Bank of Marin Bancorp (BMRC) 10-K 15 Mar 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 28, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	Bank of Marin Bancorp
Entity Central Index Key	1,403,475
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 396
Entity Common Stock, Shares Outstanding		6,970,446
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017

CONSOLIDATED STATEMENTS OF COND

CONSOLIDATED STATEMENTS OF CONDITION - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 203,545	$ 48,804
Investment securities
Held-to-maturity, at amortized cost	151,032	44,438
Available-for-sale, at fair value	332,467	372,580
Total investment securities	483,499	417,018
Loans, net of allowance for loan losses of $15,767 and $15,442 at December 31, 2017 and 2016, respectively	1,663,246	1,471,174
Bank premises and equipment, net	8,612	8,520
Goodwill	30,140	6,436
Core deposit intangible	6,492	2,580
Interest receivable and other assets	72,620	68,961
Total assets	2,468,154	2,023,493
Deposits
Non-interest bearing	1,014,103	817,031
Interest bearing
Transaction accounts	169,195	100,723
Savings accounts	178,473	163,516
Money market accounts	626,783	539,967
Time accounts	160,116	151,463
Total deposits	2,148,670	1,772,700
Subordinated debentures	5,739	5,586
Interest payable and other liabilities	16,720	14,644
Total liabilities	2,171,129	1,792,930
Stockholders' Equity
Preferred stock, no par value, Authorized - 5,000,000 shares, none issued	0	0
Common stock, no par value, Authorized - 15,000,000 shares; Issued and outstanding - 6,921,542 and 6,127,314 at December 31, 2017 and 2016, respectively	143,967	87,392
Retained earnings	155,544	146,464
Accumulated other comprehensive loss, net	(2,486)	(3,293)
Total stockholders' equity	297,025	230,563
Total liabilities and stockholders' equity	$ 2,468,154	$ 2,023,493

CONSOLIDATED STATEMENTS OF CON3

CONSOLIDATED STATEMENTS OF CONDITION (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment Securities
Loans, allowance for loan losses	$ 15,767	$ 15,442
Stockholders' Equity
Preferred stock, no par value (in dollars per share)	$ 0	$ 0
Preferred stock, authorized (in shares)	5,000,000	5,000,000
Preferred stock, issued, (in shares)	0	0
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, authorized (in shares)	15,000,000	15,000,000
Common stock, issued (in shares)	6,921,542	6,127,314
Common stock, outstanding (in shares)	6,921,542	6,127,314

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income
Interest and fees on loans	$ 66,799	$ 67,472	$ 61,754
Interest on investment securities
Securities of U.S. government agencies	6,463	5,155	4,709
Obligations of state and political subdivisions	2,195	2,339	2,155
Corporate debt securities and other	144	256	685
Interest on federal funds sold and due from banks	995	208	135
Total interest income	76,596	75,430	69,438
Interest expense
Interest on interest-bearing transaction accounts	108	109	115
Interest on savings accounts	66	58	51
Interest on money market accounts	555	445	495
Interest on time accounts	576	743	853
Interest on FHLB and overnight borrowings	0	478	317
Interest on subordinated debentures	439	436	420
Total interest expense	1,744	2,269	2,251
Net interest income	74,852	73,161	67,187
Provision for (reversal of) loan losses	500	(1,850)	500
Net interest income after provision for loan losses	74,352	75,011	66,687
Non-interest income
Service charges on deposit accounts	1,784	1,789	1,979
Wealth Management and Trust Services	2,090	2,090	2,391
Debit card interchange fees	1,531	1,503	1,445
Merchant interchange fees	398	449	545
Earnings on bank-owned life Insurance	845	844	814
Dividends on FHLB stock	766	1,153	1,003
(Losses) gains on investment securities, net	(185)	425	79
Other income	1,039	908	937
Total non-interest income	8,268	9,161	9,193
Non-interest expense
Salaries and related benefits	29,958	26,663	25,764
Occupancy and equipment	5,472	5,081	5,498
Depreciation and amortization	1,941	1,822	1,968
Federal Deposit Insurance Corporation insurance	666	825	997
Data processing	4,906	3,625	3,318
Professional services	2,858	2,044	2,121
Directors' expense	720	553	826
Information technology	769	862	736
Provision for losses on off-balance sheet commitments	57	150	(263)
Other expense	6,435	6,067	5,984
Total non-interest expense	53,782	47,692	46,949
Income before provision for income taxes	28,838	36,480	28,931
Provision for income taxes	12,862	13,346	10,490
Net income	$ 15,976	$ 23,134	$ 18,441
Net income per common share:
Basic (in dollars per share)	$ 2.58	$ 3.81	$ 3.09
Diluted (in dollars per share)	$ 2.55	$ 3.78	$ 3.04
Weighted average shares:
Basic (in shares)	6,196	6,073	5,966
Diluted (in shares)	6,273	6,115	6,065
Dividends declared per common share (in dollars per share)	$ 1.12	$ 1.02	$ 0.90
Comprehensive income:
Net income	$ 15,976	$ 23,134	$ 18,441
Other comprehensive income (loss):
Change in net unrealized gain or loss on available-for-sale securities	3,671	(5,679)	(1,481)
Reclassification adjustment for losses (gains) on available-for-sale securities in net income	185	(394)	(6)
Net unrealized loss on securities transferred from available-for-sale to held-to-maturity	(3,036)	0	0
Amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity	426	21	61
Subtotal	1,246	(6,052)	(1,426)
Deferred tax expense (benefit)	439	(2,566)	(531)
Other comprehensive income (loss), net of tax	807	(3,486)	(895)
Comprehensive income	$ 16,783	$ 19,648	$ 17,546

CONSOLIDATED STATEMENT OF CHANG

CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss), Net of Taxes
Balance (in shares) at Dec. 31, 2014		5,939,482
Balance at Dec. 31, 2014	$ 200,026	$ 82,436	$ 116,502	$ 1,088
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,441		18,441
Other comprehensive income (loss)	$ (895)			(895)
Stock options exercised (in shares)	37,071	37,071
Stock options exercised	$ 1,139	$ 1,139
Excess tax benefit - stock-based compensation	212	$ 212
Stock issued under employee stock purchase plan (in shares)		339
Stock issued under employee stock purchase plan	17	$ 17
Restricted stock granted (in shares)		15,970
Restricted stock granted	0	$ 0
Restricted stock forfeited/cancelled (in shares)		(450)
Restricted stock forfeited / cancelled	0	$ 0
Stock-based compensation - stock options	252	252
Stock-based compensation - restricted stock	384	$ 384
Cash dividends paid on common stock	(5,390)		(5,390)
Stock purchased by directors under director stock plan (in shares)		245
Stock purchased by directors under director stock plan	12	$ 12
Stock issued in payment of director fees (in shares)		5,295
Stock issued in payment of director fees	275	$ 275
Stock issued from exercise of warrants (in shares)		70,591
Stock issued from exercise of warrants	0	$ 0
Balance (in shares) at Dec. 31, 2015		6,068,543
Balance at Dec. 31, 2015	214,473	$ 84,727	129,553	193
