Columbia Financial (CLBK) 10-K 29 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Mar. 29, 2019	Jun. 29, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Columbia Financial, Inc.
Entity Central Index Key	0001723596
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Small Business	false
Entity Shell Company	false
Entity Ex Transition Period	false
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period	FY
Trading Symbol	CLBK
Amendment Flag	false
Entity Common Stock, Shares Outstanding (in shares)		115,889,175
Entity Well-known Seasoned Filer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 738.2

Consolidated Statements of Fina

Consolidated Statements of Financial Condition - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 42,065	$ 65,334
Short-term investments	136	164
Total cash and cash equivalents	42,201	65,498
Securities available for sale, at fair value	1,034,758	710,570
Securities held to maturity, at amortized cost (fair value of $254,841, and $236,125 at December 31, 2018 and 2017, respectively)	262,143	239,618
Federal Home Loan Bank stock	58,938	44,664
Loans held-for-sale, at fair value	8,081	0
Loans receivable	4,979,182	4,458,648
Less: allowance for loan losses	62,342	58,178
Loans receivable, net	4,916,840	4,400,470
Accrued interest receivable	18,894	15,915
Real estate owned	92	959
Office properties and equipment, net	52,050	42,620
Bank-owned life insurance	184,488	150,521
Goodwill and intangible assets	6,085	5,997
Other assets	107,048	89,668
Total assets	6,691,618	5,766,500
Liabilities:
Deposits	4,413,873	4,263,315
Borrowings	1,189,180	929,057
Advance payments by borrowers for taxes and insurance	32,030	25,563
Accrued expenses and other liabilities	84,475	76,495
Total liabilities	5,719,558	5,294,430
Stockholders' equity:
Preferred stock, $0.01 par value. 10,000,000 shares authorized; none issued and outstanding at December 31, 2018 and 2017	0	0
Common stock, $0.01 par value. 500,000,000 shares authorized; 115,889,175 shares issued and outstanding at December 31, 2018 and none at December 31, 2017	1,159	0
Additional paid-in capital	527,037	0
Retained earnings	560,216	537,480
Accumulated other comprehensive loss	(71,897)	(65,410)
Common stock held by the Employee Stock Ownership Plan	(43,835)	0
Stock held by Rabbi Trust	(1,259)	0
Deferred compensation obligations	639	0
Total stockholders' equity	972,060	472,070
Total liabilities and stockholders' equity	$ 6,691,618	$ 5,766,500

Consolidated Statements of Fi_2

Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Securities held to maturity	$ 254,841	$ 236,125
Preferred stock, par value (in USD per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, shares issued (in shares)	115,889,175	115,889,175
Common stock, shares outstanding (in shares)	115,889,175	115,889,175

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Interest income:
Loans receivable	$ 43,043	$ 189,869	$ 164,849	$ 152,110
Securities available for sale	5,074	25,338	17,163	15,145
Securities held to maturity	382	7,147	68	0
Federal funds and interest earning deposits	103	1,175	308	205
Federal Home Loan Bank stock dividends	567	2,761	1,838	1,517
Total interest income	49,169	226,290	184,226	168,977
Interest expense:
Deposits	7,631	39,523	25,581	24,062
Borrowings	4,609	22,733	18,865	19,900
Total interest expense	12,240	62,256	44,446	43,962
Net interest income	36,929	164,034	139,780	125,015
Provision for loan losses	3,400	6,677	6,426	417
Net interest income after provision for loan losses	33,529	157,357	133,354	124,598
Non-interest income:
Bank-owned life insurance	1,089	5,208	4,936	4,370
Title insurance fees	1,017	4,297	4,163	4,198
Gain (loss) on securities transactions, net	(60)	116	(1,689)	355
Gain (loss) on sale of loans	0	618	(380)	655
(Loss) gain on sale of real estate owned	0	(56)	233	(441)
Other non-interest income	1,162	4,999	4,264	4,548
Total non-interest income	4,733	21,688	17,172	18,927
Non-interest expense:
Compensation and employee benefits	15,624	69,907	62,993	58,115
Occupancy	3,382	14,547	13,315	12,798
Federal deposit insurance premiums	414	1,893	1,652	2,381
Advertising	1,408	4,137	4,078	2,938
Professional fees	398	1,432	1,354	1,061
Data processing	595	2,600	2,244	2,143
Charitable contribution to foundation	0	34,767	3,603	347
Other non-interest expense	3,780	16,103	14,207	13,986
Total non-interest expense	25,601	145,386	103,446	93,769
Income before income tax expense	12,661	33,659	47,080	49,756
Income tax expense	8,983	10,923	16,008	16,803
Net income	3,678	$ 22,736	31,072	32,953
Basic and diluted earnings per share (in dollars per share)		$ 0.20
Weighted average shares outstanding (in shares)		111,395,723
Deposit Account
Non-interest income:
Non-interest income	960	$ 3,987	3,669	3,271
Bank Servicing
Non-interest income:
Non-interest income	$ 565	$ 2,519	$ 1,976	$ 1,971

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 3,678	$ 22,736	$ 31,072	$ 32,953
Other comprehensive (loss) income, net of tax:
Unrealized (losses) gains on securities available for sale	(3,131)	(5,778)	(11,498)	4,674
Accretion of unrealized gain on securities reclassified as held to maturity	(58)	(13)	8	0
Reclassification adjustment for gain (loss) included in net income	47	(92)	1,689	(355)
Total other comprehensive (loss) income, net of tax	(3,142)	(5,883)	(9,801)	4,319
Derivatives, net of tax:
Unrealized (loss) on swap contracts	162	(2,230)	62	0
Employee benefit plans, net of tax:
Amortization of prior service cost included in net income	(43)	(491)	(73)	(73)
Reclassification adjustment of actuarial net loss included in net income	(103)	1,996	7,593	5,864
Change in funded status of retirement obligations	(5,670)	121	7,397	(21,397)
Tax effects resulting from the adoption of ASU No. 2018-02	(10,434)	0	0	0
Total employee benefit plans, net of tax	(16,250)	1,626	14,917	(15,606)
Total other comprehensive (loss) income	(19,230)	(6,487)	5,178	(11,287)
Total comprehensive income (loss), net of tax	$ (15,552)	$ 16,249	$ 36,250	$ 21,666

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional paid-in-capital	Retained earnings	Accumulated other comprehensive loss, net of tax	Common stock held by the employee stock ownership plan	Stock held by Rabbi Trust	Deferred compensation obligations	Columbia Bank, MHC	Columbia Bank, MHCCommon stock	Columbia Bank Foundation	Columbia Bank FoundationCommon stock	Columbia Bank FoundationAdditional paid-in-capital	IPO	IPOCommon stock	IPOAdditional paid-in-capital
Balance at beginning of period at Sep. 30, 2015	$ 417,998	$ 0	$ 0	$ 458,069	$ (40,071)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,953			32,953
Other comprehensive loss	(11,287)				(11,287)
Balance at end of year at Sep. 30, 2016	439,664	0	0	491,022	(51,358)	0	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	31,072			31,072
Other comprehensive loss	5,178				5,178
Balance at end of year at Sep. 30, 2017	475,914	0	0	522,094	(46,180)	0	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	3,678			3,678
Other comprehensive loss	(19,230)
Other comprehensive loss	(7,522)				(7,522)
Balance at end of year at Dec. 31, 2017	472,070	0	0	537,480	(65,410)	0	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02	0			11,708	(11,708)
Net income	22,736			22,736
Other comprehensive loss	(6,487)				(6,487)
Issuance of common stock									$ 626	$ 626	$ 34,767	$ 35	$ 34,732	$ 491,802	$ 498	$ 491,304
Purchase of Employee Stock Ownership Plan shares	(45,428)					(45,428)
Employee Stock Ownership Plan shares committed to be released	2,594		1,001			1,593
Funding of deferred compensation obligations	(620)						(1,259)	639
Balance at end of year at Dec. 31, 2018	$ 972,060	$ 1,159	$ 527,037	$ 560,216	(71,897)	$ (43,835)	$ (1,259)	$ 639
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02					$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 3,678,000	$ 22,736,000	$ 31,072,000	$ 32,953,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred loan fees and costs, premiums and discounts	439,000	1,965,000	1,006,000	745,000
Net amortization of premiums and discounts on securities	328,000	1,212,000	1,460,000	2,013,000
Amortization Of Mortgage Servicing Rights After Additional Charges	22,000	(88,000)	105,000	105,000
Amortization of debt issuance costs	14,000	890,000	53,000	53,000
Depreciation and amortization of office properties and equipment	863,000	3,839,000	3,364,000	3,178,000
Provision for loan losses	3,400,000	6,677,000	6,426,000	417,000
(Gain) loss on securities available for sale	60,000	(116,000)	1,689,000	(355,000)
Proceeds from sales of loans held-for-sale	0	0	40,564,000	42,411,000
Origination of loans held-for-sale	0	0	(40,280,000)	(23,812,000)
(Gain) loss on sale of loans receivable, net	0	(618,000)	380,000	(655,000)
Loss (gain) on real estate owned, net	0	56,000	(233,000)	441,000
Loss on write-down of real estate owned	0	55,000	0	0
(Gain) loss on disposal of office properties and equipment	0	(5,000)	169,000	38,000
Deferred tax (benefit) expense	7,491,000	(5,490,000)	(1,426,000)	2,930,000
Increase in accrued interest receivable	(1,228,000)	(2,979,000)	(1,531,000)	(1,864,000)
Increase in other assets	(15,557,000)	(11,053,000)	(11,681,000)	(269,000)
Increase in accrued expenses and other liabilities	3,905,000	7,980,000	9,840,000	5,033,000
Income on bank-owned life insurance	(1,089,000)	(5,208,000)	(4,936,000)	(4,370,000)
Contribution of common stock to Columbia Bank Foundation	0	34,767,000	0	0
Employee stock ownership plan expense	0	2,594,000	0	0
Increase in deferred compensation obligations under Rabbi Trust	0	(620,000)	0	0
Net cash provided by operating activities	2,326,000	56,594,000	36,041,000	58,992,000
Cash flows from investing activities:
Proceeds from sales of securities available for sale	92,000	11,513,000	187,376,000	164,203,000
Proceeds from paydowns / maturities / calls of securities available for sale	7,009,000	69,977,000	68,409,000	96,956,000
Proceeds from paydowns / maturities / calls of securities held to maturity	1,845,000	8,820,000	769,000	0
Purchases of securities available for sale	(163,721,000)	(413,804,000)	(162,788,000)	(357,477,000)
Purchases of securities held to maturity	(108,640,000)	(31,639,000)	(30,484,000)	0
Proceeds from sales of loans held-for-sale	0	3,615,000	0	0
Proceeds from sales of loans receivable	0	32,039,000	62,407,000	28,624,000
Purchases of loans receivable	(56,095,000)	(32,251,000)	(20,473,000)	(21,149,000)
Net increase in loans receivable	(41,157,000)	(536,129,000)	(425,926,000)	(196,106,000)
Purchase of bank-owned life insurance	0	(30,000,000)	(4,500,000)	(6,000,000)
Death benefit proceeds from bank-owned life insurance	0	1,241,000	1,631,000	0
Proceeds from redemptions of Federal Home Loan Bank stock	6,476,000	67,035,000	33,193,000	16,560,000
Purchases of Federal Home Loan Bank stock	(15,296,000)	(81,309,000)	(35,035,000)	(16,138,000)
Proceeds from sales of office properties and equipment	0	8,000	17,000	0
Additions to office properties and equipment	(2,648,000)	(13,272,000)	(6,527,000)	(3,665,000)
Proceeds from sales of real estate owned	0	1,007,000	1,614,000	3,620,000
Net cash used in investing activities	(372,135,000)	(943,000)	(330,317,000)	(290,572,000)
Cash flows from financing activities:
Net increase in deposits	139,887,000	150,558,000	300,613,000	250,191,000
Proceeds from long-term borrowings	0	220,980,000	168,400,000	10,000,000
Payments on long-term borrowings	(90,000,000)	(210,000,000)	(90,000,000)	(55,000,000)
Net increase (decrease) in short-term borrowings	286,000,000	299,800,000	(27,400,000)	24,400,000
Payment for trust preferred securities	0	(51,547,000)	0	0
Increase (decrease) in advance payments by borrowers for taxes and insurance	(1,555,000)	6,467,000	(2,056,000)	4,505,000
Issuance of common stock	0	492,428,000	0	0
Purchase of employee stock ownership plan shares	0	(45,428,000)	0	0
Net cash provided by financing activities	334,332,000	863,258,000	349,557,000	234,096,000
Net (decrease) increase in cash and cash equivalents	(35,477,000)	(23,297,000)	55,281,000	2,516,000
Cash and cash equivalents at beginning of period	100,975,000	65,498,000	45,694,000	43,178,000
Cash and cash equivalents at end of period	65,498,000	42,201,000	100,975,000	45,694,000
Cash paid during the period for:
Interest on deposits and borrowings	11,484,000	61,987,000	44,397,000	44,545,000
Income tax payments, net	1,393,000	21,325,000	27,784,000	8,038,000
Non-cash investing and financing activities:
Transfer of loans receivable to real estate owned	566,000	251,000	515,000	2,278,000
Transfer of loans receivable to loans held-for-sale	0	11,696,000	0	0
Transfer of securities from available for sale to held to maturity	0	0	103,680,000	0
Securitization of loans	$ 0	$ 0	$ 0	$ 17,169,000

Business

Business	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business	Business On April 19, 2018, Columbia Financial, Inc. completed its minority stock offering, after receiving all regulatory approvals. In connection with the closing, 62,580,155 shares of its common stock was issued to Columbia Bank, MHC (the "MHC"), the mutual holding company of Columbia Financial, Inc., 3,476,675 shares to the Columbia Bank Foundation, Columbia Bank's charitable foundation, and 49,832,345 shares to depositors who subscribed for and were allocated shares in the minority stock offering, as well as the Columbia Bank Employee Stock Ownership Plan (the "ESOP"). The accounts of the MHC are not consolidated in the consolidated financial statements of the Company. On May 22, 2018, the Board of Directors of the Company adopted a resolution to change the Company’s fiscal year end from September 30 to December 31, effective immediately as of the date of the Board resolution. In addition, on May 22, 2018, the Boards of Directors of the MHC and the Bank also adopted resolutions to change the MHC’s and the Bank’s fiscal year ends from September 30 to December 31, effective immediately as of the date of the Board resolutions.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Principles of Consolidation The accompanying consolidated financial statements include the accounts of Columbia Financial, Inc., its wholly-owned subsidiary, Columbia Bank (the "Bank") and the Bank's wholly-owned subsidiaries, Columbia Investment Services, Inc., 2500 Broadway Corp. 1901 Residential Management Co. LLC, Plaza Financial Services, Inc., First Jersey Title Services, Inc., Real Estate Management Corp. LLC, 1901 Commercial Management Co. LLC, and CSB Realty Corp. (collectively, the “Company”). In consolidation, all intercompany accounts and transactions are eliminated. Certain reclassifications have been made in the consolidated financial statements to conform with current year classifications. The Company also owns 100% of the common stock of Columbia Financial Capital Trust I (the "Trust"). The Trust was used to issue trust preferred securities. In accordance with Accounting Standards Codification ("ASC") Topic 810, Consolidation , the Trust was classified as a variable interest entity and did not satisfy the conditions for consolidation. Accordingly, the Trust was treated as an unconsolidated subsidiary. In August 2018, the Company redeemed, in full $51.5 million of junior subordinated debt securities, which represented 100% of the assets of the Trust. Basis of Financial Statement Presentation The consolidated financial statements of the Company have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”). In preparing the consolidated financial statements, management is required to make estimates and assumptions about future events. These estimates and the underlying assumptions affect the reported amounts of assets and liabilities and disclosures about contingent assets and liabilities as of the dates of the consolidated statements of financial condition, and revenues and expenses for the periods then ended. Such estimates are used in connection with the determination of the adequacy of the allowance for loan losses, evaluation of goodwill for impairment, evaluation of other-than-temporary impairment on securities, evaluation of the need for valuation allowances on deferred tax assets, and determination of liabilities related to retirement and other post-retirement benefits, among others. These estimates and assumptions are based on management’s best estimates and judgment. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment, which management believes to be reasonable under the circumstances. Such estimates and assumptions are adjusted when facts and circumstances dictate. Illiquid credit markets, volatile securities markets, and declines in the housing market and the economy generally have combined to increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in estimates resulting from continuing changes in the economic environment will be reflected in the consolidated financial statements in future periods. Cash and Cash Equivalents For purposes of reporting cash flows, cash and cash equivalents include cash on hand, amounts due from banks and interest-bearing deposits at other financial institutions. The Company is required by the Federal Reserve Bank System to maintain cash reserves equal to a percentage of certain deposits. At December 31, 2018 and 2017 , the reserve requirement totaled $5.9 million and $4.1 million , respectively. (2) Summary of Significant Accounting Policies (continued) Securities Securities include investment securities classified as available for sale and held to maturity. Management determines the appropriate classification of securities at the time of purchase. If the Company does not have the intent to hold securities until maturity, these securities are classified as available for sale. The available for sale securities portfolio is carried at estimated fair value, with any unrealized holding gains or losses, net of taxes, reported as a separate component of accumulated other comprehensive income or loss in Stockholders' Equity. The fair values of these securities are based on market quotations or matrix pricing as discussed in Note 3. Management conducts a periodic review and evaluation of the securities portfolio to determine if any declines in the fair value of securities are other-than-temporary. In this evaluation, if such decline were deemed other-than temporary, management would measure the total credit-related component of the unrealized loss, and recognize that portion of the loss as a charge to current period earnings. The remaining portion of the unrealized loss would be recognized as an adjustment to accumulated other comprehensive income. The fair value of the securities portfolio is significantly affected by changes in interest rates. In general, as interest rates rise, the fair value of fixed-rate securities decreases and as interest rates fall, the fair value of fixed-rate securities increases. The Company determines if it has the intent to sell these securities or if it more likely than not that the Company would be required to sell the securities before the anticipated recovery. If either exists, the decline in value is considered other-than-temporary and would be recognized as an expense in the current period. Premiums and discounts on securities are amortized and accreted to income over the contractual lives of the securities using the level-yield method. Dividend and interest income are recognized when earned. Realized gains and losses are recognized when securities are sold or called based on the specific identification method. In the ordinary course of business, securities are pledged as collateral in conjunction with the Company’s borrowings and lines of credit. Federal Home Loan Bank Stock The Bank, as a member of the Federal Home Loan Bank of New York (the "FHLB"), is required to hold shares of capital stock of the FHLB at cost based on its activities, primarily its outstanding borrowings. The Bank carries the investment at cost, which approximates fair value. Loans Held-for-Sale Loans held-for-sale consist of conforming loans originated and intended for sale in the secondary market. These loans are carried at the lower of cost or estimated fair value, less costs to sell, as determined on an individual loan basis. Net unrealized losses, if any, are recognized in a valuation allowance through charges to earnings. Origination fees and costs on loans held-for-sale are deferred and recognized as a component of the gain or loss on sale. Loans held-for-sale are generally sold with loan servicing rights retained by the Bank. Loans Receivable Loans receivable are carried at unpaid principal balances adjusted by unamortized premiums and unearned discounts, net deferred origination fees and costs less the allowance for loan losses. The Bank defers loan origination fees and certain direct loan origination costs and accretes such amounts as an adjustment to the yield over the expected lives of the related loans using the level-yield method. Interest income on loans is accrued and credited to income as earned. Premiums and discounts on loans purchased are amortized or accreted as an adjustment to yield over the contractual lives of the related loans using methodologies which approximate the level-yield method. A loan is considered delinquent when payment has not been received within 30 days of its contractual due date. The accrual of income on loans is discontinued when they are past due 90 days or more as to contractual obligations, or other circumstances indicate that collection is questionable. When a loan is placed on non-accrual status, any interest accrued but not received is reversed against interest income. Payments received on a non-accrual loan are either applied to the outstanding principal balance or recorded as interest income, depending on an assessment of the ability to collect the loan. A loan is returned to accrual status when all amounts due have been received and the remaining principal is deemed collectible. Loans are generally charged off after an analysis is completed which indicates that collectability of the full principal balance is in doubt. (2) Summary of Significant Accounting Policies (continued) Loans Receivable (continued) An impaired loan is defined as a loan for which it is probable, based on current information, that the Bank will not collect all amounts due under the contractual terms of the loan agreement. The Bank considers the population of loans in its impairment analysis to include all multifamily and commercial real estate, construction, and commercial business loans with an outstanding balance greater than $500,000 and not accruing, and loans modified in a troubled debt restructuring. The Company also considers residential real estate, and home equity loans and advances that are not accruing or modified in a troubled debt restructuring for impairment. Other loans may be included in the population of loans in its impairment analysis if management has specific information of a collateral shortfall. Loan impairment is 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 the collateral if the loan is collateral dependent. Payments received on impaired loans are recognized on a cash basis. Allowance for Loan Losses Losses on loans are charged to the allowance for loan losses. Additions to this allowance are made by recoveries of loans previously charged off and by a provision charged to expense. The determination of the balance of the allowance for loan losses is based on an analysis of the loan portfolio, economic conditions, historical loan loss experience and other factors that warrant recognition in providing an adequate allowance. Estimates and judgments required to establish the allowance include: overall economic conditions; value of collateral; strength of guarantors; loss exposure at default; the amount and timing of future cash flows on impaired loans; and determination of loss factors to be applied to the various elements of the portfolio. All of these estimates are susceptible to significant change. Management regularly reviews the level of loss experience, current economic conditions and other factors related to the collectability of the loan portfolio. While management uses available information, future additions to the allowance may be necessary based on changes in economic conditions in the Bank's market area. In addition, various regulatory agencies, as an integral part of their examination process, periodically review the Bank's allowance for loan losses and they may require the Bank to recognize additions to the allowance or additional write-downs based on judgments about information available to them at the time of their examination. Troubled Debt Restructuring Troubled debt restructured loans are those loans where the Company has granted a concession it would not otherwise consider because of economic or legal reasons pertaining to a debtor’s financial difficulties. A concession could include a reduced interest rate below a market rate, an extension of the term of the loan, or a combination of the two methods, but generally does not result in the forgiveness of principal or accrued interest. Not all concessions granted by the Company constitute a troubled debt restructuring. Once an obligation has been restructured and designated as a troubled debt restructuring, it continues to be designed as a restructured loan until paid in full. The Company records an impairment charge equal to the difference between the present value of expected future cash flows under the restructured terms discounted at the loan’s original effective interest rate, and the loan’s carrying value. Changes in the calculated impairment due to the passage of time are recorded as an adjustment to the allowance for loan losses. Restructured loans that were accruing prior to the restructuring, where income was reasonably assured subsequent to the restructuring, maintain their accrual status. Restructured loans for which collectability was not reasonably assured are placed on non-accrual status, interest accruals cease, and uncollected accrued interest is reversed and charged against current income. A non-accrual restructured loan would be returned to an accrual status when there is a sustained period of repayment performance, generally six consecutive months, and both principal and interest are deemed collectible. Loans Sold and Serviced The Company periodically enters into Guarantor Swaps with Freddie Mac. In these types of transactions, the Company sells mortgage loans in exchange for Freddie Mac Mortgage Participation Certificates backed exclusively by the mortgages sold. The Company retains the servicing of the loans in these transactions. The Company also periodically sells loans to investors and continues to service such loans for a fee. Gains or losses on the sale of loans are recorded on the trade date using the specific-identification method. (2) Summary of Significant Accounting Policies (continued) Real Estate Owned Real estate acquired through foreclosure or deed in lieu of foreclosure is carried at the lower of the recorded investment in the loan at the time of foreclosure or fair value, less estimated costs to sell. Fair value is generally based on recent appraisals. The excess, if any, of the loan amount over the fair value of the asset acquired is charged off against the allowance for loan losses at the date the property is acquired. Subsequent write-downs in the value of real estate owned, as well as holding costs, and any gains or losses realized upon sale of the property are recorded as as incurred. Office Properties and Equipment Land is carried at cost. Office properties, land and building improvements, furniture and equipment, and leasehold improvements are carried at cost, less accumulated depreciation and amortization. Depreciation and amortization of office properties and equipment is computed on a straight-line basis over their estimated useful lives (generally 40 years for buildings, 10 to 20 years for land and building improvements, 5 to 10 years for furniture and equipment). Leasehold improvements, carried at cost, net of accumulated depreciation, are amortized over the terms of the related leases or the estimated useful lives of the assets, whichever is shorter. Major improvements are capitalized, while repairs and maintenance costs are charged to expense as incurred. Upon retirement or sale, any gain or loss is recognized as incurred. Bank-owned Life Insurance Bank-owned life insurance is accounted for using the cash surrender value method and is recorded at its net realizable value. The change in the net asset value is recorded as a component of non-interest income. A deferred liability has been recorded for the estimated cost of post-retirement life insurance benefits accruing to applicable employees and directors covered by an endorsement split-dollar life insurance arrangement. Goodwill and Intangible Assets Intangible assets of the Bank consist of goodwill and mortgage servicing rights. Goodwill represents the excess of the purchase price over the estimated fair value of identifiable net assets acquired through purchase acquisitions. In accordance with GAAP, goodwill with an indefinite useful life is not amortized, but is evaluated for impairment on an annual basis, or more frequently if events or changes in circumstances indicate potential impairment between annual measurement dates. As permitted by GAAP, the Company prepares a qualitative assessment in determining whether goodwill may be impaired, annually. The factors considered in the assessment include macroeconomic conditions, industry and market conditions and overall financial performance of the Company, among others. The Company completed its annual goodwill impairment test as of December 31, 2018 based upon its qualitative assessment of goodwill and concluded that goodwill was not impaired and no further quantitative analysis was warranted. Mortgage servicing rights are recorded when purchased or when originated mortgage loans are sold, with servicing rights retained. Mortgage servicing rights are amortized on an accelerated method based upon the estimated lives of the related loans, adjusted for prepayments. Mortgage servicing rights are carried at the lower of amortized cost or fair value. Post-retirement Benefits The Company provides certain health care and life insurance benefits to eligible retired employees, along with a split-dollar BOLI death benefit. The Company accrues the cost of retiree health care and other benefits during the employees’ period of active service. The Company accounts for benefits in accordance with Accounting Standard Update ("ASU") Topic 715, Pension and Other Post-retirement Benefits . The guidance requires an employer to: (a) recognize in its statement of financial position the overfunded or underfunded status of a defined benefit post-retirement plan measured as the difference between the fair value of plan assets and the benefit obligation; (b) measure a plan’s assets and its obligations that determine its funded status as of the end of the employer’s fiscal year (with limited exceptions); and (c) recognize as a component of other comprehensive income (loss), net of tax, the actuarial gains and losses and the prior service costs and credits that arise during the period. (2) Summary of Significant Accounting Policies (continued) Employee Benefit Plans The Company maintains a tax-qualified defined benefit pension plan ( the "Pension Plan") which covers full-time employees that satisfy the plan eligibility requirements. During 2018, the pension plan was amended. Effective October 1, 2018, employees hired by the Bank are not eligible to participate in the Company's pension plan as the plan has been closed to new employees as of the effective date. The Company's policy is to fund at least the minimum contribution required by the Employee Retirement Income Security Act of 1974. GAAP requires an employer to: (a) recognize in its statement of financial position the over-funded or under-funded status of a defined benefit post-retirement plan measured as the difference between the fair value of plan assets and the benefit obligation; (b) measure a plan’s assets and its obligations that determine its funded status at the end of the employer’s fiscal year (with limited exceptions); and (c) recognize as a component of other comprehensive income (loss), net of tax, the actuarial gains and losses and the prior service costs and credits that arise during the period. The assets of the plan are primarily invested in fixed debt and equity. The Company has a retirement income maintenance plan (the "RIM Plan"). The RIM Plan is a non-qualified defined benefit plan which provides benefits to all employees of the Company if their benefits under the Pension Plan are limited by the Internal Revenue Code. The Company has a 401(k) plan covering substantially all employees of the Company. The Company may match a percentage of the first 3.00% to 4.50% contributed by participants. The Company's matching contribution, if any, is determined by the Board of Directors in its sole discretion. The Company has an Employee Stock Ownership Plan ("ESOP"). The funds borrowed by the ESOP from the Company to purchase the Company's common stock are being repaid from the Bank's contributions over a period of 20 years. The Company's common stock not allocated to participants is recorded as a reduction of stockholders' equity at cost. Compensation expense for the ESOP is based on the average price of the Company's stock and the amount of shares committed to be allocated during each period. The Company has a Supplemental Executive Retirement Plan ("SERP"). The SERP is a non-qualified plan which provides supplemental retirement benefits to eligible officers (those designated by the Board of Directors) of the Company who are prevented from receiving the full benefits contemplated by the ESOP's benefit formulas under tax law limits for tax-qualified plans. In addition, the Company maintains a stock based deferral plan (the "Stock Based Deferral Plan") for certain executives and directors. The Company records a deferred compensation equity account and corresponding contra-equity account for the cost of the shares held by the Stock Based Deferral and SERP Plans. The Company also maintains a non-qualified savings income maintenance deferred compensation plan (the "SIM Plan") that provides supplemental benefits to certain executives who are prevented from receiving the full benefits contemplated by the 401(k) Plan under tax law limits for tax-qualified plans, and a Deferred Compensation Plan for directors. Derivatives The Company records all derivatives on the consolidated statements of financial condition at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative, whether the Company has elected to designate a derivative in a hedging relationship and apply hedge accounting and whether the hedging relationship has satisfied the criteria necessary to apply hedge accounting. Interest rate swaps are designated as a cash flow hedge and satisfies hedge accounting requirements involving the receipt of variable amounts from a counter-party in exchange for the Company making fixed-rate payments over the life of the agreements without the exchange of the underlying notional amount. For derivatives which are designed as cash flow hedges and satisfy hedge accounting requirements, the effective portion of changes in the fair value of these derivatives are recorded in accumulated other comprehensive income (loss), and are subsequently reclassified into earnings in the period that the hedged forecasted transaction affects earnings. The ineffective portion of a change in the fair value of these derivatives are recognized directly in earnings. The fair value of the Company’s derivatives are determined using discounted cash flow analysis using observable market- based inputs. (2) Summary of Significant Accounting Policies (continued) Income Taxes The Company and its subsidiaries file consolidated federal income tax returns. Federal income taxes are allocated to each entity based on their respective contributions to taxable income of the consolidated income tax returns. Separate state income tax returns are filed for the Company and each of its subsidiaries. For the three months ended December 31, 2017, income tax expense included the impact of the enactment of the Tax Cuts and Jobs Act ("Tax Act"), which was enacted in December 2017, and reduced the maximum statutory federal income tax rate from 35% to 21%. This resulted in a charge to reduce the carrying value of the Company's net deferred income tax assets, which are included in the consolidated statements of financial condition. As a result, for the year ended December 31, 2018, the federal income tax rate applicable to the Company was 21%. The Company records income taxes in accordance with ASC Topic 740, Income Taxes , using the asset and liability method. The amounts reflected on the Company's federal and state income tax returns differ from these provisions due principally to temporary differences in the reporting of certain items for consolidated financial statement reporting and income tax reporting purposes. Accordingly, deferred tax assets and liabilities: (i) are recognized for the expected future tax consequences of events that have been recognized in the financial statements or tax returns; (ii) are attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases; and (iii) are measured using enacted tax rates expected to apply in the years when those temporary differences are expected to be recovered or settled. Where applicable, deferred tax assets are reduced by a valuation allowance for any portions determined not likely to be realized. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income tax expense in the period that includes the enactment date. The valuation allowance is adjusted, by a charge or credit to income tax expense, as changes in facts and circumstances warrant. Income taxes are allocated to the individual entities within the consolidated group based on the effective tax rate of the entity. The Company did not have any liabilities for uncertain tax positions or any known unrecognized tax benefits at December 31, 2018 and 2017 . The Company recognizes interest and penalties related to unrecognized tax benefits in income tax expense in the Consolidated Statements of Income. The Company did not recognize any interest and penalties during the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017. On July 1, 2018, New Jersey enacted legislation which adds to the state’s 9.0% Corporation Business Tax rate (i) a 2.5% surtax for periods beginning in 2018 and 2019 and (ii) a 1.5% surtax for periods beginning in 2020 and 2021. These surtaxes apply to corporations with more than $41.0 million of net income allocated to New Jersey and expire beginning in 2022. Also, for periods beginning in 2017, New Jersey has reduced the dividends-received deduction from 100% to 95% for certain dividend income received by a corporation from a subsidiary that is at least 80% owned by the corporation. In addition, for periods beginning in 2019, New Jersey has adopted combined income tax reporting for certain members of a commonly-controlled unitary business group. Comprehensive Income (Loss) Comprehensive income (loss) consists of net income and other comprehensive income (loss). Other comprehensive income (loss) includes unrealized holding gains and losses on securities available-for-sale, the noncredit component of other than temporary impairment losses on debt securities, unrealized gains and losses on derivatives, and the unfunded status of employee benefit plans. Comprehensive income is presented in a separate Consolidated Statements of Comprehensive Income (Loss). Securities Sold Under Agreements to Repurchase and Other Borrowings The Company enters into sales of securities under agreement to repurchase and collateral pledge agreements with selected dealers and banks. Such agreements are accounted for as secured financing transactions since the Company maintains effective control over the transferred or pledged securities. Obligations under these agreements are recorded as liabilities in the Consolidated Statements of Financial Condition. Segment Reporting The Company’s operations are solely in the financial services industry and include providing traditional banking and other financial services to its customers. The Company operates primarily in New Jersey. Management makes operating decisions and assesses performance based on an ongoing review of the Company’s consolidated financial results. Therefore, the Company has a single operating segment for financial reporting purposes. (2) Summary of Significant Accounting Policies (continued) Earnings Per Share (EPS) Basic EPS is computed by dividing net income available to common stockholders by the weighted average number of common shares outstanding for the period. For purposes of calculating basic EPS, weighted average common shares outstanding excludes unallocated employee stock ownership plan shares that have not been committed for release and deferred compensation obligations required to be settled in shares of Company stock. Diluted EPS reflects the potential dilution which could occur if securities or other contracts to issue common stock (such as stock options) were exercised and or resulted in the issuance of common stock. These potentially dilutive shares would then be included in the weighted average number of shares outstanding for the period using the treasury stock method. Shares issued and reacquired during any period are weighted for the portion of the period that they were outstanding. During the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, the Company did not have any stock options outstanding. Recent Accounting Pronouncements As an “emerging growth company” as defined in Title 1 of the Jumpstart Our Business Startups (JOBS) Act, the Company has elected to use the extended transition period to delay the adoption of new or reissued accounting pronouncements applicable to public companies until such pronouncements are made applicable to private companies. Accounting Pronouncements Adopted In February 2018, the Financial Accounting Standards Board ("FASB") issued ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220) . The updated guidance allows a reclassification from accumulated other comprehensive income to retained earnings for the stranded tax effects resulting from the Tax Cuts and Jobs Act disclosed in Note 12. The purpose of the guidance is to improve the usefulness of the information reported to the financial statement users. The guidance is effective for all entities for fiscal years beginning after December 31, 2018 and interim periods within those fiscal years. Early adoption is permitted. The Company early adopted ASU No. 2018-02 for the period ended December 31, 2017 and the impact of the adoption resulted in a reclassification adjustment between accumulated other comprehensive income and retained earnings of $11.7 million . Accounting Pronouncements Not Yet Adopted In October 2018, the FASB issued ASU No. 2018-16, Derivatives and Hedging (Topic 815)- Inclusion of the Secured Overnight Financing Rate ("SOFR") Overnight Index Swap ("OSI") Rate as a Benchmark Interest Tate for Hedge Accounting Purposes. This ASU permits the use of the OIS rate based upon SOFR as a U.S. benchmark interest rate for purposes of applying hedge accounting under Topic 815. This is the fifth U.S. benchmark interest rate eligible for use in hedge accounting in addition to the direct Treasury obligations of the U.S. Government, the LIBOR swap rate, the OIS rate based on the Fed Funds Effective Rate, and the Securities Industry and Financial Markets Association Municipal Swap Rate. The amendments in this ASU are required to be adopted concurrently with the amendments in ASU No. 2017-12, Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities, which was issued in August 2017. The purpose of this updated guidance is to better align a company’s financial reporting for hedging activities with the economic objectives of those activities. The effective date for this ASU for the Company is for fiscal years beginning after December 15, 2019, with early adoption, including adoption in an interim period, permitted. ASU 2017-12 requires a modified retrospective transition method in which the company will recognize the cumulative effect of the change on the opening balance of each affected component of equity in the statement of financial position as of the date of adoption. The Company does not expect the adoption of this guidance to have a significant impact on its consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement. The purpose of this updated guidance is to improve the effectiveness and disclosures in the notes to the financial statements . The ASU removes the requirement to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; removes the policy for timing of transfers between levels and removes the disclosure related to the valuation process for Level 3 fair value measurements. The ASU also modifies existing disclosure requirements which relate to the disclosure for investments in certain entities which calculate net asset value and clarifies the disclosure about uncertainty in the measurements as of the reporting date. For all entities, the effective date for this guidance is fiscal years beginning after December 15, 2019, including interim periods within the reporting period, with early adoption permitted. Entities are also allowed to elect early adoption of the

