four-family residential [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	5,136	7,678
Nonaccrual Status	801	843
Total TDRs	5,937	8,521
Consumer secured by one- to four-family [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	139	143
Nonaccrual Status	0	6
Total TDRs	139	149
Consumer Loan [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Accrual Status	73	166
Nonaccrual Status	0	0
Total TDRs	$ 73	$ 166

LOANS RECEIVABLE AND THE ALLO65

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Newly Restructured Loans) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)contract	Dec. 31, 2016USD ($)contract
Financing Receivable, Troubled Debt Restructurings [Line Items]
Number of Contracts | contract	1	2
Pre-Modification Outstanding Recorded Investment	$ 3,714	$ 272
Post-Modification Outstanding Recorded Investment	$ 3,714	$ 272
Commerical real estate - owner-occupied [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Number of Contracts | contract		1
Pre-Modification Outstanding Recorded Investment		$ 194
Post-Modification Outstanding Recorded Investment		$ 194
One- to four-family residential [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Number of Contracts | contract		1
Pre-Modification Outstanding Recorded Investment		$ 78
Post-Modification Outstanding Recorded Investment		$ 78
Commercial real estate - investment properties [Member]
Financing Receivable, Troubled Debt Restructurings [Line Items]
Number of Contracts | contract	1
Pre-Modification Outstanding Recorded Investment	$ 3,714
Post-Modification Outstanding Recorded Investment	$ 3,714

LOANS RECEIVABLE AND THE ALLO66

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Troubled Debt Restructuring Which Incurred Payment Default) (Details)	12 Months Ended
	Dec. 31, 2017loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDRs Which Incurred Payment Default, Number of Loans	0

LOANS RECEIVABLE AND THE ALLO67

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Risk-Rate and Non-Risk Rated Loans by Grade and Other Characteristic) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		$ 7,598,884	$ 7,451,148
Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		1,284,363	1,352,999
Commer[Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		1,937,423	1,986,336
Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		314,188	248,150
Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		148,435	124,068
Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		154,662	124,126
One-to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		415,327	375,704
Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		164,516	170,004
Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		24,583	29,184
Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		1,279,894	1,207,879
Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		338,388	369,156
One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		848,289	813,077
Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		522,931	493,211
Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		165,885	157,254
Pass (Risk Ratings 1-5) [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	7,431,182	7,282,408
Pass (Risk Ratings 1-5) [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		296,800	225,000
Pass (Risk Ratings 1-5) [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	1,246,125	1,313,142
Pass (Risk Ratings 1-5) [Member] | Commer[Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	1,918,940	1,948,822
Pass (Risk Ratings 1-5) [Member] | Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	313,432	247,258
Pass (Risk Ratings 1-5) [Member] | Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	148,435	124,068
Pass (Risk Ratings 1-5) [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	154,662	124,126
Pass (Risk Ratings 1-5) [Member] | One-to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	411,802	371,636
Pass (Risk Ratings 1-5) [Member] | Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	153,073	167,764
Pass (Risk Ratings 1-5) [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	21,665	25,090
Pass (Risk Ratings 1-5) [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	1,213,365	1,148,585
Pass (Risk Ratings 1-5) [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	321,110	356,656
Pass (Risk Ratings 1-5) [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	842,304	807,837
Pass (Risk Ratings 1-5) [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	520,675	490,877
Pass (Risk Ratings 1-5) [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	165,594	156,547
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		48,468	77,691
Special Mention [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		12,227	14,394
Special Mention [Member] | Commer[Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		9,118	23,846
Special Mention [Member] | Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Special Mention [Member] | Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Special Mention [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Special Mention [Member] | One-to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Special Mention [Member] | Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		10,554	0
Special Mention [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Special Mention [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		12,135	35,036
Special Mention [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		3,852	3,335
Special Mention [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		569	967
Special Mention [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	5
Special Mention [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		13	108
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		119,122	91,042
Substandard [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		26,011	25,463
Substandard [Member] | Commer[Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		9,365	13,668
Substandard [Member] | Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		756	892
Substandard [Member] | Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Substandard [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Substandard [Member] | One-to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		3,525	4,068
Substandard [Member] | Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		889	2,240
Substandard [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		2,918	4,094
Substandard [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		54,282	24,258
Substandard [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		13,426	9,165
Substandard [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		5,416	4,273
Substandard [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		2,256	2,327
Substandard [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		278	594
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		112	7
Doubtful [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | Commer[Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | One-to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		112	0
Doubtful [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	2
Doubtful [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	5
Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Commer[Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | One-to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		$ 0	$ 0
[1]	(1) The Pass category includes some performing loans that are part of homogenous pools which are not individually risk-rated. This includes all consumer loans, all one- to four-family residential loans and, as of December 31, 2017 and 2016, in the commercial business category, $296.8 million and $225.0 million, respectively, of credit-scored small business loans. As loans in these homogeneous pools become non-accrual, they are individually risk-rated.

LOANS RECEIVABLE AND THE ALLO68

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Age Analysis of Company's Past Due Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 45,980	$ 28,859
Carrying balance of purchased credit-impaired loans	21,310	32,322
Current	7,531,594	7,389,967
Loans receivable	7,598,884	7,451,148
Loans 90 Days or More Past Due and Accruing	1,486	2,153
Financing Receivable, Recorded Investment, Nonaccrual Status	25,543	20,426
Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	10,889	4,476
Carrying balance of purchased credit-impaired loans	7,682	13,281
Current	1,265,792	1,335,242
Loans receivable	1,284,363	1,352,999
Loans 90 Days or More Past Due and Accruing	0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	6,447	3,373
Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5,833	5,564
Carrying balance of purchased credit-impaired loans	7,166	10,168
Current	1,924,424	1,970,604
Loans receivable	1,937,423	1,986,336
Loans 90 Days or More Past Due and Accruing	0	701
Financing Receivable, Recorded Investment, Nonaccrual Status	4,199	4,864
Multifamily real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	105	147
Carrying balance of purchased credit-impaired loans	169	139
Current	313,914	247,864
Loans receivable	314,188	248,150
Loans 90 Days or More Past Due and Accruing	0	147
Financing Receivable, Recorded Investment, Nonaccrual Status	0	0
Commercial Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Carrying balance of purchased credit-impaired loans	0	0
Current	148,435	124,068
Loans receivable	148,435	124,068
Loans 90 Days or More Past Due and Accruing	0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	0	0
Multifamily construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,416	0
Carrying balance of purchased credit-impaired loans	0	0
Current	151,246	124,126
Loans receivable	154,662	124,126
Loans 90 Days or More Past Due and Accruing	0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	0	0
One-to four-family construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5,915	0
Carrying balance of purchased credit-impaired loans	446	862
Current	408,966	374,842
Loans receivable	415,327	375,704
Loans 90 Days or More Past Due and Accruing	298	0
Financing Receivable, Recorded Investment, Nonaccrual Status	0	0
Land and land development - residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	798	798
Carrying balance of purchased credit-impaired loans	0	0
Current	163,718	169,206
Loans receivable	164,516	170,004
Loans 90 Days or More Past Due and Accruing	0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	798	750
Land and land development - commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	998
Carrying balance of purchased credit-impaired loans	2,919	3,016
Current	21,664	25,170
Loans receivable	24,583	29,184
Loans 90 Days or More Past Due and Accruing	0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	0	998
Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4,555	4,552
Carrying balance of purchased credit-impaired loans	2,159	3,821
Current	1,273,180	1,199,506
Loans receivable	1,279,894	1,207,879
Loans 90 Days or More Past Due and Accruing	18	0
Financing Receivable, Recorded Investment, Nonaccrual Status	3,406	3,074
Agricultural business, including secured by farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,148	4,372
Carrying balance of purchased credit-impaired loans	565	684
Current	334,675	364,100
Loans receivable	338,388	369,156
Loans 90 Days or More Past Due and Accruing	0	0
Financing Receivable, Recorded Investment, Nonaccrual Status	6,132	3,229
One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	8,431	4,152
Carrying balance of purchased credit-impaired loans	136	274
Current	839,722	808,651
Loans receivable	848,289	813,077
Loans 90 Days or More Past Due and Accruing	1,085	1,233
Financing Receivable, Recorded Investment, Nonaccrual Status	3,264	2,263
Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,130	2,078
Carrying balance of purchased credit-impaired loans	0	18
Current	520,801	491,115
Loans receivable	522,931	493,211
Loans 90 Days or More Past Due and Accruing	85	61
Financing Receivable, Recorded Investment, Nonaccrual Status	1,239	1,660
Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	760	1,722
Carrying balance of purchased credit-impaired loans	68	59
Current	165,057	155,473
Loans receivable	165,885	157,254
Loans 90 Days or More Past Due and Accruing	0	11
Financing Receivable, Recorded Investment, Nonaccrual Status	58	215
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	24,084	8,923
30 to 59 Days Past Due [Member] | Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5,323	1,938
30 to 59 Days Past Due [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,737	117
30 to 59 Days Past Due [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	105	0
30 to 59 Days Past Due [Member] | Commercial Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
30 to 59 Days Past Due [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,416	0
30 to 59 Days Past Due [Member] | One-to four-family construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4,892	0
30 to 59 Days Past Due [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	48
30 to 59 Days Past Due [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
30 to 59 Days Past Due [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,574	2,314
30 to 59 Days Past Due [Member] | Agricultural business, including secured by farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	598	360
30 to 59 Days Past Due [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4,475	1,793
30 to 59 Days Past Due [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,355	932
30 to 59 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	609	1,421
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,177	2,454
60 to 89 Days Past Due [Member] | Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	76	0
60 to 89 Days Past Due [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60 to 89 Days Past Due [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60 to 89 Days Past Due [Member] | Commercial Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60 to 89 Days Past Due [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60 to 89 Days Past Due [Member] | One-to four-family construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	725	0
60 to 89 Days Past Due [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60 to 89 Days Past Due [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
60 to 89 Days Past Due [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	404	647
60 to 89 Days Past Due [Member] | Agricultural business, including secured by farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	533	1,244
60 to 89 Days Past Due [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,241	249
60 to 89 Days Past Due [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	62	160
60 to 89 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	136	154
90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	18,719	17,482
90 Days or More Past Due [Member] | Commerical real estate - owner-occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5,490	2,538
90 Days or More Past Due [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4,096	5,447
90 Days or More Past Due [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	147
90 Days or More Past Due [Member] | Commercial Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
90 Days or More Past Due [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
90 Days or More Past Due [Member] | One-to four-family construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	298	0
90 Days or More Past Due [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	798	750
90 Days or More Past Due [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	998
90 Days or More Past Due [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,577	1,591
90 Days or More Past Due [Member] | Agricultural business, including secured by farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,017	2,768
90 Days or More Past Due [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2,715	2,110
90 Days or More Past Due [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	713	986
90 Days or More Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 15	$ 147