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,134		23,134
Other comprehensive income (loss)	$ (3,486)			(3,486)
Stock options exercised (in shares)	36,117	36,117
Stock options exercised	$ 1,227	$ 1,227
Excess tax benefit - stock-based compensation	161	$ 161
Stock issued under employee stock purchase plan (in shares)		621
Stock issued under employee stock purchase plan	32	$ 32
Restricted stock granted (in shares)		16,910
Restricted stock granted	0	$ 0
Stock-based compensation - stock options	347	347
Stock-based compensation - restricted stock	638	$ 638
Cash dividends paid on common stock	(6,223)		(6,223)
Stock purchased by directors under director stock plan (in shares)		516
Stock purchased by directors under director stock plan	26	$ 26
Stock issued in payment of director fees (in shares)		4,607
Stock issued in payment of director fees	$ 234	$ 234
Balance (in shares) at Dec. 31, 2016	6,127,314	6,127,314
Balance at Dec. 31, 2016	$ 230,563	$ 87,392	146,464	(3,293)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15,976	0	15,976	0
Other comprehensive income (loss)	$ 807	$ 0	0
Stock options exercised (in shares)	21,474	9,266
Stock options exercised	$ 28	$ 28
Stock issued under employee stock purchase plan (in shares)		512
Stock issued under employee stock purchase plan	32	$ 32
Restricted stock granted (in shares)		16,230
Restricted stock granted	0	$ 0
Stock-based compensation - stock options	529	529
Stock-based compensation - restricted stock	742	$ 742
Cash dividends paid on common stock	(6,896)		(6,896)
Stock purchased by directors under director stock plan (in shares)		531
Stock purchased by directors under director stock plan	35	$ 35
Stock issued in payment of director fees (in shares)		2,878
Stock issued in payment of director fees	188	$ 188
Stock issued under employee stock ownership plan (ESOP) (in shares)		29,547
Stock issued under employee stock ownership plan (ESOP)	1,850	$ 1,850
Stock issued to Bank of Napa Shareholders (net of payment for fractional shares of $14 thousand) (in shares)		735,264
Stock and stock options issued to Bank of Napa shareholders (net of payment for fractional shares of $14 thousand)	$ 53,171	$ 53,171
Balance (in shares) at Dec. 31, 2017	6,921,542	6,921,542
Balance at Dec. 31, 2017	$ 297,025	$ 143,967	$ 155,544	$ (2,486)

CONSOLIDATED STATEMENT OF CHAN6

CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Statement of Stockholders' Equity [Abstract]
Fractional shares issued in acquisition, payment	$ 14

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities:
Net income	$ 15,976	$ 23,134	$ 18,441
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for (reversal of) loan losses	500	(1,850)	500
Provision for losses on off-balance sheet commitments	57	150	(263)
Write-down of deferred tax assets, net	3,017	0	0
Noncash contribution expense to employee stock ownership plan	1,152	0	0
Noncash director compensation expense-common stock	197	180	274
Stock-based compensation expense	1,271	985	636
Amortization of core deposit intangible	529	533	619
Amortization of investment security premiums, net of accretion of discounts	2,912	3,212	2,825
Accretion of discount on acquired loans	(902)	(1,775)	(1,883)
Accretion of discount on subordinated debentures	153	191	210
Net amortization of deferred loan origination costs/fees	65	114	(281)
(Gain on sale) write-down of other real estate owned	(6)	13	40
Loss (gain) on sale of investment securities	185	(425)	(79)
Depreciation and amortization	1,941	1,822	1,968
Loss on disposal of premises and equipment	0	3	4
Earnings on bank owned life insurance policies	(845)	(844)	(814)
Net change in operating assets and liabilities:
Deferred rent and other rent-related expenses	(12)	(254)	(4)
Interest receivable and other assets	(278)	581	347
Interest payable and other liabilities	1,035	(324)	1,142
Net cash provided by operating activities	26,947	25,446	23,682
Cash Flows from Investing Activities:
Purchase of held-to-maturity securities	(4,497)	(2,424)	(2,375)
Purchase of available-for-sale securities	(118,666)	(161,374)	(287,144)
Proceeds from sale of available-for-sale securities	55,408	68,673	2,099
Proceeds from sale of held-to-maturity securities	0	1,265	1,015
Proceeds from paydowns/maturities of held-to-maturity securities	48,559	25,779	47,181
Proceeds from paydowns/maturities of available-for-sale securities	26,333	129,669	64,839
Loans originated and principal collected, net	(57,181)	(32,005)	(88,123)
Purchase of bank owned life insurance policies	0	(2,133)	0
Purchase of premises and equipment	(1,434)	(1,040)	(1,418)
Proceeds from sale of loan	0	0	1,502
Proceeds from sale of other real estate owned	414	0	0
Cash acquired from the Bank of Napa acquisition	59,779	0	0
Purchase of Federal Home Loan Bank stock	0	(1,791)	(136)
Cash paid for low income housing investment	(902)	(301)	(718)
Net cash provided by (used in) investing activities	7,813	24,318	(263,278)
Cash Flows from Financing Activities:
Net increase in deposits	126,084	44,474	176,607
Proceeds from stock options exercised	88	1,388	1,326
Payment of tax withholding for stock options exercised	(60)	0	0
Federal Home Loan Bank (repayments) borrowings	0	(67,000)	52,000
Cash dividends paid on common stock	(6,896)	(6,223)	(5,390)
Proceeds from stock issued under employee and director stock purchase plans and ESOP	765	58	29
Net cash provided by (used in) financing activities	119,981	(27,303)	224,572
Net increase (decrease) in cash and cash equivalents	154,741	22,461	(15,024)
Cash and cash equivalents at beginning of period	48,804	26,343	41,367
Cash and cash equivalents at end of period	203,545	48,804	26,343
Supplemental disclosure of cash flow items, non-cash investing and financing activities:
Cash paid in interest	1,535	2,131	2,066
Cash paid in income taxes	9,761	13,365	9,068
Change in unrealized gain on available-for-sale securities	1,246	(6,052)	(1,426)
Stock issued in payment of director fees and to ESOP	1,340	234	275
Subscription in low income housing tax credit investment	0	0	1,023
Securities transferred from available-for-sale to held-to-maturity	128,965	0	0
Transfer of loan to loans held-for-sale at fair value	0	0	1,502
Merger consideration - stock and stock options issued to the Bank of Napa shareholders	53,185	0	0
Fair value of assets acquired, excluding cash acquired	245,342	0	0
Fair value of liabilities assumed	$ 251,938	$ 0	$ 0