Securities Available for Sale

Securities Available for Sale	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Securities Available for Sale	Securities Held to Maturity Securities held to maturity at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 23,404 $ 45 $ (208 ) $ 23,241 Mortgage-backed securities and collateralized mortgage obligations 238,739 28 (7,167 ) 231,600 $ 262,143 $ 73 $ (7,375 ) $ 254,841 December 31, 2017 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 8,402 $ — $ (58 ) $ 8,344 Mortgage-backed securities and collateralized mortgage obligations 231,216 — (3,435 ) 227,781 $ 239,618 $ — $ (3,493 ) $ 236,125 (4) Securities Held to Maturity (continued) The amortized cost and fair value of debt securities held to maturity at December 31, 2018 , by contractual final maturity, are shown below. Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer. December 31, 2018 Amortized cost Fair value (In thousands) More than one year to five years $ 5,000 $ 5,000 More than five years to ten years 8,404 8,196 More than ten years 10,000 10,045 23,404 23,241 Mortgage-backed securities and collateralized mortgage obligations 238,739 231,600 $ 262,143 $ 254,841 Mortgage-backed securities and collateralized mortgage obligations totaling $238.7 million at amortized cost, and $231.6 million at fair value, are excluded from the table above as their expected lives are likely to be shorter than the contractual maturity date due to principal prepayments. There were no sales of securities from the held to maturity portfolio for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017. Proceeds from calls and maturities of securities held to maturity for the years ended December 31, 2018 and September 30, 2017, totaled $5.4 million and $769,000 , respectively. There were no calls or maturities of securities held to maturity for the year ended September 30, 2016 and the three months ended December 31, 2017. Securities held to maturity having a carrying value of $187.0 million and $141.0 million , at December 31, 2018 and December 31, 2017 , respectively, were pledged to secure public funds on deposit at the Bank as required and permitted by law. The following table summarizes the fair value and gross unrealized losses of those securities that reported an unrealized loss at December 31, 2018 and 2017 and if the unrealized loss position was continuous for the twelve months prior to those respective dates: December 31, 2018 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ — $ — $ 8,197 $ (208 ) $ 8,197 $ (208 ) Mortgage-backed securities and collateralized mortgage obligations 11,265 (69 ) 213,246 (7,098 ) 224,511 (7,167 ) $ 11,265 $ (69 ) $ 221,443 $ (7,306 ) $ 232,708 $ (7,375 ) (4) Securities Held to Maturity (continued) December 31, 2017 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ 8,344 $ (58 ) $ — $ — $ 8,344 $ (58 ) Mortgage-backed securities and collateralized mortgage obligations 196,049 (2,920 ) 29,531 (515 ) 225,580 (3,435 ) $ 204,393 $ (2,978 ) $ 29,531 $ (515 ) $ 233,924 $ (3,493 ) The Company evaluates securities for other-than-temporary impairment at each reporting period and more frequently when economic or market conditions warrant such evaluation. The temporary loss position associated with securities held to maturity was the result of changes in market interest rates relative to the coupon of the individual security and changes in credit spreads. The Company does not have the intent to sell securities in a temporary loss position at December 31, 2018 , nor is it more likely than not that the Company will be required to sell the securities before the anticipated recovery. The number of securities in an unrealized loss position as of December 31, 2018 totaled 88 , compared with 84 at December 31, 2017 . All temporarily impaired securities were investment grade as of December 31, 2018 and 2017 . The Company did not record an other-than-temporary impairment charge on securities held to maturity for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017. During the year ended September 30, 2017, the Company transferred certain available for sale securities with an amortized cost of $103.7 million and a fair value of $103.3 million to the held to maturity portfolio, largely because of the nature of the securities, which were community investment related mortgage-backed securities issued by government agencies, or due to their longer durations. Securities Available for Sale S ecurities available for sale at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 54,821 $ 53 $ (717 ) $ 54,157 Mortgage-backed securities and collateralized mortgage obligations 934,631 2,812 (17,436 ) 920,007 Municipal obligations 987 — — 987 Corporate debt securities 54,493 129 (1,155 ) 53,467 Trust preferred securities 5,000 — (750 ) 4,250 Equity securities 1,196 694 — 1,890 $ 1,051,128 $ 3,688 $ (20,058 ) $ 1,034,758 December 31, 2017 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 39,909 $ 17 $ (282 ) $ 39,644 Mortgage-backed securities and collateralized mortgage obligations 615,924 383 (9,695 ) 606,612 Municipal obligations 1,957 — — 1,957 Corporate debt securities 54,489 536 (511 ) 54,514 Trust preferred securities 5,000 — (344 ) 4,656 Equity securities 2,328 859 — 3,187 $ 719,607 $ 1,795 $ (10,832 ) $ 710,570 The amortized cost and fair value of debt securities available for sale at December 31, 2018 , by contractual final maturity, excluding equity securities is shown below. Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer. December 31, 2018 Amortized cost Fair value (In thousands) One year or less $ 797 $ 797 More than one year to five years 50,131 49,613 More than five years to ten years 59,373 57,971 More than ten years 5,000 4,480 115,301 112,861 Mortgage-backed securities and collateralized mortgage obligations 934,631 920,007 $ 1,049,932 $ 1,032,868 (3) Securities Available for Sale (continued) Mortgage-backed securities and collateralized mortgage obligations totaling $934.6 million at amortized cost, and $920.0 million at fair value, are excluded from the table above as their expected lives are likely to be shorter than the contractual maturity date due to principal prepayments. During the year ended December 31, 2018 , proceeds from calls of securities available for sale totaled $11.5 million , resulting in gross realized gains of $116,000 and no gross unrealized losses. Proceeds from maturities of securities available for sale totaled $2.4 million . During the three months ended December 31, 2017, proceeds from sales of securities available for sale totaled $92,000 , resulting in no gross unrealized gains and gross realized losses of $60,000 . There were no calls or maturities of securities available for sale during the period. During the year ended September 30, 2017, proceeds from sales of securities available for sale totaled $187.4 million , resulting in gross realized gains of $1.5 million and gross realized losses of $3.2 million . Proceeds from calls and maturities of securities available for sale totaled $17.2 million . During the year ended September 31, 2016, proceeds from sales of securities available for sale totaled $164.2 million , resulting in gross realized gains of $1.1 million and gross realized losses of $743,000 . Proceeds from calls and maturities of securities available for sale totaled $5.4 million . Securities available for sale having a carrying value of $232.7 million and $301.1 million , respectively, at December 31, 2018 and 2017 , respectively, are pledged to secure securities sold under repurchase agreements or for public funds on deposit at the Bank as required and permitted by law. The following table summarizes the fair value and gross unrealized losses of those securities that reported an unrealized loss at December 31, 2018 and 2017 and if the unrealized loss position was continuous for the twelve months prior to those respective dates: December 31, 2018 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ 14,668 $ (202 ) $ 29,437 $ (515 ) $ 44,105 $ (717 ) Mortgage-backed securities and collateralized mortgage obligations 176,614 (1,034 ) 509,397 (16,402 ) 686,011 (17,436 ) Corporate debt securities 26,480 (512 ) 9,358 (643 ) 35,838 (1,155 ) Trust preferred securities — — 4,250 (750 ) 4,250 (750 ) $ 217,762 $ (1,748 ) $ 552,442 $ (18,310 ) $ 770,204 $ (20,058 ) (3) Securities Available for Sale (continued) December 31, 2017 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ 29,654 $ (282 ) $ — $ — $ 29,654 $ (282 ) Mortgage-backed securities and collateralized mortgage obligations 514,283 (8,037 ) 48,788 (1,658 ) 563,071 (9,695 ) Corporate debt securities 4,866 (135 ) 4,624 (376 ) 9,490 (511 ) Trust preferred securities — — 4,656 (344 ) 4,656 (344 ) $ 548,803 $ (8,454 ) $ 58,068 $ (2,378 ) $ 606,871 $ (10,832 ) The Company evaluates securities for other-than-temporary impairment at each reporting period and more frequently when economic or market conditions warrant such evaluation. The temporary loss position associated with securities available for sale was the result of changes in market interest rates relative to the coupon of the individual security and changes in credit spreads. The Company does not have the intent to sell securities in a temporary loss position at December 31, 2018 , nor is it more likely than not that the Company will be required to sell the securities before the anticipated recovery. The number of securities in an unrealized loss position as of December 31, 2018 totaled 151 , compared with 111 at December 31, 2017 . All temporarily impaired securities were investment grade as of December 31, 2018 and 2017 . The Company did not record an other-than-temporary impairment charge on securities available for sale for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017.

Securities Held to Maturity

Securities Held to Maturity	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Securities Held to Maturity	Securities Held to Maturity Securities held to maturity at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 23,404 $ 45 $ (208 ) $ 23,241 Mortgage-backed securities and collateralized mortgage obligations 238,739 28 (7,167 ) 231,600 $ 262,143 $ 73 $ (7,375 ) $ 254,841 December 31, 2017 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 8,402 $ — $ (58 ) $ 8,344 Mortgage-backed securities and collateralized mortgage obligations 231,216 — (3,435 ) 227,781 $ 239,618 $ — $ (3,493 ) $ 236,125 (4) Securities Held to Maturity (continued) The amortized cost and fair value of debt securities held to maturity at December 31, 2018 , by contractual final maturity, are shown below. Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer. December 31, 2018 Amortized cost Fair value (In thousands) More than one year to five years $ 5,000 $ 5,000 More than five years to ten years 8,404 8,196 More than ten years 10,000 10,045 23,404 23,241 Mortgage-backed securities and collateralized mortgage obligations 238,739 231,600 $ 262,143 $ 254,841 Mortgage-backed securities and collateralized mortgage obligations totaling $238.7 million at amortized cost, and $231.6 million at fair value, are excluded from the table above as their expected lives are likely to be shorter than the contractual maturity date due to principal prepayments. There were no sales of securities from the held to maturity portfolio for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017. Proceeds from calls and maturities of securities held to maturity for the years ended December 31, 2018 and September 30, 2017, totaled $5.4 million and $769,000 , respectively. There were no calls or maturities of securities held to maturity for the year ended September 30, 2016 and the three months ended December 31, 2017. Securities held to maturity having a carrying value of $187.0 million and $141.0 million , at December 31, 2018 and December 31, 2017 , respectively, were pledged to secure public funds on deposit at the Bank as required and permitted by law. The following table summarizes the fair value and gross unrealized losses of those securities that reported an unrealized loss at December 31, 2018 and 2017 and if the unrealized loss position was continuous for the twelve months prior to those respective dates: December 31, 2018 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ — $ — $ 8,197 $ (208 ) $ 8,197 $ (208 ) Mortgage-backed securities and collateralized mortgage obligations 11,265 (69 ) 213,246 (7,098 ) 224,511 (7,167 ) $ 11,265 $ (69 ) $ 221,443 $ (7,306 ) $ 232,708 $ (7,375 ) (4) Securities Held to Maturity (continued) December 31, 2017 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ 8,344 $ (58 ) $ — $ — $ 8,344 $ (58 ) Mortgage-backed securities and collateralized mortgage obligations 196,049 (2,920 ) 29,531 (515 ) 225,580 (3,435 ) $ 204,393 $ (2,978 ) $ 29,531 $ (515 ) $ 233,924 $ (3,493 ) The Company evaluates securities for other-than-temporary impairment at each reporting period and more frequently when economic or market conditions warrant such evaluation. The temporary loss position associated with securities held to maturity was the result of changes in market interest rates relative to the coupon of the individual security and changes in credit spreads. The Company does not have the intent to sell securities in a temporary loss position at December 31, 2018 , nor is it more likely than not that the Company will be required to sell the securities before the anticipated recovery. The number of securities in an unrealized loss position as of December 31, 2018 totaled 88 , compared with 84 at December 31, 2017 . All temporarily impaired securities were investment grade as of December 31, 2018 and 2017 . The Company did not record an other-than-temporary impairment charge on securities held to maturity for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017. During the year ended September 30, 2017, the Company transferred certain available for sale securities with an amortized cost of $103.7 million and a fair value of $103.3 million to the held to maturity portfolio, largely because of the nature of the securities, which were community investment related mortgage-backed securities issued by government agencies, or due to their longer durations. Securities Available for Sale S ecurities available for sale at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 54,821 $ 53 $ (717 ) $ 54,157 Mortgage-backed securities and collateralized mortgage obligations 934,631 2,812 (17,436 ) 920,007 Municipal obligations 987 — — 987 Corporate debt securities 54,493 129 (1,155 ) 53,467 Trust preferred securities 5,000 — (750 ) 4,250 Equity securities 1,196 694 — 1,890 $ 1,051,128 $ 3,688 $ (20,058 ) $ 1,034,758 December 31, 2017 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 39,909 $ 17 $ (282 ) $ 39,644 Mortgage-backed securities and collateralized mortgage obligations 615,924 383 (9,695 ) 606,612 Municipal obligations 1,957 — — 1,957 Corporate debt securities 54,489 536 (511 ) 54,514 Trust preferred securities 5,000 — (344 ) 4,656 Equity securities 2,328 859 — 3,187 $ 719,607 $ 1,795 $ (10,832 ) $ 710,570 The amortized cost and fair value of debt securities available for sale at December 31, 2018 , by contractual final maturity, excluding equity securities is shown below. Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer. December 31, 2018 Amortized cost Fair value (In thousands) One year or less $ 797 $ 797 More than one year to five years 50,131 49,613 More than five years to ten years 59,373 57,971 More than ten years 5,000 4,480 115,301 112,861 Mortgage-backed securities and collateralized mortgage obligations 934,631 920,007 $ 1,049,932 $ 1,032,868 (3) Securities Available for Sale (continued) Mortgage-backed securities and collateralized mortgage obligations totaling $934.6 million at amortized cost, and $920.0 million at fair value, are excluded from the table above as their expected lives are likely to be shorter than the contractual maturity date due to principal prepayments. During the year ended December 31, 2018 , proceeds from calls of securities available for sale totaled $11.5 million , resulting in gross realized gains of $116,000 and no gross unrealized losses. Proceeds from maturities of securities available for sale totaled $2.4 million . During the three months ended December 31, 2017, proceeds from sales of securities available for sale totaled $92,000 , resulting in no gross unrealized gains and gross realized losses of $60,000 . There were no calls or maturities of securities available for sale during the period. During the year ended September 30, 2017, proceeds from sales of securities available for sale totaled $187.4 million , resulting in gross realized gains of $1.5 million and gross realized losses of $3.2 million . Proceeds from calls and maturities of securities available for sale totaled $17.2 million . During the year ended September 31, 2016, proceeds from sales of securities available for sale totaled $164.2 million , resulting in gross realized gains of $1.1 million and gross realized losses of $743,000 . Proceeds from calls and maturities of securities available for sale totaled $5.4 million . Securities available for sale having a carrying value of $232.7 million and $301.1 million , respectively, at December 31, 2018 and 2017 , respectively, are pledged to secure securities sold under repurchase agreements or for public funds on deposit at the Bank as required and permitted by law. The following table summarizes the fair value and gross unrealized losses of those securities that reported an unrealized loss at December 31, 2018 and 2017 and if the unrealized loss position was continuous for the twelve months prior to those respective dates: December 31, 2018 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ 14,668 $ (202 ) $ 29,437 $ (515 ) $ 44,105 $ (717 ) Mortgage-backed securities and collateralized mortgage obligations 176,614 (1,034 ) 509,397 (16,402 ) 686,011 (17,436 ) Corporate debt securities 26,480 (512 ) 9,358 (643 ) 35,838 (1,155 ) Trust preferred securities — — 4,250 (750 ) 4,250 (750 ) $ 217,762 $ (1,748 ) $ 552,442 $ (18,310 ) $ 770,204 $ (20,058 ) (3) Securities Available for Sale (continued) December 31, 2017 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ 29,654 $ (282 ) $ — $ — $ 29,654 $ (282 ) Mortgage-backed securities and collateralized mortgage obligations 514,283 (8,037 ) 48,788 (1,658 ) 563,071 (9,695 ) Corporate debt securities 4,866 (135 ) 4,624 (376 ) 9,490 (511 ) Trust preferred securities — — 4,656 (344 ) 4,656 (344 ) $ 548,803 $ (8,454 ) $ 58,068 $ (2,378 ) $ 606,871 $ (10,832 ) The Company evaluates securities for other-than-temporary impairment at each reporting period and more frequently when economic or market conditions warrant such evaluation. The temporary loss position associated with securities available for sale was the result of changes in market interest rates relative to the coupon of the individual security and changes in credit spreads. The Company does not have the intent to sell securities in a temporary loss position at December 31, 2018 , nor is it more likely than not that the Company will be required to sell the securities before the anticipated recovery. The number of securities in an unrealized loss position as of December 31, 2018 totaled 151 , compared with 111 at December 31, 2017 . All temporarily impaired securities were investment grade as of December 31, 2018 and 2017 . The Company did not record an other-than-temporary impairment charge on securities available for sale for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017.

Loans Receivable and Allowance

Loans Receivable and Allowance for Loan Losses	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Loans Receivable and Allowance for Loan Losses	Loans Receivable and Allowance for Loan Losses Loans receivable at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 (In thousands) Real estate loans: One-to-four family $ 1,830,186 $ 1,615,000 Multifamily and commercial 2,142,154 1,870,475 Construction 261,473 233,652 Commercial business loans 333,876 277,970 Consumer loans: Home equity loans and advances 393,492 447,920 Other consumer loans 1,108 998 Total gross loans 4,962,289 4,446,015 Net deferred loan costs, fees and purchased premiums and discounts 16,893 12,633 Loans receivable $ 4,979,182 $ 4,458,648 The Company had $8.1 million of fixed rate one-to-four family real estate loans held-for-sale at December 31, 2018 . There were no loans held-for-sale at December 31, 2017 . (5) Loans Receivable and Allowance for Loan Losses (continued) The Company sold $32.0 million of one-to-four family and fixed rate home equity loans to third parties during the year ended December 31, 2018 . The Company sold $62.4 million and $28.6 million , of one-to-four family, fixed rate home equity and multifamily loans to third parties during the years ended September 30, 2017 and 2016, respectively. These loans were previously included in loans receivable. No loans were sold by the Company during the three months ended December 31, 2017. The Company purchased $32.3 million , $20.5 million and $21.1 million , respectively, of one-to-four family and multifamily and commercial real estate loans during the years ended December 31, 2018 , September 30, 2017 and 2016. The Company purchased $56.1 million of multifamily and commercial real estate loans during the three months ended December 31, 2017. At December 31, 2018 and 2017 , the carrying value of one-to four family real estate loans serviced by the Company for investors totaled $462.7 million and $478.8 million , respectively. These loans are not included in the Consolidated Statements of Financial Condition. Servicing income totaled $1.1 million for the year ended December 31, 2018 , and $1.2 million for both the years ended September 30, 2017 and 2016. For the three months ended December 31, 2017 servicing income totaled $298,000 . The Company periodically enters into Guarantor Swaps with Freddie Mac which results in improved liquidity. The Company did not sell any loans to Freddie Mac in exchange for Freddie Mac Mortgage Participation Certificates during the years ended December 31, 2018 and September 30, 2017, or the three months ended December 31, 2017. For the year ended September 30, 2016, the Company sold $17.2 million of loans in exchange for Freddie Mac Mortgage Participation Certificates. The Company retained the servicing of these loans. The Company has granted loans to certain officers and directors of the Company and its subsidiaries and to their associates. As of December 31, 2018 and 2017 such loans totaled approximately $1.4 million and $1.5 million , respectively. During the year ended December 31, 2018 and the three months ended December 31, 2017, the Bank granted no new loans to related parties. During the years ended September 30, 2017 and 2016, new loans totaling $390,000 , and $115,000 , respectively, were granted to related parties. These loans are performing in accordance with their original terms. The following tables summarize the aging of loans receivable by portfolio segment at December 31, 2018 and 2017 : December 31, 2018 30-59 days 60-89 days 90 Days or more Total past due Current Total (In thousands) Real estate loans: One-to-four family $ 8,384 $ 1,518 $ 819 $ 10,721 $ 1,819,465 $ 1,830,186 Multifamily and commercial 1,870 1,425 154 3,449 2,138,705 2,142,154 Construction — — — — 261,473 261,473 Commercial business loans 208 279 911 1,398 332,478 333,876 Consumer loans: Home equity loans and advances 1,550 173 905 2,628 390,864 393,492 Other consumer loans — — — — 1,108 1,108 Total gross loans $ 12,012 $ 3,395 $ 2,789 $ 18,196 $ 4,944,093 $ 4,962,289 (5) Loans Receivable and Allowance for Loan Losses (continued) December 31, 2017 30-59 days 60-89 days 90 Days or more Total past due Current Total (In thousands) Real estate loans: One-to-four family $ 7,080 $ 1,229 $ 3,360 $ 11,669 $ 1,603,331 $ 1,615,000 Multifamily and commercial 138 380 1,329 1,847 1,868,628 1,870,475 Construction — — — — 233,652 233,652 Commercial business loans 89 730 1,263 2,082 275,888 277,970 Consumer loans: Home equity loans and advances 1,421 26 573 2,020 445,900 447,920 Other consumer loans — — — — 998 998 Total gross loans $ 8,728 $ 2,365 $ 6,525 $ 17,618 $ 4,428,397 $ 4,446,015 The Company considers a loan to be delinquent when we have not received a payment within 30 days of its contractual due date. Generally, a loan is designated as a non-accrual loan when the payment of interest is 90 days or more in arrears of its contractual due date. The accrual of income on a non-accrual loan is reversed and discontinued until the outstanding payments in arrears have been collected and there is a sustained period of performance. The Company identifies loans that may need to be charged-off as a loss, by reviewing all delinquent loans, classified loans and other loans that management may have concerns about collectability. At December 31, 2018 and 2017 , non-accrual loans totaled $2.8 million and $6.5 million , respectively. At December 31, 2018 and 2017 , there were no loans past due 90 days or more and still accruing interest. The following table provides information with respect to our non-accrual loans at December 31, 2018 and 2017 : December 31, 2018 2017 (In thousands) Non-accrual loans: Real estate loans: One-to-four family $ 819 $ 3,360 Multifamily and commercial 154 1,329 Commercial business loans 911 1,263 Consumer loans: Home equity loans and advances 905 573 Total non-accrual loans $ 2,789 $ 6,525 If the non-accrual loans had performed in accordance with their original terms, interest income would have increased by $126,000 , $295,000 , $713,000 , and $61,000 for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, respectively. The amount of cash basis interest income that was recognized on these loans during the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 was $89,000 , $104,000 , $472,000 , and $121,000 , respectively. We may obtain physical possession of real estate collateralizing a residential mortgage loan via foreclosure or through an in-substance repossession. As of December 31, 2018 , we held one single-family property in real estate owned with a carrying value of $92,000 that was acquired through foreclosure on a residential mortgage loan. As of December 31, 2018 and 2017 , we had 14 and 15 residential mortgage loans with carrying values of $1.6 million and $2.7 million , respectively, collateralized by residential real estate which were in the process of foreclosure. (5) Loans Receivable and Allowance for Loan Losses (continued) The Company maintains the allowance for loan losses through provisions for loan losses which are charged to income. Charge-offs against the allowance for loan losses are taken on loans where management determines that the collection of loan principal is unlikely. Recoveries made on loans that have been charged-off are credited to the allowance for loan losses. As part of the evaluation of the adequacy of the allowance for loan losses, management prepares an analysis each quarter that categorizes the entire loan portfolio by certain risk characteristics such as loan type (residential mortgage, commercial mortgage, construction, commercial, etc.) and loan risk rating. When assigning a risk rating to a loan, management utilizes an eight-point risk rating system to summarize its loan portfolio into categories with similar risk characteristics. Loans deemed to be “acceptable quality” are rated 1 through 4 (Pass), with a rating of 1 established for loans with minimal risk. Loans that are deemed to be of “questionable quality” are rated 5 (Special Mention) or 6 (Substandard). Loans with adverse classifications are rated 7 (Doubtful) or 8 (Loss). The risk ratings are also confirmed through periodic loan review examinations, which are currently performed by both an independent third-party and the Company's internal loan review department. The Company requires an annual review be performed above certain dollar thresholds, depending on loan type, to help determine the appropriate risk rating. The risk ratings are also confirmed through periodic loan review examinations which are currently performed by both an independent third-party and the Company's internal loan review department. Results from examinations are presented to the Audit Committee of the Board of Directors. Management estimates the amount of loan losses for loans collectively evaluated for impairment by applying quantitative loss factors to the loan segments at the risk rating level and applying qualitative adjustments to each loan segment at the portfolio level. Quantitative loss factors give consideration to historical loss experience and migration experience by loan type based upon an appropriate look-back period, adjusted for a loss emergence period. Qualitative adjustments give consideration to other qualitative or environmental factors such as trends and levels of delinquencies, impaired loans, charge-offs, recoveries and loan volumes, as well as national and local economic trends and conditions. Qualitative adjustments reflect risks in the loan portfolio not captured by the quantitative loss factors and, as such, are evaluated from a risk level perspective relative to the risk levels present over the look-back period. The reserves resulting from the application of both the quantitative experience and qualitative factors are combined to arrive at the allowance for loan losses. Management believes the primary risks inherent in the portfolio are a general decline in the economy, a decline in real estate market values, rising or elevated unemployment, increasing vacancy rates, and increases in interest rates in the absence of economic improvement. Any one or a combination of these events may adversely affect a borrowers’ ability to repay their loan, resulting in increased delinquencies and loan losses. Accordingly, the Company has recorded loan losses at a level which is estimated to represent the current risk in its loan portfolio. Management considers it important to maintain the ratio of the allowance for loan losses to total loans at an acceptable level considering the current composition of the loan portfolio. Although management believes that the Company has established and maintains the allowance for loan losses at appropriate levels, additional reserves may be necessary if future economic and other conditions differ substantially from the current operating environment. Management evaluates its estimates and assumptions on an ongoing basis and the estimates and assumptions are adjusted when facts and circumstances necessitate a re-valuation of the estimate. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. In addition, regulatory agencies periodically review the adequacy of the Company’s allowance for loan losses as an integral part of their examination process. Such agencies may require the Company to recognize additions to the allowance or additional write-downs based on their judgments about information available to them at the time of their examination. Although management uses the best information available, the level of the allowance for loan losses remains an estimate that is subject to significant judgment. The Bank defines a loan as impaired when, based on current information and events, it is probable that a creditor will be unable to collect all amounts due under the contractual terms of the loan agreement. All multifamily and commercial real estate, construction, and commercial business loans with an outstanding balance of greater than $500,000 and not accruing, loans modified in a troubled debt restructuring (TDR), and other loans if there is specific information of a collateral shortfall are individually evaluated for impairment. Impairment is measured by determining the present value of expected future cash flows or, for collateral-dependent loans, the fair value of the collateral less estimated selling costs. The following table summarizes loans receivable and allowance for loan losses by portfolio segment and impairment method at December 31, 2018 and 2017 : (5) Loans Receivable and Allowance for Loan Losses (continued) December 31, 2018 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Unallocated Total (In thousands) Allowance for loan losses: Individually evaluated for impairment $ 537 $ — $ — $ 366 $ 12 $ — $ — $ 915 Collectively evaluated for impairment 14,695 23,251 7,217 13,810 2,446 8 — 61,427 Total $ 15,232 $ 23,251 $ 7,217 $ 14,176 $ 2,458 $ 8 $ — $ 62,342 Total loans: Individually evaluated for impairment $ 9,048 $ 2,695 $ — $ 2,944 $ 3,100 $ — $ — $ 17,787 Collectively evaluated for impairment 1,821,138 2,139,459 261,473 330,932 390,392 1,108 — 4,944,502 Total gross loans $ 1,830,186 $ 2,142,154 $ 261,473 $ 333,876 $ 393,492 $ 1,108 $ — $ 4,962,289 (5) Loans Receivable and Allowance for Loan Losses (continued) December 31, 2017 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Unallocated Total (In thousands) Allowance for loan losses: Individually evaluated for impairment $ 423 $ 28 $ — $ 80 $ 15 $ — $ — $ 546 Collectively evaluated for impairment 19,568 19,905 5,217 8,195 4,561 8 178 57,632 Total $ 19,991 $ 19,933 $ 5,217 $ 8,275 $ 4,576 $ 8 $ 178 $ 58,178 Total loans: Individually evaluated for impairment $ 11,644 $ 3,693 $ — $ 4,263 $ 2,591 $ — $ — $ 22,191 Collectively evaluated for impairment 1,603,356 1,866,782 233,652 273,707 445,329 998 — 4,423,824 Total gross loans $ 1,615,000 $ 1,870,475 $ 233,652 $ 277,970 $ 447,920 $ 998 $ — $ 4,446,015 Loan modifications to borrowers experiencing financial difficulties that are considered troubled debt restructurings ("TDRs") primarily involve the lowering of the monthly payments on such loans through either a reduction in interest rate below a market rate, an extension of the term of the loan without a corresponding adjustment to the risk premium reflected in the interest rate, or a combination of these two methods. These modifications generally do not result in the forgiveness of principal or accrued interest. In addition, the Company attempts to obtain additional collateral or guarantor support when modifying such loans. Non-accruing restructured loans may be returned to accrual status when there has been a sustained period of repayment performance (generally six consecutive months of payments) and both principal and interest are deemed collectible. (5) Loans Receivable and Allowance for Loan Losses (continued) The following tables present the number of loans modified as TDRs for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, along with their balances immediately prior to the modification date and post-modification. Post-modification recorded investment represents the net book balance immediately following modification. For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 No. of Loans Pre-modification recorded investment Post-modification recorded investment No. of Loans Pre-modification recorded investment Post-modification recorded investment ( Dollars in thousands) Troubled Debt Restructurings Real estate loans: One-to-four family 5 $ 801 $ 801 — $ — $ — Multifamily and commercial 1 65 65 — — — Commercial business loans — — — — — — Consumer loans: Home equity loans and advances 1 588 588 — — — Total restructured loans 7 $ 1,454 $ 1,454 — $ — $ — For the Years Ended September 30, 2017 2016 No. of Loans Pre-modification recorded investment Post-modification recorded investment No. of Loans Pre-modification recorded investment Post-modification recorded investment (Dollars in thousands) Troubled Debt Restructurings Real estate loans: One-to-four family 3 $ 548 $ 548 — $ — $ — Multifamily and commercial 1 3,964 3,964 — — — Commercial business loans 1 18 18 3 255 255 Consumer loans: Home equity loans and advances 2 248 248 1 103 103 Total restructured loans 7 $ 4,778 $ 4,778 4 $ 358 $ 358 The activity in the allowance for loan losses for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 are as follows: (5) Loans Receivable and Allowance for Loan Losses (continued) Year Ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Balance at beginning of period $ 58,178 $ 54,633 $ 51,867 $ 56,948 Provision charged 6,677 3,400 6,426 417 Recoveries 707 188 584 721 Charge-offs (3,220 ) (43 ) (4,244 ) (6,219 ) Balance at end of period $ 62,342 $ 58,178 $ 54,633 $ 51,867 The activity in the allowance for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 are as follows: For the Year Ended December 31, 2018 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Unallocated Total (In thousands) Balance at beginning of period $ 19,991 $ 19,933 $ 5,217 $ 8,275 $ 4,576 $ 8 $ 178 $ 58,178 Provision charged (credited) (4,503 ) 3,445 1,997 7,860 (1,949 ) 5 (178 ) 6,677 Recoveries 334 2 3 240 122 6 — 707 Charge-offs (590 ) (129 ) — (2,199 ) (291 ) (11 ) — (3,220 ) Balance at end of period $ 15,232 $ 23,251 $ 7,217 $ 14,176 $ 2,458 $ 8 $ — $ 62,342 For the Three Months Ended December 31, 2017 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Unallocated Total (In thousands) Balance at beginning of period $ 18,533 $ 18,029 $ 5,299 $ 8,480 $ 4,190 $ 8 $ 94 $ 54,633 Provision charged (credited) 1,473 1,906 (82 ) (373 ) 389 3 84 3,400 Recoveries 9 — — 171 6 2 — 188 Charge-offs (24 ) (2 ) — (3 ) (9 ) (5 ) — (43 ) Balance at end of period $ 19,991 $ 19,933 $ 5,217 $ 8,275 $ 4,576 $ 8 $ 178 $ 58,178 (5) Loans Receivable and Allowance for Loan Losses (continued) For the Year Ended September 30, 2017 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Unallocated Total (In thousands) Balance at beginning of period $ 18,638 $ 17,390 $ 5,960 $ 5,721 $ 4,052 $ 11 $ 95 $ 51,867 Provision charged (credited) 1,029 1,644 (661 ) 3,183 1,219 13 (1 ) 6,426 Recoveries 268 75 — 182 59 — — 584 Charge-offs (1,402 ) (1,080 ) — (606 ) (1,140 ) (16 ) — (4,244 ) Balance at end of period $ 18,533 $ 18,029 $ 5,299 $ 8,480 $ 4,190 $ 8 $ 94 $ 54,633 For the Year Ended September 30, 2016 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Unallocated Total (In thousands) Balance at beginning of period $ 16,442 $ 20,352 $ 6,248 $ 7,094 $ 6,111 $ 4 $ 697 $ 56,948 Provision charged (credited) 5,534 (2,106 ) (43 ) (1,323 ) (1,061 ) 18 (602 ) 417 Recoveries 158 23 76 408 55 1 — 721 Charge-offs (3,496 ) (879 ) (321 ) (458 ) (1,053 ) (12 ) — (6,219 ) Balance at end of period $ 18,638 $ 17,390 $ 5,960 $ 5,721 $ 4,052 $ 11 $ 95 $ 51,867 (5) Loans Receivable and Allowance for Loan Losses (continued) The following table presents loans individually evaluated for impairment by loan segment: At December 31, 2018 Recorded investment Unpaid principal balance Specific allowance (In thousands) With no allowance recorded: Real estate loans: One-to-four family $ 4,156 $ 5,307 $ — Multifamily and commercial 2,695 3,482 — Commercial business loans 2,285 2,374 — Consumer loans: Home equity loans and advances 2,511 2,866 — 11,647 14,029 — With a specific allowance recorded: Real estate loans: One-to-four family 4,892 4,939 537 Commercial business loans 659 768 366 Consumer loans: Home equity loans and advances 589 589 12 6,140 6,296 915 Total: Real estate loans: One-to-four family 9,048 10,246 537 Multifamily and commercial 2,695 3,482 — Commercial business loans 2,944 3,142 366 Consumer loans: Home equity loans and advances 3,100 3,455 12 Total loans $ 17,787 $ 20,325 $ 915 (5) Loans Receivable and Allowance for Loan Losses (continued) December 31, 2017 Recorded investment Unpaid principal balance Specific allowance (In thousands) With no allowance recorded: Real estate loans: One-to-four family $ 8,870 $ 9,704 $ — Multifamily and commercial 2,058 2,933 — Commercial business loans 1,522 2,015 — Consumer loans: Home equity loans and advances 2,161 2,601 — 14,611 17,253 — With a specific allowance recorded: Real estate loans: One-to-four family 2,774 2,788 423 Multifamily and commercial 1,635 2,208 28 Commercial business loans 2,741 2,741 80 Consumer loans: Home equity loans and advances 430 430 15 7,580 8,167 546 Total: Real estate loans: One-to-four family $ 11,644 $ 12,492 $ 423 Multifamily and commercial 3,693 5,141 28 Commercial business loans 4,263 4,756 80 Consumer loans: Home equity loans and advances 2,591 3,031 15 Total loans $ 22,191 $ 25,420 $ 546 Specific allocations of the allowance for loan losses attributable to impaired loans totaled $915,000 and $546,000 at December 31, 2018 and December 31, 2017 , respectively. At December 31, 2018 and December 31, 2017 , impaired loans for which there was no related allowance for loan losses totaled $11.6 million and $14.6 million , respectively. (5) Loans Receivable and Allowance for Loan Losses (continued) The following table presents interest income recognized for loans individually evaluated for impairment at December 31, 2018 and 2017, by loan segment, for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 Average recorded investment Interest income recognized Average recorded investment Interest income recognized (In thousands) Real estate loans: One-to-four family $ 10,224 $ 445 $ 14,015 $ 110 Multifamily and commercial 2,712 155 4,087 39 Commercial business loans 3,060 118 3,870 46 Consumer loans: Home equity loans and advances 3,361 173 3,618 35 Totals $ 19,357 $ 891 $ 25,590 $ 230 For the Years Ended September 30, 2017 2016 Average recorded investment Interest income recognized Average recorded investment Interest income recognized (In thousands) Real estate loans: One-to-four family $ 15,027 $ 469 $ 18,119 $ 565 Multifamily and commercial 4,328 279 9,344 57 Construction — — 505 — Commercial business loans 3,796 195 4,514 110 Consumer loans: Home equity loans and advances 3,903 136 3,446 157 Totals $ 27,054 $ 1,079 $ 35,928 $ 889 The recorded investment in TDRs totaled $16.0 million at December 31, 2018, of which one loan totaling $101,000 was over 90 days past due, and seven loans totaling $1.0 million were 30-59 days past due. The remaining loans modified were current at the time of restructuring and have complied with the terms of their restructure agreement at December 31, 2018. The recorded investment in TDRs totaled $17.6 million at December 31, 2017, of which two loans totaling $425,000 were over 90 days past due. The remaining loans modified were current at the time of restructuring and have complied with the terms of their restructure agreement at December 31, 2017. The recorded investment in TDRs totaled $21.1 million at September 30, 2017, of which seven loans totaling $1.0 million were over 90 days past due. The remaining loans modified were current at the time of restructuring and have complied with the terms of their restructure agreement at September 30, 2017. (5) Loans Receivable and Allowance for Loan Losses (continued) The following table presents loans receivable by credit quality risk indicator and by loan segment at December 31, 2018 and 2017 : December 31, 2018 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Total (In thousands) Pass $ 1,826,066 $ 2,128,680 $ 261,473 $ 320,451 $ 392,092 $ 1,108 $ 4,929,870 Special mention — — — 9,074 — — 9,074 Substandard 4,120 13,474 — 4,351 1,400 — 23,345 Doubtful — — — — — — — Total $ 1,830,186 $ 2,142,154 $ 261,473 $ 333,876 $ 393,492 $ 1,108 $ 4,962,289 December 31, 2017 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Total (In thousands) Pass $ 1,605,413 $ 1,851,037 $ 233,652 $ 268,355 $ 446,264 $ 998 $ 4,405,719 Special mention — 4,782 — 3,678 — — 8,460 Substandard 9,587 14,656 — 5,937 1,656 — 31,836 Doubtful — — — — — — — Total $ 1,615,000 $ 1,870,475 $ 233,652 $ 277,970 $ 447,920 $ 998 $ 4,446,015

Office Properties and Equipment

Office Properties and Equipment, net	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Office Properties and Equipment, net	Office Properties and Equipment, net Office properties and equipment less accumulated depreciation at December 31, 2018 and December 31, 2017 are summarized as follows: December 31, 2018 2017 (In thousands) Land $ 7,829 $ 7,829 Buildings 24,018 24,018 Land and building improvements 24,864 15,583 Leasehold improvements 21,279 19,821 Furniture and equipment 28,538 26,036 106,528 93,287 Less accumulated depreciation and amortization 54,478 50,667 Total office properties and equipment, net $ 52,050 $ 42,620 (6) Office Properties and Equipment, net (continued) Land and building improvements at December 31, 2018 and 2017 included $8.9 million and $5.5 million , respectively, in construction in progress for the renovation of the Bank's corporate headquarters and various other facilities. Depreciation and amortization expense for the years ended December 31, 2018 , September 30, 2017 and 2016, the three months ended December 31, 2017, amounted to $3.8 million , $3.4 million , $3.2 million , and $863,000 respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets Intangible assets at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 (In thousands) Goodwill $ 5,716 $ 5,716 Mortgage servicing rights 369 281 $ 6,085 $ 5,997 Mortgage servicing rights' amortization expense for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 amounted to $73,000 , $105,000 , $105,000 , and $22,000 respectively. During the year ended December 31, 2018, $161,000 in additional mortgage servicing rights were recorded. There were no additional mortgage servicing rights recorded during the years ended September 30, 2017 and 2016, and the three months ended December 31, 2017.