LOANS RECEIVABLE AND THE ALLO69

LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Allowance for Credit Losses) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				$ 85,997				$ 78,008				$ 75,907	$ 85,997	$ 78,008	$ 75,907
Provision for loan losses	$ 2,000	$ 2,000	$ 2,000	2,000	$ 2,030	$ 2,000	$ 2,000	0	$ 0	$ 0	$ 0	0	8,000	6,030	0
Recoveries													3,731	6,698	6,960
Charge-offs													(8,700)	(4,739)	(4,859)
Ending balance	89,028				85,997				78,008				89,028	85,997	78,008
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance individually evaluated for impairment																$ 782	$ 1,420
Allowance collectively evaluated for impairment																88,085	84,544
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses																	33
Allowance for loan losses	89,028			85,997	85,997			78,008	78,008			75,907	85,997	78,008	75,907	89,028	85,997
Loans individually evaluated for impairment																32,512	30,382
Loans collectively evaluated for impairment																7,545,062	7,388,444
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net																21,310	32,322
Loans receivable																7,598,884	7,451,148
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				20,993				20,716				18,784	20,993	20,716	18,784
Provision for loan losses													2,639	441	1,177
Recoveries													372	582	819
Charge-offs													(1,180)	(746)	(64)
Ending balance	22,824				20,993				20,716				22,824	20,993	20,716
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance individually evaluated for impairment																281	428
Allowance collectively evaluated for impairment																22,543	20,565
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses																0	0
Allowance for loan losses	22,824			20,993	20,993			20,716	20,716			18,784	20,993	20,716	18,784	22,824	20,993
Loans individually evaluated for impairment																16,017	10,300
Loans collectively evaluated for impairment																3,190,921	3,305,586
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net																14,848	23,449
Loans receivable																3,221,786	3,339,335
Multifamily Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				1,360				4,195				4,562	1,360	4,195	4,562
Provision for loan losses													262	(2,835)	(480)
Recoveries													11	0	113
Charge-offs													0	0	0
Ending balance	1,633				1,360				4,195				1,633	1,360	4,195
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance individually evaluated for impairment																0	64
Allowance collectively evaluated for impairment																1,633	1,296
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses																0	0
Allowance for loan losses	1,633			1,360	1,360			4,195	4,195			4,562	1,360	4,195	4,562	1,633	1,360
Loans individually evaluated for impairment																0	349
Loans collectively evaluated for impairment																314,019	247,662
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net																169	139
Loans receivable																314,188	248,150
Construction and Land [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				34,252				27,131				25,545	34,252	27,131	25,545
Provision for loan losses													(7,921)	5,566	666
Recoveries													1,237	2,171	1,811
Charge-offs													0	(616)	(891)
Ending balance	27,568				34,252				27,131				27,568	34,252	27,131
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance individually evaluated for impairment																0	374
Allowance collectively evaluated for impairment																27,567	33,845
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses																1	33
Allowance for loan losses	27,568			34,252	34,252			27,131	27,131			25,545	34,252	27,131	25,545	27,568	34,252
Loans individually evaluated for impairment																750	4,034
Loans collectively evaluated for impairment																903,408	815,174
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net																3,365	3,878
Loans receivable																907,523	823,086
Commercial business [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				16,533				13,856				12,043	16,533	13,856	12,043
Provision for loan losses													4,355	1,632	1,611
Recoveries													1,226	1,993	948
Charge-offs													(3,803)	(948)	(746)
Ending balance	18,311				16,533				13,856				18,311	16,533	13,856
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance individually evaluated for impairment																50	69
Allowance collectively evaluated for impairment																18,214	16,464
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses																47	0
Allowance for loan losses	18,311			16,533	16,533			13,856	13,856			12,043	16,533	13,856	12,043	18,311	16,533
Loans individually evaluated for impairment																1,812	2,946
Loans collectively evaluated for impairment																1,275,923	1,201,112
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net																2,159	3,821
Loans receivable																1,279,894	1,207,879
Agricultural Business [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				2,967				3,645				3,821	2,967	3,645	3,821
Provision for loan losses													3,326	(170)	(878)
Recoveries													134	59	1,927
Charge-offs													(2,374)	(567)	(1,225)
Ending balance	4,053				2,967				3,645				4,053	2,967	3,645
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance individually evaluated for impairment																264	0
Allowance collectively evaluated for impairment																3,676	2,967
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses																113	0
Allowance for loan losses	4,053			2,967	2,967			3,645	3,645			3,821	2,967	3,645	3,821	4,053	2,967
Loans individually evaluated for impairment																8,585	4,766
Loans collectively evaluated for impairment																329,238	363,706
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net																565	684
Loans receivable																338,388	369,156
One- to four-family residential [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				2,238				4,732				5,447	2,238	4,732	5,447
Provision for loan losses													(415)	(3,402)	(1,068)
Recoveries													270	1,283	772
Charge-offs													(38)	(375)	(419)
Ending balance	2,055				2,238				4,732				2,055	2,238	4,732
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance individually evaluated for impairment																178	480
Allowance collectively evaluated for impairment																1,877	1,758
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses																0	0
Allowance for loan losses	2,055			2,238	2,238			4,732	4,732			5,447	2,238	4,732	5,447	2,055	2,238
Loans individually evaluated for impairment																5,136	7,678
Loans collectively evaluated for impairment																843,017	805,125
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net																136	274
Loans receivable																848,289	813,077
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				4,104				902				483	4,104	902	483
Provision for loan losses													586	4,079	1,363
Recoveries													481	610	570
Charge-offs													(1,305)	(1,487)	(1,514)
Ending balance	3,866				4,104				902				3,866	4,104	902
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance individually evaluated for impairment																9	5
Allowance collectively evaluated for impairment																3,857	4,099
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses																0	0
Allowance for loan losses	3,866			4,104	4,104			902	902			483	4,104	902	483	3,866	4,104
Loans individually evaluated for impairment																212	309
Loans collectively evaluated for impairment																688,536	650,079
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net																68	77
Loans receivable																688,816	650,465
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				3,550				2,831				5,222	3,550	2,831	5,222
Provision for loan losses													5,168	719	(2,391)
Recoveries													0	0	0
Charge-offs													0	0	0
Ending balance	8,718				3,550				2,831				8,718	3,550	2,831
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance individually evaluated for impairment																0	0
Allowance collectively evaluated for impairment																8,718	3,550
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses																0	0
Allowance for loan losses	$ 8,718			3,550	3,550			$ 2,831	$ 2,831			$ 5,222	3,550	2,831	$ 5,222	8,718	3,550
Loans individually evaluated for impairment																0	0
Loans collectively evaluated for impairment																0	0
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net																0	0
Loans receivable																$ 0	0
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance				161									161
Ending balance					161									161
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Allowance for loan losses				$ 161	$ 161								$ 161	$ 161			$ 161