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation : The consolidated financial statements include the accounts of Bank of Marin Bancorp (“Bancorp”), a bank holding company, and its wholly-owned bank subsidiary, Bank of Marin (the “Bank”), a California state-chartered commercial bank. References to “we,” “our,” “us” mean Bancorp and the Bank that are consolidated for financial reporting purposes. All material intercompany transactions have been eliminated. We have evaluated subsequent events through the date of filing with the Securities and Exchange Commission (“SEC”) and have determined that there are no subsequent events that require additional recognition or disclosure. The NorCal Community Bancorp Trusts I and II, respectively (the "Trusts"), were formed for the sole purpose of issuing trust preferred securities. Bancorp is not considered the primary beneficiary of the Trusts (variable interest entities), therefore the Trusts are not consolidated in our consolidated financial statements, but rather the subordinated debentures are shown as a liability on our consolidated statements of condition (See Note 7, Borrowings). Bancorp's investment in the securities of the Trusts is accounted for under the equity method and is included in interest receivable and other assets on the consolidated statements of condition. Nature of Operations : Bancorp, headquartered in Novato, CA, conducts business primarily through its wholly-owned subsidiary, the Bank, which provides a wide range of financial services to customers, who are predominantly professionals, small and middle-market businesses, and individuals who work and/or reside in Marin, Sonoma, Napa, San Francisco and Alameda counties. Besides the headquarters office in Novato, CA, the Bank operates ten branches in Marin County, three in Napa County, one in San Francisco, six in Sonoma County and three in Alameda County. Our accounting and reporting policies conform to generally accepted accounting principles, general practice, and regulatory guidance within the banking industry. A summary of our significant policies follows. Cash and Cash Equivalents include cash, due from banks, federal funds sold and other short-term investments with maturity less than three months at the time of origination. Investment Securities are classified as "held-to-maturity," "trading securities" or "available-for-sale." Investments classified as held-to-maturity are those that we have the ability and intent to hold until maturity and are reported at cost, adjusted for the amortization or accretion of premiums or discounts. Investments held for resale in anticipation of short-term market movements are classified as trading securities and are reported at fair value, with unrealized gains and losses included in earnings. Investments that are neither held-to-maturity nor trading are classified as available-for-sale and are reported at fair value. Unrealized gains and losses for available-for-sale securities, net of related tax, are reported as a separate component of comprehensive income and included in stockholders' equity until realized. For discussion of our methodology in determining fair value, see Note 9, Fair Value of Assets and Liabilities. Securities transferred from the available-for-sale category to the held-to-maturity category are recorded at fair value at the date of transfer. Unrealized holding gains or losses associated with the transfer of securities from available-for-sale to held-to-maturity are included in the balance of accumulated other comprehensive income (loss), net of tax, in the consolidated balance sheets. These unrealized holding gains or losses are amortized over the remaining life of the security as a yield adjustment in a manner consistent with the amortization or accretion of the original purchase premium or discount on the associated security. At each financial statement date, we assess whether declines in the fair value of held-to-maturity and available-for-sale securities below their costs are deemed to be other-than-temporary. We consider, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer, and (iii) our intent and ability to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value. Evidence evaluated includes, but is not limited to, the remaining payment terms of the instrument and economic factors that are relevant to the collectability of the instrument, such as: current prepayment speeds, the current financial condition of the issuer(s), industry analyst reports, credit ratings, credit default rates, interest rate trends, the quality of any credit enhancement and the value of any underlying collateral. For each security in an unrealized loss position ("impaired security"), we assess whether we intend to sell the security or if it is more likely than not that we will be required to sell the security before recovery of its amortized cost basis. If we intend to sell the security or it is more likely than not we will be required to sell the security before recovery of its amortized cost basis, the entire difference between the investment’s amortized cost basis and its fair value at the balance sheet date is recognized against earnings. For impaired securities that are not intended for sale and will not be required to be sold prior to recovery of our amortized cost basis, we determine if the impairment has a credit loss component. For both held-to-maturity and available-for-sale securities, if the amount of cash flows expected to be collected are less than the amortized cost, an other-than-temporary impairment shall be considered to have occurred and the credit loss component is recognized against earnings as the difference between present value of the expected future cash flows and the amortized cost. In determining the present value of the expected cash flows, we discount the expected cash flows at the effective interest rate implicit in the security at the date of purchase. The remaining difference between the fair value and the amortized basis is deemed to be due to factors that are not credit related and is recognized in other comprehensive income, net of applicable taxes. For held-to-maturity securities, if there is no credit loss component, no impairment is recognized. The portion of other-than-temporary impairment recognized in other comprehensive income for credit impaired debt securities classified as held-to-maturity is accreted from other comprehensive income to the amortized cost of the debt security over the remaining life of the debt security in a prospective manner on the basis of the amount and timing of future estimated cash flows. Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the effective interest method. In March 2017, the Financial Accounting Standards Board ("FASB") issued ASU No. 