Deposits

Deposits	12 Months Ended
	Dec. 31, 2018
Banking and Thrift [Abstract]
Deposits	Deposits Deposits at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 Balance Weighted average rate Balance Weighted average rate (Dollars in thousands) Non-interest-bearing demand $ 723,794 — % $ 719,339 — % Interest-bearing demand 1,219,381 0.95 1,332,297 0.66 Money market accounts 259,694 0.67 262,396 0.29 Savings and club deposits 510,688 0.16 545,401 0.16 Certificates of deposit 1,700,316 2.01 1,403,882 1.43 Total deposits $ 4,413,873 1.09 % $ 4,263,315 0.72 % The aggregate amount of certificates of deposit that meet or exceed $100,000 totaled approximately $885.3 million and $640.1 million as of December 31, 2018 and 2017 , respectively. (8) Deposits (continued) Scheduled maturities of certificates of deposit accounts at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 (In thousands) One year or less $ 1,107,667 $ 669,610 After one year to two years 326,800 474,475 After two years to three years 230,468 169,069 After three years to four years 24,939 68,184 After four years 10,442 22,544 $ 1,700,316 $ 1,403,882 Interest expense on deposits for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 are summarized as follows: Year Ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Demand (including money market accounts) $ 12,933 $ 2,509 $ 8,556 $ 7,735 Savings and club deposits 993 210 630 613 Certificates of deposit 25,597 4,912 16,395 15,714 $ 39,523 $ 7,631 $ 25,581 $ 24,062

Borrowings

Borrowings	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Borrowings	Borrowings Borrowed funds at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 2018 2017 Balance Weighted average interest rate (In thousands) Overnight lines of credit $ 159,600 $ 46,000 2.60 % 1.53 % Federal Home Loan Bank advances 1,029,580 822,400 2.40 1.92 Junior subordinated debt — 50,657 — 8.00 Securities sold under agreements to repurchase — 10,000 — 3.23 $ 1,189,180 $ 929,057 2.43 % 2.25 % At December 31, 2018 and 2017 , the Company had outstanding overnight lines of credit with the Federal Home Loan Bank of $159.6 million and $46.0 million , respectively. Interest expense on the overnight advances for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, were $2.2 million , $233,000 , $42,000 , and $70,000 respectively. (9) Borrowings (continued) At December 31, 2018, the Bank could borrow funds from the FHLB under an overnight advance program up to the Bank's maximum borrowing capacity based on its ability to collateralize such borrowings. Members in good standing can borrow up to 50% of their asset size as long as they have qualifying collateral to support the advance and purchase of FHLB capital. Additionally, at both December 31, 2018 and 2017 , the Bank had unused correspondent bank lines of credit with an aggregate overnight borrowing capacity of $225.0 million . At December 31, 2018 FHLB advances were at fixed rates with maturities between January 2019 and December 2022, and at December 31, 2017 , FHLB advances were at fixed rates with maturities between January 2018 and September 2021. At December 31, 2018 and 2017 , FHLB advances were collateralized by FHLB capital stock owned by the Bank and loans with carrying values totaling $1.7 billion and $1.6 billion , respectively. Loans securing advances consists of one-to-four family, multifamily, commercial and home equity real estate loans. Interest expense on FHLB advances for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 were $17.1 million , $12.8 million , $13.2 million , and $3.3 million respectively. At December 31, 2018 and 2017, FHLB advances totaling $320.0 million and $20.0 million , respectively, were outstanding in association with an interest rate swap program. See note 19 for information regarding these transactions. Scheduled maturities of FHLB advances including lines of credit at December 31, 2018 are summarized as follows: Year Ended December 31, 2018 (In thousands) One year or less $ 761,900 After one year to two years 229,045 After two years to three years 155,010 After three years to four years 43,225 After four years — Total FHLB advances $ 1,189,180 At December 31, 2018 and 2017 , the junior subordinated debt balances were $0 and $50.7 million , respectively. In August 2018, the Company redeemed all junior subordinated debt securities. The carrying value as of December 31, 2017 included deferred issuance costs of $890,000 . Interest expense for the year ended December 31, 2018 was $3.5 million . Interest expense for both the years ended September 30, 2017 and 2016 was $4.2 million , while interest expense for the three months ended December 31, 2017 was $1.0 million . At December 31, 2018 and 2017 , the balance of securities sold under agreements to repurchase were $0 and $10.0 million , respectively. Interest expense on securities sold under agreements to repurchase for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 were $3,000 , $1.6 million , $2.4 million , and $203,000 respectively. As of December 31, 2018 and 2017 , securities available for sale with a carrying value of $0 and $12.9 million , respectively, were pledged to secure these borrowings.

Regulatory Capital

Regulatory Capital	12 Months Ended
	Dec. 31, 2018
Banking and Thrift [Abstract]
Regulatory Capital	Regulatory Capital The Company and its subsidiary Bank are subject to regulatory capital requirements promulgated by the federal banking agencies. The Federal Reserve establishes capital requirements, including well capitalized standards, for the consolidated financial holding company, and the OCC has similar requirements for the Company's subsidiary bank. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company's consolidated statements of financial condition. Federal regulators require federally insured depository institutions to meet several minimum capital standards: (1) total capital to risk-weighted assets of 8.0% ; (2) tier 1 capital to risk-weighted assets of 6.0% ; (3) common equity tier 1 capital to risk-weighted assets of 4.5% ; and (4) tier 1 capital to adjusted total assets of 4.0% . In addition to establishing the minimum regulatory capital requirements, (10) Regulatory Capital the regulations limit capital distributions and certain discretionary bonus payments to management if the institution does not hold a "capital conservation buffer" consisting of 2.5% of common equity tier 1 capital to risk-weighted assets above the amount necessary to meet its minimum risk-based capital requirements. The capital conservation buffer requirement was phased in beginning January 1, 2016, at 0.625% of risk-weighted assets and increased each year until it was fully implemented at 2.5% on January 1, 2019. The regulators established a framework for the classification of savings institutions into five categories: well capitalized, adequately capitalized, undercapitalized, significantly undercapitalized, and critically undercapitalized. Generally, an institution is considered well capitalized if it has: a total capital to risk-weighted assets ratio of at least 10.0% , a tier 1 capital to risk-weighted assets ratio of at least 8.0% , a common tier 1 capital to risk-weighted assets ratio of at least 6.5% , and a tier 1 capital to adjusted total assets ratio of at least 5.0% . As of December 31, 2018 and 2017, the Company and the Bank exceeded all capital adequacy requirements to which it is subject. Based upon most recent notification from federal banking regulators, the Bank was categorized as well capitalized as of September 30, 2018, under the regulatory framework for prompt corrective action. There are no conditions existing or events which have occurred since notification that management believes have changed the Bank's category. The following table presents the Company's and the Bank's actual capital amounts and ratios as of December 31, 2018 and 2017 as compared to the Federal Reserve Bank minimum capital adequacy requirements and the Federal Reserve Bank requirements for classification as a well-capitalized institution: (10) Regulatory Capital (continued) Actual Minimum capital adequacy requirements Minimum capital adequacy requirements with capital conservation buffer To be well capitalized under prompt corrective action provisions Amount Ratio Amount Ratio Amount Ratio Amount Ratio Company (In thousands, except ratio data) At December 31, 2018: Total capital (to risk-weighted assets) $ 1,094,062 23.45 % $ 373,276 8.00 % $ 460,763 9.88 % N/A N/A Tier 1 capital (to risk-weighted assets) 1,035,477 22.19 279,957 6.00 367,444 7.88 N/A N/A Common equity tier 1 capital (to risk-weighted assets) 1,035,477 22.19 209,968 4.50 297,455 6.38 N/A N/A Tier 1 capital (to adjusted total assets) 1,035,477 15.75 263,037 4.00 263,037 4.00 N/A N/A At December 31, 2017: Total capital (to risk-weighted assets) $ 631,952 15.01 % $ 336,730 8.00 % $ 389,244 9.25 % N/A N/A Tier 1 capital (to risk-weighted assets) 579,080 13.76 252,547 6.00 305,161 7.25 N/A N/A Common equity tier 1 capital (to risk-weighted assets) 528,080 12.55 189,410 4.50 242,025 5.75 N/A N/A Tier 1 capital (to adjusted total assets) 579,080 10.54 219,833 4.00 219,833 4.00 N/A N/A Bank At December 31, 2018: Total capital (to risk-weighted assets) $ 886,728 19.04 % $ 372,550 8.00 % $ 459,866 9.88 % $ 465,687 10.00 % Tier 1 capital (to risk-weighted assets) 828,257 17.79 279,412 6.00 366,729 7.88 372,550 8.00 Common equity tier 1 capital (to risk-weighted assets) 828,257 17.79 209,559 4.50 296,875 6.38 302,697 6.50 Tier 1 capital (to adjusted total assets) 828,257 12.60 263,025 4.00 263,025 4.00 328,781 5.00 At December 31, 2017: Total capital (to risk-weighted assets) $ 625,336 14.90 % $ 335,736 8.00 % $ 388,196 9.25 % $ 419,671 10.00 % Tier 1 capital (to risk-weighted assets) 572,617 13.64 251,802 6.00 304,262 7.25 335,736 8.00 Common equity tier 1 capital (to risk-weighted assets) 572,617 13.64 188,852 4.50 241,311 5.75 272,786 6.50 Tier 1 capital (to adjusted total assets) 572,617 10.44 221,257 4.00 221,257 4.00 276,571 5.00

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Employee Benefit Plans	Plans Pension Plan, Retirement Income Maintenance Plan (the "RIM Plan") and Post-retirement Plan The Company maintains a single employer, tax-qualified defined benefit pension plan ( the "Pension Plan") which covers full-time employees that satisfy the plan eligibility requirements. The benefits are based on years of service and the employee's compensation during the last five years of employment. During the year ended December 31, 2018, the pension plan was amended. Effective October 1, 2018, employees hired by the Bank are not eligible to participate in the Bank's pension plan as the plan has been closed to new employees as of that date, and effective January 1, 2019, the Post-retirement Plan has also been closed to new hires. The Company's policy is to fund at least the minimum contribution required by the Employee Retirement Income Security Act of 1974. GAAP requires an employer to: (a) recognize in its statement of financial position the over-funded or under-funded status of a defined benefit post-retirement plan measured as the difference between the fair value of plan assets and the benefit obligation; (b) measure a plan’s assets and its obligations that determine its funded status at the end of the employer’s fiscal year (with limited exceptions); and (c) recognize as a component of other comprehensive income (loss), net of tax, the actuarial gains and losses and the prior service costs and credits that arise during the period. The assets of the plan are primarily invested in fixed income and equity funds. The Company also has a RIM Plan, which is a non-qualified defined benefit plan which provides benefits to all employees of the Company if their benefits under the Pension Plan are limited by Internal Revenue Code 415 and 401(a)(17). In addition, the Company provides certain health care and life insurance benefits to eligible retired employees under a Post-retirement Plan. The Company accrues the cost of retiree health care and other benefits during the employees’ period of active service. The following table sets forth information regarding the Pension, RIM and Post-retirement Plans at December 31, 2018 and 2017 : December 31, 2018 2017 2018 2017 2018 2017 Pension RIM Post-retirement (In thousands) Change in benefit obligation: Benefit obligation at beginning of year $ 229,156 $ 216,992 $ 12,243 $ 11,032 $ 22,078 $ 22,133 Service cost 7,805 7,496 282 238 417 445 Interest cost 8,489 8,461 443 433 796 762 Actuarial (gain) loss (30,703 ) 4,543 (1,355 ) 874 (1,845 ) (726 ) Benefits paid (5,542 ) (8,336 ) (328 ) (334 ) (482 ) (536 ) Benefit obligation at end of year 209,205 229,156 11,285 12,243 20,964 22,078 Change in plan assets: Fair value of plan assets at beginning of year 289,390 257,513 — — — — Actuarial return on plan assets (10,874 ) 27,213 — — — — Employer contributions — 13,000 328 334 482 536 Benefits paid (5,542 ) (8,336 ) (328 ) (334 ) (482 ) (536 ) Fair value of plan assets at end of year 272,974 289,390 — — — — Funded status at end of year $ 63,769 $ 60,234 $ (11,285 ) $ (12,243 ) $ (20,964 ) $ (22,078 ) (11) Employee Benefit Plans (continued) At December 31, 2018 and 2017 , the unfunded liability for the RIM and Post-retirement Plans of $11.3 million and $21.0 million , and $12.2 million and $22.1 million , respectively, were included in other liabilities in the Consolidated Statements of Financial Condition, and the over-funded pension benefits associated with the Pension Plan totaling $63.8 million and $60.2 million , respectively, were included in other assets. The components of accumulated other comprehensive income (loss) related to the Pension, RIM , and Post-retirement Plans on a pre-tax basis, at December 31, 2018 and 2017, and September 30, 2017 and 2016 are summarized in the following table: At December 31, At December 31, 2018 2017 Pension RIM Post-retirement Pension RIM Post-retirement (In thousands) Unrecognized prior service costs $ — $ — $ — $ — $ — $ (106 ) Unrecognized net actuarial income 59,579 3,748 4,226 61,731 5,515 6,395 Total accumulated other comprehensive income $ 59,579 $ 3,748 $ 4,226 $ 61,731 $ 5,515 $ 6,289 At September 30, 2017 2016 2017 2016 2017 2016 Pension RIM Post-retirement (In thousands) Unrecognized prior service costs $ — $ — $ — $ — $ (140 ) $ (276 ) Unrecognized net actuarial income 55,438 74,768 4,725 5,154 4,611 8,374 Total accumulated other comprehensive income $ 55,438 $ 74,768 $ 4,725 $ 5,154 $ 4,471 $ 8,098 Net periodic benefit (income) cost for Pension, RIM and Post-retirement plans for the years ended December 31, 2018 , September 30, 2017 and 2016 and the three months ended December 31, 2017, includes the following components: For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 Pension RIM Post-retirement Pension RIM Post-retirement (In thousands) Service cost $ 7,805 $ 282 $ 417 $ 1,780 $ 60 $ 92 Interest cost 8,489 443 796 2,128 111 205 Expected return on plan assets (20,794 ) — — (4,814 ) — — Amortization: Prior service credit — — (106 ) — — (34 ) Net loss 3,117 413 323 707 103 70 Net periodic (income) cost $ (1,383 ) $ 1,138 $ 1,430 $ (199 ) $ 274 $ 333 (11) Employee Benefit Plans (continued) For the Years Ended September 30, 2017 2016 2017 2016 2017 2016 Pension RIM Post-retirement (In thousands) Service cost $ 7,621 $ 6,188 $ 237 $ 140 $ 471 $ 447 Interest cost 8,444 8,096 429 385 742 854 Expected return on plan assets (24,809 ) (22,706 ) — — — — Amortization: Prior service credit — — — — (136 ) (136 ) Net loss 10,998 8,490 453 283 325 339 Net periodic cost $ 2,254 $ 68 $ 1,119 $ 808 $ 1,402 $ 1,504 The weighted average actuarial assumptions used in the plan determinations at and for the years ended December 31, 2018 , September 30, 2017 and 2016 and the three months ended December 31, 2017 were as follows: At and For the Year Ended December 31, At and For the Three Months Ended December 31, 2018 2017 Pension RIM Post-retirement Pension RIM Post-retirement Weighted average assumptions used to determine benefit obligation: Discount rate 4.570 % 4.470 % 4.410 % 3.750 % 3.625 % 3.625 % Rate of compensation increase 3.500 % 3.500 % N/A 3.500 % 3.500 % N/A Weighted average assumptions used to determine net periodic benefit cost: Discount rate 3.750 % 4.470 % 3.625 % 4.000 % 3.875 % 3.875 % Expected rate of return on plan assets 7.250 % N/A N/A 7.250 % N/A N/A Rate of compensation increase 3.500 % 3.500 % N/A 3.500 % 3.500 % N/A At and For the Years Ended September 30, 2018 2017 2018 2017 2018 2017 Pension RIM Post-retirement Weighted average assumptions used to determine benefit obligation: Discount rate 4.000 % 3.875 % 3.875 % 3.625 % 3.875 % 3.625 % Rate of compensation increase 3.500 3.500 3.500 3.500 N/A N/A Weighted average assumptions used to determine net periodic benefit cost: Discount rate 3.875 % 4.500 % 3.625 % 4.375 % 3.625 % 4.375 % Expected rate of return on plan assets 7.500 7.500 N/A N/A N/A N/A Rate of compensation increase 3.500 3.500 3.500 3.500 N/A N/A The Company provides its actuaries with certain rate assumptions used in measuring the respective benefit obligations. The most significant of these is the discount rate used to calculate the period-end present value of the benefit obligations, and the expense to be included in the following year's financial statements. A lower discount rate will result in a higher benefit obligation and expense, while a higher discount rate will result in a lower benefit obligation and expense. The discount rate assumption was determined based on a cash flow-yield curve model specific to the Company's pension and post-retirement plans. (11) Employee Benefit Plans (continued) The Company compares this rate to certain market indices, such as long-term treasury bonds, or pension liability indices, for reasonableness. The Company's expected return on plan assets assumption is based on historical investment return rate experience and evaluation of input from the trustee managing the pension plan's assets and the Bank's Pension Committee which has responsibility for managing these assets. The expected return on pension plan assets is also impacted by the target allocation of assets, which is based on the Company's goal of earning the highest rate of return while maintaining risk at acceptable levels. Assumed health care cost trend rates have a significant effect on the amounts reported for health care plans. A 1% change in the assumed health care cost trend rate would have the following effects on post-retirement benefits at December 31, 2018 : 1% increase 1% decrease (In thousands) Effect on total service cost and interest cost $ 14 $ (12 ) Effect on post-retirement benefit obligations 130 (120 ) Estimated future benefit payments, which reflect expected future service, as appropriate for the next five years are as follows: Pension RIM Post-retirement (In thousands) 2019 $ 5,791 $ 329 $ 1,079 2020 6,301 341 1,114 2021 6,892 377 1,171 2022 7,471 416 1,212 2023 8,167 458 1,249 Years 2024 - 2028 52,675 3,318 6,840 The Company does not anticipate making a discretionary cash contribution to the pension plan for the year ended December 31, 2019. The weighted average asset allocation of pension assets at December 31, 2018 and 2017 were as follows: December 31, 2018 2017 (In thousands) Domestic equities 35.20 % 38.10 % Foreign equities 10.80 13.90 Fixed income 42.30 36.90 Real estate 10.50 9.30 Cash 1.20 1.80 Total 100.00 % 100.00 % Management, under the direction of the Pension Committee, strives to have pension assets sufficiently diversified so that adverse or unexpected results from one security class will not have a significant detrimental impact on the entire portfolio. The target allocation of assets and acceptable ranges around the targets are as follows: (11) Employee Benefit Plans (continued) Allowable Range Equities 40-60% Fixed income 40-60% Real estate 0-10% Cash 0-15% The Pension Committee engages an investment management advisory firm to regularly monitor the performance of the asset managers and ensure they are within compliance with policy. The maximum and minimum of the range for each class is based on the fair value of the assets in the fund. If changes in fair value should lead to allocations outside these boundaries, management shall adjust exposure back to the established guidelines within 90 days or reevaluate the guidelines. The following tables present the assets that are measured at fair value on a recurring basis by level within the U.S. GAAP fair value hierarchy as reported on the Statements of Net Assets Available for Plan benefits at December 31, 2018 and 2017 , respectively. Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. December 31, 2018 Fair value measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Money market mutual funds $ 3,459 $ 3,459 $ — $ — Mutual funds - value stock fund 22,533 22,533 — — Mutual funds - fixed income 115,500 115,500 — — Mutual funds - international stock 29,441 29,441 — — Mutual funds - institutional stock index 73,450 73,450 — — Commingled real estate funds 28,591 — 28,591 — $ 272,974 $ 244,383 $ 28,591 $ — (11) Employee Benefit Plans (continued) December 31, 2017 Fair value measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Money market mutual funds $ 5,236 $ 5,236 $ — $ — Mutual funds - value stock fund 27,364 27,364 — — Mutual funds - fixed income 106,726 106,726 — — Mutual funds - international stock 40,388 40,388 — — Mutual funds - institutional stock index 82,831 82,831 — — Commingled real estate funds 26,845 — 26,845 — $ 289,390 $ 262,545 $ 26,845 $ — Money market and other mutual funds are reported at fair value in the table above utilizing exchange quoted prices in active markets for identical instruments (Level 1 inputs). The commingled trust funds are reported at their respective net asset values (Level 2). BOLI and Split-Dollar Life Insurance The Company has Bank-owned life insurance ("BOLI") which is a tax-advantaged transaction that is used to partially fund obligations associated with employee compensation and benefit programs. Policies are purchased insuring officers of the Company using a single premium method of payment. BOLI is accounted for using the cash surrender value and the increase in cash surrender value is included in non-interest income in the Company's Statements of Income. At December 31, 2018 and 2017 , the Company had $184.5 million and $150.5 million , respectively, in BOLI. BOLI income for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, was $5.2 million , $4.9 million , $4.4 million , and $1.1 million , respectively. The Company also provides life insurance benefits to eligible employees under an endorsement split-dollar life insurance program. The Company recognizes a liability for future benefits applicable to endorsement split-dollar life insurance arrangements that provide death benefits post-retirement. At December 31, 2018 and 2017 , $10.5 million and $5.9 million , respectively, related to the liability under this program was recognized in other liabilities in the Company's Consolidated Statements of Financial Condition. The BOLI expense related to the split-dollar benefit for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, was $1.3 million , $395,000 , $356,000 and $159,000 , respectively. Savings Income Maintenance Deferred Compensation Plan (the "SIM Plan") The Company also maintains a non-qualified defined contribution plan that provides supplemental benefits to certain executives who are prevented from receiving the full benefits contemplated by the 401(k) Plan under tax law limits for tax-qualified plans. The expense for the years ended December 31, 2018, September 30, 2017 and 2016, and the three months ended December 31, 2017 , was approximately $86,000 , $14,000 , $47,000 and $1,000 , respectively. 401(k) Plan The Company has a 401(k) plan covering substantially all employees of the Bank. The Bank may match a percentage of the first 3.00% to 4.50% contributed by participants. The Bank’s matching contribution, if any, is determined by the Board of Directors in its sole discretion. The expense for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 , was approximately $1.3 million , $1.2 million , $1.1 million and $289,000 , respectively. (11) Employee Benefit Plans (continued) Employee Stock Ownership Plan ("ESOP") Effective upon the consummation of the Company's reorganization in April 2018, an ESOP was established for all eligible employees. The ESOP used $45.4 million in proceeds from a twenty year term loan obtained from the Company to purchase 4,542,855 shares of Company common stock. The term loan principal is payable in installments through April 2038. Interest on the term loan is fixed at a rate of 4.75% . Each year, the Bank makes discretionary contributions to the ESOP, which are equal to principal and interest payments required on the term loan. Shares purchased with the loan proceeds were initially pledged as collateral for the term loan and is held in a suspense account for future allocation among participants. Contributions to the ESOP and shares released form the suspense account are allocated among the participants on the basis of compensation, as described by the ESOP, in the year of allocation. The ESOP shares pledged as collateral are reported as unearned ESOP shares in the Consolidated Statements of Financial Condition. As shares are committed to be released from collateral, the Bank reports compensation expense equal to the average market price of the shares during the year, and the shares become outstanding for basic net income per common share computations. ESOP compensation expense was $2.6 million for the year ended December 31, 2018 . There was no ESOP expense recorded for the years ended September 30, 2017 and 2016, or the three months ended December 31, 2017. The ESOP shares were as follows: December 31, 2018 (In thousands) Allocated shares 159 Unearned shares 4,384 Total ESOP shares 4,543 Fair value of unearned shares $ 67,025 Supplemental Executive Retirement Plan ("SERP") The Company has a SERP, which is a non-qualified plan which provides supplemental retirement benefits to eligible officers (those designated by the Board of Directors) of the Company who are prevented from receiving the full benefits contemplated by the ESOP's benefit formulas under tax law limits for tax-qualified plans. SERP compensation expense was $165,000 for the year ended December 31, 2018 . There was no SERP expense recorded for the years ended September 30, 2017 and 2016, and the three months ended December 31, 2017. Stock Based Deferral Plan and Directors Deferred Compensation Plan In addition, the Bank maintains a stock based deferral plan for certain executives and directors, and a cash based deferred compensation plan for directors. The Company records a deferred compensation equity instrument and corresponding contra-equity account for the cost of the shares held by the Stock Based Deferral Plan. Periodic adjustments to market are not required as participants do not have the option to take the distribution in cash. The Company records a liability for the amount deferred under the Directors Deferred Compensation Plan. There were no expenses recorded under these plans.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes On December 22, 2017, the President signed into law the Tax Act. The new law reduces the federal corporate income tax rate from 35% to 21% effective January 1, 2018. Under ASC 740, "Income Taxes", companies are required to recognize the effect of tax law changes in the period of enactment; therefore, the Company re-measured its deferred tax assets and liabilities at the enacted tax rate expected to apply when its temporary differences are expected to be realized or settled. As a result of the enactment of the Act, the Company recognized an additional tax expense of $11.7 million in December 2017. In 2017, the Company estimated the accounting for the effects of the 2017 Act. In 2018, under Staff Accounting Bulletin No. 118 ("SAB 118”), we finalized the accounting for the Act and our financial statements for the year ended December 31, 2018 and the three months ended December 31, 2017 reflect these changes. (12) Income Taxes (continued) The current and deferred amounts of income tax expense (benefit) for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 are as follows: Year ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Current: Federal $ 11,284 $ 630 $ 16,198 $ 13,209 State 5,129 862 1,236 664 Total current 16,413 1,492 17,434 13,873 Deferred: Federal (4,901 ) 7,530 (1,454 ) 2,743 State (589 ) (39 ) 28 187 Total deferred (5,490 ) 7,491 (1,426 ) 2,930 $ 10,923 $ 8,983 $ 16,008 $ 16,803 The Company reported deferred tax expense (benefit) of $1.4 million , $6.4 million , $(2.6) million and $(119,000) for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, respectively, related to the unrealized gains (losses) on securities available for sale, which is reported in accumulated other comprehensive income (loss), net of tax. Additionally, the Company recorded a deferred tax (benefit) expense of $(530,000) , $(4.2) million , $(3.3) million and $(94,000) , respectively, related to the amortization of post-retirement benefit obligations, which is reported in accumulated other comprehensive income, net of tax. A reconciliation between the amount of reported total income tax expense and the amount computed by multiplying the applicable statutory income tax rate (35% for the 2017 and 2016 periods presented below, and 21% for the 2018 period) is as follows: Year ended December 31, Three Months Ended December 31, September 30, 2018 2017 2017 2016 (In thousands) Tax expense at applicable statutory rate $ 7,067 $ 4,431 $ 16,478 $ 17,415 Increase (decrease) in taxes resulting from: State tax, net of federal income tax benefit 3,587 535 822 553 ESOP fair market value adjustment 202 — — — Tax exempt interest income (4 ) (2 ) (50 ) (28 ) Income from Bank-owned life insurance (812 ) (381 ) (1,589 ) (1,405 ) Dividend received deduction (16 ) (10 ) (40 ) (39 ) Impact of tax reform — 4,700 — — Other, net 899 (290 ) 387 307 $ 10,923 $ 8,983 $ 16,008 $ 16,803 The net deferred tax asset is included in other assets in the Consolidated Statements of Financial Condition. The tax effects of temporary differences that give rise to significant portions of the deferred tax assets and deferred tax liabilities at December 31, 2018 and 2017 are as follows: (12) Income Taxes (continued) At December 31, 2018 2017 (In thousands) Deferred tax assets: Allowance for loan losses $ 13,251 $ 12,584 Post retirement benefit 3,720 3,414 Deferred compensation 2,228 1,939 Depreciation 1,042 949 Retirement income maintenance plan 1,602 1,455 ESOP 128 — Stock-based compensation 35 — Reserve for uncollected interest 24 62 Net unrealized losses on securities and defined benefit plans 19,060 18,221 State NOL 2,063 2,476 Alternative minimum assessment carryforwards 2,156 2,156 Charitable contribution carryforward 6,085 — Other items 670 1,595 Gross deferred tax assets 52,064 44,851 Valuation allowance (2,388 ) (2,786 ) 49,676 42,065 Deferred tax liabilities: Pension expense 26,071 26,234 Deferred loan costs 5,736 4,257 Intangible assets 1,621 1,642 Other items 34 48 Total gross deferred tax liabilities 33,462 32,181 Net deferred tax asset $ 16,214 $ 9,884 Retained earnings at December 31, 2018 and 2017 includes approximately $21.5 million for which no provision for income tax has been made. This amount represents an allocation of income to bad debt deductions for tax purposes only. Events that would result in taxation of these reserves include the failure to qualify as a bank for tax purposes, distributions in complete or partial liquidation, stock redemptions and excess distributions to stockholders. Management believes that not all existing net deductible temporary differences that comprise the net deferred tax asset will reverse during periods in which the Company generates sufficient net taxable income. Accordingly, management has established a valuation allowance. Significant changes in the Company's operations and or economic conditions could affect the benefits of the recognized net deferred tax asset. Based on all available evidence, a valuation allowance was established for the portion of the state tax benefit that is not more likely than not to be realized. At December 31, 2018 and 2017 , the Company's valuation allowance totaled $2.4 million and $2.8 million , respectively. Based upon projections of future taxable income and the ability to carryforward net operating losses indefinitely, management believes it is more likely than not the Company will realize the remaining deferred tax asset. The Company had New Jersey net operating loss carryforwards of $2.1 million and $2.5 million , respectively, available to offset future taxable income as of December 31, 2018 and 2017 , respectively. If not utilized, these carryforwards will expire periodically through 2038. The Company files income tax returns in the United States federal jurisdiction and in the states of New Jersey, New York and Pennsylvania. As of December 31, 2018 , the Company is no longer subject to federal income tax examination for the years prior to 2014. Columbia Bank MHC and its subsidiaries' federal return is currently under audit for the tax year 2014. The Company is open for examination by the State of New Jersey for 2014, 2015, 2016 and 2017 and the States of New York and Pennsylvania for 2016 and 2017.