REAL ESTATE OWNED, HELD FOR S70

REAL ESTATE OWNED, HELD FOR SALE, NET (REO Rollforward) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate [Abstract]
Real Estate Acquired Through Foreclosure, Residential	$ 0	$ 917,000
Mortgage Loans in Process of Foreclosure, Amount	2	700,000
Real Estate Owned [Roll Forward]
Balance, beginning of period	11,081,000	11,627,000	$ 3,352,000
Additions from loan foreclosures	46,000	8,909,000	4,351,000
Additions from capitalized costs	54,000	0	298,000
Additions from acquisitions	0	400,000	8,231,000
Proceeds from dispositions of REO	(13,474,000)	(10,812,000)	(4,740,000)
Gain on sale of REO	2,909,000	1,833,000	351,000
Valuation adjustments in the period	(256,000)	(876,000)	(216,000)
Balance, end of period	$ 360,000	$ 11,081,000	$ 11,627,000

PROPERTY AND EQUIPMENT, NET (De

PROPERTY AND EQUIPMENT, NET (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Real Estate Held for Development and Sale		$ 3,800	$ 8,500
Land1	[1]	35,080	35,463
Buildings and leasehold improvements(1)	[1]	154,374	163,879
Furniture and equipment		105,643	94,999
Property and equipment, gross		295,097	294,341
Less accumulated depreciation		(140,282)	(127,860)
Property and equipment, net		$ 154,815	$ 166,481
[1]	The Company had $3.8 million and $8.5 million of properties held for sale that were included in land and buildings at December 31, 2017 and 2016, respectively.

PROPERTY AND EQUIPMENT, NET (Op

PROPERTY AND EQUIPMENT, NET (Operating Lease Commitments) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Property, Plant and Equipment [Abstract]
2,016	$ 16,029
2,017	13,199
2,018	12,080
2,019	10,100
2,020	6,725
Thereafter	13,926
Total	$ 72,059

PROPERTY AND EQUIPMENT, NET PRO

PROPERTY AND EQUIPMENT, NET PROPERTY AND EQUIPMENT, NET (Textual) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 14,701	$ 13,464	$ 9,957
Rental expense	$ 16,400	$ 16,700	$ 10,200

DEPOSITS (Deposit Liabilities)

DEPOSITS (Deposit Liabilities) (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016
Deposit Liabilities [Line Items]
Non-interest-bearing checking		$ 3,265,544,000	$ 3,140,451,000
Interest-bearing checking		971,137,000	914,484,000
Regular savings accounts		1,557,500,000	1,523,391,000
Money market accounts		1,422,313,000	1,497,755,000
Total interest-bearing transaction and savings accounts		3,950,950,000	3,935,630,000
Time Deposits, $250,000 or less		813,997,000	884,403,000
Time Deposits, More than $250,000		152,940,000	160,930,000
Interest-bearing certificates	[1]	966,937,000	1,045,333,000
Total deposits		8,183,431,000	8,121,414,000
Included in total deposits:
Public fund transaction accounts		198,719,000	221,765,000
Public fund interest-bearing certificates		23,685,000	25,650,000
Total public deposits		222,404,000	247,415,000
Total brokered deposits		57,228,000	34,074,000
Related Party Deposit Liabilities		10,000,000	7,200,000
Business Combination, Acquired Deposits, Time Deposit Premium		11,000	426,000
Time deposits equal to or greater than $250,000		$ 155,900,000	$ 165,400,000
[1]	)Certificates of deposit included $11,000 and $426,000 of acquisition premiums at December 31, 2017 and 2016, respectively.

DEPOSITS (Maturities and Weight

DEPOSITS (Maturities and Weighted Average Interest Rates of Certificates of Deposit) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Maturities of Time Deposits [Abstract]
Maturing in one year or less		$ 685,592
Maturing after one year through two years		98,257
Maturing after two years through three years		141,209
Maturing after three years through four years		25,902
Maturing after four years through five years		13,775
Maturing after five years		2,202
Total certificates of deposit	[1]	$ 966,937	$ 1,045,333
Weighted Average Rate [Abstract]
Maturing in one year or less		0.49%
Maturing after one year through two years		0.72%
Maturing after two years through three years		1.30%
Maturing after three years through four years		1.08%
Maturing after four years through five years		1.26%
Maturing after five years		1.05%
Total certificates of deposits		0.66%
[1]	)Certificates of deposit included $11,000 and $426,000 of acquisition premiums at December 31, 2017 and 2016, respectively.

ADVANCES FROM FEDERAL HOME LO76

ADVANCES FROM FEDERAL HOME LOAN BANK OF DES MOINES (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Advances from Federal Home Loan Banks [Abstract]
Federal Home Loan Bank, advances, collateral pledged	$ 0
Federal Home Loan Bank, Advances, Fiscal Year Maturity [Abstract]
Maturing in one year or less	0	$ 54,000,000
Maturing after one year through three years	0	0
Maturing after three years through five years	0	0
Maturing after five years	169,000	179,000
Total FHLB advances, at par	169,000	54,179,000
Fair value adjustment	33,000	37,000
Total FHLB advances, carried at fair value	202,000	54,216,000
Federal Home Loan Bank, advances, maximum outstanding at any month end	453,200,000	300,200,000
Federal Home Loan Bank, advances, average balance outstanding	$ 151,300,000	$ 141,900,000
Federal Home Loan Bank, advances, average interest rate for year	1.26%	0.67%
Subsidiary, Banner Bank [Member]
Federal Home Loan Bank, Advances, Fiscal Year Maturity [Abstract]
Federal Home Loan Bank, advances, percentage of total assets to support credit line	35.00%
Federal Home Loan Bank, advances, maximum credit line	$ 3,550,000,000
Subsidiary, Islanders Bank [Member]
Federal Home Loan Bank, Advances, Fiscal Year Maturity [Abstract]
Federal Home Loan Bank, advances, percentage of total assets to support credit line	35.00%
Federal Home Loan Bank, advances, maximum credit line	$ 98,700,000

OTHER BORROWINGS (Schedule of O

OTHER BORROWINGS (Schedule of Other Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Amount:
Total year-end outstanding	$ 95,860	$ 105,685
Repurchase Agreements [Member] | Retail repurchase agreements [Member]
Amount:
Maturing in one year or less	95,860	100,685
Maturing after one year through two years	0	5,000
Maturing after two years	0	0
Total year-end outstanding	$ 95,860	$ 105,685
Weighted Average Rate:
Maturing in one year or less, weighted average interest rate	0.29%	0.19%
Maturing after one year through two years, weighted average interest rate	0.00%	2.15%
Maturing after two years, weighted average interest rate	0.00%	0.00%
Total year-end outstanding, weighted average interest rate	0.29%	0.28%
Other Borrowings, Activity for Year [Abstract]
Average outstanding	$ 111,872	$ 108,427
Average outstanding, weighted average interest rate	0.28%	0.29%
Maximum outstanding at any month end	$ 120,245	$ 112,309

OTHER BORROWINGS (Textuals) (De

OTHER BORROWINGS (Textuals) (Details)	Dec. 31, 2017USD ($)agreement	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Securities pledged to secure retail repurchase agreements	$ 123,911,000
Funds Borrowed Against Current Borrowing Capacity	95,860,000	$ 105,685,000
Repurchase Agreements [Member] | Retail repurchase agreements [Member]
Debt Instrument [Line Items]
Funds Borrowed Against Current Borrowing Capacity	$ 95,860,000	105,685,000
Repurchase Agreements [Member] | Retail repurchase agreements [Member] | Minimum [Member]
Debt Instrument [Line Items]
Repurchase agreements, interest rate	0.15%
Repurchase Agreements [Member] | Retail repurchase agreements [Member] | Maximum [Member]
Debt Instrument [Line Items]
Repurchase agreements, interest rate	0.40%
Repurchase Agreements [Member] | Repurchase Agreement, Wholesale [Member]
Debt Instrument [Line Items]
Repurchase agreements, interest rate	2.15%
Number of repurchase agreements | agreement	1
Federal Reserve Bank Advances [Member] | Federal Reserve Bank of San Francisco [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,150,000,000
Funds Borrowed Against Current Borrowing Capacity	0	0
Subsidiary, Banner Bank [Member] | Federal Funds Purchased [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	110,000,000
Line of credit, current	0	0
Balance outstanding	0
Subsidiary, Islanders Bank [Member] | Federal Funds Purchased [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	5,000,000
Line of credit, current	$ 0	$ 0