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities . The amendments in this ASU shorten the amortization period for certain callable debt securities purchased at a premium and require the premium to be amortized to the earliest call date. The ASU is effective for annual periods beginning after December 15, 2018, including interim periods within those periods. We early adopted this ASU effective January 1, 2017, which did not have a material impact on our financial condition and results of operations. Dividend and interest income are recognized when earned. Realized gains and losses on the sale of securities and credit losses related to other-than-temporary impairment on available-for-sale and held-to-maturity securities are included in non-interest income as gains (losses) on investment securities, net. The specific identification method is used to calculate realized gains and losses on sales of securities. Originated Loans are reported at the principal amount outstanding net of deferred fees (costs), charge-offs and the allowance for loan losses (“ALLL”). Interest income is accrued daily using the simple interest method. Loans are placed on non-accrual status when Management believes that there is doubt as to the collection of principal or interest, generally when they become contractually past due by ninety days or more with respect to principal or interest, except for loans that are well-secured and in the process of collection. When loans are placed on non-accrual status, any accrued but uncollected interest is reversed from current-period interest income. Non-accrual loans may be returned to accrual status when one of the following occurs: • The borrower has resumed paying the full amount of the principal and interest and we are satisfied with the borrower's financial position. In order to meet this test, we must have received repayment of all past due principal and interest unless the amounts contractually due are reasonably assured of repayment within a reasonable period of time, and there has been a sustained period of repayment performance (generally, six consecutive monthly payments), according to the original contractual terms or modified terms for loans whose contractual terms have been restructured in a manner which grants a concession to a borrower experiencing financial difficulties (“troubled debt restructuring”). • The loan has become well secured and is in the process of collection. Loan origination fees and commitment fees, offset by certain direct loan origination costs, are deferred and amortized as yield adjustments over the contractual lives of the related loans. Loan Charge-Off Policy: For all loan types excluding overdraft accounts, we generally make a charge-off determination at or before 90 days past due. A collateral-dependent loan is partially charged down to the fair value of collateral securing it if: (1) it is deemed uncollectable, or (2) it has been classified as a loss by either our internal loan review process or external examiners. A non-collateral-dependent loan is partially charged down to its net realizable value under the same circumstances. Overdraft accounts are generally charged off when they exceed 60 days past due. Acquired Loans : Acquired loans are recorded at their estimated fair values at acquisition date in accordance with Accounting Standards Code ("ASC") 805, Business Combinations , factoring in credit losses expected to be incurred over the life of the loan. Accordingly, an allowance for loan losses is not carried over or recorded for acquired loans as of the acquisition date. We estimated the fair value of acquired loans at the acquisition date based on a discounted cash flow methodology that considered factors including the type of loan and related collateral, risk classification, fixed or variable interest rate, term of loan, whether or not the loan was amortizing, and current discount rates. Loans, except for purchased credit impaired ("PCI") loans, were grouped together according to similar risk characteristics and treated in the aggregate when applying various valuation techniques. Expected cash flows incorporated our best estimate of key assumptions at the time, such as property values, default rates, loss severity and prepayment speeds. Discount rates were based on market rates for new originations of comparable loans, where available, and included adjustments for liquidity factors. To the extent comparable market rates were not readily available, a discount rate was derived based on the assumptions of market participants' cost of funds, servicing costs and return requirements for comparable risk assets. In either case, the discount rate did not include a factor for credit losses, as that had been considered in estimating the cash flows. The process of calculating fair values of acquired loans, including estimates of losses expected to be incurred over the estimated remaining lives of the loans at acquisition date and ongoing updates to Management's expectation of future cash flows, requires significant subjective judgments and assumptions. The economic environment and lack of market liquidity and transparency are factors that have influenced, and may continue to affect, these assumptions and estimates. We acquired loans with evidence of significant credit quality deterioration subsequent to their origination and for which it was probable, at acquisition, that we would be unable to collect all contractually required payments. Management applied significant subjective judgment in determining which loans were PCI loans. Evidence of credit quality deterioration as of the purchase date may include data such as past due and nonaccrual status, risk grades and charge-off history. The difference between the undiscounted expected cash flows expected to be collected and the fair value at acquisition date ("accretable difference") is accreted into interest income at a level yield of return over the estimated remaining life of the PCI loan, provided that the timing and amount of future cash flows is reasonably estimable. The accretable yield is affected by: • Changes in interest rate indices for variable rate loans – Expected future cash flows are based on the variable rates in effect at the time of the regular evaluations of cash flows expected to be collected; • Changes in prepayment assumptions – Prepayments affect the estimated life of the loans which may change the amount of interest income, and possibly principal, expected to be collected; and • Changes in the expected principal and interest payments over the estimated life – Updates to expected cash flows are driven by the credit outlook and actions taken with borrowers. Changes in expected future cash flows from loan modifications are included in the regular evaluations of cash flows expected to be collected. The cash flows expected to be collected are updated each quarter based on current assumptions regarding default rates, loss severities, and other factors that are reflective of current financial conditions of the borrowers and the market conditions. Probable decreases in expected cash flows after acquisition result in impairment recorded as a specific allowance for loan losses or a charge-off to the allowance. Impairment is calculated as the present value of the