Financial Transactions with Off

Financial Transactions with Off-Balance-Sheet Risk and Concentrations of Credit Risk	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Financial Transactions with Off-Balance-Sheet Risk and Concentrations of Credit Risk	Financial Transactions with Off-Balance-Sheet Risk and Concentrations of Credit Risk The Company is a party to transactions with off-balance-sheet risk in the normal course of business in order to meet the financing needs of its customers. These transactions consist of commitments to extend credit and involve, to varying degrees, elements of credit and interest rate risk in excess of the amounts recognized in the consolidated statements of financial condition. At December 31, 2018 and 2017 , the following commitments existed which are not reflected in the consolidated statements of financial condition: December 31, 2018 2017 (In thousands) Loan commitments: Residential real estate $ 29,622 $ 58,860 Commercial real estate 73,201 17,994 Commercial business 13,000 14,796 Construction loans 71,062 20,715 Consumer home equity loans and lines of credit 8,344 5,858 Total loan commitments $ 195,229 $ 118,223 Unused lines of credit consisting of home equity lines, and undisbursed business and construction lines totaled approximately $714.6 million and $679.4 million as of December 31, 2018 and 2017 , respectively. Amounts drawn on the unused lines of credit are predominantly assessed interest at rates that fluctuate with the base rate. The Company uses the same credit policies and collateral requirements in making commitments and conditional obligations as it does for on-balance-sheet loans. Commitments to extend credit are agreements to lend customers 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. Since the commitments may expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. The Company evaluates each customer's creditworthiness on a case-by-case basis. The amount of collateral obtained, if deemed necessary by the Company upon extension of credit, is based on management's credit evaluation of the borrower. The Company principally grants residential, multifamily and commercial real estate loans, construction loans, commercial and industrial loans, home equity loans and advances and other consumer loans to borrowers primarily throughout New Jersey, in New York and Pennsylvania, and to a much lesser extent in a few other east coast states. Its borrowers' abilities to repay their obligations are dependent upon various factors, including the borrowers' income and net worth, cash flows generated by the underlying collateral, if any, or from business operations, value of the underlying collateral and priority of the Company's lien on the property. These factors are dependent on various economic conditions and circumstances beyond the Company's control , and as a result, the Company is subject to the risk of loss. The Company believes that its lending policies and procedures adequately minimize the potential exposure to such risks and adequate provisions for loan losses are provided for all probable and estimable losses. In the normal course of business, the Company sells residential real estate loans to third parties. These loan sales are subject to customary representations and warranties. In the event that the Company is found to be in breach of these representations and warranties, it may be obligated to repurchase certain of these loans. The Company has entered into derivative financial instruments to manage exposures that arise from business activities that result in the receipt or payment of future known and uncertain cash amounts, the value of which are determined by interest rates. The Company's derivative financial instruments are used to manage differences in the amount, timing, and duration of the Company's known or expected cash receipts and its know or expected cash payments principally related to the Company's borrowings. These derivatives were used to hedge the variability in cash flows associated with certain short-term funding transactions. The fair value of the derivatives as of December 31, 2018 was a net liability of $2.6 million , inclusive of accrued interest and variation margin posted in accordance with the Chicago Mercantile Exchange. (13) Financial Transactions with Off-Balance-Sheet Risk and Concentrations of Credit Risk (continued) In connection with its mortgage banking activities, the Company at December 31, 2018 , had commitments of approximately $8.1 million to sell loans, with serving retained by the Bank. In addition to the commitments noted above, the Company is party to standby letters of credit which are conditional commitments issued by the Bank to guarantee the performance of a customer to a third party. The guarantees generally extend for a term of up to one year and may be secured or unsecured. Outstanding letters of credit totaled $7.0 million and $11.6 million at December 31, 2018 and 2017 , respectively. Certain bank facilities are occupied under non-cancelable operating leases on buildings and land used for office space and banking purposes, which expire at various dates through February 2030. Certain lease agreements provide for renewal options and increases in rental payments based upon increases in the consumer price index or the lessor's cost of operating the facility. Minimum aggregate lease payments for the remainder of the lease terms are as follows: December 31, 2018 (In thousands) 2019 $ 3,596 2020 3,511 2021 3,288 2022 2,921 2023 2,590 Thereafter 5,209 Total lease commitments $ 21,115 Net occupancy expense, which represents rental expenses for Bank facilities, for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, totaled $4.6 million , $4.3 million , $4.0 million , and $1.1 million , respectively. In the normal course of business, there are outstanding various legal proceedings, claims, and contingent liabilities which are not included in the consolidated financial statements. In the opinion of management, the financial position of the Company will not be materially affected by the outcome of such legal proceedings and claims.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company utilizes fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures. The determination of fair values of financial instruments often requires the use of estimates. Where quoted market values in an active market are not readily available, the Company utilizes various valuation techniques to estimate fair value. Fair value is an estimate of 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. However, in many instances, fair value estimates may not be substantiated by comparison to independent markets and may not be realized in an immediate sale of the financial instrument. GAAP establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The three levels of fair value hierarchy are as follows: Level 1: Unadjusted quoted market prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities; Level 2: Quoted prices for identical or similar instruments in markets that are active or not active, or inputs that are observable or can be corroborated by observable market data for substantially the full term of the asset or liability; and (14) Fair Value Measurements (continued) Level 3: Prices or valuation techniques that require unobservable inputs that are both significant to the fair value measurement and unobservable (i.e., supported by minimal or no market activity). Valuation techniques include the use of option pricing models, discounted cash flow models and similar techniques. A financial instrument’s level within the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement. The valuation techniques are based upon the unpaid principal balance only and exclude any accrued interest or dividends at the measurement date. Interest income and expense and dividend income are recorded within the Consolidated Statements of Income depending on the nature of the instrument using the effective interest method based on the discount or premium. Assets and Liabilities Measured at Fair Value on a Recurring Basis The valuation techniques described below were used to measure fair value of financial instruments as reflected in the accompanying tables below on a recurring basis as of December 31, 2018 and 2017 . Securities Available for Sale For securities available for sale, fair value was estimated using a market approach. The majority of the Company’s securities are fixed income instruments that are not quoted on an exchange, but are traded in active markets. Prices for these instruments are obtained through third-party data service providers or dealer market participants with which the Company has historically transacted both purchases and sales of securities. Prices obtained from these sources include market quotations and matrix pricing. Matrix pricing, a Level 2 input, is a mathematical technique used principally to value certain securities to benchmark or to comparable securities. The Company evaluates the quality of Level 2 matrix pricing through comparison to similar assets with greater liquidity and evaluation of projected cash flows. As the Company is responsible for the determination of fair value, it performs quarterly analysis on the prices received from the pricing service to determine whether the prices are reasonable estimates of fair value. Specifically, the Company compares the prices received from the pricing service to a secondary pricing source. Additionally, the Company compares changes in the reported market values and returns to relevant market indices to assess the reasonableness of the reported prices. The Company’s internal price verification procedures and review of fair value methodology documentation provided by independent pricing services has not historically resulted in an adjustment in the prices obtained from the pricing service. The Company may hold equity securities and debt instruments issued by the U.S. government and U.S. government-sponsored agencies that are traded in active markets with readily accessible quoted market prices that are considered Level 1 inputs. Derivatives The Company records all derivatives on the Consolidated Statements of Financial Condition at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative, whether the Company has elected to designate a derivative in a hedging relationship and apply hedge accounting and whether the hedging relationship has satisfied the criteria necessary to apply hedge accounting. The Company has interest rate derivatives resulting from a service provided to certain qualified borrowers in a loan related transaction and, therefore, are not used to manage interest rate risk in the Company's assets or liabilities. As such, all changes in fair value of the Company's derivatives are recognized directly in earnings. The fair value of the Company's derivatives are determined using discounted cash flow analysis using observable market-based inputs, which are considered Level 2 inputs. (14) Fair Value Measurements (continued) The following tables present the assets and liabilities reported on the Consolidated Statements of Financial Condition at their fair values as of December 31, 2018 and 2017 , by level within the fair value hierarchy: December 31, 2018 Fair Value Measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Securities available for sale: U.S. government and agency obligations $ 54,157 $ 54,157 $ — $ — Mortgage-backed securities and collateralized mortgage obligations 920,007 — 920,007 — Municipal obligations 987 — 987 — Corporate debt securities 53,467 — 53,467 — Trust preferred securities 4,250 — 4,250 — Equity securities 1,890 1,890 — — Total securities available for sale 1,034,758 56,047 978,711 — Derivative assets 865 — 865 — $ 1,035,623 $ 56,047 $ 979,576 $ — Derivative liabilities $ 3,467 $ — $ 3,467 $ — December 31, 2017 Fair Value Measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Securities available for sale: U.S. government and agency obligations $ 39,644 $ 39,644 $ — $ — Mortgage-backed securities and collateralized mortgage obligations 606,612 — 606,612 — Municipal obligations 1,957 — 1,957 — Corporate debt securities 54,514 — 54,514 — Trust preferred securities 4,656 — 4,656 — Equity securities 3,187 3,187 — — Total securities available for sale 710,570 42,831 667,739 — Derivative assets 490 — 490 — $ 711,060 $ 42,831 $ 668,229 $ — Derivative liabilities $ 203 $ — $ 203 $ — There were no transfers between Level 1, Level 2, and Level 3 during the years ended December 31, 2018 , September 30, 2016 and the three months ended December 31, 2017. During the year ended September 30, 2017, U.S. Government and agency obligations with a carrying value of $20.4 million were transferred from Level 2 to Level 1. (14) Fair Value Measurements (continued) There were no Level 3 assets measured at fair value on a recurring basis at December 31, 2018 and 2017. Assets Measured at Fair Value on a Non-Recurring Basis The valuation techniques described below were used to estimate fair value of financial instruments measured on a non-recurring basis as of December 31, 2018 and 2017 . Collateral Dependent Impaired Loans Loans which meet certain criteria are evaluated individually for impairment. For loans measured for impairment based on the fair value of the underlying collateral, fair value was estimated using a market approach. The Company measures the fair value of collateral underlying impaired loans primarily through obtaining independent appraisals that rely upon quoted market prices for similar assets in active markets. These appraisals include adjustments, on an individual case-by-case basis, to comparable assets based on the appraisers’ market knowledge and experience, as well as adjustments for estimated costs to sell between 6% and 8% . The Company classifies these loans as Level 3 within the fair value hierarchy. Real Estate Owned Assets acquired through foreclosure or deed in lieu of foreclosure are carried at fair value, less estimated costs to sell between 6% and 8% . Fair value is generally based on independent appraisals that rely upon quoted market prices for similar assets in active markets. These appraisals include adjustments, on an individual case basis, to comparable assets based on the appraiser's market knowledge and experience, and are classified as Level 3. When an asset is acquired, the excess of the loan balance over fair value less estimated selling costs is charged to the allowance for loan losses. Operating results from real estate owned, including rental income, operating expenses, and gains and losses realized from the sales of real estate owned, are recorded as incurred. Mortgage Servicing Rights, Net Mortgage servicing rights are carried at the lower of cost or estimated fair value. The estimated fair value of MSRs is obtained through an analysis of future cash flows, incorporating assumptions that market participants would use in determining fair value including market discount rates, prepayments speeds, servicing income, servicing costs, default rates and other market driven data, including the market's perception of future interest rate movements. The prepayment speed and the discount rate are considered two of the most significant inputs in the model. A significant degree of judgment is involved in valuing the mortgage servicing rights using Level 3 inputs. The use of different assumptions could have a significant effect on this fair value estimate. The following tables present the assets and liabilities reported on the Consolidated Statements of Financial Condition at their fair values as of December 31, 2018 and 2017 , by level within the fair value hierarchy: December 31, 2018 Fair Value Measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Impaired loans $ 1,525 $ — $ — $ 1,525 Real estate owned 92 — — 92 Mortgage servicing rights 442 — — 442 $ 2,059 $ — $ — $ 2,059 (14) Fair Value Measurements (continued) December 31, 2017 Fair Value Measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Impaired loans $ 10,251 $ — $ — $ 10,251 Real estate owned 959 — — 959 Mortgage servicing rights 316 — — 316 $ 11,526 $ — $ — 23 $ 11,526 The following table presents qualitative information for Level 3 assets measured at fair value on a non-recurring basis as of December 31, 2018 and 2017 : December 31, 2018 Fair value Valuation methodology Unobservable inputs Range Weighted average (In thousands) Impaired loans $ 1,525 Appraised value (2) Discount for cost to sell (3) 6.0% - 8.0% 7.5% Real estate owned 92 Contract sales price (1) Discount for cost to sell (3) 6.0% 6.0% Mortgage servicing rights 442 Estimated cash flow Prepayment speeds 3.3% - 26.8% 12% December 31, 2017 Fair value Valuation methodology Unobservable inputs Range of inputs Weighted average (In thousands) Impaired loans $ 10,251 Appraised value (2) Discount for cost to sell (3) 6.0% - 8.0% 7.2% Real estate owned 959 Appraised value (2) Discount for cost to sell (3) 6.0% 6.0% Mortgage servicing rights 316 Estimated cash flow Prepayment speeds 3.6% -11.0% 3.9% (1) Value is based on signed contract for sale. (2) Value is based on an independent appraisal of the market or fair value of the loan's underlying collateral. (3) Includes commissions, fees and other costs. Other Fair Value Disclosures The Company is required to disclose estimated fair value of financial instruments, both assets and liabilities on and off the balance sheet, for which it is practicable to estimate fair value. A description of the valuation methodologies used for those assets and liabilities not recorded at fair value on a recurring or non-recurring basis are set forth below. (14) Fair Value Measurements (continued) Cash and Cash Equivalents For cash and due from banks, federal funds sold and short-term investments, the carrying amount approximates fair value due to their nature and short-term maturities. Securities Held to Maturity For securities held to maturity, fair value was estimated using a market approach. The majority of the Company’s securities are fixed income instruments that are not quoted on an exchange, but are traded in active markets. Prices for these instruments are obtained through third party data service providers or dealer market participants with which the Company has historically transacted both purchases and sales of securities. Prices obtained from these sources include market quotations and matrix pricing. Matrix pricing, a Level 2 input, is a mathematical technique used principally to value certain securities to benchmark or to compare securities. The Company evaluates the quality of Level 2 matrix pricing through comparison to similar assets with greater liquidity and evaluation of projected cash flows. As the Company is responsible for the determination of fair value, it performs quarterly analysis on the prices received from the pricing service to determine whether the prices are reasonable estimates of fair value. Specifically, the Company compares the prices received from the pricing service to a secondary pricing source. Additionally, the Company compares changes in the reported market values and returns to relevant market indices to assess the reasonableness of the reported prices. The Company’s internal price verification procedures and review of fair value methodology documentation provided by independent pricing services has not historically resulted in an adjustment in the prices obtained from the pricing service. The Company also holds debt instruments issued by the U.S. government and U.S. government sponsored agencies that are traded in active markets with readily accessible quoted market prices that are considered Level 1 within the fair value hierarchy. Federal Home Loan Bank Stock ("FHLB") The carrying value of FHLB stock is its cost. The fair value of FHLB stock is based on redemption at par value. There is no active market for this stock. The Company classifies the estimated fair value as Level 2 within the fair value hierarchy. Loans Receivable Fair values are estimated for portfolios of loans with similar financial characteristics. Loans are segregated by type such as commercial mortgage, residential mortgage, commercial, construction, and consumer and other. Each loan category is further segmented into fixed and adjustable rate interest terms and into performing and non-performing categories. The fair value of performing loans was estimated using a combination of techniques, including a discounted cash flow model that utilizes a discount rate that reflects the Company’s current pricing for loans with similar characteristics and remaining maturity, adjusted by an amount for estimated credit losses inherent in the portfolio at the balance sheet date. The rates take into account the expected yield curve, as well as an adjustment for prepayment risk, when applicable. The fair value estimated does not incorporate an exit value. The Company classifies the estimated fair value of its loan portfolio as Level 3. The fair value for significant non-performing loans was based on recent external appraisals of collateral securing such loans, adjusted for the timing of anticipated cash flows. The Company classifies the estimated fair value of its non-performing loan portfolio as Level 3. Deposits The fair value of deposits with no stated maturity, such as demand, money market, savings and club deposits, was equal to the amount payable on demand and classified as Level 2. The estimated fair value of certificates of deposit was based on the discounted value of contractual cash flows. The discount rate was estimated using the Company’s current rates offered for deposits with similar remaining maturities. The Company classifies the estimated fair value of its certificates of deposit portfolio as Level 2. Borrowings The fair value of borrowings was estimated by discounting future cash flows using rates available for debt with similar terms and maturities and is classified by the Company as Level 2 within the fair value hierarchy. (14) Fair Value Measurements (continued) Commitments to Extend Credit and Letters of Credit The fair value of commitments to extend credit and letters of credit was estimated using the fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements and the present creditworthiness of the counterparties. For fixed rate loan commitments, fair value also considers the difference between current levels of interest rates and the committed rates. The fair value estimates of commitments to extend credit and letters of credit are deemed immaterial in comparison to their carrying value. The following tables present the assets and liabilities reported on the Consolidated Statements of Financial Condition at their fair values as of December 31, 2018 and 2017 : December 31, 2018 Fair Value Measurements Carrying value Total fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Financial assets: Cash and cash equivalents $ 42,201 $ 42,201 $ 42,201 $ — $ — Securities available for sale 1,034,758 1,034,758 56,047 978,711 — Securities held to maturity 262,143 254,841 23,241 254,841 — Federal Home Loan Bank stock 58,938 58,938 — 58,938 — Loans held-for-sale 8,081 8,081 8,081 — Loans receivable, net 4,979,182 4,841,830 — — 4,841,830 Derivative assets 865 865 — 865 — Financial liabilities: — Deposits $ 4,413,873 $ 4,402,336 $ — $ 4,402,336 $ — Borrowings 1,189,180 1,185,007 — 1,185,007 — Derivative liabilities 3,467 3,467 — 3,467 — (14) Fair Value Measurements (continued) December 31, 2017 Fair Value Measurements Carrying value Total fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) (In thousands) Financial assets: Cash and cash equivalents $ 65,498 $ 65,498 $ 65,498 $ — $ — Securities available for sale 710,570 710,570 42,831 667,739 — Securities held to maturity 239,618 236,125 8,344 227,781 — Federal Home Loan Bank Stock 44,664 44,664 — 44,664 — Loans receivable, net 4,400,470 4,367,945 — — 4,367,945 Derivative assets 490 490 — 490 — Financial liabilities: — Deposits $ 4,263,315 $ 3,959,460 $ — $ 3,959,460 $ — Borrowings 929,057 925,032 — 925,032 — Derivative liabilities 203 203 — 203 — Limitations Fair value estimates are made at a specific point in time, based on relevant market information and information about the financial instrument. These estimates do not reflect any premium or discount that could result from offering for sale at one time the Company’s entire holdings of a particular financial instrument. Because limited markets exist for a significant portion of the Company’s financial instruments, fair value estimates are based on judgments regarding future expected loss experience, current economic conditions, risk characteristics of various financial instruments, and other factors. These estimates are subjective in nature and involve uncertainties and matters of significant judgment and, therefore, cannot be determined with precision. Changes in assumptions could significantly affect the estimates. Fair value estimates are based on existing on and off balance sheet financial instruments without attempting to estimate the value of anticipated future business and the value of assets and liabilities that are not considered financial instruments. Significant assets and liabilities that are not considered financial assets or liabilities include goodwill and other intangibles, deferred tax assets, office properties and equipment, and bank-owned life insurance. In addition, the tax ramifications related to the realization of the unrealized gains and losses can have a significant effect on fair value estimates and have not been considered in the estimates. Finally, reasonable comparability between financial institutions may not be likely due to the wide range of permitted valuation techniques and numerous estimates which must be made given the absence of active markets for many of these financial instruments. The lack of uniform methodologies introduces a greater degree of subjectivity to these estimates.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	Selected Quarterly Financial Data (Unaudited) The following tables are a summary of certain quarterly financial data for the years ended December 31, 2018 , September 30, 2017 and 2016 and the three months ended December 31, 2017: Quarters Ended December 31, 2018 March 31 June 30 September 30 December 31 (Dollars in thousands, except per share data) Total interest income $ 51,791 $ 55,019 $ 57,695 $ 61,785 Total interest expense 12,730 14,004 17,112 18,410 Net interest income 39,061 41,015 40,583 43,375 Provision for loan losses 2,000 2,400 1,500 777 Net interest income after provision for loan losses 37,061 38,615 39,083 42,598 Total non-interest income 4,543 5,450 5,290 6,405 Total non-interest expense 26,015 61,768 26,590 31,013 Income (loss) before income tax expense 15,589 (17,703 ) 17,783 17,990 Income tax expense 3,805 (2,961 ) 6,956 3,123 Net income (loss) $ 11,784 $ (14,742 ) $ 10,827 $ 14,867 Basic and diluted earnings per share N/A $ (0.13 ) $ 0.10 $ 0.13 (15) Selected Quarterly Financial Data (Unaudited) (continued) Quarter Ended December 31, 2017 (In thousands) Total interest income $ 49,169 Total interest expense 12,240 Net interest income 36,929 Provision for loan losses 3,400 Net interest income after provision for loan losses 33,529 Total non-interest income 4,733 Total non-interest expense 25,601 Income before income tax expense 12,661 Income tax expense 8,983 Net income $ 3,678 Basic and diluted earnings per share N/A Quarters Ended September 30, 2017 December 31 March 31 June 30 September 30 (Dollars in thousands, except per share data) Total interest income $ 44,129 $ 45,428 $ 46,850 $ 47,820 Total interest expense 10,724 10,651 11,211 11,860 Net interest income 33,405 34,777 35,639 35,960 Provision for loan losses — 375 375 5,676 Net interest income after provision for loan losses 33,405 34,402 35,264 30,284 Total non-interest income 5,534 5,806 4,645 1,630 Total non-interest expense 24,078 24,903 24,703 30,206 Income before income tax expense 14,861 15,305 15,206 1,708 Income tax expense 4,868 5,012 5,934 194 Net income $ 9,993 $ 10,293 $ 9,272 $ 1,514 Basic and diluted earnings per share N/A N/A N/A N/A (15) Selected Quarterly Financial Data (Unaudited) (continued) Quarters Ended September 30, 2016 December 31 March 31 June 30 September 30 (Dollars in thousands, except per share data) Total interest income $ 41,616 $ 41,929 $ 42,421 $ 43,011 Total interest expense 10,996 10,840 11,003 11,123 Net interest income 30,620 31,089 31,418 31,888 Provision for loan losses — 417 — — Net interest income after provision for loan losses 30,620 30,672 31,418 31,888 Total non-interest income 4,537 4,738 4,525 4,702 Total non-interest expense 23,388 22,816 23,658 23,482 Income before income tax expense 11,769 12,594 12,285 13,108 Income tax expense 3,859 4,281 4,052 4,611 Net income $ 7,910 $ 8,313 $ 8,233 $ 8,497 Basic and diluted earnings per share N/A N/A N/A N/A

Earnings per Share

Earnings per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings per Share	Earnings per Share Basic EPS is computed by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period. For purposes of calculating basic EPS, weighted average common shares outstanding excludes unallocated employee stock ownership plan shares that have not been committed for release and deferred compensation obligations required to be settled in shares of Company stock. Diluted EPS is computed using the same method as basic EPS and reflects the potential dilution which could occur if stock options and unvested shares were exercised and converted into common stock. The potentially diluted shares would then be included in the weighted average number of shares outstanding for the period using the treasury stock method. For the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, the Company did not have any stock options outstanding. The following is a reconciliation of the numerators and denominators of the basic and diluted earnings per share calculations for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: December 31, Three Months Ended December 31, September 30, 2018 2017 2017 2016 (Dollars in thousands, except per share data) Net income $ 22,736 $ 3,678 $ 31,072 $ 32,953 Basic earnings per share: Weighted average shares outstanding - basic 111,395,723 N/A N/A N/A Basic earnings per share $ 0.20 N/A N/A N/A Diluted earnings per share: Weighted average shares outstanding - diluted 111,395,723 N/A N/A N/A Diluted earnings per share $ 0.20 N/A N/A N/A

Parent-only Financial Informati

Parent-only Financial Information	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Parent-only Financial Information	Parent-only Financial Information The condensed financial statements of Columbia Financial, Inc. (parent company) are presented below: Statements of Financial Condition December 31, 2018 2017 (In thousands) Assets Cash and due from Bank $ 153,697 $ 1,537 Short-term investments 136 164 Total cash and cash equivalents 153,833 1,701 Securities available for sale, at fair value 1,420 2,783 Investment in subsidiaries 764,663 516,607 Loan receivable from Bank 44,439 — Other assets 7,852 3,281 Total assets $ 972,207 $ 524,372 Liabilities and Stockholders' Equity Liabilities: Borrowings $ — $ 50,657 Accrued expenses and other liabilities 147 1,645 Total liabilities 147 52,302 Total stockholders' equity 972,060 472,070 Total liabilities and stockholders' equity $ 972,207 $ 524,372 (17) Parent-only Financial Information (continued) Statements of Comprehensive Income (Loss) Year Ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Income: Dividend from subsidiary $ — $ — $ 2,000 $ 3,000 Securities available for sale 123 41 162 157 Interest earnings 2,384 — 1 — Total income 2,507 41 2,163 3,157 Interest expense on borrowings 3,468 1,044 4,177 4,177 Net interest expense (961 ) (1,003 ) (2,014 ) (1,020 ) Equity earnings in subsidiary 51,401 4,288 32,230 32,743 Expense: Loss on securities available for sale — 60 — — Charitable contribution to foundation 34,767 — — — Other non-interest expense 425 2 460 355 Total expense 35,192 62 460 355 Income before income tax benefit 15,248 3,223 29,756 31,368 Income tax benefit 7,488 455 1,316 1,585 Net income 22,736 3,678 31,072 32,953 Other comprehensive (loss) income (6,487 ) (19,230 ) 5,178 (11,287 ) Comprehensive income (loss) $ 16,249 $ (15,552 ) $ 36,250 $ 21,666 (17) Parent-only Financial Information (continued) Statements of Cash Flows Year Ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Cash flows from operating activities: Net income $ 22,736 $ 3,678 $ 31,072 $ 32,953 Adjustments to reconcile net income to net cash provided by operating activities: Amortization of debt issuance costs 890 14 53 53 Loss on securities available for sale — 60 — — Deferred tax (benefit) expense (6,086 ) 42 1 (2 ) Increase (decrease) in other assets 1,515 (494 ) 1,404 (1,600 ) (Decrease) increase in accrued expenses and other liabilities (1,498 ) 989 62 10 Contribution of common stock to Columbia Bank Foundation 34,767 — — — Equity in undistributed earnings of subsidiary (51,401 ) (4,288 ) (32,295 ) (32,744 ) Net cash provided by (used in) operating activities 923 1 297 (1,330 ) Cash flows from financing activities: Capital contribution to subsidiary (246,420 ) — — — Proceeds from sales of securities available for sale — 92 — — Proceeds from call / paydowns of securities available for sale 1,601 10 — — Purchases of securities available for sale (414 ) — — — Loan to ESOP (45,428 ) — — — Repayment of loans receivable from Bank 989 — — — Net cash (used in) provided by investing activities (289,672 ) 102 — — Cash flows from financing activities: Payment for trust preferred securities (51,547 ) — Issuance of common stock 492,428 — Net cash provided by financing activities 440,881 — — — Net increase (decrease) in cash and cash equivalents 152,132 103 297 (1,330 ) Cash and cash equivalents at beginning of period 1,701 1,598 1,301 2,631 Cash and cash equivalents at end of period $ 153,833 $ 1,701 $ 1,598 $ 1,301

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) The following tables present the components of other comprehensive income (loss), both gross and net of tax, for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 Before Tax Tax Effect After Tax Before Tax Tax Effect After Tax (In thousands) Components of Other Comprehensive (Loss) Income: Unrealized gains and losses on securities available for sale: Net (loss) gain arising during the period $ (7,224 ) $ 1,446 $ (5,778 ) $ (3,012 ) $ (119 ) $ (3,131 ) Accretion of unrealized loss on securities reclassified as held to maturity (13 ) — (13 ) (2 ) (56 ) (58 ) Reclassification adjustment for (gain) loss included in net income (116 ) 24 (92 ) 60 (13 ) 47 (7,353 ) 1,470 (5,883 ) (2,954 ) (188 ) (3,142 ) Unrealized (loss) gain on swap contract (2,825 ) 595 (2,230 ) 192 (30 ) 162 Employee benefit plans: Amortization of prior service cost included in net income (623 ) 132 (491 ) (24 ) (19 ) (43 ) Reclassification adjustment of actuarial net (loss) gain included in net income 2,526 (530 ) 1,996 (9 ) (94 ) (103 ) Change in funded status of retirement obligations 897 (776 ) 121 (9,024 ) 3,354 (5,670 ) Tax effects resulting from the adoption of ASU No. 2018-02 — — — — (10,434 ) (10,434 ) 2,800 (1,174 ) 1,626 (9,057 ) (7,193 ) (16,250 ) Total other comprehensive (loss) $ (7,378 ) $ 891 $ (6,487 ) $ (11,819 ) $ (7,411 ) $ (19,230 ) The Company, in accordance with ASU No. 2018-02, elected to reclassify the income tax effects of the Tax Act from accumulated other comprehensive (loss) income to retained earnings for the year ended December 31, 2017 . (18) Other Comprehensive Income (Loss) (continued) For the Years Ended September 30, 2017 2016 Before Tax Tax Effect After Tax Before Tax Tax Effect After Tax (In thousands) Components of Other Comprehensive (Loss) Income: Unrealized gains and losses on securities available for sale: Net (loss) gain arising during the period $ (17,877 ) $ 6,379 $ (11,498 ) $ 7,271 $ (2,597 ) $ 4,674 Accretion of unrealized gain on securities reclassified as held to maturity 12 (4 ) 8 — — — Reclassification adjustment for loss (gain) included in net income 2,626 (937 ) 1,689 (552 ) 197 (355 ) (15,239 ) 5,438 (9,801 ) 6,719 (2,400 ) 4,319 Unrealized gain on swap contract 95 (33 ) 62 — — — 95 (33 ) 62 — — — Employee benefit plans: Amortization of prior service cost included in net income (114 ) 41 (73 ) (114 ) 41 (73 ) Reclassification adjustment of actuarial net gains (losses) included in net income 11,806 (4,213 ) 7,593 9,123 (3,259 ) 5,864 Change in funded status of retirement obligations 11,503 (4,106 ) 7,397 (33,287 ) 11,890 (21,397 ) 23,195 (8,278 ) 14,917 (24,278 ) 8,672 (15,606 ) Total other comprehensive income (loss) $ 8,051 $ (2,873 ) $ 5,178 $ (17,559 ) $ 6,272 $ (11,287 ) (18) Other Comprehensive Income (Loss) (continued) The following tables present the changes in the components of accumulated other comprehensive (loss) income, net of tax, for the years ended ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 Unrealized (losses) gains on securities available for sale Unrealized gains (losses) on swaps Employee benefit plans Accumulated other comprehensive loss Unrealized (losses) gains on securities available for sale Unrealized gains (losses) on swaps Employee benefit plans Accumulated other comprehensive loss (In thousands) Balance at beginning of period $ (7,279 ) $ 224 $ (58,355 ) $ (65,410 ) $ (4,137 ) $ 62 $ (42,105 ) $ (46,180 ) Current period changes in other comprehensive (loss) income (5,883 ) (2,230 ) 1,626 (6,487 ) (1,828 ) 122 (5,816 ) (7,522 ) Reclassification of tax effects resulting from the adoption of ASU No. 2018-02 — — — — (1,314 ) 40 (10,434 ) (11,708 ) Total other comprehensive (loss) income $ (13,162 ) $ (2,006 ) $ (56,729 ) $ (71,897 ) $ (7,279 ) $ 224 $ (58,355 ) $ (65,410 ) (18) Other Comprehensive Income (Loss) (continued) For the Years Ended September 30, 2017 2016 Unrealized (losses) gains on securities available for sale Unrealized gains (losses) on swaps Employee benefit plans Accumulated other comprehensive loss Unrealized (losses) gains on securities available for sale Unrealized gains (losses) on swaps Employee benefit plans Accumulated other comprehensive loss (In thousands) Balance at beginning of period $ 5,664 $ — $ (57,022 ) $ (51,358 ) $ 1,345 $ — $ (41,416 ) $ (40,071 ) Current period changes in other comprehensive (loss) income (9,801 ) 62 14,917 5,178 4,319 — (15,606 ) (11,287 ) Total other comprehensive (loss) income $ (4,137 ) $ 62 $ (42,105 ) $ (46,180 ) $ 5,664 $ — $ (57,022 ) $ (51,358 ) The following table reflects amounts reclassified out of accumulated other comprehensive (loss) income to the Consolidated Statements of Income and the affected line item in the statement where net income is presented for the years ended ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: Accumulated other comprehensive (loss) income components For the Year Ended December 31, For the Three Months Ended December 31, Affected line items in the Consolidated Statements of Income 2018 2017 (In thousands) Reclassification adjustment for gains included in net income $ (116 ) $ 60 Gains on securities transactions, net Reclassification adjustment of actuarial net gain included in net income 2,526 (9 ) Compensation and employee benefits expense Total before tax 2,410 51 Income tax benefit (506 ) (107 ) Net of tax $ 1,904 $ (56 ) (18) Other Comprehensive Income (Loss) (continued) Accumulated other comprehensive (loss) income components For the Years Ended September 30, Affected line items in the Consolidated Statements of Income 2017 2016 (In thousands) Reclassification adjustment for gains included in net income $ 2,626 $ (552 ) Gains on securities transactions, net Reclassification adjustment of actuarial net gain included in net income 11,806 9,123 Compensation and employee benefits expense Total before tax 14,432 8,571 Income tax (benefit) expense (5,150 ) (3,062 ) Net of tax $ 9,282 $ 5,509