JUNIOR SUBORDINATED DEBENTURE79

JUNIOR SUBORDINATED DEBENTURES AND MANDATORILY REDEEMABLE TRUST PREFERRED SECURITIES (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)subsidiary	Dec. 31, 2016USD ($)
Schedule of Trust Preferred Securities [Line Items]
Number of wholly-owned Grantor Trusts | subsidiary	9
Grantor trusts amount of tier one risk based capital	$ 1,123,154	$ 1,125,267
Debentures Subject to Mandatory Redemption [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	140,212
Fair value adjustment	(41,505)
Total TPS liability at fair value	$ 98,707
Current Interest Rate	3.57%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trusts [Member]
Schedule of Trust Preferred Securities [Line Items]
Grantor trusts amount of tier one risk based capital	$ 136,000
Grantor trusts percentage of tier one risk based capital	11.20%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust II [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 15,464
Current Interest Rate	4.71%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	3.35%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust III [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 15,465
Current Interest Rate	4.26%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	2.90%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust IV [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 15,465
Current Interest Rate	4.21%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	2.85%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust V [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 25,774
Current Interest Rate	3.02%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	1.57%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust VI [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 25,774
Current Interest Rate	3.10%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	1.62%
Debentures Subject to Mandatory Redemption [Member] | Banner Capital Trust VII [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 25,774
Current Interest Rate	2.72%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	1.38%
Debentures Subject to Mandatory Redemption [Member] | Siuslaw Statutory Trust One [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 8,248
Current Interest Rate	4.30%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	2.70%
Debentures Subject to Mandatory Redemption [Member] | Greater Sacramento Bancorp Statutory Trust one [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 4,124
Current Interest Rate	4.71%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	3.35%
Debentures Subject to Mandatory Redemption [Member] | Greater Sacramento Bancorp Statutory Trust Two [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 4,124
Current Interest Rate	3.27%
Interest Rate Spread, Description	Three-month LIBOR
Interest Rate Spread	1.68%
Aggregate Liquidation Amount of Trust Preferred Securities [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 136,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust II [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	15,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust III [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	15,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust IV [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	15,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust V [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	25,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust VI [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	25,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Banner Capital Trust VII [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	25,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Siuslaw Statutory Trust One [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	8,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Greater Sacramento Bancorp Statutory Trust one [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	4,000
Aggregate Liquidation Amount of Trust Preferred Securities [Member] | Greater Sacramento Bancorp Statutory Trust Two [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	4,000
Aggregate Liquidation Amount of Common Capital Securities [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	4,212
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust II [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	464
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust III [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	465
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust IV [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	465
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust V [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	774
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust VI [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	774
Aggregate Liquidation Amount of Common Capital Securities [Member] | Banner Capital Trust VII [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	774
Aggregate Liquidation Amount of Common Capital Securities [Member] | Siuslaw Statutory Trust One [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	248
Aggregate Liquidation Amount of Common Capital Securities [Member] | Greater Sacramento Bancorp Statutory Trust one [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	124
Aggregate Liquidation Amount of Common Capital Securities [Member] | Greater Sacramento Bancorp Statutory Trust Two [Member]
Schedule of Trust Preferred Securities [Line Items]
Total TPS liability at par	$ 124

INCOME TAXES (Components of Inc

INCOME TAXES (Components of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Federal, State and Local, Tax Expense (Benefit) [Abstract]
Current Federal Tax Expense (Benefit)													$ 30,961	$ 29,787	$ 24,683
Current State and Local Tax Expense (Benefit)													3,085	2,477	1,399
Current													34,046	32,264	26,082
Deferred Federal, State and Local, Tax Expense (Benefit) [Abstract]
Deferred Federal Income Tax Expense (Benefit)													58,646	9,908	(3,310)
Deferred State and Local Income Tax Expense (Benefit)													(2,204)	2,083	(23)
Deferred													56,442	11,991	(3,333)
Provision for (benefit from) income taxes	$ 54,985	$ 10,883	$ 12,791	$ 11,828	$ 11,943	$ 12,277	$ 10,841	$ 9,194	$ 3,308	$ 6,642	$ 6,615	$ 6,184	$ 90,488	$ 44,255	$ 22,749

INCOME TAXES (Effective Income

INCOME TAXES (Effective Income Tax Rate Reconciliation) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Federal income tax statutory rate	35.00%	35.00%	35.00%
Increase (decrease) in tax rate due to:
Tax-exempt interest	(2.60%)	(2.60%)	(3.90%)
Investment in life insurance	(1.10%)	(1.20%)	(1.30%)
State income taxes, net of federal tax offset	2.00%	2.20%	1.10%
Tax credits	(0.60%)	(0.80%)	(1.60%)
Merger and acquisition costs	0.00%	0.00%	1.90%
Increase in federal statutory income tax rate due to 2017 Tax Cuts and Jobs Act	28.20%
Other	(1.10%)	1.50%	2.30%
Effective income tax rate	59.80%	34.10%	33.50%

INCOME TAXES (Schedule of Net D

INCOME TAXES (Schedule of Net Deferred Tax Asset ) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Loan loss and REO	$ 22,294	$ 36,719
Deferred compensation	13,045	23,189
Net operating loss carryforward	43,721	82,714
Federal and state tax credits	7,614	7,711
State net operating losses	6,706	7,396
Deferred Tax Asset, Loan Discount	4,736	9,696
Other	4,326	6,217
Total deferred tax assets	102,442	173,642
Deferred tax liabilities:
Depreciation	(1,343)	(2,218)
Deferred loan fees, servicing rights and loan origination costs	9,564	13,291
Intangibles	(5,690)	(11,178)
Financial instruments accounted for under fair value accounting	(9,702)	(16,186)
Other	(325)	(880)
Total deferred tax liabilities	(26,624)	(43,753)
Deferred income tax asset	75,818	129,889
Valuation allowance	4,391	2,195
Deferred tax asset, net	$ 71,427	$ 127,694

INCOME TAXES (Textuals) (Detail

INCOME TAXES (Textuals) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Operating loss carryforward, amount expected to be utilized on an annual basis	$ 6,900
Valuation Allowance, Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Valuation Allowance	4,200
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	208,200	$ 236,300
Operating loss carryforward, amount expected to be utilized on an annual basis	21,500
Tax basis bad debt reserves for which no income tax liability has been booked	5,400
Unrecognized deferred tax liability related to bad debt reserves	1,900
Domestic Tax Authority [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Federal and state tax credit carryforwards	3,400	3,300
Domestic Tax Authority [Member] | Alternative Minimum Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Federal and state tax credit carryforwards	4,200	4,200
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	94,600	$ 145,800
Operating loss carryforwards, valuation allowance	200
Operating loss carryforward, amount expected to be utilized on an annual basis, valuation allowance	200
State and Local Jurisdiction [Member] | Alternative Minimum Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Federal and state tax credit carryforwards	$ 0

INCOME TAXES Affordable Housing

INCOME TAXES Affordable Housing Tax Credit Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Amortization Method Qualified Affordable Housing Project Investments	$ 7,311	$ 4,654
Qualified Affordable Housing Project Investments, Commitment	4,417	665
Affordable Housing Tax Credits and Other Tax Benefits, Amount	1,140	1,136
Amortization Method Qualified Affordable Housing Project Investments, Amortization	$ 1,144	$ 672

EMPLOYEE BENEFIT PLANS (Details

EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined contribution plan expense	$ 4,800	$ 4,600	$ 2,800
Defined contribution plan, employer matching contribution percent	4.00%
Deferred compensation liability	$ 41,039	40,074
Carrying value of shares held in trust for stock related compensation plans	7,351	7,283
Cash surrender value of bank-owned life insurance policies	162,700	158,900
Supplemental Retirement and Salary Contribution Plans [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation plans expense	3,500	2,700	$ 1,300
Deferred compensation liability	38,600	38,300
Deferred Compensation Plans and Rabbi Trusts [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability	9,900	9,000
Carrying value of shares held in trust for stock related compensation plans	$ 7,400	$ 7,300

STOCK-BASED COMPENSATION PLAN86

STOCK-BASED COMPENSATION PLANS (Restricted Stock and Restricted Stock Units Activity) (Details) - Restricted Stock and Restricted Stock Units [Member] - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unvested Shares: [Roll Forward]
Unvested, Beginning Balance	290,719	231,562	195,106
Granted	153,777	177,775	155,183
Vested	(103,259)	(104,297)	(109,416)
Forfeited	(39,160)	(14,321)	(9,311)
Unvested, Ending Balance	302,077	290,719	231,562
Weighted Average Grant-Date Fair Value (in dollars per share):
Unvested, Beginning Balance	$ 42.26	$ 42.33	$ 32.83
Granted	55.86	41.74	45.59
Vested	43.81	41.47	30.28
Forfeited	39.83	42.54	39.07
Unvested, Ending Balance	$ 48.97	$ 42.26	$ 42.33