expected future cash flows on the PCI loan, discounted at the loan's effective interest rate implicit in the loan. The nonaccretable difference on the date of acquisition is defined as the difference between the contractually required payments and the cash flows expected to be collected, considering the result of prepayments, and is not recorded. For purposes of accounting for the PCI loans from past business combinations, we elected not to apply the pooling method but to account for these loans individually. Disposals of loans, which may include sales of loans to third parties, receipt of payments in full by the borrower, or foreclosure of the collateral, result in removal of the loan from the PCI loan portfolio at its carrying amount. If a PCI loan pays off earlier than expected, a gain is recorded as interest income when the payoff amount exceeds the recorded investment. For acquired loans not considered credit impaired ("non-PCI"), we recognize the entire fair value discount accretion to interest income, based on contractual cash flows using an effective interest rate method for term loans, and on a straight line basis for revolving lines. When a non-PCI loan is placed on non-accrual status subsequent to acquisition, accretion stops until the loan is returned to accrual status. The level of accretion on non-PCI loans varies from period to period due to maturities and early pay-offs of these loans during the reporting periods. Subsequent to acquisition, if the probable and estimable losses for non-PCI loans exceed the amount of the remaining unaccreted discount, the excess is established as an allowance for loan losses. For further information regarding our acquired loans, see Note 3, Loans and Allowance for Loan Losses. Allowance for Loan Losses is based upon estimates of loan losses and is maintained at a level considered adequate to provide for probable losses inherent in the loan portfolio. The allowance is increased by provisions for loan losses charged against earnings and reduced by charge-offs, net of recoveries. In periodic evaluations of the adequacy of the allowance balance, Management considers current economic conditions, known and inherent risks in the portfolio, adverse situations that may affect the borrower's ability to repay, the estimated value of any underlying collateral, our past loan loss experience and other factors. The ALLL is based on estimates, and ultimate losses may vary from current estimates. Our Board of Directors' Asset/Liability Management Committee (“ALCO”) reviews the adequacy of the ALLL at least quarterly. The overall allowance consists of 1) specific allowances for individually identified impaired loans ("ASC 310-10") and 2) general allowances for pools of loans ("ASC 450-20"), which incorporate quantitative (e.g., historical loan loss rates) and qualitative risk factors (e.g., portfolio growth and trends, credit concentrations, economic and regulatory factors, etc.). The first component, specific allowances, results from the analysis of identified problem credits and the evaluation of sources of repayment including collateral, as applicable. Through Management's ongoing loan grading and credit monitoring process, individual loans are identified that have conditions indicating the borrower may be unable to pay all amounts due in accordance with the contractual terms. These loans are evaluated for impairment individually by Management. Management considers an originated loan to be impaired when it is probable we will be unable to collect all amounts due according to the contractual terms of the loan agreement. When the fair value of the impaired loan is less than the recorded investment in the loan, the difference is recorded as an impairment through the establishment of a specific allowance. For loans determined to be impaired, the extent of the impairment is measured based on the present value of expected future cash flows discounted at the loan's effective interest rate at origination (for originated loans), based on the loan's observable market price, or based on the fair value of the collateral if the loan is collateral dependent or if foreclosure is imminent. Generally, with problem credits that are collateral dependent, we obtain appraisals of the collateral at least annually. We may obtain appraisals more frequently if we believe the collateral value is subject to market volatility, if a specific event has occurred to the collateral, or if we believe foreclosure is imminent. The second component is an estimate of the probable inherent losses in each loan pool with similar characteristics. This analysis encompasses the entire loan portfolio, excluding individually identified impaired loans and acquired loans whose purchase discount has not been fully accreted. Under our allowance model, loans are evaluated on a pool basis by federal regulatory reporting codes ("CALL codes" or "segments"), which are further delineated by assigned credit risk ratings, as described in Note 3, Loans and Allowance for Loan Losses. Segments include the following: • Loans secured by real estate: - 1-4 family residential construction loans - Other construction loans and all land development and other land loans - Secured by farmland (including residential and other improvements) - Revolving, open-end loans secured by 1-4 family residential properties and extended under lines of credit - Closed-end loans secured by 1-4 family residential properties, secured by first liens - Closed-end loans secured by 1-4 family residential properties, secured by junior liens - Secured by multifamily (5 or more) residential properties - Loans secured by owner-occupied non-farm nonresidential properties - Loans secured by other non-farm nonresidential properties • Loans to finance agricultural production and other loans to farmers • Commercial and industrial loans • Loans to individuals for household, family and other personal expenditures (i.e., consumer loans) • Other loans The model determines general allowances by loan segment based on quantitative (loss history) and qualitative risk factors. Qualitative internal and external risk factors include, but are not limited to, the following: • Changes in the nature and volume of the loan portfolio. • Changes in the volume and severity of past due loans, the volume of non-accruals loans, and the volume and severity of adversely classified or graded loans. • The existence and effect of individual loan and loan segment concentrations. • Changes in lending policies and procedures, including changes in underwriting standards and collection, charge-off, and recovery practices not considered elsewhere. • Changes in the experience, ability, and depth of lending management and other relevant staff. • Changes in the quality of our systematic loan review