Derivatives and Hedging Activit

Derivatives and Hedging Activities	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging Activities	Derivatives and Hedging Activities The Company is a party to interest rate derivatives that may be designated as hedging instruments. The Company offers currency forward contracts and interest rate swap contracts to certain commercial banking customers to manage their risk of exposure and risk management strategies. These contracts are simultaneously hedged by offsetting contracts with a third party, such that the Company would minimize its net risk exposure resulting from these transactions. In addition, the Company executes interest rate swaps with third parties to in order to hedge the interest expense of short-term FHLB advances. These contracts are simultaneously hedged with short-term FHLB advances. Currency Forward Contracts. At December 31, 2018 , the Company had no currency forward contracts in place with commercial banking customers. At December 31, 2017 , the Company had a currency forward contract in place with a commercial banking customer with a notional amount of $1.6 million . An offsetting currency forward contract with a third party was also in place at December 31, 2017 . This currency forward contract did not meet hedge accounting requirements. Changes in the fair value of both the customer currency forward contract and the offsetting third party contract are recognized directly in earnings. Derivatives not designated in qualifying hedging relationships are not speculative and result from a service the Company provides to certain qualified commercial banking customers and are not used to manage interest rate risk in the Company's assets or liabilities. Interest Rate Swaps. At December 31, 2018 the Company had interest rate swaps in place with three commercial banking customers hedged by offsetting interest rate swaps with third parties. The aggregated notional amount of the interest rate swaps at December 31, 2018 was $36.6 million . At December 31, 2017 , the Company did no t have any interest rate swaps with commercial banking customers. These derivatives are not designated as hedges and are not speculative. These interest rate swaps do not meet hedge accounting requirements. Changes in the fair value of both the customer swap and offsetting third party swaps are recognized directly in earnings. The Company had 24 interest rate swaps at December 31, 2018 with a notional amount of $320.0 million hedging certain FHLB advances. At December 31, 2017 , the Company had two interest rate swaps with a notional amount of $20.0 million hedging certain FHLB advances. These interest rate swaps meet the hedge accounting requirements. The effective portion of changes in the fair value of the derivatives designated that qualify as cash flow hedges are recorded in accumulated other comprehensive income (loss). The ineffective portion of changes in the fair value of the derivatives designated that qualify as cash flow hedges are recorded in earnings. Interest rate swaps designated as cash flow hedges involve the receipt of variable amounts from a counter-party in exchange for the Company making fixed-rate payment payments over the life of the agreements without the exchange of the underlying notional amount. For the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, the Company did not record any hedge ineffectiveness associated with these contracts. (19) Derivatives and Hedging Activities (continued) The tables below present the fair value of the Company’s derivative financial instruments as well as their classification in the Consolidated Statements of Financial Condition at December 31, 2018 and 2017 : December 31, 2018 Asset Derivative Liability Derivative Consolidated Statements of Financial Condition Fair value Consolidated Statements of Financial Condition Fair value (In thousands) (In thousands) Derivatives: Interest rate products-designated Other Assets $ 865 Other Liabilities $ 3,467 Total derivative instruments $ 865 $ 3,467 December 31, 2017 Asset Derivative Liability Derivative Consolidated Statements of Financial Condition Fair value Consolidated Statements of Financial Condition Fair value (In thousands) (In thousands) Derivatives: Interest rate products-designated Other Assets $ 287 Other Liabilities $ — Currency forward contract - non-designated hedge Other Assets $ 203 Other Liabilities $ 203 Total derivative instruments $ 490 $ 203 For the year ended December 31, 2018 , a loss of approximately $52,000 was recorded for changes in fair value of interest rate swaps with third parties. For the years ended September 30, 2017 and 2016, and the three months ended December 31, 2017, no gains or losses were recorded for these transactions. At December 31, 2018 and 2017 , accrued interest was $65,000 and $7,000 , respectively. The Company has agreements with counterparties that contain a provision that if the Company defaults on any of its indebtedness, including default where repayment of the indebtedness has not been accelerated by the lender, then the Company could also be declared in default of its derivative obligations. At December 31, 2018 , the termination value of derivatives in a net liability position, which includes accrued interest, was $2.6 million . The Company has minimum collateral posting thresholds with certain of its derivative counterparties, and has posted collateral of $2.6 million against its obligations under these agreements. If the Company had breached any of these provisions at December 31, 2018 , it could have been required to settle its obligations under the agreements at the termination value.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated events subsequent to December 31, 2018 and through the financial statement issuance date of March 29, 2019 . The Company has not identified any material subsequent events the would require adjustment or disclosure in the consolidated financial statements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Columbia Financial, Inc., its wholly-owned subsidiary, Columbia Bank (the "Bank") and the Bank's wholly-owned subsidiaries, Columbia Investment Services, Inc., 2500 Broadway Corp. 1901 Residential Management Co. LLC, Plaza Financial Services, Inc., First Jersey Title Services, Inc., Real Estate Management Corp. LLC, 1901 Commercial Management Co. LLC, and CSB Realty Corp. (collectively, the “Company”). In consolidation, all intercompany accounts and transactions are eliminated. Certain reclassifications have been made in the consolidated financial statements to conform with current year classifications. The Company also owns 100% of the common stock of Columbia Financial Capital Trust I (the "Trust"). The Trust was used to issue trust preferred securities. In accordance with Accounting Standards Codification ("ASC") Topic 810, Consolidation , the Trust was classified as a variable interest entity and did not satisfy the conditions for consolidation. Accordingly, the Trust was treated as an unconsolidated subsidiary. In August 2018, the Company redeemed, in full $51.5 million of junior subordinated debt securities, which represented 100% of the assets of the Trust.
Basis of Financial Statement Presentation	Basis of Financial Statement Presentation The consolidated financial statements of the Company have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”). In preparing the consolidated financial statements, management is required to make estimates and assumptions about future events. These estimates and the underlying assumptions affect the reported amounts of assets and liabilities and disclosures about contingent assets and liabilities as of the dates of the consolidated statements of financial condition, and revenues and expenses for the periods then ended. Such estimates are used in connection with the determination of the adequacy of the allowance for loan losses, evaluation of goodwill for impairment, evaluation of other-than-temporary impairment on securities, evaluation of the need for valuation allowances on deferred tax assets, and determination of liabilities related to retirement and other post-retirement benefits, among others. These estimates and assumptions are based on management’s best estimates and judgment. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment, which management believes to be reasonable under the circumstances. Such estimates and assumptions are adjusted when facts and circumstances dictate. Illiquid credit markets, volatile securities markets, and declines in the housing market and the economy generally have combined to increase the uncertainty inherent in such estimates and assumptions. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in estimates resulting from continuing changes in the economic environment will be reflected in the consolidated financial statements in future periods.
Cash and Cash Equivalents	Cash and Cash Equivalents For purposes of reporting cash flows, cash and cash equivalents include cash on hand, amounts due from banks and interest-bearing deposits at other financial institutions. The Company is required by the Federal Reserve Bank System to maintain cash reserves equal to a percentage of certain deposits.
Securities	Securities Securities include investment securities classified as available for sale and held to maturity. Management determines the appropriate classification of securities at the time of purchase. If the Company does not have the intent to hold securities until maturity, these securities are classified as available for sale. The available for sale securities portfolio is carried at estimated fair value, with any unrealized holding gains or losses, net of taxes, reported as a separate component of accumulated other comprehensive income or loss in Stockholders' Equity. The fair values of these securities are based on market quotations or matrix pricing as discussed in Note 3. Management conducts a periodic review and evaluation of the securities portfolio to determine if any declines in the fair value of securities are other-than-temporary. In this evaluation, if such decline were deemed other-than temporary, management would measure the total credit-related component of the unrealized loss, and recognize that portion of the loss as a charge to current period earnings. The remaining portion of the unrealized loss would be recognized as an adjustment to accumulated other comprehensive income. The fair value of the securities portfolio is significantly affected by changes in interest rates. In general, as interest rates rise, the fair value of fixed-rate securities decreases and as interest rates fall, the fair value of fixed-rate securities increases. The Company determines if it has the intent to sell these securities or if it more likely than not that the Company would be required to sell the securities before the anticipated recovery. If either exists, the decline in value is considered other-than-temporary and would be recognized as an expense in the current period. Premiums and discounts on securities are amortized and accreted to income over the contractual lives of the securities using the level-yield method. Dividend and interest income are recognized when earned. Realized gains and losses are recognized when securities are sold or called based on the specific identification method. In the ordinary course of business, securities are pledged as collateral in conjunction with the Company’s borrowings and lines of credit.
Federal Home Loan Bank Stock	Federal Home Loan Bank Stock The Bank, as a member of the Federal Home Loan Bank of New York (the "FHLB"), is required to hold shares of capital stock of the FHLB at cost based on its activities, primarily its outstanding borrowings. The Bank carries the investment at cost, which approximates fair value.
Loans Held-for-Sale	Loans Held-for-Sale Loans held-for-sale consist of conforming loans originated and intended for sale in the secondary market. These loans are carried at the lower of cost or estimated fair value, less costs to sell, as determined on an individual loan basis. Net unrealized losses, if any, are recognized in a valuation allowance through charges to earnings. Origination fees and costs on loans held-for-sale are deferred and recognized as a component of the gain or loss on sale. Loans held-for-sale are generally sold with loan servicing rights retained by the Bank.
Loans Receivable	Loans Receivable Loans receivable are carried at unpaid principal balances adjusted by unamortized premiums and unearned discounts, net deferred origination fees and costs less the allowance for loan losses. The Bank defers loan origination fees and certain direct loan origination costs and accretes such amounts as an adjustment to the yield over the expected lives of the related loans using the level-yield method. Interest income on loans is accrued and credited to income as earned. Premiums and discounts on loans purchased are amortized or accreted as an adjustment to yield over the contractual lives of the related loans using methodologies which approximate the level-yield method. A loan is considered delinquent when payment has not been received within 30 days of its contractual due date. The accrual of income on loans is discontinued when they are past due 90 days or more as to contractual obligations, or other circumstances indicate that collection is questionable. When a loan is placed on non-accrual status, any interest accrued but not received is reversed against interest income. Payments received on a non-accrual loan are either applied to the outstanding principal balance or recorded as interest income, depending on an assessment of the ability to collect the loan. A loan is returned to accrual status when all amounts due have been received and the remaining principal is deemed collectible. Loans are generally charged off after an analysis is completed which indicates that collectability of the full principal balance is in doubt. (2) Summary of Significant Accounting Policies (continued) Loans Receivable (continued) An impaired loan is defined as a loan for which it is probable, based on current information, that the Bank will not collect all amounts due under the contractual terms of the loan agreement. The Bank considers the population of loans in its impairment analysis to include all multifamily and commercial real estate, construction, and commercial business loans with an outstanding balance greater than $500,000 and not accruing, and loans modified in a troubled debt restructuring. The Company also considers residential real estate, and home equity loans and advances that are not accruing or modified in a troubled debt restructuring for impairment. Other loans may be included in the population of loans in its impairment analysis if management has specific information of a collateral shortfall. Loan impairment is 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 the collateral if the loan is collateral dependent. Payments received on impaired loans are recognized on a cash basis.
Allowance for Loan Losses	Allowance for Loan Losses Losses on loans are charged to the allowance for loan losses. Additions to this allowance are made by recoveries of loans previously charged off and by a provision charged to expense. The determination of the balance of the allowance for loan losses is based on an analysis of the loan portfolio, economic conditions, historical loan loss experience and other factors that warrant recognition in providing an adequate allowance. Estimates and judgments required to establish the allowance include: overall economic conditions; value of collateral; strength of guarantors; loss exposure at default; the amount and timing of future cash flows on impaired loans; and determination of loss factors to be applied to the various elements of the portfolio. All of these estimates are susceptible to significant change. Management regularly reviews the level of loss experience, current economic conditions and other factors related to the collectability of the loan portfolio. While management uses available information, future additions to the allowance may be necessary based on changes in economic conditions in the Bank's market area. In addition, various regulatory agencies, as an integral part of their examination process, periodically review the Bank's allowance for loan losses and they may require the Bank to recognize additions to the allowance or additional write-downs based on judgments about information available to them at the time of their examination.
Troubled Debt Restructuring	Troubled Debt Restructuring Troubled debt restructured loans are those loans where the Company has granted a concession it would not otherwise consider because of economic or legal reasons pertaining to a debtor’s financial difficulties. A concession could include a reduced interest rate below a market rate, an extension of the term of the loan, or a combination of the two methods, but generally does not result in the forgiveness of principal or accrued interest. Not all concessions granted by the Company constitute a troubled debt restructuring. Once an obligation has been restructured and designated as a troubled debt restructuring, it continues to be designed as a restructured loan until paid in full. The Company records an impairment charge equal to the difference between the present value of expected future cash flows under the restructured terms discounted at the loan’s original effective interest rate, and the loan’s carrying value. Changes in the calculated impairment due to the passage of time are recorded as an adjustment to the allowance for loan losses. Restructured loans that were accruing prior to the restructuring, where income was reasonably assured subsequent to the restructuring, maintain their accrual status. Restructured loans for which collectability was not reasonably assured are placed on non-accrual status, interest accruals cease, and uncollected accrued interest is reversed and charged against current income. A non-accrual restructured loan would be returned to an accrual status when there is a sustained period of repayment performance, generally six consecutive months, and both principal and interest are deemed collectible.
Loans Sold and Serviced	Loans Sold and Serviced The Company periodically enters into Guarantor Swaps with Freddie Mac. In these types of transactions, the Company sells mortgage loans in exchange for Freddie Mac Mortgage Participation Certificates backed exclusively by the mortgages sold. The Company retains the servicing of the loans in these transactions. The Company also periodically sells loans to investors and continues to service such loans for a fee. Gains or losses on the sale of loans are recorded on the trade date using the specific-identification method.
Real Estate Owned	Real Estate Owned Real estate acquired through foreclosure or deed in lieu of foreclosure is carried at the lower of the recorded investment in the loan at the time of foreclosure or fair value, less estimated costs to sell. Fair value is generally based on recent appraisals. The excess, if any, of the loan amount over the fair value of the asset acquired is charged off against the allowance for loan losses at the date the property is acquired. Subsequent write-downs in the value of real estate owned, as well as holding costs, and any gains or losses realized upon sale of the property are recorded as as incurred.
Office Properties and Equipment	Office Properties and Equipment Land is carried at cost. Office properties, land and building improvements, furniture and equipment, and leasehold improvements are carried at cost, less accumulated depreciation and amortization. Depreciation and amortization of office properties and equipment is computed on a straight-line basis over their estimated useful lives (generally 40 years for buildings, 10 to 20 years for land and building improvements, 5 to 10 years for furniture and equipment). Leasehold improvements, carried at cost, net of accumulated depreciation, are amortized over the terms of the related leases or the estimated useful lives of the assets, whichever is shorter. Major improvements are capitalized, while repairs and maintenance costs are charged to expense as incurred. Upon retirement or sale, any gain or loss is recognized as incurred.
Bank-owned Life Insurance	Bank-owned Life Insurance Bank-owned life insurance is accounted for using the cash surrender value method and is recorded at its net realizable value. The change in the net asset value is recorded as a component of non-interest income. A deferred liability has been recorded for the estimated cost of post-retirement life insurance benefits accruing to applicable employees and directors covered by an endorsement split-dollar life insurance arrangement.
Goodwill and Intangible Assets	Goodwill and Intangible Assets Intangible assets of the Bank consist of goodwill and mortgage servicing rights. Goodwill represents the excess of the purchase price over the estimated fair value of identifiable net assets acquired through purchase acquisitions. In accordance with GAAP, goodwill with an indefinite useful life is not amortized, but is evaluated for impairment on an annual basis, or more frequently if events or changes in circumstances indicate potential impairment between annual measurement dates. As permitted by GAAP, the Company prepares a qualitative assessment in determining whether goodwill may be impaired, annually. The factors considered in the assessment include macroeconomic conditions, industry and market conditions and overall financial performance of the Company, among others. The Company completed its annual goodwill impairment test as of December 31, 2018 based upon its qualitative assessment of goodwill and concluded that goodwill was not impaired and no further quantitative analysis was warranted. Mortgage servicing rights are recorded when purchased or when originated mortgage loans are sold, with servicing rights retained. Mortgage servicing rights are amortized on an accelerated method based upon the estimated lives of the related loans, adjusted for prepayments. Mortgage servicing rights are carried at the lower of amortized cost or fair value.
Post-retirement Benefits	Post-retirement Benefits The Company provides certain health care and life insurance benefits to eligible retired employees, along with a split-dollar BOLI death benefit. The Company accrues the cost of retiree health care and other benefits during the employees’ period of active service. The Company accounts for benefits in accordance with Accounting Standard Update ("ASU") Topic 715, Pension and Other Post-retirement Benefits . The guidance requires an employer to: (a) recognize in its statement of financial position the overfunded or underfunded status of a defined benefit post-retirement plan measured as the difference between the fair value of plan assets and the benefit obligation; (b) measure a plan’s assets and its obligations that determine its funded status as of the end of the employer’s fiscal year (with limited exceptions); and (c) recognize as a component of other comprehensive income (loss), net of tax, the actuarial gains and losses and the prior service costs and credits that arise during the period.
Employee Benefits	Employee Benefit Plans The Company maintains a tax-qualified defined benefit pension plan ( the "Pension Plan") which covers full-time employees that satisfy the plan eligibility requirements. During 2018, the pension plan was amended. Effective October 1, 2018, employees hired by the Bank are not eligible to participate in the Company's pension plan as the plan has been closed to new employees as of the effective date. The Company's policy is to fund at least the minimum contribution required by the Employee Retirement Income Security Act of 1974. GAAP requires an employer to: (a) recognize in its statement of financial position the over-funded or under-funded status of a defined benefit post-retirement plan measured as the difference between the fair value of plan assets and the benefit obligation; (b) measure a plan’s assets and its obligations that determine its funded status at the end of the employer’s fiscal year (with limited exceptions); and (c) recognize as a component of other comprehensive income (loss), net of tax, the actuarial gains and losses and the prior service costs and credits that arise during the period. The assets of the plan are primarily invested in fixed debt and equity. The Company has a retirement income maintenance plan (the "RIM Plan"). The RIM Plan is a non-qualified defined benefit plan which provides benefits to all employees of the Company if their benefits under the Pension Plan are limited by the Internal Revenue Code. The Company has a 401(k) plan covering substantially all employees of the Company. The Company may match a percentage of the first 3.00% to 4.50% contributed by participants. The Company's matching contribution, if any, is determined by the Board of Directors in its sole discretion. The Company has an Employee Stock Ownership Plan ("ESOP"). The funds borrowed by the ESOP from the Company to purchase the Company's common stock are being repaid from the Bank's contributions over a period of 20 years. The Company's common stock not allocated to participants is recorded as a reduction of stockholders' equity at cost. Compensation expense for the ESOP is based on the average price of the Company's stock and the amount of shares committed to be allocated during each period. The Company has a Supplemental Executive Retirement Plan ("SERP"). The SERP is a non-qualified plan which provides supplemental retirement benefits to eligible officers (those designated by the Board of Directors) of the Company who are prevented from receiving the full benefits contemplated by the ESOP's benefit formulas under tax law limits for tax-qualified plans. In addition, the Company maintains a stock based deferral plan (the "Stock Based Deferral Plan") for certain executives and directors. The Company records a deferred compensation equity account and corresponding contra-equity account for the cost of the shares held by the Stock Based Deferral and SERP Plans. The Company also maintains a non-qualified savings income maintenance deferred compensation plan (the "SIM Plan") that provides supplemental benefits to certain executives who are prevented from receiving the full benefits contemplated by the 401(k) Plan under tax law limits for tax-qualified plans, and a Deferred Compensation Plan for directors.
Derivatives	Derivatives The Company records all derivatives on the consolidated statements of financial condition at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative, whether the Company has elected to designate a derivative in a hedging relationship and apply hedge accounting and whether the hedging relationship has satisfied the criteria necessary to apply hedge accounting. Interest rate swaps are designated as a cash flow hedge and satisfies hedge accounting requirements involving the receipt of variable amounts from a counter-party in exchange for the Company making fixed-rate payments over the life of the agreements without the exchange of the underlying notional amount. For derivatives which are designed as cash flow hedges and satisfy hedge accounting requirements, the effective portion of changes in the fair value of these derivatives are recorded in accumulated other comprehensive income (loss), and are subsequently reclassified into earnings in the period that the hedged forecasted transaction affects earnings. The ineffective portion of a change in the fair value of these derivatives are recognized directly in earnings. The fair value of the Company’s derivatives are determined using discounted cash flow analysis using observable market- based inputs.
Income Taxes	Income Taxes The Company and its subsidiaries file consolidated federal income tax returns. Federal income taxes are allocated to each entity based on their respective contributions to taxable income of the consolidated income tax returns. Separate state income tax returns are filed for the Company and each of its subsidiaries. For the three months ended December 31, 2017, income tax expense included the impact of the enactment of the Tax Cuts and Jobs Act ("Tax Act"), which was enacted in December 2017, and reduced the maximum statutory federal income tax rate from 35% to 21%. This resulted in a charge to reduce the carrying value of the Company's net deferred income tax assets, which are included in the consolidated statements of financial condition. As a result, for the year ended December 31, 2018, the federal income tax rate applicable to the Company was 21%. The Company records income taxes in accordance with ASC Topic 740, Income Taxes , using the asset and liability method. The amounts reflected on the Company's federal and state income tax returns differ from these provisions due principally to temporary differences in the reporting of certain items for consolidated financial statement reporting and income tax reporting purposes. Accordingly, deferred tax assets and liabilities: (i) are recognized for the expected future tax consequences of events that have been recognized in the financial statements or tax returns; (ii) are attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases; and (iii) are measured using enacted tax rates expected to apply in the years when those temporary differences are expected to be recovered or settled. Where applicable, deferred tax assets are reduced by a valuation allowance for any portions determined not likely to be realized. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income tax expense in the period that includes the enactment date. The valuation allowance is adjusted, by a charge or credit to income tax expense, as changes in facts and circumstances warrant. Income taxes are allocated to the individual entities within the consolidated group based on the effective tax rate of the entity. The Company did not have any liabilities for uncertain tax positions or any known unrecognized tax benefits at December 31, 2018 and 2017 . The Company recognizes interest and penalties related to unrecognized tax benefits in income tax expense in the Consolidated Statements of Income. The Company did not recognize any interest and penalties during the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017. On July 1, 2018, New Jersey enacted legislation which adds to the state’s 9.0% Corporation Business Tax rate (i) a 2.5% surtax for periods beginning in 2018 and 2019 and (ii) a 1.5% surtax for periods beginning in 2020 and 2021. These surtaxes apply to corporations with more than $41.0 million of net income allocated to New Jersey and expire beginning in 2022. Also, for periods beginning in 2017, New Jersey has reduced the dividends-received deduction from 100% to 95% for certain dividend income received by a corporation from a subsidiary that is at least 80% owned by the corporation. In addition, for periods beginning in 2019, New Jersey has adopted combined income tax reporting for certain members of a commonly-controlled unitary business group.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) consists of net income and other comprehensive income (loss). Other comprehensive income (loss) includes unrealized holding gains and losses on securities available-for-sale, the noncredit component of other than temporary impairment losses on debt securities, unrealized gains and losses on derivatives, and the unfunded status of employee benefit plans. Comprehensive income is presented in a separate Consolidated Statements of Comprehensive Income (Loss).
Securities Sold Under Agreements to Repurchase and Other Borrowings	Securities Sold Under Agreements to Repurchase and Other Borrowings The Company enters into sales of securities under agreement to repurchase and collateral pledge agreements with selected dealers and banks. Such agreements are accounted for as secured financing transactions since the Company maintains effective control over the transferred or pledged securities. Obligations under these agreements are recorded as liabilities in the Consolidated Statements of Financial Condition.
Segment Reporting	Segment Reporting The Company’s operations are solely in the financial services industry and include providing traditional banking and other financial services to its customers. The Company operates primarily in New Jersey. Management makes operating decisions and assesses performance based on an ongoing review of the Company’s consolidated financial results. Therefore, the Company has a single operating segment for financial reporting purposes.
Earnings Per Share	Earnings Per Share (EPS) Basic EPS is computed by dividing net income available to common stockholders by the weighted average number of common shares outstanding for the period. For purposes of calculating basic EPS, weighted average common shares outstanding excludes unallocated employee stock ownership plan shares that have not been committed for release and deferred compensation obligations required to be settled in shares of Company stock. Diluted EPS reflects the potential dilution which could occur if securities or other contracts to issue common stock (such as stock options) were exercised and or resulted in the issuance of common stock. These potentially dilutive shares would then be included in the weighted average number of shares outstanding for the period using the treasury stock method. Shares issued and reacquired during any period are weighted for the portion of the period that they were outstanding. During the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, the Company did not have any stock options outstanding.
Recent Accounting Pronouncements	Recent Accounting Pronouncements As an “emerging growth company” as defined in Title 1 of the Jumpstart Our Business Startups (JOBS) Act, the Company has elected to use the extended transition period to delay the adoption of new or reissued accounting pronouncements applicable to public companies until such pronouncements are made applicable to private companies. Accounting Pronouncements Adopted In February 2018, the Financial Accounting Standards Board ("FASB") issued ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220) . The updated guidance allows a reclassification from accumulated other comprehensive income to retained earnings for the stranded tax effects resulting from the Tax Cuts and Jobs Act disclosed in Note 12. The purpose of the guidance is to improve the usefulness of the information reported to the financial statement users. The guidance is effective for all entities for fiscal years beginning after December 31, 2018 and interim periods within those fiscal years. Early adoption is permitted. The Company early adopted ASU No. 2018-02 for the period ended December 31, 2017 and the impact of the adoption resulted in a reclassification adjustment between accumulated other comprehensive income and retained earnings of $11.7 million . Accounting Pronouncements Not Yet Adopted In October 2018, the FASB issued ASU No. 2018-16, Derivatives and Hedging (Topic 815)- Inclusion of the Secured Overnight Financing Rate ("SOFR") Overnight Index Swap ("OSI") Rate as a Benchmark Interest Tate for Hedge Accounting Purposes. This ASU permits the use of the OIS rate based upon SOFR as a U.S. benchmark interest rate for purposes of applying hedge accounting under Topic 815. This is the fifth U.S. benchmark interest rate eligible for use in hedge accounting in addition to the direct Treasury obligations of the U.S. Government, the LIBOR swap rate, the OIS rate based on the Fed Funds Effective Rate, and the Securities Industry and Financial Markets Association Municipal Swap Rate. The amendments in this ASU are required to be adopted concurrently with the amendments in ASU No. 2017-12, Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities, which was issued in August 2017. The purpose of this updated guidance is to better align a company’s financial reporting for hedging activities with the economic objectives of those activities. The effective date for this ASU for the Company is for fiscal years beginning after December 15, 2019, with early adoption, including adoption in an interim period, permitted. ASU 2017-12 requires a modified retrospective transition method in which the company will recognize the cumulative effect of the change on the opening balance of each affected component of equity in the statement of financial position as of the date of adoption. The Company does not expect the adoption of this guidance to have a significant impact on its consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement. The purpose of this updated guidance is to improve the effectiveness and disclosures in the notes to the financial statements . The ASU removes the requirement to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; removes the policy for timing of transfers between levels and removes the disclosure related to the valuation process for Level 3 fair value measurements. The ASU also modifies existing disclosure requirements which relate to the disclosure for investments in certain entities which calculate net asset value and clarifies the disclosure about uncertainty in the measurements as of the reporting date. For all entities, the effective date for this guidance is fiscal years beginning after December 15, 2019, including interim periods within the reporting period, with early adoption permitted. Entities are also allowed to elect early adoption of the eliminated or modified disclosure requirements and delay adoption of the new disclosure requirements until their effective date. The Company is currently evaluating the impact of the new guidance on its consolidated financial statements. (2) Summary of Significant Accounting Policies (continued) Accounting Pronouncements Not Yet Adopted (continued) In March 2017, the FASB issued ASU No. 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities. This guidance shortens the amortization period for premiums on callable debt securities by requiring that premiums be amortized to the first (or earliest) call date instead of as an adjustment to the yield over the contractual life. This change more closely aligns the accounting with the economics of a callable debt security and the amortization period with expectations that already are included in market pricing on callable debt securities. This guidance does not change the accounting for discounts on callable debt securities, which will continue to be amortized to the maturity date. This guidance includes only instruments that are held at a premium and have explicit call features. It does not include instruments that contain prepayment features, such as mortgage backed securities; nor does it include call options that are contingent upon future events or in which the timing or amount to be paid is not fixed. The effective date for this ASU for the Company is fiscal years beginning after December 15, 2019, including interim periods within the reporting period, with early adoption permitted. Transition is on a modified retrospective basis with an adjustment to retained earnings as of the beginning of the period of adoption. If early adopted in an interim period, adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. The Company does not expect the adoption of this ASU to have a significant impact on the its consolidated financial statements. In March 2017, the FASB issued ASU No. 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post-retirement Benefit Cost, which requires that companies disaggregate the service cost component from other components of net benefit cost. This update calls for companies that offer post-retirement benefits to present the service cost, which is the amount an employer has to set aside each quarter or fiscal year to cover the benefits, in the same line item with other current employee compensation costs. Other components of net benefit cost will be presented in the income statement separately from service costs component and outside the subtotal of income from operations, if one is presented. The effective date for this ASU for the Company is fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. The adoption of this standard, effective January 1, 2019, did not have a significant impact on the Company's consolidated financial statements. In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The main objective of this guidance is to simplify the accounting for goodwill impairment by requiring that impairment charges be based upon the first step in the current two-step impairment test under ASC 350. Currently, if the fair value of a reporting unit is lower than its carrying amount (Step 1), an entity calculates any impairment charge by comparing the implied fair value of goodwill with its carrying amount (Step 2). The implied fair value of goodwill is calculated by deducting the fair value of all assets and liabilities of the reporting unit from the reporting unit’s fair value as determined in Step 1. To determine the implied fair value of goodwill, entities estimate the fair value of any unrecognized intangible assets and any corporate-level assets or liabilities that were included in the determination of the carrying amount and fair value of the reporting unit in Step 1. Under this guidance, if a reporting unit’s carrying amount exceeds its fair value, an entity will record an impairment charge based on that difference. The impairment charge will be limited to the amount of goodwill allocated to that reporting unit. This guidance eliminates the requirement to calculate a goodwill impairment charge using Step 2. This guidance does not change the guidance on completing Step 1 of the goodwill impairment test. Under this guidance, an entity will still be able to perform the current optional qualitative goodwill impairment assessment before determining whether to proceed to Step 1. The guidance in the ASU will be applied prospectively and is effective for the Company for annual and interim impairment tests performed in periods beginning after December 15, 2019. The Company does not expect the adoption of this ASU to have a significant impact on the its consolidated financial statements. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, a new standard which addresses diversity in practice related to eight specific cash flow issues: debt prepayment or extinguishment costs, settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned life insurance policies (including bank-owned life insurance policies), distributions received from equity method investees, beneficial interests in securitization transactions and separately identifiable cash flows and application of the predominance principle. This guidance in the ASU is effective for the Company for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Entities will apply the standard’s provisions using a retrospective transition method to each period presented. If it is impracticable to apply the amendments retrospectively for some of the issues, the amendments for those issues would be applied prospectively as of the earliest (2) Summary of Significant Accounting Policies (continued) Accounting Pronouncements Not Yet Adopted (continued) date practicable. The adoption of this standard, effective January 1, 2019, did not have a significant impact on the Company's consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments. This guidance provides financial statement users with more decision-useful information about expected credit losses on financial instruments by a reporting entity at each reporting date. The amendments of this guidance require financial assets measured at amortized cost to be presented at the net amount expected to be collected. The allowance for credit losses would represent a valuation account that would be 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 income statement would reflect the measurement of credit losses that have taken place during the period. The measurement of expected credit losses would 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. An entity would be required to use judgment in determining the relevant information and estimation methods that are appropriate in its circumstances. The guidance in the ASU is effective for the Company for fiscal years beginning after December 15, 2019, including interim periods within that reporting period. Early adoption is permitted. The Company is currently evaluating its existing systems and data to support the new standard as well as assessing the impact that the guidance will have on the Company's consolidated financial statements. The Company has formed a working group under the direction of the Chief Accounting Officer that is primarily comprised of individuals from various functional areas including finance, credit, risk management, and operations, among others. A detailed implementation plan was developed which includes an assessment of the processes, portfolio segmentation, model development and validation, and system requirements and resources needed. The Company has engaged a third-party vendor to assist with model development, data governance and operational controls to support the adoption of this ASU. Furthermore, this ASU will necessitate establishing an allowance for expected credit losses on debt securities. The Company has begun its evaluation of the guidance including the potential impact on its consolidated financial statements. The extent of the change is indeterminable at this time as it will be dependent upon portfolio composition and credit quality at the adoption date, as well as economic conditions and forecasts at that time. Upon adoption, any impact to the allowance for credit losses will have an impact on retained earnings. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This guidance requires all lessees to recognize a lease liability and a right-of-use asset, measured at the present value of the future minimum lease payments, at the lease commencement date for leases classified as operating leases as well as finance leases. The update also requires new quantitative disclosures related to leases in the Company's consolidated financial statements. There are also practical expedients in this update related to leases that commenced before the effective date, initial direct costs and the use of hindsight to extend or terminate a lease or purchase a leased asset. Lessor accounting remains largely unchanged under this new guidance. In January 2018, the FASB issued ASU 2018-01, Leases (Topic 842)-Land Easement Practical Expedient for Transition to Topic 842 , which provides an optional practical expedient to not evaluate land easements which were existing or expired before the adoption of Topic 842 that were not accounted for as leases under Topic 840. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842, Leases and ASU 2018-11, Leases (Topic 842) -Targeted Improvements which provides entities with an optional transition method under which comparative periods presented in the financial statements will continue to be in accordance with current Topic 840, Leases, and a practical expedient to not separate non-lease components from the associated lease component. The guidance is effective for the Company for annual periods beginning after December 15, 2019, including interim periods within that reporting period. The Company is currently in the process of identifying and evaluating the impact of this guidance and, as such, no conclusions have yet been reached regarding the potential impact on adoption on the Company's consolidated financial statements, however, the Company does not expect the adoption to have a material impact on its results of operations. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments- Overall: Recognition and Measurement of Financial Assets and Financial Liabilities. This guidance requires an entity to: i) measure equity investments at fair value through net income, with certain exceptions; (ii) present in other comprehensive income the changes in instrument-specific credit risk for financial liabilities measured using the fair value option; (iii) present financial assets and financial liabilities by measurement category and form of financial asset; (iv) calculate the fair value of financial instruments for disclosure purposes based on an exit price and; (v) assess a valuation allowance on deferred tax assets related to unrealized losses on available-for-sale debt securities in combination with other deferred tax assets. This guidance provides an election to subsequently measure certain non-marketable equity investments at cost less any impairment and adjusted for certain observable price changes. The guidance also requires a qualitative impairment assessment of such equity investments and amends certain fair value disclosure requirements. The guidance in the ASU is effective for the Company for annual (2) Summary of Significant Accounting Policies (continued) Accounting Pronouncements Not Yet Adopted (continued) periods beginning after December 15, 2018. Upon adoption of this standard, effective January 1, 2019, the Company recorded a cumulative adjustment of $548,000 from other comprehensive income (loss) to retained earnings. In May 2014, the FASB issued ASU No. 2014-09, "Revenue from Contracts with Customers." The objective of this amendment is to clarify the principles for recognizing revenue and to develop a common revenue standard for U.S. GAAP. This update affects any entity that either enters into contracts with customers to transfer goods or services or enters into contracts for the transfer of non-financial assets unless those contracts are in the scope of other standards. The guidance in the ASU is effective for the Company for fiscal years beginning after December 15, 2018, and early adoption is permitted. Subsequently, the FASB issued the following standards related to ASU No. 2014-09: ASU No. 2016-08, “Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations;” ASU No. 2016-10, “Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing;” ASU No. 2016-11, “Revenue Recognition (Topic 605) and Derivatives and Hedging (Topic 815): Rescission of SEC Guidance Because of ASU No. 2014-09 and 2014-16 Pursuant to Staff Announcements at the March 3, 2016 EITF Meeting;” and ASU No. 2016-12, “Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients”. These amendments are intended to improve and clarify the implementation guidance of ASU No. 2014-09 and have the same effective date as the original guidance. The Company's revenue is primarily comprised of net interest income on interest earning assets and liabilities and non-interest income. The scope of guidance explicitly excludes net interest income as well as other revenues associated with financial assets and liabilities, including loans, leases, securities and derivatives. The Company adopted the guidance effective January 1, 2019, and concluded that there are no material changes related to the timing or amount of revenue recognition. The Company will disaggregate significant categories of revenue within the scope of the guidance and provide the required disclosures starting in the first quarter of 2019.

Securities Available for Sale (

Securities Available for Sale (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of amortized cost, gross unrealized gains, gross unrealized losses and the fair value of securities available-for-sale	S ecurities available for sale at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 54,821 $ 53 $ (717 ) $ 54,157 Mortgage-backed securities and collateralized mortgage obligations 934,631 2,812 (17,436 ) 920,007 Municipal obligations 987 — — 987 Corporate debt securities 54,493 129 (1,155 ) 53,467 Trust preferred securities 5,000 — (750 ) 4,250 Equity securities 1,196 694 — 1,890 $ 1,051,128 $ 3,688 $ (20,058 ) $ 1,034,758 December 31, 2017 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 39,909 $ 17 $ (282 ) $ 39,644 Mortgage-backed securities and collateralized mortgage obligations 615,924 383 (9,695 ) 606,612 Municipal obligations 1,957 — — 1,957 Corporate debt securities 54,489 536 (511 ) 54,514 Trust preferred securities 5,000 — (344 ) 4,656 Equity securities 2,328 859 — 3,187 $ 719,607 $ 1,795 $ (10,832 ) $ 710,570
Schedule of securities by contractual maturity	The amortized cost and fair value of debt securities available for sale at December 31, 2018 , by contractual final maturity, excluding equity securities is shown below. Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer. December 31, 2018 Amortized cost Fair value (In thousands) One year or less $ 797 $ 797 More than one year to five years 50,131 49,613 More than five years to ten years 59,373 57,971 More than ten years 5,000 4,480 115,301 112,861 Mortgage-backed securities and collateralized mortgage obligations 934,631 920,007 $ 1,049,932 $ 1,032,868 The amortized cost and fair value of debt securities held to maturity at December 31, 2018 , by contractual final maturity, are shown below. Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer. December 31, 2018 Amortized cost Fair value (In thousands) More than one year to five years $ 5,000 $ 5,000 More than five years to ten years 8,404 8,196 More than ten years 10,000 10,045 23,404 23,241 Mortgage-backed securities and collateralized mortgage obligations 238,739 231,600 $ 262,143 $ 254,841
Schedule of available-for-sale securities reported in a continuous unrealized loss position	The following table summarizes the fair value and gross unrealized losses of those securities that reported an unrealized loss at December 31, 2018 and 2017 and if the unrealized loss position was continuous for the twelve months prior to those respective dates: December 31, 2018 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ 14,668 $ (202 ) $ 29,437 $ (515 ) $ 44,105 $ (717 ) Mortgage-backed securities and collateralized mortgage obligations 176,614 (1,034 ) 509,397 (16,402 ) 686,011 (17,436 ) Corporate debt securities 26,480 (512 ) 9,358 (643 ) 35,838 (1,155 ) Trust preferred securities — — 4,250 (750 ) 4,250 (750 ) $ 217,762 $ (1,748 ) $ 552,442 $ (18,310 ) $ 770,204 $ (20,058 ) (3) Securities Available for Sale (continued) December 31, 2017 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ 29,654 $ (282 ) $ — $ — $ 29,654 $ (282 ) Mortgage-backed securities and collateralized mortgage obligations 514,283 (8,037 ) 48,788 (1,658 ) 563,071 (9,695 ) Corporate debt securities 4,866 (135 ) 4,624 (376 ) 9,490 (511 ) Trust preferred securities — — 4,656 (344 ) 4,656 (344 ) $ 548,803 $ (8,454 ) $ 58,068 $ (2,378 ) $ 606,871 $ (10,832 )

Securities Held to Maturity (Ta

Securities Held to Maturity (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of amortized cost, gross unrealized gains, gross unrealized losses and the fair value of securities held-to-maturity	Securities held to maturity at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 23,404 $ 45 $ (208 ) $ 23,241 Mortgage-backed securities and collateralized mortgage obligations 238,739 28 (7,167 ) 231,600 $ 262,143 $ 73 $ (7,375 ) $ 254,841 December 31, 2017 Amortized cost Gross unrealized gains Gross unrealized (losses) Fair value (In thousands) U.S. government and agency obligations $ 8,402 $ — $ (58 ) $ 8,344 Mortgage-backed securities and collateralized mortgage obligations 231,216 — (3,435 ) 227,781 $ 239,618 $ — $ (3,493 ) $ 236,125
Schedule of securities by contractual maturity	The amortized cost and fair value of debt securities available for sale at December 31, 2018 , by contractual final maturity, excluding equity securities is shown below. Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer. December 31, 2018 Amortized cost Fair value (In thousands) One year or less $ 797 $ 797 More than one year to five years 50,131 49,613 More than five years to ten years 59,373 57,971 More than ten years 5,000 4,480 115,301 112,861 Mortgage-backed securities and collateralized mortgage obligations 934,631 920,007 $ 1,049,932 $ 1,032,868 The amortized cost and fair value of debt securities held to maturity at December 31, 2018 , by contractual final maturity, are shown below. Expected maturities may differ from contractual maturities due to prepayment or early call privileges of the issuer. December 31, 2018 Amortized cost Fair value (In thousands) More than one year to five years $ 5,000 $ 5,000 More than five years to ten years 8,404 8,196 More than ten years 10,000 10,045 23,404 23,241 Mortgage-backed securities and collateralized mortgage obligations 238,739 231,600 $ 262,143 $ 254,841
Schedule of unrealized loss on investments	The following table summarizes the fair value and gross unrealized losses of those securities that reported an unrealized loss at December 31, 2018 and 2017 and if the unrealized loss position was continuous for the twelve months prior to those respective dates: December 31, 2018 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ — $ — $ 8,197 $ (208 ) $ 8,197 $ (208 ) Mortgage-backed securities and collateralized mortgage obligations 11,265 (69 ) 213,246 (7,098 ) 224,511 (7,167 ) $ 11,265 $ (69 ) $ 221,443 $ (7,306 ) $ 232,708 $ (7,375 ) (4) Securities Held to Maturity (continued) December 31, 2017 Less than 12 months 12 months or longer Total Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) Fair value Gross unrealized (losses) (In thousands) U.S. government and agency obligations $ 8,344 $ (58 ) $ — $ — $ 8,344 $ (58 ) Mortgage-backed securities and collateralized mortgage obligations 196,049 (2,920 ) 29,531 (515 ) 225,580 (3,435 ) $ 204,393 $ (2,978 ) $ 29,531 $ (515 ) $ 233,924 $ (3,493 )

Loans Receivable and Allowanc_2

Loans Receivable and Allowance for Loan Losses (Tables)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Schedule of loans receivable	Loans receivable at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 (In thousands) Real estate loans: One-to-four family $ 1,830,186 $ 1,615,000 Multifamily and commercial 2,142,154 1,870,475 Construction 261,473 233,652 Commercial business loans 333,876 277,970 Consumer loans: Home equity loans and advances 393,492 447,920 Other consumer loans 1,108 998 Total gross loans 4,962,289 4,446,015 Net deferred loan costs, fees and purchased premiums and discounts 16,893 12,633 Loans receivable $ 4,979,182 $ 4,458,648 The following table provides information with respect to our non-accrual loans at December 31, 2018 and 2017 : December 31, 2018 2017 (In thousands) Non-accrual loans: Real estate loans: One-to-four family $ 819 $ 3,360 Multifamily and commercial 154 1,329 Commercial business loans 911 1,263 Consumer loans: Home equity loans and advances 905 573 Total non-accrual loans $ 2,789 $ 6,525
Schedule of aging of loans receivable by portfolio segment	The following tables summarize the aging of loans receivable by portfolio segment at December 31, 2018 and 2017 : December 31, 2018 30-59 days 60-89 days 90 Days or more Total past due Current Total (In thousands) Real estate loans: One-to-four family $ 8,384 $ 1,518 $ 819 $ 10,721 $ 1,819,465 $ 1,830,186 Multifamily and commercial 1,870 1,425 154 3,449 2,138,705 2,142,154 Construction — — — — 261,473 261,473 Commercial business loans 208 279 911 1,398 332,478 333,876 Consumer loans: Home equity loans and advances 1,550 173 905 2,628 390,864 393,492 Other consumer loans — — — — 1,108 1,108 Total gross loans $ 12,012 $ 3,395 $ 2,789 $ 18,196 $ 4,944,093 $ 4,962,289 December 31, 2017 30-59 days 60-89 days 90 Days or more Total past due Current Total (In thousands) Real estate loans: One-to-four family $ 7,080 $ 1,229 $ 3,360 $ 11,669 $ 1,603,331 $ 1,615,000 Multifamily and commercial 138 380 1,329 1,847 1,868,628 1,870,475 Construction — — — — 233,652 233,652 Commercial business loans 89 730 1,263 2,082 275,888 277,970 Consumer loans: Home equity loans and advances 1,421 26 573 2,020 445,900 447,920 Other consumer loans — — — — 998 998 Total gross loans $ 8,728 $ 2,365 $ 6,525 $ 17,618 $ 4,428,397 $ 4,446,015
Schedule of loans receivable by portfolio segment and impairment method	The activity in the allowance for loan losses for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 are as follows: (5) Loans Receivable and Allowance for Loan Losses (continued) Year Ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Balance at beginning of period $ 58,178 $ 54,633 $ 51,867 $ 56,948 Provision charged 6,677 3,400 6,426 417 Recoveries 707 188 584 721 Charge-offs (3,220 ) (43 ) (4,244 ) (6,219 ) Balance at end of period $ 62,342 $ 58,178 $ 54,633 $ 51,867 The following table summarizes loans receivable and allowance for loan losses by portfolio segment and impairment method at December 31, 2018 and 2017 : The activity in the allowance for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 are as follows: For the Year Ended December 31, 2018 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Unallocated Total (In thousands) Balance at beginning of period $ 19,991 $ 19,933 $ 5,217 $ 8,275 $ 4,576 $ 8 $ 178 $ 58,178 Provision charged (credited) (4,503 ) 3,445 1,997 7,860 (1,949 ) 5 (178 ) 6,677 Recoveries 334 2 3 240 122 6 — 707 Charge-offs (590 ) (129 ) — (2,199 ) (291 ) (11 ) — (3,220 ) Balance at end of period $ 15,232 $ 23,251 $ 7,217 $ 14,176 $ 2,458 $ 8 $ — $ 62,342 December 31, 2017 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Unallocated Total (In thousands) Allowance for loan losses: Individually evaluated for impairment $ 423 $ 28 $ — $ 80 $ 15 $ — $ — $ 546 Collectively evaluated for impairment 19,568 19,905 5,217 8,195 4,561 8 178 57,632 Total $ 19,991 $ 19,933 $ 5,217 $ 8,275 $ 4,576 $ 8 $ 178 $ 58,178 Total loans: Individually evaluated for impairment $ 11,644 $ 3,693 $ — $ 4,263 $ 2,591 $ — $ — $ 22,191 Collectively evaluated for impairment 1,603,356 1,866,782 233,652 273,707 445,329 998 — 4,423,824 Total gross loans $ 1,615,000 $ 1,870,475 $ 233,652 $ 277,970 $ 447,920 $ 998 $ — $ 4,446,015 December 31, 2018 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Unallocated Total (In thousands) Allowance for loan losses: Individually evaluated for impairment $ 537 $ — $ — $ 366 $ 12 $ — $ — $ 915 Collectively evaluated for impairment 14,695 23,251 7,217 13,810 2,446 8 — 61,427 Total $ 15,232 $ 23,251 $ 7,217 $ 14,176 $ 2,458 $ 8 $ — $ 62,342 Total loans: Individually evaluated for impairment $ 9,048 $ 2,695 $ — $ 2,944 $ 3,100 $ — $ — $ 17,787 Collectively evaluated for impairment 1,821,138 2,139,459 261,473 330,932 390,392 1,108 — 4,944,502 Total gross loans $ 1,830,186 $ 2,142,154 $ 261,473 $ 333,876 $ 393,492 $ 1,108 $ — $ 4,962,289
Schedule of troubled debt restructuring	The following tables present the number of loans modified as TDRs for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017, along with their balances immediately prior to the modification date and post-modification. Post-modification recorded investment represents the net book balance immediately following modification. For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 No. of Loans Pre-modification recorded investment Post-modification recorded investment No. of Loans Pre-modification recorded investment Post-modification recorded investment ( Dollars in thousands) Troubled Debt Restructurings Real estate loans: One-to-four family 5 $ 801 $ 801 — $ — $ — Multifamily and commercial 1 65 65 — — — Commercial business loans — — — — — — Consumer loans: Home equity loans and advances 1 588 588 — — — Total restructured loans 7 $ 1,454 $ 1,454 — $ — $ — For the Years Ended September 30, 2017 2016 No. of Loans Pre-modification recorded investment Post-modification recorded investment No. of Loans Pre-modification recorded investment Post-modification recorded investment (Dollars in thousands) Troubled Debt Restructurings Real estate loans: One-to-four family 3 $ 548 $ 548 — $ — $ — Multifamily and commercial 1 3,964 3,964 — — — Commercial business loans 1 18 18 3 255 255 Consumer loans: Home equity loans and advances 2 248 248 1 103 103 Total restructured loans 7 $ 4,778 $ 4,778 4 $ 358 $ 358
Schedule of loans individually evaluated for impairment	The following table presents interest income recognized for loans individually evaluated for impairment at December 31, 2018 and 2017, by loan segment, for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 Average recorded investment Interest income recognized Average recorded investment Interest income recognized (In thousands) Real estate loans: One-to-four family $ 10,224 $ 445 $ 14,015 $ 110 Multifamily and commercial 2,712 155 4,087 39 Commercial business loans 3,060 118 3,870 46 Consumer loans: Home equity loans and advances 3,361 173 3,618 35 Totals $ 19,357 $ 891 $ 25,590 $ 230 For the Years Ended September 30, 2017 2016 Average recorded investment Interest income recognized Average recorded investment Interest income recognized (In thousands) Real estate loans: One-to-four family $ 15,027 $ 469 $ 18,119 $ 565 Multifamily and commercial 4,328 279 9,344 57 Construction — — 505 — Commercial business loans 3,796 195 4,514 110 Consumer loans: Home equity loans and advances 3,903 136 3,446 157 Totals $ 27,054 $ 1,079 $ 35,928 $ 889 December 31, 2017 Recorded investment Unpaid principal balance Specific allowance (In thousands) With no allowance recorded: Real estate loans: One-to-four family $ 8,870 $ 9,704 $ — Multifamily and commercial 2,058 2,933 — Commercial business loans 1,522 2,015 — Consumer loans: Home equity loans and advances 2,161 2,601 — 14,611 17,253 — With a specific allowance recorded: Real estate loans: One-to-four family 2,774 2,788 423 Multifamily and commercial 1,635 2,208 28 Commercial business loans 2,741 2,741 80 Consumer loans: Home equity loans and advances 430 430 15 7,580 8,167 546 Total: Real estate loans: One-to-four family $ 11,644 $ 12,492 $ 423 Multifamily and commercial 3,693 5,141 28 Commercial business loans 4,263 4,756 80 Consumer loans: Home equity loans and advances 2,591 3,031 15 Total loans $ 22,191 $ 25,420 $ 546 The following table presents loans individually evaluated for impairment by loan segment: At December 31, 2018 Recorded investment Unpaid principal balance Specific allowance (In thousands) With no allowance recorded: Real estate loans: One-to-four family $ 4,156 $ 5,307 $ — Multifamily and commercial 2,695 3,482 — Commercial business loans 2,285 2,374 — Consumer loans: Home equity loans and advances 2,511 2,866 — 11,647 14,029 — With a specific allowance recorded: Real estate loans: One-to-four family 4,892 4,939 537 Commercial business loans 659 768 366 Consumer loans: Home equity loans and advances 589 589 12 6,140 6,296 915 Total: Real estate loans: One-to-four family 9,048 10,246 537 Multifamily and commercial 2,695 3,482 — Commercial business loans 2,944 3,142 366 Consumer loans: Home equity loans and advances 3,100 3,455 12 Total loans $ 17,787 $ 20,325 $ 915
Schedule of loans receivable by credit quality risk	The following table presents loans receivable by credit quality risk indicator and by loan segment at December 31, 2018 and 2017 : December 31, 2018 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Total (In thousands) Pass $ 1,826,066 $ 2,128,680 $ 261,473 $ 320,451 $ 392,092 $ 1,108 $ 4,929,870 Special mention — — — 9,074 — — 9,074 Substandard 4,120 13,474 — 4,351 1,400 — 23,345 Doubtful — — — — — — — Total $ 1,830,186 $ 2,142,154 $ 261,473 $ 333,876 $ 393,492 $ 1,108 $ 4,962,289 December 31, 2017 One-to-four family Multifamily and commercial Construction Commercial business Home equity loans and advances Other consumer loans Total (In thousands) Pass $ 1,605,413 $ 1,851,037 $ 233,652 $ 268,355 $ 446,264 $ 998 $ 4,405,719 Special mention — 4,782 — 3,678 — — 8,460 Substandard 9,587 14,656 — 5,937 1,656 — 31,836 Doubtful — — — — — — — Total $ 1,615,000 $ 1,870,475 $ 233,652 $ 277,970 $ 447,920 $ 998 $ 4,446,015