STOCK-BASED COMPENSATION PLAN87

STOCK-BASED COMPENSATION PLANS (Textuals) (Details) - USD ($) $ in Millions	12 Months Ended			44 Months Ended	68 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2017
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 6	$ 4.5	$ 3.5
Unrecognized compensation expense	$ 8			$ 8	$ 8
Unrecognized compensation expense, period for recognition	31 months
2012 Restricted Stock and Incentive Bonus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	300,000			300,000	300,000
2012 Restricted Stock and Incentive Bonus Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted in period					270,699
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					263,400
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	7,299			7,299	7,299
Award vesting period	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	900,000			900,000	900,000
2014 Omnibus Incentive Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted in period				371,342
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period				91,117
2014 Omnibus Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted in period				34,975
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period				20,422

PREFERRED STOCK AND RELATED W88

PREFERRED STOCK AND RELATED WARRANT (Details) - U.S. Treasury Capital Purchase Program [Member] $ / shares in Units, $ in Millions	Nov. 21, 2008USD ($)$ / sharesshares
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued | shares	124,000
Preferred stock, liquidation value per share	$ 1,000
Preferred stock aggregate liquidation preference | $	$ 124
Common Stock [Member] | Warrant [Member]
Class of Stock [Line Items]
U.S. Treasury warrants, term (in years)	10 years
Warrant, option to purchase common stock (in shares) | shares	243,998
Common stock, par value per share	$ 0.01
U.S. Treasury warrants, exercise price per share	$ 76.23
U.S. Treasury warrants, aggregate exercise price | $	$ 18.6

REGULATORY CAPITAL REQUIREMEN89

REGULATORY CAPITAL REQUIREMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Total capital to risk-weighted assets:
Actual	$ 1,214,631	$ 1,214,913
Actual, Ratio	13.81%	13.40%
Minimum for Capital Adequacy Purposes	$ 703,508	$ 725,566
Minimum for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 879,385	$ 906,957
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 capital to risk-weighted assets:
Actual	$ 1,123,154	$ 1,125,267
Actual, Ratio	12.77%	12.41%
Minimum for Capital Adequacy Purposes	$ 527,631	$ 544,174
Minimum for Capital Adequacy Purposes, Ratio	6.00%	6.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 527,631	$ 544,174
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	6.00%	6.00%
Common Equity Tier One Capital	$ 994,080
Common Equity Tier One Capital Ratio	11.30%
Tier 1 common equity to risk-weighted assets:
Actual		$ 1,014,994
Actual, Ratio		11.19%
Common Equity Tier One Capital Required for Capital Adequacy	$ 395,723	$ 408,131
Minimum for Capital Adequacy Purposes, Ratio	4.50%	4.50%
Tier 1 leverage capital to average assets:
Actual	$ 1,123,154	$ 1,125,267
Actual, Ratio	11.34%	11.83%
Minimum for Capital Adequacy Purposes	$ 396,313	$ 380,519
Minimum for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Banner Bank [Member]
Total capital to risk-weighted assets:
Actual	$ 1,102,195	$ 1,043,837
Actual, Ratio	12.83%	11.76%
Minimum for Capital Adequacy Purposes	$ 687,266	$ 709,882
Minimum for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 859,083	$ 887,352
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 capital to risk-weighted assets:
Actual	$ 1,013,079	$ 956,298
Actual, Ratio	11.79%	10.78%
Minimum for Capital Adequacy Purposes	$ 515,450	$ 532,411
Minimum for Capital Adequacy Purposes, Ratio	6.00%	6.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 687,266	$ 709,882
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%
Common Equity Tier One Capital	$ 1,013,079
Common Equity Tier One Capital Ratio	11.79%
Tier 1 common equity to risk-weighted assets:
Actual		$ 956,298
Actual, Ratio		10.78%
Common Equity Tier One Capital Required for Capital Adequacy	$ 386,587	$ 399,308
Minimum for Capital Adequacy Purposes, Ratio	4.50%	4.50%
Common Equity Tier One Capital Required to be Well-Capitalized	$ 558,404	$ 576,779
Tier One Risk Based Common Equity Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier 1 leverage capital to average assets:
Actual	$ 1,013,079	$ 956,298
Actual, Ratio	10.53%	10.34%
Minimum for Capital Adequacy Purposes	$ 384,920	$ 369,936
Minimum for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 481,150	$ 462,420
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%
Islanders Bank
Total capital to risk-weighted assets:
Actual	$ 32,122	$ 35,207
Actual, Ratio	16.39%	18.43%
Minimum for Capital Adequacy Purposes	$ 15,681	$ 15,281
Minimum for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 19,602	$ 19,101
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier 1 capital to risk-weighted assets:
Actual	$ 29,761	$ 33,099
Actual, Ratio	15.18%	17.33%
Minimum for Capital Adequacy Purposes	$ 11,761	$ 11,461
Minimum for Capital Adequacy Purposes, Ratio	6.00%	6.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 15,681	$ 15,281
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%
Common Equity Tier One Capital	$ 29,761
Common Equity Tier One Capital Ratio	15.18%
Tier 1 common equity to risk-weighted assets:
Actual		$ 33,099
Actual, Ratio		17.33%
Common Equity Tier One Capital Required for Capital Adequacy	$ 8,821	$ 8,598
Minimum for Capital Adequacy Purposes, Ratio	4.50%	4.50%
Common Equity Tier One Capital Required to be Well-Capitalized	$ 12,741	$ 12,416
Tier One Risk Based Common Equity Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier 1 leverage capital to average assets:
Actual	$ 29,761	$ 33,099
Actual, Ratio	10.65%	12.72%
Minimum for Capital Adequacy Purposes	$ 11,183	$ 10,405
Minimum for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions	$ 13,979	$ 13,006
Minimum to be Categorized as Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%

GOODWILL, OTHER INTANGIBLE AS90

GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS (Details)	12 Months Ended
	Dec. 31, 2017
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	3 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years

GOODWILL, OTHER INTANGIBLE AS91

GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS (Finite-Lived Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Goodwill [Line Items]
Goodwill, beginning of period	$ 244,583	$ 247,738		$ 0
Intangible Assets, Net (Including Goodwill), beginning of period	274,745	285,210		2,831
Goodwill, Acquired During Period				247,738
Acquired Intangible Assets (Including Goodwill)				285,909
Amortization	(6,431)	(7,310)		(3,230)
Goodwill, Other Changes	(1,924)	(3,155)
Finite-Lived Intangible Assets, Other Changes	(1,076)	0	[1]	(300)
Intangible Assets (including Goodwill), Other Changes	(3,000)	(3,155)	[1]	(300)
Goodwill, end of period	242,659	244,583		247,738
Balance, end of period	22,378
Intangible Assets, Net (Including Goodwill), end of period	265,314	274,745		285,210
Core Deposit Intangibles [Member]
Goodwill [Line Items]
Balance, beginning of period	29,701	36,762		2,831
Additions through acquisition				37,395
Amortization	(6,247)	(7,061)		(3,164)
Balance, end of period	22,378	29,701		36,762
Other Intangible Assets [Member]
Goodwill [Line Items]
Balance, beginning of period	461	710
Additions through acquisition				776
Amortization	(184)	(249)		(66)
Balance, end of period	$ 277	$ 461		$ 710
[1]	Acquired Goodwill and CDI were adjusted for the sale of the Utah branches in 2017 and acquired CDI was adjusted for a branch that was subsequently sold during 2015.

GOODWILL, OTHER INTANGIBLE AS92

GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS (Estimated Annual Amortization Expense) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Year Ended December 31, 2017	$ 5,372
Year Ended December 31, 2018	4,683
Year Ended December 31, 2019	3,996
Year Ended December 31, 2020	3,307
Thereafter	5,020
Net carrying amount	22,378
Core Deposit Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Net carrying amount	$ 22,378	$ 29,701	$ 36,762	$ 2,831

GOODWILL, OTHER INTANGIBLE AS93

GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS (Mortgage Servicing Rights) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Servicing Asset at Amortized Value, Balance [Roll Forward]
Servicing Asset at Amortized Cost, Additions, Acquisitions		$ 0		$ 0		$ 2,172
Servicing Asset at Amortized Cost, Additions		94		0		0
Serviced Loans
Servicing Assets at Amortized Value [Line Items]
Loans serviced for others		2,190,000		2,050,000
Mortgage Servicing Rights
Servicing Assets at Amortized Value [Line Items]
Custodial accounts		10,200		10,300
Servicing Asset at Amortized Value, Balance [Roll Forward]
Balance, beginning of the year		15,249	[1]	13,295	[1]	9,030
Amounts capitalized		3,361		5,965		5,313
Amortization	[2]	(3,966)		(4,011)		(3,220)
Valuation adjustments in the period		0
Balance, end of the year	[1]	14,738		$ 15,249		13,295
Valuation Allowance		$ 0				$ 0
[1]	no valuation allowance
[2]	Amortization of mortgage servicing rights is recorded as a reduction of loan servicing income and any unamortized balance is fully written off if the loan repays in full.