processes. • Changes in economic and business conditions, and developments that affect the collectability of the portfolio. • Changes in the value of underlying collateral, where applicable. • The effect of other external factors such as legal and regulatory requirements on the level of estimated credit losses in the portfolio. • The effect of acquisitions of other loan portfolios on our infrastructure, including risk associated with entering new geographic areas as a result of such acquisitions. • The presence of specialized lending segments in the portfolio. Beginning with the quarter ended March 31, 2016, Management enhanced its methodology for determining the quantitative and qualitative risk factors assigned to unimpaired loans in order to capture historical loss information at the loan level, track loss migration through risk grade deterioration, increase efficiencies related to performing the calculations, and refine how we incorporate environmental and other unique risk elements into our estimation of credit losses. The changes in methodology did not result in a material difference in general allowances. Prior to March 31, 2016, under the Bank's allowance model, each segment was assigned a quantitative loss factor that was primarily based on a rolling twenty-quarter look-back at our historical losses for that particular segment, as well as a number of other assumptions. Under the current methodology, the quantitative risk factor for each segment utilizes the greater of either the historical loss method or migration analysis loss method based on loss history beginning March 2010. Under the historical loss method, quarterly loss rates are calculated for each segment by dividing annualized net charge-offs during each quarter by the quarter's average segment balances. The quarterly loss rates are averaged over the entire loss history period. Under the migration analysis method, loss rates are calculated at the risk grade and segment levels by dividing the net charge-off amount by the total segment balance at the beginning of each migration period where the charged-off loan in question was present. Migration loss rates are averaged for each risk grade and segment for the entire loss history period. For each segment, the loss rates that result in the larger of the migration loss reserves or segment historical loss reserves are applied to the current loan balances. Qualitative factors are combined with these quantitative factors at the segment level to arrive at the overall general allowances. We establish specific allowances to account for credit deterioration for probable decreases in cash flows for PCI loans subsequent to acquisition. The estimated cash flows expected to be collected on PCI loans is updated quarterly and requires the use of key assumptions and estimates based on factors such as the current economic environment, changes in collateral values, loan workout plans, changes in the probability of default, loss severities, and prepayments. Probable decreases in expected cash flows after acquisition result in impairment recorded as a specific allowance for loan losses or a charge-off to the allowance. Impairment is calculated as the present value of the expected future cash flows on the PCI loan, discounted at the loan's effective interest rate implicit in the loan. While we believe we use the best information available to determine the allowance for loan losses, our results of operations could be significantly affected if circumstances differ substantially from the assumptions used in determining the allowance. A decline in local and national economic conditions, or significant changes in other assumptions, could result in a material increase in the allowance for loan losses and may adversely affect our financial condition and results of operations. In addition, the determination of the amount of the allowance for loan losses is subject to review by bank regulators as part of their routine examination process, which may result in the establishment of additional allowance for loan losses based upon their judgment of information available to them at the time of their examination. For further information regarding the allowance for loan losses, see Note 3, Loans and Allowance for Loan Losses. Allowance for Losses on Off-Balance Sheet Commitments : We make commitments to extend credit to meet the financing needs of our customers in the form of loans or standby letters of credit. We are exposed to credit loss in the event that a decline in credit quality of the borrower leads to nonperformance. We record an allowance for losses on these off-balance sheet commitments based on estimates of probability that these commitments will be drawn upon according to our historical utilization experience on different types of commitments and expected loss severity. This allowance is included in interest payable and other liabilities on the consolidated statements of condition. Transfers of Financial Assets : We have entered into certain participation agreements with other organizations. We account for these transfers of financial assets as sales when control over the transferred financial assets has been surrendered. Control over transferred assets is deemed to be surrendered when (1) the assets and liabilities have been isolated from us, (2) the transferee has the right to pledge or exchange the assets (or beneficial interests) it received, free of conditions that constrain it from taking advantage of that right, beyond a trivial benefit and (3) we do not maintain effective control over the transferred financial assets or third-party beneficial interests related to those transferred assets. No gain or loss has been recognized by us on the sale of these participation interests in 2017 , 2016 and 2015 . Premises and Equipment : Premises and equipment consist of leasehold improvements, furniture, fixtures, software and equipment and are stated at cost, less accumulated depreciation and amortization, which are calculated on a straight-line basis. Furniture and fixtures are depreciated over eight years and equipment is generally depreciated over three to twenty years. Leasehold improvements are amortized over the lesser of their estimated useful lives or the terms of the leases. When assets are sold or otherwise disposed of, the cost and related accumulated depreciation or amortization are removed from the accounts and any resulting gain or loss is recognized in income for the period. The cost of maintenance and repairs is charged to expense as incurred. Business Combinations : Business combinations are accounted for under the acquisition method of accounting in accordance with ASC 805, Business Combinations . Under the acquisition method the acquiring entity in a business combination recognizes the