Office Properties and Equipme_2

Office Properties and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of Office Properties and Equipment	Office properties and equipment less accumulated depreciation at December 31, 2018 and December 31, 2017 are summarized as follows: December 31, 2018 2017 (In thousands) Land $ 7,829 $ 7,829 Buildings 24,018 24,018 Land and building improvements 24,864 15,583 Leasehold improvements 21,279 19,821 Furniture and equipment 28,538 26,036 106,528 93,287 Less accumulated depreciation and amortization 54,478 50,667 Total office properties and equipment, net $ 52,050 $ 42,620

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill and Intangible Assets	Intangible assets at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 (In thousands) Goodwill $ 5,716 $ 5,716 Mortgage servicing rights 369 281 $ 6,085 $ 5,997

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2018
Banking and Thrift [Abstract]
Schedule of Deposits	Deposits at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 Balance Weighted average rate Balance Weighted average rate (Dollars in thousands) Non-interest-bearing demand $ 723,794 — % $ 719,339 — % Interest-bearing demand 1,219,381 0.95 1,332,297 0.66 Money market accounts 259,694 0.67 262,396 0.29 Savings and club deposits 510,688 0.16 545,401 0.16 Certificates of deposit 1,700,316 2.01 1,403,882 1.43 Total deposits $ 4,413,873 1.09 % $ 4,263,315 0.72 %
Schedule of Certificate Accounts by Maturity	certificates of deposit accounts at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 (In thousands) One year or less $ 1,107,667 $ 669,610 After one year to two years 326,800 474,475 After two years to three years 230,468 169,069 After three years to four years 24,939 68,184 After four years 10,442 22,544 $ 1,700,316 $ 1,403,882 Interest expense on deposits for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 are summarized as follows: Year Ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Demand (including money market accounts) $ 12,933 $ 2,509 $ 8,556 $ 7,735 Savings and club deposits 993 210 630 613 Certificates of deposit 25,597 4,912 16,395 15,714 $ 39,523 $ 7,631 $ 25,581 $ 24,062

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of borrowed funds	Borrowed funds at December 31, 2018 and 2017 are summarized as follows: December 31, 2018 2017 2018 2017 Balance Weighted average interest rate (In thousands) Overnight lines of credit $ 159,600 $ 46,000 2.60 % 1.53 % Federal Home Loan Bank advances 1,029,580 822,400 2.40 1.92 Junior subordinated debt — 50,657 — 8.00 Securities sold under agreements to repurchase — 10,000 — 3.23 $ 1,189,180 $ 929,057 2.43 % 2.25 %
Schedule of borrowed funds contractual maturity	Scheduled maturities of FHLB advances including lines of credit at December 31, 2018 are summarized as follows: Year Ended December 31, 2018 (In thousands) One year or less $ 761,900 After one year to two years 229,045 After two years to three years 155,010 After three years to four years 43,225 After four years — Total FHLB advances $ 1,189,180

Regulatory Capital (Tables)

Regulatory Capital (Tables)	12 Months Ended
	Dec. 31, 2018
Banking and Thrift [Abstract]
Public Utilities General Disclosures	The following table presents the Company's and the Bank's actual capital amounts and ratios as of December 31, 2018 and 2017 as compared to the Federal Reserve Bank minimum capital adequacy requirements and the Federal Reserve Bank requirements for classification as a well-capitalized institution: (10) Regulatory Capital (continued) Actual Minimum capital adequacy requirements Minimum capital adequacy requirements with capital conservation buffer To be well capitalized under prompt corrective action provisions Amount Ratio Amount Ratio Amount Ratio Amount Ratio Company (In thousands, except ratio data) At December 31, 2018: Total capital (to risk-weighted assets) $ 1,094,062 23.45 % $ 373,276 8.00 % $ 460,763 9.88 % N/A N/A Tier 1 capital (to risk-weighted assets) 1,035,477 22.19 279,957 6.00 367,444 7.88 N/A N/A Common equity tier 1 capital (to risk-weighted assets) 1,035,477 22.19 209,968 4.50 297,455 6.38 N/A N/A Tier 1 capital (to adjusted total assets) 1,035,477 15.75 263,037 4.00 263,037 4.00 N/A N/A At December 31, 2017: Total capital (to risk-weighted assets) $ 631,952 15.01 % $ 336,730 8.00 % $ 389,244 9.25 % N/A N/A Tier 1 capital (to risk-weighted assets) 579,080 13.76 252,547 6.00 305,161 7.25 N/A N/A Common equity tier 1 capital (to risk-weighted assets) 528,080 12.55 189,410 4.50 242,025 5.75 N/A N/A Tier 1 capital (to adjusted total assets) 579,080 10.54 219,833 4.00 219,833 4.00 N/A N/A Bank At December 31, 2018: Total capital (to risk-weighted assets) $ 886,728 19.04 % $ 372,550 8.00 % $ 459,866 9.88 % $ 465,687 10.00 % Tier 1 capital (to risk-weighted assets) 828,257 17.79 279,412 6.00 366,729 7.88 372,550 8.00 Common equity tier 1 capital (to risk-weighted assets) 828,257 17.79 209,559 4.50 296,875 6.38 302,697 6.50 Tier 1 capital (to adjusted total assets) 828,257 12.60 263,025 4.00 263,025 4.00 328,781 5.00 At December 31, 2017: Total capital (to risk-weighted assets) $ 625,336 14.90 % $ 335,736 8.00 % $ 388,196 9.25 % $ 419,671 10.00 % Tier 1 capital (to risk-weighted assets) 572,617 13.64 251,802 6.00 304,262 7.25 335,736 8.00 Common equity tier 1 capital (to risk-weighted assets) 572,617 13.64 188,852 4.50 241,311 5.75 272,786 6.50 Tier 1 capital (to adjusted total assets) 572,617 10.44 221,257 4.00 221,257 4.00 276,571 5.00

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Changes in Projected Benefit Obligations, Fair Value of Plan Assets, and Funded Status of Plan	The following table sets forth information regarding the Pension, RIM and Post-retirement Plans at December 31, 2018 and 2017 : December 31, 2018 2017 2018 2017 2018 2017 Pension RIM Post-retirement (In thousands) Change in benefit obligation: Benefit obligation at beginning of year $ 229,156 $ 216,992 $ 12,243 $ 11,032 $ 22,078 $ 22,133 Service cost 7,805 7,496 282 238 417 445 Interest cost 8,489 8,461 443 433 796 762 Actuarial (gain) loss (30,703 ) 4,543 (1,355 ) 874 (1,845 ) (726 ) Benefits paid (5,542 ) (8,336 ) (328 ) (334 ) (482 ) (536 ) Benefit obligation at end of year 209,205 229,156 11,285 12,243 20,964 22,078 Change in plan assets: Fair value of plan assets at beginning of year 289,390 257,513 — — — — Actuarial return on plan assets (10,874 ) 27,213 — — — — Employer contributions — 13,000 328 334 482 536 Benefits paid (5,542 ) (8,336 ) (328 ) (334 ) (482 ) (536 ) Fair value of plan assets at end of year 272,974 289,390 — — — — Funded status at end of year $ 63,769 $ 60,234 $ (11,285 ) $ (12,243 ) $ (20,964 ) $ (22,078 )
Schedule of Net Benefit Costs	Net periodic benefit (income) cost for Pension, RIM and Post-retirement plans for the years ended December 31, 2018 , September 30, 2017 and 2016 and the three months ended December 31, 2017, includes the following components: For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 Pension RIM Post-retirement Pension RIM Post-retirement (In thousands) Service cost $ 7,805 $ 282 $ 417 $ 1,780 $ 60 $ 92 Interest cost 8,489 443 796 2,128 111 205 Expected return on plan assets (20,794 ) — — (4,814 ) — — Amortization: Prior service credit — — (106 ) — — (34 ) Net loss 3,117 413 323 707 103 70 Net periodic (income) cost $ (1,383 ) $ 1,138 $ 1,430 $ (199 ) $ 274 $ 333 (11) Employee Benefit Plans (continued) For the Years Ended September 30, 2017 2016 2017 2016 2017 2016 Pension RIM Post-retirement (In thousands) Service cost $ 7,621 $ 6,188 $ 237 $ 140 $ 471 $ 447 Interest cost 8,444 8,096 429 385 742 854 Expected return on plan assets (24,809 ) (22,706 ) — — — — Amortization: Prior service credit — — — — (136 ) (136 ) Net loss 10,998 8,490 453 283 325 339 Net periodic cost $ 2,254 $ 68 $ 1,119 $ 808 $ 1,402 $ 1,504
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	The weighted average actuarial assumptions used in the plan determinations at and for the years ended December 31, 2018 , September 30, 2017 and 2016 and the three months ended December 31, 2017 were as follows: At and For the Year Ended December 31, At and For the Three Months Ended December 31, 2018 2017 Pension RIM Post-retirement Pension RIM Post-retirement Weighted average assumptions used to determine benefit obligation: Discount rate 4.570 % 4.470 % 4.410 % 3.750 % 3.625 % 3.625 % Rate of compensation increase 3.500 % 3.500 % N/A 3.500 % 3.500 % N/A Weighted average assumptions used to determine net periodic benefit cost: Discount rate 3.750 % 4.470 % 3.625 % 4.000 % 3.875 % 3.875 % Expected rate of return on plan assets 7.250 % N/A N/A 7.250 % N/A N/A Rate of compensation increase 3.500 % 3.500 % N/A 3.500 % 3.500 % N/A At and For the Years Ended September 30, 2018 2017 2018 2017 2018 2017 Pension RIM Post-retirement Weighted average assumptions used to determine benefit obligation: Discount rate 4.000 % 3.875 % 3.875 % 3.625 % 3.875 % 3.625 % Rate of compensation increase 3.500 3.500 3.500 3.500 N/A N/A Weighted average assumptions used to determine net periodic benefit cost: Discount rate 3.875 % 4.500 % 3.625 % 4.375 % 3.625 % 4.375 % Expected rate of return on plan assets 7.500 7.500 N/A N/A N/A N/A Rate of compensation increase 3.500 3.500 3.500 3.500 N/A N/A The components of accumulated other comprehensive income (loss) related to the Pension, RIM , and Post-retirement Plans on a pre-tax basis, at December 31, 2018 and 2017, and September 30, 2017 and 2016 are summarized in the following table: At December 31, At December 31, 2018 2017 Pension RIM Post-retirement Pension RIM Post-retirement (In thousands) Unrecognized prior service costs $ — $ — $ — $ — $ — $ (106 ) Unrecognized net actuarial income 59,579 3,748 4,226 61,731 5,515 6,395 Total accumulated other comprehensive income $ 59,579 $ 3,748 $ 4,226 $ 61,731 $ 5,515 $ 6,289 At September 30, 2017 2016 2017 2016 2017 2016 Pension RIM Post-retirement (In thousands) Unrecognized prior service costs $ — $ — $ — $ — $ (140 ) $ (276 ) Unrecognized net actuarial income 55,438 74,768 4,725 5,154 4,611 8,374 Total accumulated other comprehensive income $ 55,438 $ 74,768 $ 4,725 $ 5,154 $ 4,471 $ 8,098
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates	A 1% change in the assumed health care cost trend rate would have the following effects on post-retirement benefits at December 31, 2018 : 1% increase 1% decrease (In thousands) Effect on total service cost and interest cost $ 14 $ (12 ) Effect on post-retirement benefit obligations 130 (120 )
Schedule of Expected Benefit Payments	Estimated future benefit payments, which reflect expected future service, as appropriate for the next five years are as follows: Pension RIM Post-retirement (In thousands) 2019 $ 5,791 $ 329 $ 1,079 2020 6,301 341 1,114 2021 6,892 377 1,171 2022 7,471 416 1,212 2023 8,167 458 1,249 Years 2024 - 2028 52,675 3,318 6,840
Schedule of Allocation of Plan Assets	The weighted average asset allocation of pension assets at December 31, 2018 and 2017 were as follows: December 31, 2018 2017 (In thousands) Domestic equities 35.20 % 38.10 % Foreign equities 10.80 13.90 Fixed income 42.30 36.90 Real estate 10.50 9.30 Cash 1.20 1.80 Total 100.00 % 100.00 % The following tables present the assets that are measured at fair value on a recurring basis by level within the U.S. GAAP fair value hierarchy as reported on the Statements of Net Assets Available for Plan benefits at December 31, 2018 and 2017 , respectively. Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. December 31, 2018 Fair value measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Money market mutual funds $ 3,459 $ 3,459 $ — $ — Mutual funds - value stock fund 22,533 22,533 — — Mutual funds - fixed income 115,500 115,500 — — Mutual funds - international stock 29,441 29,441 — — Mutual funds - institutional stock index 73,450 73,450 — — Commingled real estate funds 28,591 — 28,591 — $ 272,974 $ 244,383 $ 28,591 $ — (11) Employee Benefit Plans (continued) December 31, 2017 Fair value measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Money market mutual funds $ 5,236 $ 5,236 $ — $ — Mutual funds - value stock fund 27,364 27,364 — — Mutual funds - fixed income 106,726 106,726 — — Mutual funds - international stock 40,388 40,388 — — Mutual funds - institutional stock index 82,831 82,831 — — Commingled real estate funds 26,845 — 26,845 — $ 289,390 $ 262,545 $ 26,845 $ — The target allocation of assets and acceptable ranges around the targets are as follows: (11) Employee Benefit Plans (continued) Allowable Range Equities 40-60% Fixed income 40-60% Real estate 0-10% Cash 0-15%
Employee Stock Ownership Plan (ESOP) Disclosures	The ESOP shares were as follows: December 31, 2018 (In thousands) Allocated shares 159 Unearned shares 4,384 Total ESOP shares 4,543 Fair value of unearned shares $ 67,025

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The current and deferred amounts of income tax expense (benefit) for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017 are as follows: Year ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Current: Federal $ 11,284 $ 630 $ 16,198 $ 13,209 State 5,129 862 1,236 664 Total current 16,413 1,492 17,434 13,873 Deferred: Federal (4,901 ) 7,530 (1,454 ) 2,743 State (589 ) (39 ) 28 187 Total deferred (5,490 ) 7,491 (1,426 ) 2,930 $ 10,923 $ 8,983 $ 16,008 $ 16,803
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation between the amount of reported total income tax expense and the amount computed by multiplying the applicable statutory income tax rate (35% for the 2017 and 2016 periods presented below, and 21% for the 2018 period) is as follows: Year ended December 31, Three Months Ended December 31, September 30, 2018 2017 2017 2016 (In thousands) Tax expense at applicable statutory rate $ 7,067 $ 4,431 $ 16,478 $ 17,415 Increase (decrease) in taxes resulting from: State tax, net of federal income tax benefit 3,587 535 822 553 ESOP fair market value adjustment 202 — — — Tax exempt interest income (4 ) (2 ) (50 ) (28 ) Income from Bank-owned life insurance (812 ) (381 ) (1,589 ) (1,405 ) Dividend received deduction (16 ) (10 ) (40 ) (39 ) Impact of tax reform — 4,700 — — Other, net 899 (290 ) 387 307 $ 10,923 $ 8,983 $ 16,008 $ 16,803
Schedule of Deferred Tax Assets and Liabilities	The net deferred tax asset is included in other assets in the Consolidated Statements of Financial Condition. The tax effects of temporary differences that give rise to significant portions of the deferred tax assets and deferred tax liabilities at December 31, 2018 and 2017 are as follows: (12) Income Taxes (continued) At December 31, 2018 2017 (In thousands) Deferred tax assets: Allowance for loan losses $ 13,251 $ 12,584 Post retirement benefit 3,720 3,414 Deferred compensation 2,228 1,939 Depreciation 1,042 949 Retirement income maintenance plan 1,602 1,455 ESOP 128 — Stock-based compensation 35 — Reserve for uncollected interest 24 62 Net unrealized losses on securities and defined benefit plans 19,060 18,221 State NOL 2,063 2,476 Alternative minimum assessment carryforwards 2,156 2,156 Charitable contribution carryforward 6,085 — Other items 670 1,595 Gross deferred tax assets 52,064 44,851 Valuation allowance (2,388 ) (2,786 ) 49,676 42,065 Deferred tax liabilities: Pension expense 26,071 26,234 Deferred loan costs 5,736 4,257 Intangible assets 1,621 1,642 Other items 34 48 Total gross deferred tax liabilities 33,462 32,181 Net deferred tax asset $ 16,214 $ 9,884

Financial Transactions with O_2

Financial Transactions with Off-Balance-Sheet risk and Concentrations of Credit risk (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedules of Concentration of Risk, by Risk Factor	At December 31, 2018 and 2017 , the following commitments existed which are not reflected in the consolidated statements of financial condition: December 31, 2018 2017 (In thousands) Loan commitments: Residential real estate $ 29,622 $ 58,860 Commercial real estate 73,201 17,994 Commercial business 13,000 14,796 Construction loans 71,062 20,715 Consumer home equity loans and lines of credit 8,344 5,858 Total loan commitments $ 195,229 $ 118,223
Contractual Obligation, Fiscal Year Maturity Schedule	Minimum aggregate lease payments for the remainder of the lease terms are as follows: December 31, 2018 (In thousands) 2019 $ 3,596 2020 3,511 2021 3,288 2022 2,921 2023 2,590 Thereafter 5,209 Total lease commitments $ 21,115

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of fair value assets and liabilities measured on recurring basis	The following tables present the assets and liabilities reported on the Consolidated Statements of Financial Condition at their fair values as of December 31, 2018 and 2017 , by level within the fair value hierarchy: December 31, 2018 Fair Value Measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Securities available for sale: U.S. government and agency obligations $ 54,157 $ 54,157 $ — $ — Mortgage-backed securities and collateralized mortgage obligations 920,007 — 920,007 — Municipal obligations 987 — 987 — Corporate debt securities 53,467 — 53,467 — Trust preferred securities 4,250 — 4,250 — Equity securities 1,890 1,890 — — Total securities available for sale 1,034,758 56,047 978,711 — Derivative assets 865 — 865 — $ 1,035,623 $ 56,047 $ 979,576 $ — Derivative liabilities $ 3,467 $ — $ 3,467 $ — December 31, 2017 Fair Value Measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Securities available for sale: U.S. government and agency obligations $ 39,644 $ 39,644 $ — $ — Mortgage-backed securities and collateralized mortgage obligations 606,612 — 606,612 — Municipal obligations 1,957 — 1,957 — Corporate debt securities 54,514 — 54,514 — Trust preferred securities 4,656 — 4,656 — Equity securities 3,187 3,187 — — Total securities available for sale 710,570 42,831 667,739 — Derivative assets 490 — 490 — $ 711,060 $ 42,831 $ 668,229 $ — Derivative liabilities $ 203 $ — $ 203 $ —
Schedule of fair value assets and liabilities measured on non-recurring basis	December 31, 2018 Fair Value Measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Impaired loans $ 1,525 $ — $ — $ 1,525 Real estate owned 92 — — 92 Mortgage servicing rights 442 — — 442 $ 2,059 $ — $ — $ 2,059 (14) Fair Value Measurements (continued) December 31, 2017 Fair Value Measurements Fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Impaired loans $ 10,251 $ — $ — $ 10,251 Real estate owned 959 — — 959 Mortgage servicing rights 316 — — 316 $ 11,526 $ — $ — 23 $ 11,526
Schedule of qualitative information for Level 3 assets measured at fair value on a non-recurring basis	The following table presents qualitative information for Level 3 assets measured at fair value on a non-recurring basis as of December 31, 2018 and 2017 : December 31, 2018 Fair value Valuation methodology Unobservable inputs Range Weighted average (In thousands) Impaired loans $ 1,525 Appraised value (2) Discount for cost to sell (3) 6.0% - 8.0% 7.5% Real estate owned 92 Contract sales price (1) Discount for cost to sell (3) 6.0% 6.0% Mortgage servicing rights 442 Estimated cash flow Prepayment speeds 3.3% - 26.8% 12% December 31, 2017 Fair value Valuation methodology Unobservable inputs Range of inputs Weighted average (In thousands) Impaired loans $ 10,251 Appraised value (2) Discount for cost to sell (3) 6.0% - 8.0% 7.2% Real estate owned 959 Appraised value (2) Discount for cost to sell (3) 6.0% 6.0% Mortgage servicing rights 316 Estimated cash flow Prepayment speeds 3.6% -11.0% 3.9% (1) Value is based on signed contract for sale. (2) Value is based on an independent appraisal of the market or fair value of the loan's underlying collateral. (3) Includes commissions, fees and other costs.
Schedule of fair value assets and liabilities on Consolidated Balance Sheets	The following tables present the assets and liabilities reported on the Consolidated Statements of Financial Condition at their fair values as of December 31, 2018 and 2017 : December 31, 2018 Fair Value Measurements Carrying value Total fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (In thousands) Financial assets: Cash and cash equivalents $ 42,201 $ 42,201 $ 42,201 $ — $ — Securities available for sale 1,034,758 1,034,758 56,047 978,711 — Securities held to maturity 262,143 254,841 23,241 254,841 — Federal Home Loan Bank stock 58,938 58,938 — 58,938 — Loans held-for-sale 8,081 8,081 8,081 — Loans receivable, net 4,979,182 4,841,830 — — 4,841,830 Derivative assets 865 865 — 865 — Financial liabilities: — Deposits $ 4,413,873 $ 4,402,336 $ — $ 4,402,336 $ — Borrowings 1,189,180 1,185,007 — 1,185,007 — Derivative liabilities 3,467 3,467 — 3,467 — (14) Fair Value Measurements (continued) December 31, 2017 Fair Value Measurements Carrying value Total fair value Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) (In thousands) Financial assets: Cash and cash equivalents $ 65,498 $ 65,498 $ 65,498 $ — $ — Securities available for sale 710,570 710,570 42,831 667,739 — Securities held to maturity 239,618 236,125 8,344 227,781 — Federal Home Loan Bank Stock 44,664 44,664 — 44,664 — Loans receivable, net 4,400,470 4,367,945 — — 4,367,945 Derivative assets 490 490 — 490 — Financial liabilities: — Deposits $ 4,263,315 $ 3,959,460 $ — $ 3,959,460 $ — Borrowings 929,057 925,032 — 925,032 — Derivative liabilities 203 203 — 203 —

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	The following tables are a summary of certain quarterly financial data for the years ended December 31, 2018 , September 30, 2017 and 2016 and the three months ended December 31, 2017: Quarters Ended December 31, 2018 March 31 June 30 September 30 December 31 (Dollars in thousands, except per share data) Total interest income $ 51,791 $ 55,019 $ 57,695 $ 61,785 Total interest expense 12,730 14,004 17,112 18,410 Net interest income 39,061 41,015 40,583 43,375 Provision for loan losses 2,000 2,400 1,500 777 Net interest income after provision for loan losses 37,061 38,615 39,083 42,598 Total non-interest income 4,543 5,450 5,290 6,405 Total non-interest expense 26,015 61,768 26,590 31,013 Income (loss) before income tax expense 15,589 (17,703 ) 17,783 17,990 Income tax expense 3,805 (2,961 ) 6,956 3,123 Net income (loss) $ 11,784 $ (14,742 ) $ 10,827 $ 14,867 Basic and diluted earnings per share N/A $ (0.13 ) $ 0.10 $ 0.13 (15) Selected Quarterly Financial Data (Unaudited) (continued) Quarter Ended December 31, 2017 (In thousands) Total interest income $ 49,169 Total interest expense 12,240 Net interest income 36,929 Provision for loan losses 3,400 Net interest income after provision for loan losses 33,529 Total non-interest income 4,733 Total non-interest expense 25,601 Income before income tax expense 12,661 Income tax expense 8,983 Net income $ 3,678 Basic and diluted earnings per share N/A Quarters Ended September 30, 2017 December 31 March 31 June 30 September 30 (Dollars in thousands, except per share data) Total interest income $ 44,129 $ 45,428 $ 46,850 $ 47,820 Total interest expense 10,724 10,651 11,211 11,860 Net interest income 33,405 34,777 35,639 35,960 Provision for loan losses — 375 375 5,676 Net interest income after provision for loan losses 33,405 34,402 35,264 30,284 Total non-interest income 5,534 5,806 4,645 1,630 Total non-interest expense 24,078 24,903 24,703 30,206 Income before income tax expense 14,861 15,305 15,206 1,708 Income tax expense 4,868 5,012 5,934 194 Net income $ 9,993 $ 10,293 $ 9,272 $ 1,514 Basic and diluted earnings per share N/A N/A N/A N/A (15) Selected Quarterly Financial Data (Unaudited) (continued) Quarters Ended September 30, 2016 December 31 March 31 June 30 September 30 (Dollars in thousands, except per share data) Total interest income $ 41,616 $ 41,929 $ 42,421 $ 43,011 Total interest expense 10,996 10,840 11,003 11,123 Net interest income 30,620 31,089 31,418 31,888 Provision for loan losses — 417 — — Net interest income after provision for loan losses 30,620 30,672 31,418 31,888 Total non-interest income 4,537 4,738 4,525 4,702 Total non-interest expense 23,388 22,816 23,658 23,482 Income before income tax expense 11,769 12,594 12,285 13,108 Income tax expense 3,859 4,281 4,052 4,611 Net income $ 7,910 $ 8,313 $ 8,233 $ 8,497 Basic and diluted earnings per share N/A N/A N/A N/A

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following is a reconciliation of the numerators and denominators of the basic and diluted earnings per share calculations for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: December 31, Three Months Ended December 31, September 30, 2018 2017 2017 2016 (Dollars in thousands, except per share data) Net income $ 22,736 $ 3,678 $ 31,072 $ 32,953 Basic earnings per share: Weighted average shares outstanding - basic 111,395,723 N/A N/A N/A Basic earnings per share $ 0.20 N/A N/A N/A Diluted earnings per share: Weighted average shares outstanding - diluted 111,395,723 N/A N/A N/A Diluted earnings per share $ 0.20 N/A N/A N/A

Parent-only Financial Informa_2

Parent-only Financial Information (Tables)	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Condensed Balance Sheet	The condensed financial statements of Columbia Financial, Inc. (parent company) are presented below: Statements of Financial Condition December 31, 2018 2017 (In thousands) Assets Cash and due from Bank $ 153,697 $ 1,537 Short-term investments 136 164 Total cash and cash equivalents 153,833 1,701 Securities available for sale, at fair value 1,420 2,783 Investment in subsidiaries 764,663 516,607 Loan receivable from Bank 44,439 — Other assets 7,852 3,281 Total assets $ 972,207 $ 524,372 Liabilities and Stockholders' Equity Liabilities: Borrowings $ — $ 50,657 Accrued expenses and other liabilities 147 1,645 Total liabilities 147 52,302 Total stockholders' equity 972,060 472,070 Total liabilities and stockholders' equity $ 972,207 $ 524,372
Condensed Statement of Comprehensive Income	Statements of Comprehensive Income (Loss) Year Ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Income: Dividend from subsidiary $ — $ — $ 2,000 $ 3,000 Securities available for sale 123 41 162 157 Interest earnings 2,384 — 1 — Total income 2,507 41 2,163 3,157 Interest expense on borrowings 3,468 1,044 4,177 4,177 Net interest expense (961 ) (1,003 ) (2,014 ) (1,020 ) Equity earnings in subsidiary 51,401 4,288 32,230 32,743 Expense: Loss on securities available for sale — 60 — — Charitable contribution to foundation 34,767 — — — Other non-interest expense 425 2 460 355 Total expense 35,192 62 460 355 Income before income tax benefit 15,248 3,223 29,756 31,368 Income tax benefit 7,488 455 1,316 1,585 Net income 22,736 3,678 31,072 32,953 Other comprehensive (loss) income (6,487 ) (19,230 ) 5,178 (11,287 ) Comprehensive income (loss) $ 16,249 $ (15,552 ) $ 36,250 $ 21,666
Condensed Cash Flow Statement	Statements of Cash Flows Year Ended December 31, Three Months Ended December 31, Years Ended September 30, 2018 2017 2017 2016 (In thousands) Cash flows from operating activities: Net income $ 22,736 $ 3,678 $ 31,072 $ 32,953 Adjustments to reconcile net income to net cash provided by operating activities: Amortization of debt issuance costs 890 14 53 53 Loss on securities available for sale — 60 — — Deferred tax (benefit) expense (6,086 ) 42 1 (2 ) Increase (decrease) in other assets 1,515 (494 ) 1,404 (1,600 ) (Decrease) increase in accrued expenses and other liabilities (1,498 ) 989 62 10 Contribution of common stock to Columbia Bank Foundation 34,767 — — — Equity in undistributed earnings of subsidiary (51,401 ) (4,288 ) (32,295 ) (32,744 ) Net cash provided by (used in) operating activities 923 1 297 (1,330 ) Cash flows from financing activities: Capital contribution to subsidiary (246,420 ) — — — Proceeds from sales of securities available for sale — 92 — — Proceeds from call / paydowns of securities available for sale 1,601 10 — — Purchases of securities available for sale (414 ) — — — Loan to ESOP (45,428 ) — — — Repayment of loans receivable from Bank 989 — — — Net cash (used in) provided by investing activities (289,672 ) 102 — — Cash flows from financing activities: Payment for trust preferred securities (51,547 ) — Issuance of common stock 492,428 — Net cash provided by financing activities 440,881 — — — Net increase (decrease) in cash and cash equivalents 152,132 103 297 (1,330 ) Cash and cash equivalents at beginning of period 1,701 1,598 1,301 2,631 Cash and cash equivalents at end of period $ 153,833 $ 1,701 $ 1,598 $ 1,301

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Other Comprehensive Income (Loss)	The following tables present the components of other comprehensive income (loss), both gross and net of tax, for the years ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 Before Tax Tax Effect After Tax Before Tax Tax Effect After Tax (In thousands) Components of Other Comprehensive (Loss) Income: Unrealized gains and losses on securities available for sale: Net (loss) gain arising during the period $ (7,224 ) $ 1,446 $ (5,778 ) $ (3,012 ) $ (119 ) $ (3,131 ) Accretion of unrealized loss on securities reclassified as held to maturity (13 ) — (13 ) (2 ) (56 ) (58 ) Reclassification adjustment for (gain) loss included in net income (116 ) 24 (92 ) 60 (13 ) 47 (7,353 ) 1,470 (5,883 ) (2,954 ) (188 ) (3,142 ) Unrealized (loss) gain on swap contract (2,825 ) 595 (2,230 ) 192 (30 ) 162 Employee benefit plans: Amortization of prior service cost included in net income (623 ) 132 (491 ) (24 ) (19 ) (43 ) Reclassification adjustment of actuarial net (loss) gain included in net income 2,526 (530 ) 1,996 (9 ) (94 ) (103 ) Change in funded status of retirement obligations 897 (776 ) 121 (9,024 ) 3,354 (5,670 ) Tax effects resulting from the adoption of ASU No. 2018-02 — — — — (10,434 ) (10,434 ) 2,800 (1,174 ) 1,626 (9,057 ) (7,193 ) (16,250 ) Total other comprehensive (loss) $ (7,378 ) $ 891 $ (6,487 ) $ (11,819 ) $ (7,411 ) $ (19,230 ) The Company, in accordance with ASU No. 2018-02, elected to reclassify the income tax effects of the Tax Act from accumulated other comprehensive (loss) income to retained earnings for the year ended December 31, 2017 . (18) Other Comprehensive Income (Loss) (continued) For the Years Ended September 30, 2017 2016 Before Tax Tax Effect After Tax Before Tax Tax Effect After Tax (In thousands) Components of Other Comprehensive (Loss) Income: Unrealized gains and losses on securities available for sale: Net (loss) gain arising during the period $ (17,877 ) $ 6,379 $ (11,498 ) $ 7,271 $ (2,597 ) $ 4,674 Accretion of unrealized gain on securities reclassified as held to maturity 12 (4 ) 8 — — — Reclassification adjustment for loss (gain) included in net income 2,626 (937 ) 1,689 (552 ) 197 (355 ) (15,239 ) 5,438 (9,801 ) 6,719 (2,400 ) 4,319 Unrealized gain on swap contract 95 (33 ) 62 — — — 95 (33 ) 62 — — — Employee benefit plans: Amortization of prior service cost included in net income (114 ) 41 (73 ) (114 ) 41 (73 ) Reclassification adjustment of actuarial net gains (losses) included in net income 11,806 (4,213 ) 7,593 9,123 (3,259 ) 5,864 Change in funded status of retirement obligations 11,503 (4,106 ) 7,397 (33,287 ) 11,890 (21,397 ) 23,195 (8,278 ) 14,917 (24,278 ) 8,672 (15,606 ) Total other comprehensive income (loss) $ 8,051 $ (2,873 ) $ 5,178 $ (17,559 ) $ 6,272 $ (11,287 )
Components of Other Comprehensive Income (Loss)	The following tables present the changes in the components of accumulated other comprehensive (loss) income, net of tax, for the years ended ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: For the Year Ended December 31, For the Three Months Ended December 31, 2018 2017 Unrealized (losses) gains on securities available for sale Unrealized gains (losses) on swaps Employee benefit plans Accumulated other comprehensive loss Unrealized (losses) gains on securities available for sale Unrealized gains (losses) on swaps Employee benefit plans Accumulated other comprehensive loss (In thousands) Balance at beginning of period $ (7,279 ) $ 224 $ (58,355 ) $ (65,410 ) $ (4,137 ) $ 62 $ (42,105 ) $ (46,180 ) Current period changes in other comprehensive (loss) income (5,883 ) (2,230 ) 1,626 (6,487 ) (1,828 ) 122 (5,816 ) (7,522 ) Reclassification of tax effects resulting from the adoption of ASU No. 2018-02 — — — — (1,314 ) 40 (10,434 ) (11,708 ) Total other comprehensive (loss) income $ (13,162 ) $ (2,006 ) $ (56,729 ) $ (71,897 ) $ (7,279 ) $ 224 $ (58,355 ) $ (65,410 ) (18) Other Comprehensive Income (Loss) (continued) For the Years Ended September 30, 2017 2016 Unrealized (losses) gains on securities available for sale Unrealized gains (losses) on swaps Employee benefit plans Accumulated other comprehensive loss Unrealized (losses) gains on securities available for sale Unrealized gains (losses) on swaps Employee benefit plans Accumulated other comprehensive loss (In thousands) Balance at beginning of period $ 5,664 $ — $ (57,022 ) $ (51,358 ) $ 1,345 $ — $ (41,416 ) $ (40,071 ) Current period changes in other comprehensive (loss) income (9,801 ) 62 14,917 5,178 4,319 — (15,606 ) (11,287 ) Total other comprehensive (loss) income $ (4,137 ) $ 62 $ (42,105 ) $ (46,180 ) $ 5,664 $ — $ (57,022 ) $ (51,358 )
Reclassification out of AOCI	The following table reflects amounts reclassified out of accumulated other comprehensive (loss) income to the Consolidated Statements of Income and the affected line item in the statement where net income is presented for the years ended ended December 31, 2018 , September 30, 2017 and 2016, and the three months ended December 31, 2017: Accumulated other comprehensive (loss) income components For the Year Ended December 31, For the Three Months Ended December 31, Affected line items in the Consolidated Statements of Income 2018 2017 (In thousands) Reclassification adjustment for gains included in net income $ (116 ) $ 60 Gains on securities transactions, net Reclassification adjustment of actuarial net gain included in net income 2,526 (9 ) Compensation and employee benefits expense Total before tax 2,410 51 Income tax benefit (506 ) (107 ) Net of tax $ 1,904 $ (56 ) (18) Other Comprehensive Income (Loss) (continued) Accumulated other comprehensive (loss) income components For the Years Ended September 30, Affected line items in the Consolidated Statements of Income 2017 2016 (In thousands) Reclassification adjustment for gains included in net income $ 2,626 $ (552 ) Gains on securities transactions, net Reclassification adjustment of actuarial net gain included in net income 11,806 9,123 Compensation and employee benefits expense Total before tax 14,432 8,571 Income tax (benefit) expense (5,150 ) (3,062 ) Net of tax $ 9,282 $ 5,509

Derivatives and Hedging Activ_2

Derivatives and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of derivative financial instruments on the Consolidated Balance Sheets	The tables below present the fair value of the Company’s derivative financial instruments as well as their classification in the Consolidated Statements of Financial Condition at December 31, 2018 and 2017 : December 31, 2018 Asset Derivative Liability Derivative Consolidated Statements of Financial Condition Fair value Consolidated Statements of Financial Condition Fair value (In thousands) (In thousands) Derivatives: Interest rate products-designated Other Assets $ 865 Other Liabilities $ 3,467 Total derivative instruments $ 865 $ 3,467 December 31, 2017 Asset Derivative Liability Derivative Consolidated Statements of Financial Condition Fair value Consolidated Statements of Financial Condition Fair value (In thousands) (In thousands) Derivatives: Interest rate products-designated Other Assets $ 287 Other Liabilities $ — Currency forward contract - non-designated hedge Other Assets $ 203 Other Liabilities $ 203 Total derivative instruments $ 490 $ 203

Business (Details)

Business (Details) - Minority Stock Offering	Apr. 19, 2018shares
Columbia Bank, MHC
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares)	62,580,155
Columbia Bank Foundation
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares)	3,476,675
Columbia Bank Employee Stock Ownership Plan
Subsidiary, Sale of Stock [Line Items]
Shares issued (in shares)	49,832,345

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Aug. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Junior subordinated debenture owed to unconsolidated subsidiary trust					$ 51,500
Cash reserves		$ 5,900	$ 4,100
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02			0
Retained earnings
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from AOCI to retained earnings due to TCJA			11,700
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02			$ 11,708
Buildings
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		40 years
Minimum | Land and building improvements
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		10 years
Minimum | Furniture and equipment
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		5 years
Maximum | Land and building improvements
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		20 years
Maximum | Furniture and equipment
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		10 years
Columbia Financial Capital Trust I
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Ownership percentage by parent		100.00%
Scenario, Forecast | Subsequent Event | Accounting Standards Update 2016-01
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02				$ 548
Pension | Minimum
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Defined contribution plan, employer matching contribution, percent of match		3.00%
Pension | Maximum
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Defined contribution plan, employer matching contribution, percent of match		4.50%
Columbia Bank Employee Stock Ownership Plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Loan term	20 years