FAIR VALUE OF FINANCIAL INSTR94

FAIR VALUE OF FINANCIAL INSTRUMENTS (Assets and Liabilities Measured at Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value	$ 22,318	$ 24,568
Securities—available-for-sale	919,485	806,428
Held-to-maturity Securities, Fair Value	262,188	270,528
Loans receivable held for sale	32,400	9,600
Advances from FHLB at fair value	202	54,216
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	261,200	247,719
Trading Securities, Fair Value	22,318	24,568
Securities—available-for-sale	919,485	806,428
Held-to-maturity Securities, Fair Value	256,793	263,997
Held to Maturity Securities, Fair Value, Level 3	3,478	3,876
Loans receivable held for sale	40,725	246,353
Loans receivable	7,598,884	7,451,148
FHLB stock	10,334	12,506
Bank-owned life insurance	162,668	158,936
MSRs	14,738	15,249
Deposits, Demand NOW and Money Market Accounts, Fair Value Disclosure	5,658,994	5,552,690
Deposits, Savings, Fair Value Disclosure	1,557,500	1,523,391
Deposits, Certificates of Deposit, Fair Value Disclosure	966,937	1,045,333
Advances from FHLB at fair value	202	54,216
Junior subordinated debentures net of unamortized deferred issuance costs at fair value	98,707	95,200
Other borrowings	95,860	105,685
Reported Value Measurement [Member] | Interest Rate Forward Sales Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	523	482
Derivative liabilities	201	289
Reported Value Measurement [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	5,083	8,330
Derivative liabilities	5,083	8,330
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	261,200	247,719
Trading Securities, Fair Value	22,318	24,568
Securities—available-for-sale	919,485	806,428
Held-to-maturity Securities, Fair Value	258,710	266,652
Held to Maturity Securities, Fair Value, Level 3	3,478	3,876
Loans receivable held for sale	40,923	246,815
Loans receivable	7,445,990	7,337,608
FHLB stock	10,334	12,506
Bank-owned life insurance	162,668	158,936
MSRs	19,835	16,740
Deposits, Demand NOW and Money Market Accounts, Fair Value Disclosure	5,658,994	5,552,690
Deposits, Savings, Fair Value Disclosure	1,557,500	1,523,391
Deposits, Certificates of Deposit, Fair Value Disclosure	947,517	1,028,866
Advances from FHLB at fair value	202	54,216
Junior subordinated debentures net of unamortized deferred issuance costs at fair value	98,707	95,200
Other borrowings	95,860	105,685
Estimate of Fair Value Measurement [Member] | Interest Rate Forward Sales Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	523	482
Derivative liabilities	201	289
Estimate of Fair Value Measurement [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	5,083	8,330
Derivative liabilities	$ 5,083	$ 8,330

FAIR VALUE OF FINANCIAL INSTR95

FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value By Balance Sheet Location) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Trading Securities, Fair Value	$ 22,318	$ 24,568
Securities—available-for-sale	919,485	806,428
Loans Held-for-sale, Fair Value	32,400	9,600
Liabilities:
Advances from FHLB at fair value	202	54,216
Fair Value, Measurements, Recurring [Member]
Assets:
Trading Securities, Fair Value	22,318	24,568
Securities—available-for-sale	919,485	806,428
Assets, Fair Value Disclosure	979,801	849,408
Liabilities:
Advances from FHLB at fair value	202	54,216
Junior subordinated debentures at fair value	98,707	95,200
Financial and Nonfinancial Liabilities, Fair Value Disclosure	104,193	158,035
Fair Value, Measurements, Recurring [Member] | Interest Rate Contract [Member]
Assets:
Derivatives	523	8,330
Liabilities:
Derivatives	201	8,330
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	5,083	482
Liabilities:
Derivatives	5,083	289
Fair Value, Measurements, Recurring [Member] | U.S. Government and agency obligations
Assets:
Trading Securities, Fair Value		1,326
Securities—available-for-sale	72,466	56,978
Fair Value, Measurements, Recurring [Member] | Municipal bonds
Assets:
Trading Securities, Fair Value	100	335
Securities—available-for-sale	68,733	109,853
Fair Value, Measurements, Recurring [Member] | Corporate bonds
Assets:
Securities—available-for-sale	5,393	10,283
Fair Value, Measurements, Recurring [Member] | TPS and TRUP CDOs [Member]
Assets:
Trading Securities, Fair Value	22,058	21,143
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities, Other [Member]
Assets:
Trading Securities, Fair Value		1,641
Securities—available-for-sale	739,557	594,712
Fair Value, Measurements, Recurring [Member] | Equity securities
Assets:
Trading Securities, Fair Value	160	123
Securities—available-for-sale	5,578	5,609
Fair Value, Measurements, Recurring [Member] | Asset-backed securities
Assets:
Securities—available-for-sale	27,758	28,993
Fair Value, Measurements, Recurring [Member] | Loans [Member]
Assets:
Loans Held-for-sale, Fair Value	32,392	9,600
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
Trading Securities, Fair Value	0	0
Securities—available-for-sale	0	0
Assets, Fair Value Disclosure	0	0
Liabilities:
Advances from FHLB at fair value	0	0
Junior subordinated debentures at fair value	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Interest Rate Contract [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Government and agency obligations
Assets:
Trading Securities, Fair Value		0
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Municipal bonds
Assets:
Trading Securities, Fair Value	0	0
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate bonds
Assets:
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | TPS and TRUP CDOs [Member]
Assets:
Trading Securities, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Mortgage Backed Securities, Other [Member]
Assets:
Trading Securities, Fair Value		0
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Equity securities
Assets:
Trading Securities, Fair Value	0	0
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Asset-backed securities
Assets:
Securities—available-for-sale	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Loans [Member]
Assets:
Loans Held-for-sale, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Trading Securities, Fair Value	260	3,425
Securities—available-for-sale	919,485	806,428
Assets, Fair Value Disclosure	957,743	828,265
Liabilities:
Advances from FHLB at fair value	202	54,216
Junior subordinated debentures at fair value	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	5,486	62,835
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest Rate Contract [Member]
Assets:
Derivatives	523	8,330
Liabilities:
Derivatives	201	8,330
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	5,083	482
Liabilities:
Derivatives	5,083	289
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Government and agency obligations
Assets:
Trading Securities, Fair Value		1,326
Securities—available-for-sale	72,466	56,978
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Municipal bonds
Assets:
Trading Securities, Fair Value	100	335
Securities—available-for-sale	68,733	109,853
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate bonds
Assets:
Securities—available-for-sale	5,393	10,283
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | TPS and TRUP CDOs [Member]
Assets:
Trading Securities, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Mortgage Backed Securities, Other [Member]
Assets:
Trading Securities, Fair Value		1,641
Securities—available-for-sale	739,557	594,712
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Equity securities
Assets:
Trading Securities, Fair Value	160	123
Securities—available-for-sale	5,578	5,609
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Asset-backed securities
Assets:
Securities—available-for-sale	27,758	28,993
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Loans [Member]
Assets:
Loans Held-for-sale, Fair Value	32,392	9,600
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Assets:
Trading Securities, Fair Value	22,058	21,143
Securities—available-for-sale	0	0
Assets, Fair Value Disclosure	22,058	21,143
Liabilities:
Advances from FHLB at fair value	0	0
Junior subordinated debentures at fair value	98,707	95,200
Financial and Nonfinancial Liabilities, Fair Value Disclosure	98,707	95,200
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Interest Rate Contract [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. Government and agency obligations
Assets:
Trading Securities, Fair Value		0
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Municipal bonds
Assets:
Trading Securities, Fair Value	0	0
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate bonds
Assets:
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | TPS and TRUP CDOs [Member]
Assets:
Trading Securities, Fair Value	22,058	21,143
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Mortgage Backed Securities, Other [Member]
Assets:
Trading Securities, Fair Value		0
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Equity securities
Assets:
Trading Securities, Fair Value	0	0
Securities—available-for-sale	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Asset-backed securities
Assets:
Securities—available-for-sale	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Loans [Member]
Assets:
Loans Held-for-sale, Fair Value	$ 0	$ 0

FAIR VALUE OF FINANCIAL INSTR96

FAIR VALUE OF FINANCIAL INSTRUMENTS (Asset Inputs) (Details) - Weighted Average [Member] - Level 3 [Member] - Income Approach Valuation Technique [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
TPS Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	6.69%	6.00%
Junior Subordinated Debt [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	6.69%	6.00%