acquired assets and assumed liabilities at their estimated fair values as of the date of acquisition. Any excess of the purchase price over the fair value of net assets and other identifiable intangible assets acquired is recorded as goodwill. To the extent the fair value of net assets acquired, including other identifiable assets, exceed the purchase price, a bargain purchase gain is recognized. Assets acquired and liabilities assumed from contingencies must also be recognized at fair value, if the fair value can be determined during the measurement period. Results of operations of an acquired business are included in the consolidated statements of operations from the date of acquisition. Acquisition-related costs, including conversion and restructuring charges, are expensed as incurred. Goodwill and Other Intangible Assets : Goodwill is determined as the excess of the fair value of the consideration transferred, plus the fair value of any noncontrolling interests in the acquiree, over the fair value of the net assets acquired and liabilities assumed as of the acquisition date. Goodwill that arises from a business combination is periodically evaluated for impairment at the reporting unit level, at least annually. Intangible assets with definite useful lives are amortized over their estimated useful lives to their estimated residual values. Core deposit intangible ("CDI") represents the estimated future benefit of deposits related to an acquisition and is booked separately from the related deposits and evaluated periodically for impairment. The CDI asset is amortized on an accelerated method over its estimated useful life of ten years. At December 31, 2017, the future estimated amortization expense for the CDI arising from our past acquisitions is as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Core deposit intangible amortization $ 921 $ 887 $ 853 $ 818 $ 782 $ 2,231 $ 6,492 We make a qualitative assessment of whether it is more likely than not that the fair value of a reporting unit where goodwill is assigned is less than its carrying amount. If we conclude that it is more likely than not that the fair value is more than its carrying amount, no impairment is recorded. Goodwill is tested for impairment on an interim basis if circumstances change or an event occurs between annual tests that would more likely than not reduce the fair value of the reporting unit below its carrying amount. The qualitative assessment includes adverse events or circumstances identified that could negatively affect the reporting units’ fair value as well as positive and mitigating events. Such indicators may include, among others, a significant change in legal factors or in the general business climate, significant change in our stock price and market capitalization, unanticipated competition, and an action or assessment by a regulator. If the fair value of a reporting unit is less than its carrying amount, an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value is recognized. The loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. In January 2017, the FASB issued ASU No. 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment . The ASU is effective for fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. We early adopted this ASU effective January 1, 2017, which did not have a material impact on our financial condition and results of operations. Other Real Estate Owned ("OREO") : OREO is comprised of property acquired through foreclosure, in substance repossession or acceptance of deeds-in-lieu of foreclosure when the related loan receivable is de-recognized. OREO is recorded at fair value of the collateral less estimated costs to sell, establishing a new cost basis, and subsequently accounted for at the lower of cost or fair value less estimated costs to sell. Any shortfall of collateral value from the recorded investment of the related loan is recognized as loss at the time of foreclosure and is charged against the allowance for loan losses. Fair value of collateral is generally based on an independent appraisal of the property. Revenues and expenses associated with OREO, and subsequent adjustments to the fair value of the property and to the estimated costs of disposal, are realized and reported as a component of non-interest income and expense when incurred. Bank Owned Life Insurance ("BOLI") : The Bank owns life insurance policies on

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investment Securities	12 continuous months Total securities in a loss position (in thousands) Fair value Unrealized loss Fair value Unrealized loss Fair value Unrealized loss Held-to-maturity: MBS pass-through securities issued by FHLMC and FNMA $ 2,250 $ (154 ) $ — $ — $ 2,250 $ (154 ) Obligations of state and political subdivisions 3,362 (6 ) — — 3,362 (6 ) Corporate bonds 3,518 (1 ) — — 3,518 (1 ) Total held-to-maturity 9,130 (161 ) — — 9,130 (161 ) Available-for-sale: MBS pass-through securities issued by FHLMC and FNMA 161,409 (3,570 ) — — 161,409 (3,570 ) SBA-backed securities 607 (7 ) — — 607 (7 ) CMOs issued by FNMA 9,498 (109 ) — — 9,498 (109 ) CMOs issued by FHLMC 31,545 (731 ) — — 31,545 (731 ) CMOs issued by GNMA 1,583 (1 ) — — 1,583 (1 ) Debentures of government- sponsored agencies 19,951 (38 ) 9,946 (52 ) 29,897 (90 ) Obligations of state and political subdivisions 59,567 (1,740 ) — — 59,567 (1,740 ) Corporate bonds 154 (1 ) — — 154 (1 ) Total available-for-sale 284,314 (6,197 ) 9,946 (52 ) 294,260 (6,249 ) Total temporarily impaired securities $ 293,444 $ (6,358 ) $ 9,946 $ (52 ) $ 303,390 $ (6,410 ) As of December 31, 2017 , fifty-five investment securities in our portfolio had been in a continuous loss position for twelve months or more. They consisted of thirty-two obligations of U.S. state and political subdivisions, four CMOs issued by FHLMC, three CMOs issued by FNMA and sixteen agency MBS securities. We have evaluated each issuer's financial information as well as credit enhancement and guarantees, and believe that the decline in fair value is primarily driven by factors other than credit. It is probable that we will be able to collect all amounts due according to the contractual terms and no other-than-temporary impairment exists on these securities. Based upon our assessment of the credit fundamentals, we concluded that these securities were not other-than-temporarily impaired at December 31, 2017 . There were one hundred forty-three investment securities in our portfolio that had been in temporary loss positions for less than twelve months as of December 31, 2017 , and their temporary loss positions mainly arose from changes in interest rates since purchase. They consisted of eighty-one obligations of U.S. state and political subdivisions, five corporate bonds, sixteen agency MBS