- Securities Available-for-Sale

- Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, amortized cost	$ 1,051,128	$ 719,607
Securities available-for-sale, gross unrealized gains	3,688	1,795
Securities available-for-sale, gross unrealized (losses)	(20,058)	(10,832)
Securities available for sale, at fair value	1,034,758	710,570
U.S. government and agency obligations
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, amortized cost	54,821	39,909
Securities available-for-sale, gross unrealized gains	53	17
Securities available-for-sale, gross unrealized (losses)	(717)	(282)
Securities available for sale, at fair value	54,157	39,644
Mortgage-backed securities and collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, amortized cost	934,631	615,924
Securities available-for-sale, gross unrealized gains	2,812	383
Securities available-for-sale, gross unrealized (losses)	(17,436)	(9,695)
Securities available for sale, at fair value	920,007	606,612
Municipal obligations
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, amortized cost	987	1,957
Securities available-for-sale, gross unrealized gains	0	0
Securities available-for-sale, gross unrealized (losses)	0	0
Securities available for sale, at fair value	987	1,957
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, amortized cost	54,493	54,489
Securities available-for-sale, gross unrealized gains	129	536
Securities available-for-sale, gross unrealized (losses)	(1,155)	(511)
Securities available for sale, at fair value	53,467	54,514
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, amortized cost	5,000	5,000
Securities available-for-sale, gross unrealized gains	0	0
Securities available-for-sale, gross unrealized (losses)	(750)	(344)
Securities available for sale, at fair value	4,250	4,656
Equity securities
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, amortized cost	1,196	2,328
Securities available-for-sale, gross unrealized gains	694	859
Securities available-for-sale, gross unrealized (losses)	0	0
Securities available for sale, at fair value	$ 1,890	$ 3,187

Securities Available for Sale -

Securities Available for Sale - Expected Maturities of Available-for-Sale Securities (Details) $ in Thousands	Dec. 31, 2018USD ($)
Amortized cost
Securities available-for-sale, amortized cost	$ 1,049,932
Fair value
Securities available for sale, at fair value	1,032,868
Debt Securities Excluding Mortgage-Based Securities
Amortized cost
One year or less	797
More than one year to five years	50,131
More than five years to ten years	59,373
More than ten years	5,000
Securities available-for-sale, amortized cost	115,301
Fair value
One year or less	797
More than one year to five years	49,613
More than five years to ten years	57,971
More than ten years	4,480
Securities available for sale, at fair value	112,861
Mortgage-backed securities and collateralized mortgage obligations
Amortized cost
Securities available-for-sale, amortized cost	934,631
Fair value
Securities available for sale, at fair value	$ 920,007

Securities Available for Sale_2

Securities Available for Sale - Narrative (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, amortized cost	$ 719,607,000	$ 1,051,128,000
Securities available for sale, at fair value	710,570,000	1,034,758,000
Proceeds from available-for-sale securities	92,000	11,500,000	$ 187,400,000	$ 164,200,000
Available-for-sale securities, gross realized gains	0	116,000	1,500,000	1,100,000
Proceeds from sale and maturity of debt securities, available for sale	0	2,400,000	17,200,000	5,400,000
Available-for-sale securities, gross realized losses	(60,000)		(3,200,000)	(743,000)
Securities available-for-sale sold under agreements	$ 301,100,000	$ 232,700,000
Number of unrealized loss positions	111	151
Other-than-temporary impairment loss, debt securities, available for sale		$ 0	$ 0	$ 0
Mortgage-backed securities and collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, amortized cost	$ 615,924,000	934,631,000
Securities available for sale, at fair value	606,612,000	920,007,000
Securities available-for-sale sold under agreements	$ 141,000,000	$ 187,000,000

Securities Available for Sale_3

Securities Available for Sale - Continuous Unrealized Loss Position of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	$ 217,762	$ 548,803
Less than 12 months, gross unrealized (losses)	(1,748)	(8,454)
12 months or longer, fair value	552,442	58,068
12 months or longer, gross unrealized (losses)	(18,310)	(2,378)
Total, fair value	770,204	606,871
Total, gross unrealized (losses)	(20,058)	(10,832)
U.S. government and agency obligations
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	14,668	29,654
Less than 12 months, gross unrealized (losses)	(202)	(282)
12 months or longer, fair value	29,437	0
12 months or longer, gross unrealized (losses)	(515)	0
Total, fair value	44,105	29,654
Total, gross unrealized (losses)	(717)	(282)
Mortgage-backed securities and collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	176,614	514,283
Less than 12 months, gross unrealized (losses)	(1,034)	(8,037)
12 months or longer, fair value	509,397	48,788
12 months or longer, gross unrealized (losses)	(16,402)	(1,658)
Total, fair value	686,011	563,071
Total, gross unrealized (losses)	(17,436)	(9,695)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	26,480	4,866
Less than 12 months, gross unrealized (losses)	(512)	(135)
12 months or longer, fair value	9,358	4,624
12 months or longer, gross unrealized (losses)	(643)	(376)
Total, fair value	35,838	9,490
Total, gross unrealized (losses)	(1,155)	(511)
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	0	0
Less than 12 months, gross unrealized (losses)	0	0
12 months or longer, fair value	4,250	4,656
12 months or longer, gross unrealized (losses)	(750)	(344)
Total, fair value	4,250	4,656
Total, gross unrealized (losses)	$ (750)	$ (344)

Securities Held-to-Maturity (De

Securities Held-to-Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 262,143	$ 239,618
Gross unrealized gains	73	0
Gross unrealized (losses)	(7,375)	(3,493)
Securities held to maturity	254,841	236,125
U.S. government and agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	23,404	8,402
Gross unrealized gains	45	0
Gross unrealized (losses)	(208)	(58)
Securities held to maturity	23,241	8,344
Mortgage-backed securities and collateralized mortgage obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	238,739	231,216
Gross unrealized gains	28	0
Gross unrealized (losses)	(7,167)	(3,435)
Securities held to maturity	$ 231,600	$ 227,781

Expected Maturities of Held-to-

Expected Maturities of Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Amortized cost
Amortized cost	$ 262,143	$ 239,618
Fair value
Fair value	254,841	236,125
U.S. government and agency obligations
Amortized cost
More than one year to five years	5,000
More than five years to ten years	8,404
More than ten years	10,000
Amortized cost	23,404	8,402
Fair value
More than one year to five years	5,000
More than five years to ten years	8,196
More than ten years	10,045
Fair value	23,241	8,344
Mortgage-backed securities and collateralized mortgage obligations
Amortized cost
Amortized cost	238,739	231,216
Fair value
Fair value	$ 231,600	$ 227,781

Narrative (Details)

Narrative (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Number of unrealized loss positions	84	88
Amortized cost	$ 239,618,000	$ 262,143,000
Securities held-to-maturity, fair value	236,125,000	254,841,000
Proceeds from sale of held-to-maturity securities		0	$ 0	$ 0
Proceeds from maturities, prepayments and calls of held-to-maturity securities	0	5,400,000	769,000	0
Securities available-for-sale sold under agreements	301,100,000	232,700,000
Transfer of securities from available for sale securities	0	0	103,680,000	0
Transfer of securities from available for sale securities, fair value			103,300,000
Other-than-temporary impairment loss, debt securities, held-to-maturity, before tax		0	$ 0	$ 0
Mortgage-backed securities and collateralized mortgage obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	231,216,000	238,739,000
Securities held-to-maturity, fair value	227,781,000	231,600,000
Securities available-for-sale sold under agreements	$ 141,000,000	$ 187,000,000

Securities Held to Maturity Con

Securities Held to Maturity Continuous Unrealized Loss Position of Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months, Fair Value	$ 11,265	$ 204,393
Less than 12 months, Gross unrealized (losses)	(69)	(2,978)
12 months or longer, Fair value	221,443	29,531
12 months or longer, Gross unrealized (losses)	(7,306)	(515)
Total, Fair value	232,708	233,924
Total, Gross unrealized (losses)	(7,375)	(3,493)
U.S. government and agency obligations
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months, Fair Value	0	8,344
Less than 12 months, Gross unrealized (losses)	0	(58)
12 months or longer, Fair value	8,197	0
12 months or longer, Gross unrealized (losses)	(208)	0
Total, Fair value	8,197	8,344
Total, Gross unrealized (losses)	(208)	(58)
Mortgage-backed securities and collateralized mortgage obligations
Schedule of Held-to-maturity Securities [Line Items]
Less than 12 months, Fair Value	11,265	196,049
Less than 12 months, Gross unrealized (losses)	(69)	(2,920)
12 months or longer, Fair value	213,246	29,531
12 months or longer, Gross unrealized (losses)	(7,098)	(515)
Total, Fair value	224,511	225,580
Total, Gross unrealized (losses)	$ (7,167)	$ (3,435)

Loans Receivable and Allowanc_3

Loans Receivable and Allowance for Loan Losses - Loans Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 4,962,289	$ 4,446,015
Net deferred loan costs, fees and purchased premiums and discounts	16,893	12,633
Loans receivable	4,979,182	4,458,648
Real estate loans | One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	1,830,186	1,615,000
Real estate loans | Multifamily and commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	2,142,154	1,870,475
Real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	261,473	233,652
Commercial business loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	333,876	277,970
Consumer loans | Home equity loans and advances
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	393,492	447,920
Consumer loans | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 1,108	$ 998

Loans Receivable and Allowanc_4

Loans Receivable and Allowance for Loan Losses - Narrative (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)loan	Sep. 30, 2016USD ($)	Dec. 31, 2018USD ($)loan	Dec. 31, 2017USD ($)loan	Sep. 30, 2017USD ($)loan	Sep. 30, 2016USD ($)loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-sale amount			$ 8,081,000
Proceeds from sales of loans receivable	$ 0		32,039,000		$ 62,407,000	$ 28,624,000
Purchases and grants of loans receivable	56,095,000		32,251,000		20,473,000	21,149,000
Carrying value of servicing liability	(478,800,000)		(462,700,000)	$ (478,800,000)
Servicing income	298,000		1,100,000		1,200,000	1,200,000
Loans receivable	4,400,470,000		4,916,840,000	4,400,470,000
Non-accrual loans	17,618,000		18,196,000	17,618,000
Increase in interest income if non-accrual had performed in line with their original terms	61,000		126,000		295,000	713,000
Cash basis interest income on non-accrual loans	121,000		89,000		104,000	$ 472,000
Property acquired through foreclosure	$ 959,000		$ 92,000	$ 959,000
Number of loans in the process of foreclosure | loan	15		14	15
Loans in process of foreclosure	$ 2,700,000		$ 1,600,000	$ 2,700,000
Loan threshold for individual evaluation for impairment			500,000
Specific allowance for loan losses attributable to impaired loans	546,000		915,000	546,000
Impaired loans for which there are no related allowance for loan losses	14,611,000		11,647,000	14,611,000
Investment in troubled debt restructuring	17,600,000		$ 16,000,000	$ 17,600,000	$ 21,100,000
Number of loans in troubled debt restructuring | loan			7	0	7	4
90 Days or more
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	6,525,000		$ 2,789,000	$ 6,525,000
Investment in troubled debt restructuring	$ 425,000		$ 101,000	425,000	$ 1,000,000
Number of loans in troubled debt restructuring | loan	2		1		7
30-59 days
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 8,728,000		$ 12,012,000	8,728,000
Investment in troubled debt restructuring			$ 1,000,000
Number of loans in troubled debt restructuring | loan			7
Related Parties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases and grants of loans receivable	0		$ 0		$ 390,000	$ 115,000
Loans receivable	$ 1,500,000		$ 1,400,000	$ 1,500,000
Freddie Mac
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sales of loans receivable		$ 17,200,000

Loans Receivable and Allowanc_5

Loans Receivable and Allowance for Loan Losses - Aging of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 18,196	$ 17,618
Current	4,944,093	4,428,397
Total	4,962,289	4,446,015
30-59 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	12,012	8,728
60-89 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,395	2,365
90 Days or more
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,789	6,525
Real estate loans | One-to-four family
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	10,721	11,669
Current	1,819,465	1,603,331
Total	1,830,186	1,615,000
Real estate loans | One-to-four family | 30-59 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	8,384	7,080
Real estate loans | One-to-four family | 60-89 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,518	1,229
Real estate loans | One-to-four family | 90 Days or more
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	819	3,360
Real estate loans | Multifamily and commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,449	1,847
Current	2,138,705	1,868,628
Total	2,142,154	1,870,475
Real estate loans | Multifamily and commercial | 30-59 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,870	138
Real estate loans | Multifamily and commercial | 60-89 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,425	380
Real estate loans | Multifamily and commercial | 90 Days or more
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	154	1,329
Real estate loans | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Current	261,473	233,652
Total	261,473	233,652
Real estate loans | Construction | 30-59 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Real estate loans | Construction | 60-89 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Real estate loans | Construction | 90 Days or more
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Commercial business loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,398	2,082
Current	332,478	275,888
Total	333,876	277,970
Commercial business loans | 30-59 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	208	89
Commercial business loans | 60-89 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	279	730
Commercial business loans | 90 Days or more
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	911	1,263
Consumer loans | Home equity loans and advances
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,628	2,020
Current	390,864	445,900
Total	393,492	447,920
Consumer loans | Home equity loans and advances | 30-59 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,550	1,421
Consumer loans | Home equity loans and advances | 60-89 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	173	26
Consumer loans | Home equity loans and advances | 90 Days or more
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	905	573
Consumer loans | Other consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Current	1,108	998
Total	1,108	998
Consumer loans | Other consumer loans | 30-59 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Consumer loans | Other consumer loans | 60-89 days
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Consumer loans | Other consumer loans | 90 Days or more
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 0	$ 0

Loans Receivable and Allowanc_6

Loans Receivable and Allowance for Loan Losses - Non-accrual Status of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, recorded investment, nonaccrual status	$ 2,789	$ 6,525
Commercial business loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, recorded investment, nonaccrual status	911	1,263
One-to-four family | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, recorded investment, nonaccrual status	819	3,360
Multifamily and commercial | Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, recorded investment, nonaccrual status	154	1,329
Home equity loans and advances | Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, recorded investment, nonaccrual status	$ 905	$ 573

Loans Receivable and Allowanc_7

Loans Receivable and Allowance for Loan Losses - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Allowance for loan losses:
Individually evaluated for impairment	$ 915	$ 546
Collectively evaluated for impairment	61,427	57,632
Total	62,342	58,178	$ 54,633	$ 51,867	$ 56,948
Total loans:
Individually evaluated for impairment	17,787	22,191
Collectively evaluated for impairment	4,944,502	4,423,824
Total	4,962,289	4,446,015
Real estate loans | One-to-four family
Allowance for loan losses:
Individually evaluated for impairment	537	423
Collectively evaluated for impairment	14,695	19,568
Total	15,232	19,991	18,533	18,638	16,442
Total loans:
Individually evaluated for impairment	9,048	11,644
Collectively evaluated for impairment	1,821,138	1,603,356
Total	1,830,186	1,615,000
Real estate loans | Multifamily and commercial
Allowance for loan losses:
Individually evaluated for impairment	0	28
Collectively evaluated for impairment	23,251	19,905
Total	23,251	19,933	18,029	17,390	20,352
Total loans:
Individually evaluated for impairment	2,695	3,693
Collectively evaluated for impairment	2,139,459	1,866,782
Total	2,142,154	1,870,475
Real estate loans | Construction
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	7,217	5,217
Total	7,217	5,217	5,299	5,960	6,248
Total loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	261,473	233,652
Total	261,473	233,652
Commercial business loans
Allowance for loan losses:
Individually evaluated for impairment	366	80
Collectively evaluated for impairment	13,810	8,195
Total	14,176	8,275	8,480	5,721	7,094
Total loans:
Individually evaluated for impairment	2,944	4,263
Collectively evaluated for impairment	330,932	273,707
Total	333,876	277,970
Consumer loans | Home equity loans and advances
Allowance for loan losses:
Individually evaluated for impairment	12	15
Collectively evaluated for impairment	2,446	4,561
Total	2,458	4,576	4,190	4,052	6,111
Total loans:
Individually evaluated for impairment	3,100	2,591
Collectively evaluated for impairment	390,392	445,329
Total	393,492	447,920
Consumer loans | Other consumer loans
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	8	8
Total	8	8	8	11	4
Total loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,108	998
Total	1,108	998
Unallocated
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	0	178
Total	0	178	$ 94	$ 95	$ 697
Total loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	0	0
Total	$ 0	$ 0

Loans Receivable and Allowanc_8

Loans Receivable and Allowance for Loan Losses - Troubled Debt Restructuring (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)loan	Dec. 31, 2017USD ($)loan	Sep. 30, 2017USD ($)loan	Sep. 30, 2016USD ($)loan
Financing Receivable, Modifications [Line Items]
No. of Loans | loan	7	0	7	4
Pre-modification recorded investment	$ 1,454	$ 0	$ 4,778	$ 358
Post-modification recorded investment	$ 1,454	$ 0	$ 4,778	$ 358
Real estate loans | One-to-four family
Financing Receivable, Modifications [Line Items]
No. of Loans | loan	5	0	3	0
Pre-modification recorded investment	$ 801	$ 0	$ 548	$ 0
Post-modification recorded investment	$ 801	$ 0	$ 548	$ 0
Real estate loans | Multifamily and commercial
Financing Receivable, Modifications [Line Items]
No. of Loans | loan	1	0	1	0
Pre-modification recorded investment	$ 65	$ 0	$ 3,964	$ 0
Post-modification recorded investment	$ 65	$ 0	$ 3,964	$ 0
Commercial business loans | Commercial business loans
Financing Receivable, Modifications [Line Items]
No. of Loans | loan	0	0	1	3
Pre-modification recorded investment	$ 0	$ 0	$ 18	$ 255
Post-modification recorded investment	$ 0	$ 0	$ 18	$ 255
Consumer loans | Home equity loans and advances
Financing Receivable, Modifications [Line Items]
No. of Loans | loan	1	0	2	1
Pre-modification recorded investment	$ 588	$ 0	$ 248	$ 103
Post-modification recorded investment	$ 588	$ 0	$ 248	$ 103

Loans Receivable and Allowanc_9

Loans Receivable and Allowance for Loan Losses - Rollforward of Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Allowance for loan losses:
Beginning balance	$ 54,633	$ 58,178	$ 51,867	$ 56,948
Provision for loan losses	3,400	6,677	6,426	417
Recoveries	188	707	584	721
Charge-offs	(43)	(3,220)	(4,244)	(6,219)
Ending balance	58,178	62,342	54,633	51,867
Real estate loans | One-to-four family
Allowance for loan losses:
Beginning balance	18,533	19,991	18,638	16,442
Provision for loan losses	1,473	(4,503)	1,029	5,534
Recoveries	9	334	268	158
Charge-offs	(24)	(590)	(1,402)	(3,496)
Ending balance	19,991	15,232	18,533	18,638
Real estate loans | Multifamily and commercial
Allowance for loan losses:
Beginning balance	18,029	19,933	17,390	20,352
Provision for loan losses	1,906	3,445	1,644	(2,106)
Recoveries	0	2	75	23
Charge-offs	(2)	(129)	(1,080)	(879)
Ending balance	19,933	23,251	18,029	17,390
Real estate loans | Construction
Allowance for loan losses:
Beginning balance	5,299	5,217	5,960	6,248
Provision for loan losses	(82)	1,997	(661)	(43)
Recoveries	0	3	0	76
Charge-offs	0	0	0	(321)
Ending balance	5,217	7,217	5,299	5,960
Commercial business loans
Allowance for loan losses:
Beginning balance	8,480	8,275	5,721	7,094
Provision for loan losses	(373)	7,860	3,183	(1,323)
Recoveries	171	240	182	408
Charge-offs	(3)	(2,199)	(606)	(458)
Ending balance	8,275	14,176	8,480	5,721
Consumer loans | Home equity loans and advances
Allowance for loan losses:
Beginning balance	4,190	4,576	4,052	6,111
Provision for loan losses	389	(1,949)	1,219	(1,061)
Recoveries	6	122	59	55
Charge-offs	(9)	(291)	(1,140)	(1,053)
Ending balance	4,576	2,458	4,190	4,052
Consumer loans | Other consumer loans
Allowance for loan losses:
Beginning balance	8	8	11	4
Provision for loan losses	3	5	13	18
Recoveries	2	6	0	1
Charge-offs	(5)	(11)	(16)	(12)
Ending balance	8	8	8	11
Unallocated
Allowance for loan losses:
Beginning balance	94	178	95	697
Provision for loan losses	84	(178)	(1)	(602)
Recoveries	0	0	0	0
Charge-offs	0	0	0	0
Ending balance	$ 178	$ 0	$ 94	$ 95

Loans Receivable and Allowan_10

Loans Receivable and Allowance for Loan Losses - Loans Individually Evaluated for Impairment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
With no allowance recorded: Recorded investment	$ 11,647	$ 14,611
With no allowance recorded: Unpaid principal balance	14,029	17,253
With a specific allowance recorded: Recorded investment	6,140	7,580
With a specific allowance recorded: Unpaid principal balance	6,296	8,167
Recorded investment	17,787	22,191
Unpaid principal balance	20,325	25,420
Specific allowance	915	546
Real estate loans | One-to-four family
Financing Receivable, Impaired [Line Items]
With no allowance recorded: Recorded investment	4,156	8,870
With no allowance recorded: Unpaid principal balance	5,307	9,704
With a specific allowance recorded: Recorded investment	4,892	2,774
With a specific allowance recorded: Unpaid principal balance	4,939	2,788
Recorded investment	9,048	11,644
Unpaid principal balance	10,246	12,492
Specific allowance	537	423
Real estate loans | Multifamily and commercial
Financing Receivable, Impaired [Line Items]
With no allowance recorded: Recorded investment	2,695	2,058
With no allowance recorded: Unpaid principal balance	3,482	2,933
With a specific allowance recorded: Recorded investment		1,635
With a specific allowance recorded: Unpaid principal balance		2,208
Recorded investment	2,695	3,693
Unpaid principal balance	3,482	5,141
Specific allowance	0	28
Commercial business loans
Financing Receivable, Impaired [Line Items]
With no allowance recorded: Recorded investment	2,285	1,522
With no allowance recorded: Unpaid principal balance	2,374	2,015
With a specific allowance recorded: Recorded investment	659	2,741
With a specific allowance recorded: Unpaid principal balance	768	2,741
Recorded investment	2,944	4,263
Unpaid principal balance	3,142	4,756
Specific allowance	366	80
Consumer loans | Home equity loans and advances
Financing Receivable, Impaired [Line Items]
With no allowance recorded: Recorded investment	2,511	2,161
With no allowance recorded: Unpaid principal balance	2,866	2,601
With a specific allowance recorded: Recorded investment	589	430
With a specific allowance recorded: Unpaid principal balance	589	430
Recorded investment	3,100	2,591
Unpaid principal balance	3,455	3,031
Specific allowance	$ 12	$ 15

Loans Receivable and Allowan_11

Loans Receivable and Allowance for Loan Losses - Interest Income on Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Impaired [Line Items]
Average recorded Investment	$ 25,590	$ 19,357	$ 27,054	$ 35,928
Interest Income Recognized	230	891	1,079	889
Real estate loans | One-to-four family
Financing Receivable, Impaired [Line Items]
Average recorded Investment	14,015	10,224	15,027	18,119
Interest Income Recognized	110	445	469	565
Real estate loans | Multifamily and commercial
Financing Receivable, Impaired [Line Items]
Average recorded Investment	4,087	2,712	4,328	9,344
Interest Income Recognized	39	155	279	57
Real estate loans | Construction
Financing Receivable, Impaired [Line Items]
Average recorded Investment			0	505
Interest Income Recognized			0	0
Commercial business loans
Financing Receivable, Impaired [Line Items]
Average recorded Investment	3,870	3,060	3,796	4,514
Interest Income Recognized	46	118	195	110
Consumer loans | Home equity loans and advances
Financing Receivable, Impaired [Line Items]
Average recorded Investment	3,618	3,361	3,903	3,446
Interest Income Recognized	$ 35	$ 173	$ 136	$ 157

Loans Receivable and Allowan_12

Loans Receivable and Allowance for Loan Losses - Credit Quality Indicators (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	$ 4,962,289	$ 4,446,015
Pass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	4,929,870	4,405,719
Special mention
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	9,074	8,460
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	23,345	31,836
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Real estate loans | One-to-four family
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	1,830,186	1,615,000
Real estate loans | One-to-four family | Pass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	1,826,066	1,605,413
Real estate loans | One-to-four family | Special mention
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Real estate loans | One-to-four family | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	4,120	9,587
Real estate loans | One-to-four family | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Real estate loans | Multifamily and commercial
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	2,142,154	1,870,475
Real estate loans | Multifamily and commercial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	2,128,680	1,851,037
Real estate loans | Multifamily and commercial | Special mention
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	4,782
Real estate loans | Multifamily and commercial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	13,474	14,656
Real estate loans | Multifamily and commercial | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Real estate loans | Construction
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	261,473	233,652
Real estate loans | Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	261,473	233,652
Real estate loans | Construction | Special mention
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Real estate loans | Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Real estate loans | Construction | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Commercial business loans
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	333,876	277,970
Commercial business loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	320,451	268,355
Commercial business loans | Special mention
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	9,074	3,678
Commercial business loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	4,351	5,937
Commercial business loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Consumer loans | Home equity loans and advances
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	393,492	447,920
Consumer loans | Home equity loans and advances | Pass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	392,092	446,264
Consumer loans | Home equity loans and advances | Special mention
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Consumer loans | Home equity loans and advances | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	1,400	1,656
Consumer loans | Home equity loans and advances | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Consumer loans | Other consumer loans
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	1,108	998
Consumer loans | Other consumer loans | Pass
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	1,108	998
Consumer loans | Other consumer loans | Special mention
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Consumer loans | Other consumer loans | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	0	0
Consumer loans | Other consumer loans | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total gross loans	$ 0	$ 0

Office Properties and Equipme_3

Office Properties and Equipment, net - Schedule of Office Properties and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Office property and equipment, gross	$ 106,528	$ 93,287
Less accumulated depreciation and amortization	54,478	50,667
Total office properties and equipment, net	52,050	42,620
Land
Property, Plant and Equipment [Line Items]
Office property and equipment, gross	7,829	7,829
Buildings
Property, Plant and Equipment [Line Items]
Office property and equipment, gross	24,018	24,018
Land and building improvements
Property, Plant and Equipment [Line Items]
Office property and equipment, gross	24,864	15,583
Leasehold improvements
Property, Plant and Equipment [Line Items]
Office property and equipment, gross	21,279	19,821
Furniture and equipment
Property, Plant and Equipment [Line Items]
Office property and equipment, gross	$ 28,538	$ 26,036

Office Properties and Equipme_4

Office Properties and Equipment, net - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 863
Depreciation and amortization of office properties and equipment	$ 863	$ 3,839		$ 3,364	$ 3,178
Land and building improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, additions		$ 8,900	$ 5,500

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Schedule of Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 5,716	$ 5,716
Mortgage servicing rights	369	281
Goodwill and intangible assets	$ 6,085	$ 5,997

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of mortgage servicing rights (MSRs)	$ 22,000	$ 73,000	$ 105,000	$ 105,000
Mortgage servicing rights impairment (recovery)		$ (161,000)	$ 0

Deposits - Schedule of Deposits

Deposits - Schedule of Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Balance
Non-interest-bearing demand	$ 723,794	$ 719,339
Interest-bearing demand	1,219,381	1,332,297
Money market accounts	259,694	262,396
Savings and club deposits	510,688	545,401
Certificates of deposit	1,700,316	1,403,882
Total deposits	$ 4,413,873	$ 4,263,315
Weighted Average Rate
Interest-bearing demand	0.95%	0.66%
Money market accounts	0.67%	0.29%
Savings and club deposits	0.16%	0.16%
Certificates of deposit	2.01%	1.43%
Total deposits	1.09%	0.72%

Deposits - Narrative (Details)

Deposits - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Banking and Thrift [Abstract]
Aggregate amount of certificates of deposit exceeding threshold amount	$ 885.3	$ 640.1

Deposits - Schedule of Deposit

Deposits - Schedule of Deposit Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Banking and Thrift [Abstract]
One year or less	$ 1,107,667	$ 669,610
After one year to two years	326,800	474,475
After two years to three years	230,468	169,069
After three years to four years	24,939	68,184
After four years	10,442	22,544
Total term certificate accounts	$ 1,700,316	$ 1,403,882

Deposits - Interest Expense on

Deposits - Interest Expense on Deposits (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Interest expense on deposits	$ 7,631	$ 39,523	$ 25,581	$ 24,062
Demand Deposits
Assets Sold under Agreements to Repurchase [Line Items]
Interest expense on deposits	2,509	12,933	8,556	7,735
Savings and Clubs
Assets Sold under Agreements to Repurchase [Line Items]
Interest expense on deposits	210	993	630	613
Certificates of Deposit
Assets Sold under Agreements to Repurchase [Line Items]
Interest expense on deposits	$ 4,912	$ 25,597	$ 16,395	$ 15,714

Borrowings - Schedule of borrow

Borrowings - Schedule of borrowed funds (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Borrowings	$ 1,189,180	$ 929,057
Weighted average interest rate	2.43%	2.25%
Lines of credit
Debt Instrument [Line Items]
Borrowings	$ 159,600	$ 46,000
Weighted average interest rate	2.60%	1.53%
Federal Home Loan Bank advances
Debt Instrument [Line Items]
Borrowings	$ 1,029,580	$ 822,400
Weighted average interest rate	2.40%	1.92%
Junior subordinated debt
Debt Instrument [Line Items]
Borrowings	$ 0	$ 50,657
Weighted average interest rate	0.00%	8.00%
Securities sold under agreements to repurchase
Debt Instrument [Line Items]
Borrowings	$ 0	$ 10,000
Weighted average interest rate	0.00%	3.23%

Borrowings - Schedule of contra

Borrowings - Schedule of contractual maturity of borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
One year or less	$ 761,900
After one year to two years	229,045
After two years to three years	155,010
After three years to four years	43,225
After four years	0
Total FHLB advances	$ 1,189,180	$ 929,057

Borrowings - Narrative (Details

Borrowings - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Debt Instrument [Line Items]
Borrowings	$ 929,057	$ 1,189,180	$ 929,057
Unused line of credit		225,000
Advances from federal home loan banks	1,600,000	1,700,000	1,600,000
Line of Credit
Debt Instrument [Line Items]
Borrowings	46,000	159,600	46,000
Interest expense, debt	70	2,200		$ 233		$ 42
Federal Home Loan Bank advances
Debt Instrument [Line Items]
Borrowings	822,400	1,029,580	822,400
Interest expense, debt	3,300	17,100		12,800		13,200
Junior subordinated debt
Debt Instrument [Line Items]
Borrowings	50,657	0	50,657
Interest expense, debt	1,000	3,500		$ 4,200		$ 4,200
Deferred issuance costs	890		890
Securities sold under agreements to repurchase
Debt Instrument [Line Items]
Borrowings	10,000	0	10,000
Interest expense, debt	203	3	1,600		$ 2,400
Pledged collateral	12,900	0	12,900
Interest rate products-designated | Federal Home Loan Bank advances
Debt Instrument [Line Items]
Notional amount of derivative	$ 20,000	$ 320,000	$ 20,000

Regulatory Capital (Details)

Regulatory Capital (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Parent Company
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer, ratio	2.50%		0.625%
Capital, amount	$ 1,094,062	$ 631,952
Capital to risk weighted assets, ratio	23.45%	15.01%
Capital required for capital adequacy, amount	$ 373,276	$ 336,730
Capital required for capital adequacy to risk weighted assets, ratio	8.00%	8.00%
Capital required for capital adequacy with capital buffer, amount	$ 460,763	$ 389,244
Capital required for capital adequacy with capital buffer to risk weighted assets, ratio	9.88%	9.25%
Tier one risk based capital, amount	$ 1,035,477	$ 579,080
Tier one risk based capital to risk weighted assets, ratio	22.19%	13.76%
Tier one risk based capital required for capital adequacy, amount	$ 279,957	$ 252,547
Tier one risk based capital required for capital adequacy to risk weighted assets, ratio	6.00%	6.00%
Tier one risk based capital required for capital adequacy with capital buffer, amount	$ 367,444	$ 305,161
Tier one risk based capital required for capital adequacy with capital buffer to risk weighted assets, ratio	7.88%	7.25%
Common equity tier one capital, amount	$ 1,035,477	$ 528,080
Common equity tier one capital ratio	22.19%	12.55%
Common equity tier one capital required for capital adequacy, amount	$ 209,968	$ 189,410
Common equity tier one capital required for capital adequacy to risk weighted assets, ratio	4.50%	4.50%
Common equity tier one risk based capital required for capital adequacy with capital buffer, amount	$ 297,455	$ 242,025
Common equity tier one risk based capital requirement for capital adequacy with capital buffer to risk weighted assets, ratio	6.38%	5.75%
Tier one leverage capital, amount	$ 1,035,477	$ 579,080
Tier one leverage capital to average assets, ratio	15.75%	10.54%
Tier one leverage capital required for capital adequacy, amount	$ 263,037	$ 219,833
Tier one leverage capital required for capital adequacy to average assets, ratio	4.00%	4.00%
Tier one leverage capital required for capital adequacy with capital buffer to average assets, amount	$ 263,037	$ 219,833
Tier one leverage capital requirement for capital adequacy with capital buffer to average assets, ratio	4.00%	4.00%
Subsidiaries
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital, amount	$ 886,728	$ 625,336
Capital to risk weighted assets, ratio	19.04%	14.90%
Capital required for capital adequacy, amount	$ 372,550	$ 335,736
Capital required for capital adequacy to risk weighted assets, ratio	8.00%	8.00%
Capital required for capital adequacy with capital buffer, amount	$ 459,866	$ 388,196
Capital required for capital adequacy with capital buffer to risk weighted assets, ratio	9.88%	9.25%
Capital required to be well capitalized, amount	$ 465,687	$ 419,671
Capital required to be well capitalized to risk weighted assets, ratio	10.00%	10.00%
Tier one risk based capital, amount	$ 828,257	$ 572,617
Tier one risk based capital to risk weighted assets, ratio	17.79%	13.64%
Tier one risk based capital required for capital adequacy, amount	$ 279,412	$ 251,802
Tier one risk based capital required for capital adequacy to risk weighted assets, ratio	6.00%	6.00%
Tier one risk based capital required for capital adequacy with capital buffer, amount	$ 366,729	$ 304,262
Tier one risk based capital required for capital adequacy with capital buffer to risk weighted assets, ratio	7.88%	7.25%
Tier one risk based capital required to be well capitalized, amount	$ 372,550	$ 335,736
Tier one risk based capital required to be well capitalized to risk weighted assets, ratio	8.00%	8.00%
Common equity tier one capital, amount	$ 828,257	$ 572,617
Common equity tier one capital ratio	17.79%	13.64%
Common equity tier one capital required for capital adequacy, amount	$ 209,559	$ 188,852
Common equity tier one capital required for capital adequacy to risk weighted assets, ratio	4.50%	4.50%
Common equity tier one risk based capital required for capital adequacy with capital buffer, amount	$ 296,875	$ 241,311
Common equity tier one risk based capital requirement for capital adequacy with capital buffer to risk weighted assets, ratio	6.38%	5.75%
Common equity tier one capital required to be well-capitalized, amount	$ 302,697	$ 272,786
Common equity tier one capital required to be well-capitalized to risk weighted assets, ratio	6.50%	6.50%
Tier one leverage capital, amount	$ 828,257	$ 572,617
Tier one leverage capital to average assets, ratio	12.60%	10.44%
Tier one leverage capital required for capital adequacy, amount	$ 263,025	$ 221,257
Tier one leverage capital required for capital adequacy to average assets, ratio	4.00%	4.00%
Tier one leverage capital required for capital adequacy with capital buffer to average assets, amount	$ 263,025	$ 221,257
Tier one leverage capital requirement for capital adequacy with capital buffer to average assets, ratio	4.00%	4.00%
Tier one leverage capital required to be well capitalized, amount	$ 328,781	$ 276,571
Tier one leverage capital required to be well capitalized to average assets, ratio	5.00%	5.00%

Employee Benefit Plans - Schedu

Employee Benefit Plans - Schedule of Change in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Pension
Change in benefit obligation:
Benefit obligation, beginning balance		$ 229,156	$ 216,992
Service cost	$ 1,780	7,805	7,496	$ 7,621	$ 6,188
Interest cost	2,128	8,489	8,461	8,444	8,096
Actuarial (gain) loss		(30,703)	4,543
Benefits paid		(5,542)	(8,336)
Benefit obligation, ending balance	229,156	209,205	229,156
Change in plan assets:
Fair value of plan assets, beginning balance		289,390	257,513
Actuarial return on plan assets		(10,874)	27,213
Employer contributions		0	13,000
Benefits paid		(5,542)	(8,336)
Fair value of plan assets, ending balance	289,390	272,974	289,390
Funded status at end of year	60,234	63,769	60,234
RIM
Change in benefit obligation:
Benefit obligation, beginning balance		12,243	11,032
Service cost	60	282	238	237	140
Interest cost	111	443	433	429	385
Actuarial (gain) loss		(1,355)	874
Benefits paid		(328)	(334)
Benefit obligation, ending balance	12,243	11,285	12,243
Change in plan assets:
Fair value of plan assets, beginning balance		0	0
Actuarial return on plan assets		0	0
Employer contributions		328	334
Benefits paid		(328)	(334)
Fair value of plan assets, ending balance	0	0	0
Funded status at end of year	(12,243)	(11,285)	(12,243)
Post-retirement
Change in benefit obligation:
Benefit obligation, beginning balance		22,078	22,133
Service cost	92	417	445	471	447
Interest cost	205	796	762	$ 742	$ 854
Actuarial (gain) loss		(1,845)	(726)
Benefits paid		(482)	(536)
Benefit obligation, ending balance	22,078	20,964	22,078
Change in plan assets:
Fair value of plan assets, beginning balance		0	0
Actuarial return on plan assets		0	0
Employer contributions		482	536
Benefits paid		(482)	(536)
Fair value of plan assets, ending balance	0	0	0
Funded status at end of year	$ (22,078)	$ (20,964)	$ (22,078)

Employee Benefit Plans - Sche_2

Employee Benefit Plans - Schedule of Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Pension
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs	$ 0	$ 0	$ 0	$ 0
Unrecognized net actuarial income	59,579	61,731	55,438	74,768
Total accumulated other comprehensive income	59,579	61,731	55,438	74,768
RIM
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs	0	0	0	0
Unrecognized net actuarial income	3,748	5,515	4,725	5,154
Total accumulated other comprehensive income	3,748	5,515	4,725	5,154
Post-retirement
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service costs	0	(106)	(140)	(276)
Unrecognized net actuarial income	4,226	6,395	4,611	8,374
Total accumulated other comprehensive income	$ 4,226	$ 6,289	$ 4,471	$ 8,098