FAIR VALUE OF FINANCIAL INSTR97

FAIR VALUE OF FINANCIAL INSTRUMENTS (Unobservable Inputs Rollforward) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Borrowings - Junior Subordinated Debentures [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 95,200	$ 92,480
Liabilities (gains) losses	3,507	2,720
Purchases, issuances and settlements		0
Ending balance	98,707	95,200
TPS and TRUP CDOs [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	21,143	18,699
Assets gains (losses)	915	719
Purchases, issuances and settlements		1,725
Ending balance	$ 22,058	$ 21,143

FAIR VALUE OF FINANCIAL INSTR98

FAIR VALUE OF FINANCIAL INSTRUMENTS (Assets Measured on Nonrecurring Basis) (Details) - Nonrecurring [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 6,535
REO	360	$ 11,081
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0
REO	0	0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0
REO	0	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	(3,108)	(1,058)
Impaired loans	6,535
REO	360	11,081
Impaired Loans [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	(2,852)	(182)
Real Estate [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	$ (256)	$ (876)

BANNER CORPORATION (PARENT CO99

BANNER CORPORATION (PARENT COMPANY ONLY) (Statements of Financial Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Other assets	$ 53,177	$ 53,955
Total assets	9,763,209	9,793,668
LIABILITIES AND SHAREHOLDERS’ EQUITY
Junior subordinated debentures at fair value	98,707	95,200
Shareholders’ equity	1,272,626	1,305,710	$ 1,300,059	$ 582,888
Total liabilities and stockholders' equity	9,763,209	9,793,668
Banner Corporation
ASSETS
Cash	44,887	86,268
Investment in trust equities	4,212	4,212
Investment in subsidiaries	1,329,165	1,307,475
Other assets	3,072	13,784
Total assets	1,381,336	1,411,739
LIABILITIES AND SHAREHOLDERS’ EQUITY
Miscellaneous liabilities	9,607	8,990
Deferred tax liability	396	1,839
Junior subordinated debentures at fair value	98,707	95,200
Shareholders’ equity	1,272,626	1,305,710
Total liabilities and stockholders' equity	$ 1,381,336	$ 1,411,739

BANNER CORPORATION (PARENT C100

BANNER CORPORATION (PARENT COMPANY ONLY) (Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INTEREST INCOME:
Interest-bearing deposits	$ 98,264	$ 100,210	$ 99,706	$ 94,854	$ 97,171	$ 93,708	$ 93,148	$ 91,043	$ 92,099	$ 52,188	$ 51,457	$ 46,536	$ 393,034	$ 375,069	$ 242,279
OTHER INCOME (EXPENSE):
Other income													8,985	6,001	2,821
Other expenses													(27,142)	(30,131)	(17,565)
Income before provision for income taxes	41,437	35,960	38,245	35,621	34,747	36,128	31,798	26,968	10,201	19,589	19,864	18,318	151,264	129,640	67,971
PROVISION FOR INCOME TAXES	54,985	10,883	12,791	11,828	11,943	12,277	10,841	9,194	3,308	6,642	6,615	6,184	90,488	44,255	22,749
NET INCOME	$ (13,548)	$ 25,077	$ 25,454	$ 23,793	$ 22,804	$ 23,851	$ 20,957	$ 17,774	$ 6,893	$ 12,947	$ 13,249	$ 12,134	60,776	85,385	45,222
Banner Corporation
INTEREST INCOME:
Interest-bearing deposits													62	127	122
OTHER INCOME (EXPENSE):
Dividend income from subsidiaries													40,570	50,971	170,260
Equity in undistributed (distributions in excess of) income of subsidiaries													27,477	40,852	(116,120)
Other income													53	60	69
Net change in valuation of financial instruments carried at fair value													(3,507)	(2,720)	(2,714)
Interest on other borrowings													(4,752)	(4,040)	(3,247)
Other expenses													(3,291)	(3,450)	(7,175)
Income before provision for income taxes													56,612	81,800	41,195
PROVISION FOR INCOME TAXES													(4,164)	(3,585)	(4,027)
NET INCOME													$ 60,776	$ 85,385	$ 45,222

BANNER CORPORATION (PARENT C101

BANNER CORPORATION (PARENT COMPANY ONLY) (Statements of Cash Flows) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES:
Net income	$ (13,548)	$ 25,077	$ 25,454	$ 23,793	$ 22,804	$ 23,851	$ 20,957	$ 17,774	$ 6,893	$ 12,947	$ 13,249	$ 12,134	$ 60,776	$ 85,385	$ 45,222
Adjustments to reconcile net income to net cash provided from (used by) operating activities:
Decrease in deferred taxes													56,267	7,883	(3,906)
Net change in valuation of financial instruments carried at fair value													2,844	2,620	813
Equity-based compensation													5,965	4,305	4,334
Decrease (increase) in other assets													2,546	3,759	(7,319)
Increase (decrease) in other liabilities													(179)	(6,664)	4,090
Net cash provided from (used by) operating activities													346,702	(75,818)	16,217
INVESTING ACTIVITIES:
Net cash (used by) provided from investing activities													(393,287)	146,447	15,059
FINANCING ACTIVITIES:
Issuance of stock for shareholder reinvestment program													0	0	34
Payments Related to Tax Withholding for Share-based Compensation													(1,630)	(870)	(848)
Payments for Repurchase of Common Stock													31,045	50,772	0
Cash dividends paid													(65,759)	(28,282)	(17,170)
Net cash provided from (used by) financing activities													60,066	(84,827)	104,569
NET CHANGE IN CASH AND CASH EQUIVALENTS													13,481	(14,198)	135,845
CASH AND DUE FROM BANKS, BEGINNING OF YEAR				177,083									177,083
CASH AND DUE FROM BANKS, END OF YEAR	199,624				177,083								199,624	177,083
Banner Corporation
OPERATING ACTIVITIES:
Net income													60,776	85,385	45,222
Adjustments to reconcile net income to net cash provided from (used by) operating activities:
Distributions in excess of (equity in undistributed) income of subsidiaries													(27,477)	(40,852)	116,120
Decrease in deferred taxes													(1,442)	(702)	(1,398)
Net change in valuation of financial instruments carried at fair value													3,507	2,720	2,714
Equity-based compensation													5,965	4,305	4,334
Decrease (increase) in other assets													10,684	7,332	(10,655)
Increase (decrease) in other liabilities													69	(202)	433
Net cash provided from (used by) operating activities													52,082	57,986	156,770
INVESTING ACTIVITIES:
Funds transferred to deferred compensation trust													(29)	(26)	(26)
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries													5,000	50,000	0
Acquisitions													0	0	132,652
Net cash (used by) provided from investing activities													4,971	49,974	(132,678)
FINANCING ACTIVITIES:
Issuance of stock for shareholder reinvestment program													0	0	34
Payments Related to Tax Withholding for Share-based Compensation													(1,630)	(870)	(848)
Payments for Repurchase of Common Stock													31,045	50,772	0
Cash dividends paid													(65,759)	(28,282)	(17,170)
Net cash provided from (used by) financing activities													(98,434)	(79,924)	(17,984)
NET CHANGE IN CASH AND CASH EQUIVALENTS													(41,381)	28,036	6,108
CASH AND DUE FROM BANKS, BEGINNING OF YEAR				$ 86,268				$ 58,232				$ 52,124	86,268	58,232	52,124
CASH AND DUE FROM BANKS, END OF YEAR	$ 44,887				$ 86,268				$ 58,232				$ 44,887	$ 86,268	$ 58,232

STOCK REPURCHASES (Details)

STOCK REPURCHASES (Details) - Common Stock [Member] - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017	Apr. 04, 2016
Stock repurchases
Stock surrendered during period, shares	29,579	25,628
Banner Corporation Share Repurchase Plan [Member]
Stock repurchases
Stock Repurchase Program, Number of Shares Authorized to be Repurchased				1,711,540
Stock Repurchase Program, Number of Shares Authorized to be Repurchased, Percent of Total Outstanding				5.00%
Stock trading plan, number of shares to be repurchased	1,300,000
Stock Repurchased During Period, Shares		1,145,250
Banner Corporation 2017 Share Repurchase Authorization [Member]
Stock repurchases
Stock Repurchase Program, Number of Shares Authorized to be Repurchased			1,658,245
Stock Repurchase Program, Number of Shares Authorized to be Repurchased, Percent of Total Outstanding			0.00%
Stock Repurchased During Period, Shares	545,166
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased	1,113,079

CALCULATION OF EARNINGS PER 103

CALCULATION OF EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
NET INCOME AVAILABLE TO COMMON SHAREHOLDERS													$ 60,776	$ 85,385	$ 45,222
Weighted average number of common shares outstanding
Basic weighted average shares outstanding (in shares)													32,888,007	33,820,148	23,801,373
Diluted weighted shares outstanding (in shares)													32,986,707	33,853,511	23,866,621
Earnings per common share
Basic (in dollars per share)	$ (0.41)	$ 0.76	$ 0.77	$ 0.72	$ 0.69	$ 0.70	$ 0.62	$ 0.52	$ 0.20	$ 0.62	$ 0.64	$ 0.61	$ 1.85	$ 2.52	$ 1.90
Diluted (in dollars per share)	$ (0.41)	$ 0.76	$ 0.77	$ 0.72	$ 0.69	$ 0.70	$ 0.61	$ 0.52	$ 0.20	$ 0.62	$ 0.64	$ 0.61	$ 1.84	$ 2.52	$ 1.89

CALCULATION OF EARNINGS PER 104

CALCULATION OF EARNINGS PER COMMON SHARE (Textuals) (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Unvested restricted stock shares included in computation of diluted earnings per share	302,077	290,719	231,562
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	5,000
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	243,998

SELECTED QUARTERLY FINANCIAL105

SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Information [Abstract]
Interest income	$ 103,475	$ 105,278	$ 104,436	$ 99,096	$ 101,007	$ 97,849	$ 97,321	$ 95,301	$ 96,495	$ 54,793	$ 54,076	$ 49,069	$ 412,284	$ 391,477	$ 254,433
Interest expense	5,211	5,068	4,730	4,242	3,836	4,141	4,173	4,258	4,396	2,605	2,619	2,533	19,250	16,408	12,154
Interest-bearing deposits	98,264	100,210	99,706	94,854	97,171	93,708	93,148	91,043	92,099	52,188	51,457	46,536	393,034	375,069	242,279
Provision for loan losses	2,000	2,000	2,000	2,000	2,030	2,000	2,000	0	0	0	0	0	8,000	6,030	0
Net interest income	96,264	98,210	97,706	92,854	95,141	91,708	91,148	91,043	92,099	52,188	51,457	46,536	385,034	369,039	242,279
Non-interest income	29,882	20,339	22,469	20,845	19,463	23,512	20,537	19,959	18,356	14,098	16,141	13,696	93,535	83,470	62,292
Other operating expenses	84,709	82,589	81,930	78,078	79,857	79,092	79,887	84,034	100,254	46,697	47,734	41,914	327,305	322,869	236,600
Income before provision for income taxes	41,437	35,960	38,245	35,621	34,747	36,128	31,798	26,968	10,201	19,589	19,864	18,318	151,264	129,640	67,971
PROVISION FOR INCOME TAXES	54,985	10,883	12,791	11,828	11,943	12,277	10,841	9,194	3,308	6,642	6,615	6,184	90,488	44,255	22,749
NET INCOME	$ (13,548)	$ 25,077	$ 25,454	$ 23,793	$ 22,804	$ 23,851	$ 20,957	$ 17,774	$ 6,893	$ 12,947	$ 13,249	$ 12,134	$ 60,776	$ 85,385	$ 45,222
Basic earnings (loss) per share (in dollars per share)	$ (0.41)	$ 0.76	$ 0.77	$ 0.72	$ 0.69	$ 0.70	$ 0.62	$ 0.52	$ 0.20	$ 0.62	$ 0.64	$ 0.61	$ 1.85	$ 2.52	$ 1.90
Diluted earnings (loss) per share (in dollars per share)	(0.41)	0.76	0.77	0.72	0.69	0.70	0.61	0.52	0.20	0.62	0.64	0.61	1.84	2.52	1.89
Cumulative dividends declared per common share (in dollars per share)	$ 0.25	$ 0.25	$ 1.25	$ 0.25	$ 0.23	$ 0.23	$ 0.21	$ 0.21	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 2	$ 0.88	$ 0.72

COMMITMENTS AND CONTINGENCIE106

COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Reserve for Unfunded Loan Commitments	$ 2,400	$ 3,600
Mortgage loan applications, day Interest rate is locked	45 days
Minimum [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Mortgage loan applications, day Interest rate is locked	30 days
Maximum [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Mortgage loan applications, day Interest rate is locked	60 days
Commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract or Notional Amount	$ 2,300,593	2,204,795
Standby letters of credit and financial guarantees
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract or Notional Amount	14,579	17,694
Commitments to originate loans
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract or Notional Amount	56,030	69,833
Risk Participation Agreement [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract or Notional Amount	11,451	7,488
Commitments to originate loans held for sale
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract or Notional Amount	43,502	69,487
Commitments to sell loans secured by one- to four-family residential properties
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract or Notional Amount	33,069	36,907
Loss on Contract Termination for Default	0
Commitments to sell securities related to mortgage banking activities
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract or Notional Amount	$ 57,000	$ 44,000

DERIVATIVES AND HEDGING DERI107

DERIVATIVES AND HEDGING DERIVATIVES AND HEDGING (Derivatives Designated as Hedging, by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 5,083	$ 8,330
Derivative Liability, Fair Value, Gross Liability		5,083	8,330
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		5,083	8,330
Derivative Liability, Fair Value, Gross Liability		5,083	8,330
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount		4,350	5,855
Derivative Liability, Notional Amount		4,350	5,855
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Loans Receivable [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	447	660
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[2]	$ 447	$ 660
[1]	Included in Loans Receivable on the Consolidated Statements of Financial Condition.
[2]	Included in Other Liabilities on the Consolidated Statements of Financial Condition.

DERIVATIVES AND HEDGING DERI108

DERIVATIVES AND HEDGING DERIVATIVES AND HEDGING (Derivatives Not Designated as Hedging, by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 5,083	$ 8,330
Derivative Liability, Fair Value, Gross Liability		5,083	8,330
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		5,083	8,330
Derivative Liability, Fair Value, Gross Liability		5,083	8,330
Interest Rate Swap [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount		282,300
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount		357,855	423,424
Derivative Liability, Notional Amount		345,810	346,842
Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	5,159	8,152
Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[2]	4,837	7,959
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount		285,047	309,936
Derivative Liability, Notional Amount		285,047	309,936
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Loans Receivable [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		499	822
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	4,636	7,670
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[2]	4,636	7,670
Not Designated as Hedging Instrument [Member] | Mortgage Loan Commitments [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount		29,739	42,296
Derivative Liability, Notional Amount		13,763	27,191
Not Designated as Hedging Instrument [Member] | Mortgage Loan Commitments [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	225	30
Not Designated as Hedging Instrument [Member] | Mortgage Loan Commitments [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[2]	153	174
Not Designated as Hedging Instrument [Member] | Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount		43,069	71,192
Derivative Liability, Notional Amount		47,000	9,715
Not Designated as Hedging Instrument [Member] | Forward Contracts [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	298	452
Not Designated as Hedging Instrument [Member] | Forward Contracts [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[2]	$ 48	$ 115
[1]	Included in Other Assets on the Consolidated Statements of Financial Condition, with the exception of those interest rate swaps from prior to 2009 that were not designated in hedge relationships (with a fair value of $499,000 at December 31, 2017 and $822,000 at December 31, 2016), which are included in Loans Receivable.
[2]	Included in Other Liabilities on the Consolidated Statements of Financial Condition.

DERIVATIVES AND HEDGING DERI109

DERIVATIVES AND HEDGING DERIVATIVES AND HEDGING (Gain (Loss) On Derivatives Not Designated in Hedging Relationship) (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ (296)	$ (52)
Mortgage Loan Commitments [Member] | Mortgage Banking Operations [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	195	(348)
Forward Sales Contracts [Member] | Mortgage Banking Operations [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ (491)	$ 296

DERIVATIVES AND HEDGING DERI110

DERIVATIVES AND HEDGING DERIVATIVES AND HEDGING (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative, Net Liability Position, Aggregate Fair Value	$ 3.7	$ 7.6
Collateral Already Posted, Aggregate Fair Value	$ 16.9	$ 29.3

DERIVATIVES AND HEDGING DERI111

DERIVATIVES AND HEDGING DERIVATIVES AND HEDGING (Derivative Offsetting) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 5,083	$ 8,330
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	5,083	8,330
Derivative, Collateral, Obligation to Return Securities	(656)	(362)
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	4,427	7,968
Derivative Liability, Fair Value, Gross Liability	5,083	8,330
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	5,083	8,330
Derivative, Collateral, Right to Reclaim Securities	(656)	(362)
Derivative, Collateral, Right to Reclaim Cash	(3,467)	(7,557)
Derivative Liability, Fair Value, Amount Offset Against Collateral	960	411
Interest Rate Swap [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	5,083	8,330
Derivative Asset, Fair Value, Gross Liability	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	5,083	8,330
Derivative, Collateral, Obligation to Return Securities	(656)	(362)
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	4,427	7,968
Derivative Liability, Fair Value, Gross Liability	5,083	8,330
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	5,083	8,330
Derivative, Collateral, Right to Reclaim Securities	(656)	(362)
Derivative, Collateral, Right to Reclaim Cash	(3,467)	(7,557)
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 960	$ 411