Employee Benefit Plans - Sche_3

Employee Benefit Plans - Schedule of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1,780	$ 7,805	$ 7,496	$ 7,621	$ 6,188
Interest cost	2,128	8,489	8,461	8,444	8,096
Expected return on plan assets	(4,814)	(20,794)		(24,809)	(22,706)
Amortization of Prior service cost	0	0		0	0
Amortization of Net loss	707	3,117		10,998	8,490
Net periodic (income) cost	(199)	(1,383)		2,254	68
RIM
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	60	282	238	237	140
Interest cost	111	443	433	429	385
Expected return on plan assets	0	0		0	0
Amortization of Prior service cost	0	0		0	0
Amortization of Net loss	103	413		453	283
Net periodic (income) cost	274	1,138		1,119	808
Post-retirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	92	417	445	471	447
Interest cost	205	796	$ 762	742	854
Expected return on plan assets	0	0		0	0
Amortization of Prior service cost	(34)	(106)		(136)	(136)
Amortization of Net loss	70	323		325	339
Net periodic (income) cost	$ 333	$ 1,430		$ 1,402	$ 1,504

Employee Benefit Plans - Sche_4

Employee Benefit Plans - Schedule of Weighted Average Actuarial Assumptions (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Pension
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.75%	4.57%	4.00%	3.88%
Rate of compensation increase	3.50%	3.50%	3.50%	3.50%
Discount rate	4.00%	3.75%	3.88%	4.50%
Expected rate of return on plan assets	7.25%	7.25%	7.50%	7.50%
Rate of compensation increase	3.50%	3.50%	3.50%	3.50%
RIM
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.63%	4.47%	3.88%	3.63%
Rate of compensation increase	3.50%	3.50%	3.50%	3.50%
Discount rate	3.88%	4.47%	3.63%	4.38%
Rate of compensation increase	3.50%	3.50%	3.50%	3.50%
Post-retirement
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.63%	4.41%	3.88%	3.63%
Discount rate	3.88%	3.63%	3.63%	4.38%

Employee Benefit Plans - Sche_5

Employee Benefit Plans - Schedule of Assumed Health Care Cost Trend Rates (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Retirement Benefits [Abstract]
Effect on total service cost and interest cost, increase	$ 14
Effect on post-retirement benefit obligations, increase	130
Effect on total service cost and interest cost, decrease	(12)
Effect on post-retirement benefit obligations, decrease	$ (120)

Employee Benefit Plans - Sche_6

Employee Benefit Plans - Schedule of Estimated Future Benefit Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Pension
Defined Benefit Plan Disclosure [Line Items]
2019	$ 5,791
2020	6,301
2021	6,892
2022	7,471
2023	8,167
Years 2024-2028	52,675
RIM
Defined Benefit Plan Disclosure [Line Items]
2019	329
2020	341
2021	377
2022	416
2023	458
Years 2024-2028	3,318
Post-retirement
Defined Benefit Plan Disclosure [Line Items]
2019	1,079
2020	1,114
2021	1,171
2022	1,212
2023	1,249
Years 2024-2028	$ 6,840

Employee Benefit Plans - Sche_7

Employee Benefit Plans - Schedule of Weighted Average and Target Allocations of Pension Assets (Details) - Pension	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Weighted average assets allocations, percentage	100.00%	100.00%
Domestic equities
Defined Benefit Plan Disclosure [Line Items]
Weighted average assets allocations, percentage	35.20%	38.10%
Foreign equities
Defined Benefit Plan Disclosure [Line Items]
Weighted average assets allocations, percentage	10.80%	13.90%
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Weighted average assets allocations, percentage	42.30%	36.90%
Commingled real estate funds
Defined Benefit Plan Disclosure [Line Items]
Weighted average assets allocations, percentage	10.50%	9.30%
Money market mutual funds
Defined Benefit Plan Disclosure [Line Items]
Weighted average assets allocations, percentage	1.20%	1.80%
Minimum | Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percent	40.00%
Minimum | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percent	40.00%
Minimum | Commingled real estate funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percent	0.00%
Minimum | Money market mutual funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percent	0.00%
Maximum | Equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percent	60.00%
Maximum | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percent	60.00%
Maximum | Commingled real estate funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percent	10.00%
Maximum | Money market mutual funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percent	15.00%

Employee Benefit Plans - Sche_8

Employee Benefit Plans - Schedule of Fair Value of Plan Assets (Details) - Pension - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 272,974	$ 289,390	$ 257,513
Quoted prices in active markets for identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	244,383	262,545
Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28,591	26,845
Significant unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Money market mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,459	5,236
Money market mutual funds | Quoted prices in active markets for identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,459	5,236
Money market mutual funds | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Money market mutual funds | Significant unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual funds - value stock fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22,533	27,364
Mutual funds - value stock fund | Quoted prices in active markets for identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22,533	27,364
Mutual funds - value stock fund | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual funds - value stock fund | Significant unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual funds - fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	115,500	106,726
Mutual funds - fixed income | Quoted prices in active markets for identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	115,500	106,726
Mutual funds - fixed income | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual funds - fixed income | Significant unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual funds - international stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29,441	40,388
Mutual funds - international stock | Quoted prices in active markets for identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29,441	40,388
Mutual funds - international stock | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual funds - international stock | Significant unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual funds - institutional stock index
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	73,450	82,831
Mutual funds - institutional stock index | Quoted prices in active markets for identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	73,450	82,831
Mutual funds - institutional stock index | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual funds - institutional stock index | Significant unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Commingled real estate funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28,591	26,845
Commingled real estate funds | Quoted prices in active markets for identical assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Commingled real estate funds | Significant other observable inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28,591	26,845
Commingled real estate funds | Significant unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0

Employee Benefit Plans - Narrat

Employee Benefit Plans - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, years of employment				5 years
Bank-owned life insurance		$ 184,488,000	$ 150,521,000	$ 184,488,000
Bank-owned life insurance income			1,089,000	5,208,000	$ 4,936,000	$ 4,370,000
Defined benefit plan, accumulated benefit obligation		10,500,000	5,900,000	10,500,000
Defined contribution plan, cost			159,000	1,342,000	395,000	356,000
Proceeds from repayments of loans by employee stock ownership plans			0	45,428,000	0	0
Employee stock ownership plan, compensation expense			0	2,594,000	0	0
RIM
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan		(11,285,000)	(12,243,000)	(11,285,000)
Defined contribution plan, cost			1,000	86,000	14,000	47,000
Employee stock ownership plan, compensation expense				165,000
Deferred Compensation Arrangement with Individual, Compensation Expense		0			0	0
Pension
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan		$ 63,769,000	60,234,000	63,769,000
Defined contribution plan, cost			289,000	$ 1,342,000	1,245,000	1,142,000
Maximum | Pension
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match				4.50%
Minimum | Pension
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match				3.00%
Columbia Bank Employee Stock Ownership Plan
Defined Benefit Plan Disclosure [Line Items]
Proceeds from repayments of loans by employee stock ownership plans	$ 45,400,000
Loan term	20 years
Shares contributed to ESOP	4,542,855
Fixed interest rate	4.75%
Employee stock ownership plan, compensation expense			$ 0		$ 0	$ 0

Employee Benefit Plans - Sche_9

Employee Benefit Plans - Schedule of Employee Stock Ownership Plan (Details) shares in Thousands, $ in Thousands	Dec. 31, 2018USD ($)shares
Retirement Benefits [Abstract]
Allocated shares	159
Unearned shares	4,384
Total ESOP shares	4,543
Fair value of unearned shares | $	$ 67,025

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended													12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Current:
Federal					$ 630									$ 11,284	$ 16,198	$ 13,209
State					862									5,129	1,236	664
Current income tax provision					1,492									16,413	17,434	13,873
Deferred:
Federal					7,530									(4,901)	(1,454)	2,743
State					(39)									(589)	28	187
Deferred income tax provision (benefit)					7,491									(5,490)	(1,426)	2,930
Total continuing operations	$ 3,123	$ 6,956	$ (2,961)	$ 3,805	$ 8,983	$ 194	$ 5,934	$ 5,012	$ 4,868	$ 4,611	$ 4,052	$ 4,281	$ 3,859	$ 10,923	$ 16,008	$ 16,803

- Income Taxes - Narrative (Det

- Income Taxes - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income tax expense, Tax Cuts And Jobs Act Of 2017, deferred tax assets and liabilities	$ 11,700
Deferred income tax expense (benefit), unrealized gains (losses)		$ (119)	$ 1,400	$ 6,400	$ (2,600)
Other comprehensive income (loss), defined benefit plan, gain (loss), reclassification adjustment from AOCI, tax		(94)	(530)	$ (4,213)	$ (3,259)
Included in retained earnings, no provision for income tax	21,500	21,500	21,500
Valuation allowance	2,786	2,786	2,388
State NOL	$ 2,476	$ 2,476	$ 2,063

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended													12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Tax expense at applicable statutory rate					$ 4,431									$ 7,067	$ 16,478	$ 17,415
Increase (decrease) in taxes resulting from:
State tax, net of federal income tax benefit					535									3,587	822	553
ESOP fair market value adjustment					0									202	0	0
Tax exempt interest income					(2)									(4)	(50)	(28)
Income from Bank-owned life insurance					(381)									(812)	(1,589)	(1,405)
Dividend received deduction					(10)									(16)	(40)	(39)
Impact of tax reform					4,700									0	0	0
Other, net					(290)									899	387	307
Total continuing operations	$ 3,123	$ 6,956	$ (2,961)	$ 3,805	$ 8,983	$ 194	$ 5,934	$ 5,012	$ 4,868	$ 4,611	$ 4,052	$ 4,281	$ 3,859	$ 10,923	$ 16,008	$ 16,803

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Allowance for loan losses	$ 13,251	$ 12,584
Post retirement benefit	3,720	3,414
Deferred compensation	2,228	1,939
Depreciation	1,042	949
Retirement income maintenance plan	1,602	1,455
ESOP	128	0
Stock-based compensation	35	0
Reserve for uncollected interest	24	62
Net unrealized losses on securities and defined benefit plans	19,060	18,221
State NOL	2,063	2,476
Alternative minimum assessment carryforwards	2,156	2,156
Charitable contribution carryforward	6,085	0
Other items	670	1,595
Gross deferred tax assets	52,064	44,851
Valuation allowance	(2,388)	(2,786)
Total deferred tax assets, net	49,676	42,065
Deferred tax liabilities:
Pension expense	26,071	26,234
Deferred loan costs	5,736	4,257
Intangible assets	1,621	1,642
Other items	34	48
Total gross deferred tax liabilities	33,462	32,181
Net deferred tax asset	$ 16,214	$ 9,884

Financial Transactions with O_3

Financial Transactions with Off-Balance-Sheet Risk and Concentrations of Credit Risk - Schedule of Loan Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Concentration Risk [Line Items]
Loan commitments	$ 195,229	$ 118,223
Residential real estate
Concentration Risk [Line Items]
Loan commitments	29,622	58,860
Commercial real estate
Concentration Risk [Line Items]
Loan commitments	73,201	17,994
Commercial business loans
Concentration Risk [Line Items]
Loan commitments	13,000	14,796
Construction
Concentration Risk [Line Items]
Loan commitments	71,062	20,715
Home equity loans and advances
Concentration Risk [Line Items]
Loan commitments	$ 8,344	$ 5,858

Financial Transactions with O_4

Financial Transactions with Off-Balance-Sheet Risk and Concentrations of Credit Risk - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019	$ 3,596
2020	3,511
2021	3,288
2022	2,921
2023	2,590
Thereafter	5,209
Total lease commitments	$ 21,115

Financial Transactions with O_5

Financial Transactions with Off-Balance-Sheet Risk and Concentrations of Credit Risk - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Loss Contingencies [Line Items]
Derivative (liabilities), at fair value, net		$ (2,600)
Occupancy expense, net	$ 3,382	14,547	$ 13,315	$ 12,798
Unused lines of Credit
Loss Contingencies [Line Items]
Fair value disclosure, off-balance sheet risk, amount, liability	679,400	714,600
Mortgages
Loss Contingencies [Line Items]
Fair value disclosure, off-balance sheet risk, amount, liability		8,100
Letter of Credit
Loss Contingencies [Line Items]
Fair value disclosure, off-balance sheet risk, amount, liability	11,600	7,000
Bank Facilities
Loss Contingencies [Line Items]
Occupancy expense, net	$ 1,100	$ 4,600	$ 4,300	$ 4,000

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	$ 1,034,758	$ 710,570
U.S. government and agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	54,157	39,644
Mortgage-backed securities and collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	920,007	606,612
Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	987	1,957
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	53,467	54,514
Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	4,250	4,656
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,890	3,187
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale		42,831
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale		667,739
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,034,758	710,570
Derivative assets	865	490
Assets	1,035,623	711,060
Derivative liabilities	3,467	203
Measured on recurring basis | U.S. government and agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	54,157	39,644
Measured on recurring basis | Mortgage-backed securities and collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	920,007	606,612
Measured on recurring basis | Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	987	1,957
Measured on recurring basis | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	53,467	54,514
Measured on recurring basis | Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	4,250	4,656
Measured on recurring basis | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,890	3,187
Measured on recurring basis | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	56,047	42,831
Derivative assets	0	0
Assets	56,047	42,831
Derivative liabilities	0	0
Measured on recurring basis | Quoted prices in active markets for identical assets (Level 1) | U.S. government and agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	54,157	39,644
Measured on recurring basis | Quoted prices in active markets for identical assets (Level 1) | Mortgage-backed securities and collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Quoted prices in active markets for identical assets (Level 1) | Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Quoted prices in active markets for identical assets (Level 1) | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Quoted prices in active markets for identical assets (Level 1) | Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Quoted prices in active markets for identical assets (Level 1) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	1,890	3,187
Measured on recurring basis | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	978,711	667,739
Derivative assets	865	490
Assets	979,576	668,229
Derivative liabilities	3,467	203
Measured on recurring basis | Significant other observable inputs (Level 2) | U.S. government and agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Significant other observable inputs (Level 2) | Mortgage-backed securities and collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	920,007	606,612
Measured on recurring basis | Significant other observable inputs (Level 2) | Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	987	1,957
Measured on recurring basis | Significant other observable inputs (Level 2) | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	53,467	54,514
Measured on recurring basis | Significant other observable inputs (Level 2) | Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	4,250	4,656
Measured on recurring basis | Significant other observable inputs (Level 2) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Derivative assets	0	0
Assets	0	0
Derivative liabilities	0	0
Measured on recurring basis | Significant unobservable inputs (Level 3) | U.S. government and agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Significant unobservable inputs (Level 3) | Mortgage-backed securities and collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Significant unobservable inputs (Level 3) | Municipal obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Significant unobservable inputs (Level 3) | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Significant unobservable inputs (Level 3) | Trust preferred securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	0	0
Measured on recurring basis | Significant unobservable inputs (Level 3) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	$ 0	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2017
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustments for estimated costs to sell collateral dependent impaired loans	6.00%
Estimated costs to sell foreclosed assets	6.00%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustments for estimated costs to sell collateral dependent impaired loans	8.00%
Estimated costs to sell foreclosed assets	8.00%
U.S. government and agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 2 to Level 1, amount		$ 20.4

Fair Value Measurements - Ass_2

Fair Value Measurements - Assets and Liabilities Measured on Non-Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	$ 8,081	$ 0
Real estate owned	92	959
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	0	0
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	0	0
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	4,841,830	4,367,945
Measured on non-recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	1,525	10,251
Real estate owned	92	959
Mortgage servicing rights	442	316
Assets	2,059	11,526
Measured on non-recurring basis | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	0	0
Real estate owned	0	0
Mortgage servicing rights	0	0
Assets	0	0
Measured on non-recurring basis | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	0	0
Real estate owned	0	0
Mortgage servicing rights	0	0
Assets	0	0
Measured on non-recurring basis | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, at fair value	1,525	10,251
Real estate owned	92	959
Mortgage servicing rights	442	316
Assets	$ 2,059	$ 11,526

Fair Value Measurements - Quali

Fair Value Measurements - Qualitative Valuation (Details) $ in Thousands	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Loans held-for-sale, at fair value	$ 8,081	$ 0
Real estate owned	92	959
Measured on non-recurring basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Loans held-for-sale, at fair value	1,525	10,251
Mortgage servicing rights	442	316
Real estate owned	92	959
Significant unobservable inputs (Level 3)
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Loans held-for-sale, at fair value	4,841,830	4,367,945
Significant unobservable inputs (Level 3) | Measured on non-recurring basis
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Loans held-for-sale, at fair value	1,525	10,251
Mortgage servicing rights	442	316
Real estate owned	$ 92	$ 959
Significant unobservable inputs (Level 3) | Measurement Input, Discount Rate | Measured on non-recurring basis | Impaired loans | Weighted Average | Appraisal
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.075	0.072
Significant unobservable inputs (Level 3) | Measurement Input, Discount Rate | Measured on non-recurring basis | Impaired loans | Minimum | Appraisal
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.060	0.060
Significant unobservable inputs (Level 3) | Measurement Input, Discount Rate | Measured on non-recurring basis | Impaired loans | Maximum | Appraisal
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.080	0.080
Significant unobservable inputs (Level 3) | Measurement Input, Discount Rate | Measured on non-recurring basis | Real estate owned | Appraisal
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate		0.060
Significant unobservable inputs (Level 3) | Measurement Input, Discount Rate | Measured on non-recurring basis | Real estate owned | Contract Sales Price
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.060
Significant unobservable inputs (Level 3) | Measurement Input, Discount Rate | Measured on non-recurring basis | Real estate owned | Weighted Average | Appraisal
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate		0.060
Significant unobservable inputs (Level 3) | Measurement Input, Discount Rate | Measured on non-recurring basis | Real estate owned | Weighted Average | Contract Sales Price
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.060
Significant unobservable inputs (Level 3) | Measurement Input, Prepayment Rate | Measured on non-recurring basis | Mortgage servicing rights | Weighted Average | Estimated Cash Flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.120	0.039
Significant unobservable inputs (Level 3) | Measurement Input, Prepayment Rate | Measured on non-recurring basis | Mortgage servicing rights | Minimum | Estimated Cash Flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.033	0.036
Significant unobservable inputs (Level 3) | Measurement Input, Prepayment Rate | Measured on non-recurring basis | Mortgage servicing rights | Maximum | Estimated Cash Flow
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Discount rate	0.268	0.110

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value on Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial assets:
Securities available for sale, at fair value	$ 1,034,758	$ 710,570
Securities held to maturity	254,841	236,125
Loans held-for-sale amount	8,081
Loans receivable, net	8,081	0
Derivative asset, gross	865	490
Financial liabilities:
Derivative liability, gross	3,467	203
Quoted prices in active markets for identical assets (Level 1)
Financial assets:
Cash and cash equivalents	42,201	65,498
Securities available for sale, at fair value		42,831
Securities held to maturity	23,241	8,344
Federal Home Loan Bank stock	0	0
Loans held-for-sale amount
Loans receivable, net	0	0
Derivative asset, gross	0	0
Financial liabilities:
Deposits	0	0
Borrowings	0	0
Derivative liability, gross	0	0
Significant other observable inputs (Level 2)
Financial assets:
Cash and cash equivalents	0	0
Securities available for sale, at fair value		667,739
Securities held to maturity	254,841	227,781
Federal Home Loan Bank stock	58,938	44,664
Loans held-for-sale amount	8,081
Loans receivable, net	0	0
Derivative asset, gross	865	490
Financial liabilities:
Deposits	4,402,336	3,959,460
Borrowings	1,185,007	925,032
Derivative liability, gross	3,467	203
Significant unobservable inputs (Level 3)
Financial assets:
Cash and cash equivalents	0	0
Securities available for sale, at fair value	0	0
Securities held to maturity	0	0
Federal Home Loan Bank stock	0	0
Loans held-for-sale amount	0
Loans receivable, net	4,841,830	4,367,945
Derivative asset, gross	0	0
Financial liabilities:
Deposits	0	0
Borrowings	0	0
Derivative liability, gross	0	0
Carrying value
Financial assets:
Cash and cash equivalents	42,201	65,498
Securities available for sale, at fair value	1,034,758	710,570
Securities held to maturity	262,143	239,618
Federal Home Loan Bank stock	58,938	44,664
Loans held-for-sale amount	8,081
Loans receivable, net	4,979,182	4,400,470
Derivative asset, gross		490
Financial liabilities:
Deposits	4,413,873	4,263,315
Borrowings	1,189,180	929,057
Derivative liability, gross		203
Total fair value
Financial assets:
Cash and cash equivalents	42,201	65,498
Securities available for sale, at fair value	1,034,758	710,570
Securities held to maturity	254,841	236,125
Federal Home Loan Bank stock	58,938	44,664
Loans held-for-sale amount	8,081
Loans receivable, net	4,841,830	4,367,945
Derivative asset, gross	865	490
Financial liabilities:
Deposits	4,402,336	3,959,460
Borrowings	1,185,007	925,032
Derivative liability, gross	$ 3,467	$ 203

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended													12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Quarterly Financial Information Disclosure [Abstract]
Total interest income	$ 61,785	$ 57,695	$ 55,019	$ 51,791	$ 49,169	$ 47,820	$ 46,850	$ 45,428	$ 44,129	$ 43,011	$ 42,421	$ 41,929	$ 41,616	$ 226,290	$ 184,226	$ 168,977
Total interest expense	18,410	17,112	14,004	12,730	12,240	11,860	11,211	10,651	10,724	11,123	11,003	10,840	10,996	62,256	44,446	43,962
Net interest income	43,375	40,583	41,015	39,061	36,929	35,960	35,639	34,777	33,405	31,888	31,418	31,089	30,620	164,034	139,780	125,015
Provision for loan losses	777	1,500	2,400	2,000	3,400	5,676	375	375	0	0	0	417	0
Net interest income after provision for loan losses	42,598	39,083	38,615	37,061	33,529	30,284	35,264	34,402	33,405	31,888	31,418	30,672	30,620	157,357	133,354	124,598
Total non-interest income	6,405	5,290	5,450	4,543	4,733	1,630	4,645	5,806	5,534	4,702	4,525	4,738	4,537	21,688	17,172	18,927
Total non-interest expense	31,013	26,590	61,768	26,015	25,601	30,206	24,703	24,903	24,078	23,482	23,658	22,816	23,388	145,386	103,446	93,769
Income (loss) before income tax expense	17,990	17,783	(17,703)	15,589	12,661	1,708	15,206	15,305	14,861	13,108	12,285	12,594	11,769
Income tax expense	3,123	6,956	(2,961)	3,805	8,983	194	5,934	5,012	4,868	4,611	4,052	4,281	3,859	10,923	16,008	16,803
Net income	$ 14,867	$ 10,827	$ (14,742)	$ 11,784	$ 3,678	$ 1,514	$ 9,272	$ 10,293	$ 9,993	$ 8,497	$ 8,233	$ 8,313	$ 7,910	$ 22,736	$ 31,072	$ 32,953
Basic and diluted earnings per share (in dollars per share)	$ 0.13	$ 0.10	$ (0.13)											$ 0.20

Earnings per Share (Details)

Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended													12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 14,867	$ 10,827	$ (14,742)	$ 11,784	$ 3,678	$ 1,514	$ 9,272	$ 10,293	$ 9,993	$ 8,497	$ 8,233	$ 8,313	$ 7,910	$ 22,736	$ 31,072	$ 32,953
Basic earnings per share:
Weighted average shares outstanding - basic (in shares)														111,395,723
Basic earning per share (in usd per share)														$ 0.20
Diluted earnings per share:
Weighted average shares outstanding - diluted (in shares)														111,395,723
Diluted earnings per share (in usd per share)														$ 0.20

Parent-only Financial Informa_3

Parent-only Financial Information - Statement of Financial Condition (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Oct. 01, 2015	Sep. 30, 2015
Assets
Cash and due from banks	$ 42,065	$ 65,334
Short-term investments	136	164
Total cash and cash equivalents	42,201	65,498	$ 100,975	$ 45,694		$ 43,178
Securities available for sale, at fair value	1,032,868
Loans receivable, net	8,081	0
Other assets	107,048	89,668
Total assets	6,691,618	5,766,500
Liabilities:
Accrued expenses and other liabilities	84,475	76,495
Total liabilities	5,719,558	5,294,430
Total stockholders' equity	972,060	472,070	475,914	439,664		$ 417,998
Total liabilities and stockholders' equity	6,691,618	5,766,500
Parent Company
Assets
Cash and due from banks	153,697	1,537
Short-term investments	136	164
Total cash and cash equivalents	153,833	1,701	$ 1,598	$ 1,301	$ 2,631
Securities available for sale, at fair value	1,420	2,783
Investment in subsidiaries	764,663	516,607
Loans receivable, net	44,439	0
Other assets	7,852	3,281
Total assets	972,207	524,372
Liabilities:
Borrowings	0	50,657
Accrued expenses and other liabilities	147	1,645
Total liabilities	147	52,302
Total stockholders' equity	972,060	472,070
Total liabilities and stockholders' equity	$ 972,207	$ 524,372

Parent-only Financial Informa_4

Parent-only Financial Information - Statement of Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended													12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Income:
Unrealized (losses) gains on securities available for sale					$ (3,131)									$ (5,778)	$ (11,498)	$ 4,674
Borrowings					4,609									22,733	18,865	19,900
Net interest income	$ 43,375	$ 40,583	$ 41,015	$ 39,061	36,929	$ 35,960	$ 35,639	$ 34,777	$ 33,405	$ 31,888	$ 31,418	$ 31,089	$ 30,620	164,034	139,780	125,015
Expense:
Charitable contribution to foundation					0									34,767	3,603	347
Other non-interest expense					3,780									16,103	14,207	13,986
Income before income tax expense					12,661									33,659	47,080	49,756
Income tax expense	(3,123)	(6,956)	2,961	(3,805)	(8,983)	(194)	(5,934)	(5,012)	(4,868)	(4,611)	(4,052)	(4,281)	(3,859)	(10,923)	(16,008)	(16,803)
Net income	$ 14,867	$ 10,827	$ (14,742)	$ 11,784	3,678	$ 1,514	$ 9,272	$ 10,293	$ 9,993	$ 8,497	$ 8,233	$ 8,313	$ 7,910	22,736	31,072	32,953
Other comprehensive (loss) income					(19,230)									(6,487)	5,178	(11,287)
Total comprehensive income (loss), net of tax					(15,552)									16,249	36,250	21,666
Parent Company
Income:
Dividend from subsidiary					0									0	2,000	3,000
Unrealized (losses) gains on securities available for sale					41									123	162	157
Interest earnings					0									2,384	1	0
Total income					41									2,507	2,163	3,157
Borrowings					1,044									3,468	4,177	4,177
Net interest income					(1,003)									(961)	(2,014)	(1,020)
Equity earnings in subsidiary					4,288									51,401	32,230	32,743
Expense:
Loss on securities available for sale					60									0	0	0
Charitable contribution to foundation					0									34,767	0	0
Other non-interest expense					2									425	460	355
Total expense					62									35,192	460	355
Income before income tax expense					3,223									15,248	29,756	31,368
Income tax expense					455									7,488	1,316	1,585
Net income					3,678									22,736	31,072	32,953
Other comprehensive (loss) income					(19,230)									(6,487)	5,178	(11,287)
Total comprehensive income (loss), net of tax					$ (15,552)									$ 16,249	$ 36,250	$ 21,666

Parent-only Financial Informa_5

Parent-only Financial Information - Statement of Cash Flows (Details) - USD ($)	3 Months Ended													12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 14,867,000	$ 10,827,000	$ (14,742,000)	$ 11,784,000	$ 3,678,000	$ 1,514,000	$ 9,272,000	$ 10,293,000	$ 9,993,000	$ 8,497,000	$ 8,233,000	$ 8,313,000	$ 7,910,000	$ 22,736,000	$ 31,072,000	$ 32,953,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of debt issuance costs					14,000									890,000	53,000	53,000
Loss on securities available for sale					60,000									(116,000)	1,689,000	(355,000)
Deferred tax (benefit) expense					7,491,000									(5,490,000)	(1,426,000)	2,930,000
Increase in other assets					(15,557,000)									(11,053,000)	(11,681,000)	(269,000)
Increase in accrued expenses and other liabilities					3,905,000									7,980,000	9,840,000	5,033,000
Contribution of common stock to Columbia Bank Foundation					0									34,767,000	0	0
Net cash provided by operating activities					2,326,000									56,594,000	36,041,000	58,992,000
Cash flows from investing activities:
Proceeds from sales of securities available for sale					92,000									11,513,000	187,376,000	164,203,000
Proceeds from calls and maturities					7,009,000									69,977,000	68,409,000	96,956,000
Loan to ESOP					0									(45,428,000)	0	0
Repayment of loans receivable from Bank					0									32,039,000	62,407,000	28,624,000
Net cash used in investing activities					(372,135,000)									(943,000)	(330,317,000)	(290,572,000)
Cash flows from financing activities:
Payment for trust preferred securities					0									(51,547,000)	0	0
Issuance of common stock					0									492,428,000	0	0
Net cash provided by financing activities					334,332,000									863,258,000	349,557,000	234,096,000
Net increase (decrease) in cash and cash equivalents					(35,477,000)									(23,297,000)	55,281,000	2,516,000
Cash and cash equivalents at beginning of period				65,498,000	100,975,000				45,694,000				$ 43,178,000	65,498,000	45,694,000	43,178,000
Cash and cash equivalents at end of period	42,201,000				65,498,000	100,975,000				45,694,000				42,201,000	100,975,000	45,694,000
Parent Company
Cash flows from operating activities:
Net income					3,678,000									22,736,000	31,072,000	32,953,000
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of debt issuance costs					14,000									890,000	53,000	53,000
Loss on securities available for sale					60,000									0	0	0
Deferred tax (benefit) expense					42,000									(6,086,000)	1,000	(2,000)
Increase in other assets					(494,000)									1,515,000	1,404,000	(1,600,000)
Increase in accrued expenses and other liabilities					989,000									(1,498,000)	62,000	10,000
Contribution of common stock to Columbia Bank Foundation					0									34,767,000	0	0
Equity in undistributed earnings of subsidiary					(4,288,000)									(51,401,000)	(32,295,000)	(32,744,000)
Net cash provided by operating activities					1,000									923,000	297,000	(1,330,000)
Cash flows from investing activities:
Capital contribution to subsidiary					0									(246,420,000)	0	0
Proceeds from sales of securities available for sale					92,000									0	0	0
Proceeds from calls and maturities					10,000									1,601,000	0	0
Purchases of securities available for sale					0									(414,000)	0	0
Loan to ESOP					0									(45,428,000)	0	0
Repayment of loans receivable from Bank					0									989,000	0	0
Net cash used in investing activities					102,000									(289,672,000)	0	0
Cash flows from financing activities:
Payment for trust preferred securities					0									(51,547,000)
Issuance of common stock					0									492,428,000
Net cash provided by financing activities					0									440,881,000	0	0
Net increase (decrease) in cash and cash equivalents					103,000									152,132,000	297,000	(1,330,000)
Cash and cash equivalents at beginning of period				$ 1,701,000	1,598,000				$ 1,301,000					1,701,000	1,301,000
Cash and cash equivalents at end of period	$ 153,833,000				$ 1,701,000	$ 1,598,000				$ 1,301,000				$ 153,833,000	$ 1,598,000	$ 1,301,000

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) - Tax effects of components in other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Components of Other Comprehensive (Loss) Income:
Net (loss) gain arising during the period	$ (3,012)	$ (7,224)	$ (17,877)	$ 7,271
Accretion of unrealized loss on securities reclassified as held to maturity	(2)	(13)	12	0
Reclassification adjustment for (gain) loss included in net income	60	(116)	2,626	(552)
Total other comprehensive (loss) income, before tax	(2,954)	(7,353)	(15,239)	6,719
Unrealized gain (loss) on swap contract, before tax	192	(2,825)	95	0
Employee benefit plans:
Amortization of prior service cost included in net income	(24)	(623)	(114)	(114)
Reclassification adjustment of actuarial net (loss) gain included in net income	(9)	2,526	11,806	9,123
Change in funded status of retirement obligations	(9,024)	897	11,503	(33,287)
Tax effects resulting from the adoption of ASU No. 2018-02	0	0
Total employee benefit plans, before tax	(9,057)	2,800	23,195	(24,278)
Total other comprehensive (loss)	(11,819)	(7,378)	8,051	(17,559)
Components of Other Comprehensive Income (Loss), Tax Effect
Net (loss) gain arising during the period	(119)	1,446	6,379	(2,597)
Accretion of unrealized loss on securities reclassified as held to maturity	(56)	0	(4)	0
Reclassification adjustment for (gain) loss included in net income	(13)	24	(937)	197
Total other comprehensive (loss) income, tax	(188)	1,470	5,438	(2,400)
Unrealized (loss) gain on swap contract	(30)	595	(33)	0
Employee benefit plans, Tax Effect
Amortization of prior service cost included in net income	(19)	132	41	41
Reclassification adjustment of actuarial net (loss) gain included in net income	(94)	(530)	(4,213)	(3,259)
Change in funded status of retirement obligations	3,354	(776)	(4,106)	11,890
Tax effects resulting from the adoption of ASU No. 2018-02	(10,434)	0
Total employee benefit plans, tax	(7,193)	(1,174)	(8,278)	8,672
Total other comprehensive (loss)	(7,411)	891	(2,873)	6,272
Components of Other Comprehensive Income (Loss), After Tax
Net (loss) gain arising during the period	(3,131)	(5,778)	(11,498)	4,674
Accretion of unrealized gain on securities reclassified as held to maturity	(58)	(13)	8	0
Reclassification adjustment for (gain) loss included in net income	47	(92)	1,689	(355)
Total other comprehensive (loss) income, net of tax	(3,142)	(5,883)	(9,801)	4,319
Unrealized (loss) gain on swap contract	162	(2,230)	62	0
Employee benefit plans, After Tax
Amortization of prior service cost included in net income	(43)	(491)	(73)	(73)
Reclassification adjustment of actuarial net (loss) gain included in net income	(103)	1,996	7,593	5,864
Change in funded status of retirement obligations	(5,670)	121	7,397	(21,397)
Tax effects resulting from the adoption of ASU No. 2018-02	(10,434)	0
Total employee benefit plans, net of tax	(16,250)	1,626	14,917	(15,606)
Other comprehensive loss	$ (19,230)	$ (6,487)	$ 5,178	$ (11,287)

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) - Changes in components of other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 475,914	$ 472,070	$ 439,664	$ 417,998
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02	0
Balance at end of year	472,070	972,060	475,914	439,664
Accumulated other comprehensive loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(46,180)	(65,410)	(51,358)	(40,071)
Current period changes in other comprehensive (loss) income	(7,522)	(6,487)	5,178	(11,287)
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02	(11,708)	0
Balance at end of year	(65,410)	(71,897)	(46,180)	(51,358)
Unrealized (losses) gains on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(4,137)	(7,279)	5,664	1,345
Current period changes in other comprehensive (loss) income	(1,828)	(5,883)	(9,801)	4,319
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02	(1,314)	0
Balance at end of year	(7,279)	(13,162)	(4,137)	5,664
Unrealized gains (losses) on swaps
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	62	224	0	0
Current period changes in other comprehensive (loss) income	122	(2,230)	62	0
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02	40	0
Balance at end of year	224	(2,006)	62	0
Employee benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(42,105)	(58,355)	(57,022)	(41,416)
Current period changes in other comprehensive (loss) income	(5,816)	1,626	14,917	(15,606)
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02	(10,434)	0
Balance at end of year	$ (58,355)	$ (56,729)	$ (42,105)	$ (57,022)

Other Comprehensive Income (L_5

Other Comprehensive Income (Loss) - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended													12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains on securities transactions, net					$ 60									$ (116)	$ 1,689	$ (355)
Compensation and employee benefits expense					15,624									69,907	62,993	58,115
Total before tax					(12,661)									(33,659)	(47,080)	(49,756)
Income tax (benefit) expense	$ 3,123	$ 6,956	$ (2,961)	$ 3,805	8,983	$ 194	$ 5,934	$ 5,012	$ 4,868	$ 4,611	$ 4,052	$ 4,281	$ 3,859	10,923	16,008	16,803
Net of tax	$ (14,867)	$ (10,827)	$ 14,742	$ (11,784)	(3,678)	$ (1,514)	$ (9,272)	$ (10,293)	$ (9,993)	$ (8,497)	$ (8,233)	$ (8,313)	$ (7,910)	(22,736)	(31,072)	(32,953)
Accumulated other comprehensive (loss) income components
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax					51									2,410	14,432	8,571
Income tax (benefit) expense					(107)									(506)	(5,150)	(3,062)
Net of tax					(56)									1,904	9,282	5,509
Accumulated other comprehensive (loss) income components | Reclassification adjustment for gains included in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gains on securities transactions, net					60									(116)	2,626	(552)
Accumulated other comprehensive (loss) income components | Reclassification adjustment of actuarial net gain included in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Compensation and employee benefits expense					$ (9)									$ 2,526	$ 11,806	$ 9,123

Derivatives and Hedging Activ_3

Derivatives and Hedging Activities - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)swap	Dec. 31, 2018USD ($)swap	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Derivative [Line Items]
Accrued interest on derivatives, at fair value	$ (7)	$ (65)
Net liability position		2,600
Collateral against obligations		2,600
Interest rate products-designated
Derivative [Line Items]
Derivative gains (losses) recorded in the Statements of Income	0	52	$ 0	$ 0
Federal Home Loan Bank advances | Interest rate products-designated
Derivative [Line Items]
Notional amount of derivative	20,000	320,000
Not-designated hedge | Currency forward contract - non-designated hedge
Derivative [Line Items]
Notional amount of derivative	1,600	0
Not-designated hedge | Interest rate products-designated
Derivative [Line Items]
Notional amount of derivative	0	$ 36,600
Number of swaps with customers offset by third party swaps | swap		3
Designated as hedging instrument | Federal Home Loan Bank advances | Interest rate products-designated
Derivative [Line Items]
Notional amount of derivative	$ 20,000	$ 320,000
Number of interest rate derivatives held | swap	2	24

Derivatives and Hedging Activ_4

Derivatives and Hedging Activities - Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative asset, gross	$ 865	$ 490
Derivative liability, gross	3,467	203
Interest rate products-designated | Designated as hedging instrument | Other Assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross	865	287
Interest rate products-designated | Designated as hedging instrument | Other Liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross	$ 3,467	0
Currency forward contract - non-designated hedge | Not-designated hedge | Other Assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross		203
Currency forward contract - non-designated hedge | Not-designated hedge | Other Liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross		$ 203