securities, thirty-four agency CMOs, two privately issued CMOs and five debentures of government-sponsored agencies. Securities of government-sponsored agencies are supported by the U.S. Federal Government, which protects us from credit losses. Other temporarily impaired securities are deemed creditworthy after internal analysis of the issuers' latest financial information and credit enhancement. Additionally, all are rated as investment grade by at least one major rating agency. As a result of this impairment analysis, we concluded that these securities were not other-than-temporarily impaired at December 31, 2017 . Non-Marketable Securities As a member of the FHLB, we are required to maintain a minimum investment in FHLB capital stock determined by the Board of Directors of the FHLB. The minimum investment requirements can increase in the event we increase our total asset size or borrowings with the FHLB. Shares cannot be purchased or sold except between the FHLB and its members at the $100 per share par value. We held $11.1 million and $10.2 million of FHLB stock recorded at cost in other assets on the consolidated statements of condition at December 31, 2017 and 2016 , respectively. The carrying amounts of these investments are reasonable estimates of fair value because the securities are restricted to member banks and they do not have a readily determinable market value. Management does not believe that the FHLB stock is other-than-temporarily-impaired, due to FHLB's current financial position. On February 21, 2018, FHLB announced a cash dividend for the fourth quarter of 2017 at an annualized dividend rate of 7.00% to be distributed in mid-March 2018. Cash dividends paid on FHLB capital stock are recorded as non-interest income. As a member bank of Visa U.S.A., we hold 16,939 shares of Visa Inc. Class B common stock with a carrying value of zero , which is equal to our cost basis. These shares are restricted from resale until their conversion into Class A (voting) shares upon the termination of Visa Inc.'s Covered Litigation escrow account. As a result of the restriction, these shares are not considered available-for-sale and are not carried at fair value. When converting this Class B common stock to Class A common stock under the conversion rate of 1.6483 , as of the latest SEC Form 10-Q filed by Visa, Inc. on February 1, 2018, and the closing stock price of Class A shares, the value of our shares of Class B common stock would have been $3.2 million and $2.2 million at December 31, 2017 and 2016 , respectively. The conversion rate is subject to further reduction upon the final settlement of the covered litigation against Visa Inc. and its member banks. See Note 12, Commitments and Contingencies herein. We invest in low income housing tax credit funds as a limited partner, which totaled $2.1 million and $2.5 million recorded in other assets as of December 31, 2017 and 2016 , respectively. In 2017 , we recognized $332 thousand of low income housing tax credits and other tax benefits, net of $331 thousand of amortization expense of low income housing tax credit investment, as a component of income tax expense. As of December 31, 2017 , our unfunded commitments for these low income housing tax credit funds totaled $546 thousand . We did not recognize any impairment losses on these low income housing tax credit investments during 2017 or 2016 , as the value of the future tax benefits exceeds the carrying value of the investments. On December 22, 2017, the Tax Cuts and Jobs Act of 2017 was signed into law, which reduces the federal corporate income tax rate from 35% to 21% for tax years beginning 2018. Due to the tax rate change, we revised the amortization schedule according to the proportional amortization method for the tax deduction benefits on these low income housing tax credit investments starting in 2018 using the 21% federal tax rate and recorded a catch-up amortization expense of $67 thousand in 2017 as a component of income tax expense." id="sjs-B4">Investment Securities Our investment securities portfolio consists of obligations of state and political subdivisions, corporate bonds, U.S. government agency securities, including mortgage-backed securities (“MBS”) and collateralized mortgage obligations (“CMOs”) issued or guaranteed by Federal National Mortgage Association ("FNMA"), Federal Home Loan Mortgage Corporation ("FHLMC"), or Government National Mortgage Association ("GNMA"), Small Business Administration ("SBA") backed securities, debentures issued by government-sponsored agencies such as FNMA, Federal Farm Credit Bureau, FHLB and FHLMC, as well as privately issued CMOs, as reflected in the table below: December 31, 2017 December 31, 2016 Amortized Fair Gross Unrealized Amortized Fair Gross Unrealized (in thousands) Cost Value Gains (Losses) Cost Value Gains (Losses) Held-to-maturity: Obligations of state and political subdivisions $ 19,646 $ 19,998 $ 383 $ (31 ) $ 30,856 $ 31,544 $ 694 $ (6 ) Corporate bonds — — — — 3,519 3,518 — (1 ) MBS pass-through securities issued by FHLMC and FNMA 100,376 100,096 234 (514 ) 10,063 10,035 126 (154 ) CMOs issued by FHLMC 31,010 30,938 2 (74 ) — — — — Total held-to-maturity 151,032 151,032 619 (619 ) 44,438 45,097 820 (161 ) Available-for-sale: Securities of U.S. government agencies: MBS pass-through securities issued by FHLMC and FNMA 65,559 65,262 126 (423 ) 193,384 189,959 145 (3,570 ) SBA-backed securities 25,979 25,982 58 (55 ) 614 607 — (7 ) CMOs issued by FNMA 35,340 35,125 33 (248 ) 13,790 13,772 91 (109 ) CMOs issued by FHLMC 70,514 69,889 3 (628 ) 43,452 42,758 37 (731 ) CMOs issued by GNMA 17,953 17,785 26 (194 ) 6,844 6,945 102 (1 ) Debentures of government- sponsored agencies 12,940 12,938 3 (5 ) 35,486 35,403 7 (90 ) Privately issued CMOs 1,432 1,431 1 (2 ) 419 419 1 (1 ) Obligations of state and political subdivisions 98,027 97,491 298 (834 ) 79,306 77,701 135 (1,740 ) Corporate bonds 6,541 6,564 26 (3 ) 4,959 5,016 57 — Total available-for-sale 334,285 332,467 574 (2,392 ) 378,254 372,580 575 (6,249 ) Total investment securities $ 485,317 $ 483,499 $ 1,193 $ (3,011 ) $ 422,692 $ 417,677 $ 1,395 $ (6,410 ) The amortized cost and fair value of investment debt securities by contractual maturity at December 31, 2017 are shown below. Expected maturities may differ from contractual maturities if the issuers of the securities have the right to call or prepay obligations with or without call or prepayment penalties. December 31, 2017 December 31, 2016 Held-to-Maturity Available-for-Sale Held-to-Maturity Available-for-Sale (in thousands) Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Within one year $ 2,151 $ 2,172 $ 10,268 $ 10,272 $ 13,473 $ 13,506 $ 20,136 $ 20,109 After one but within five years 15,577 15,791 71,576 71,237 16,706 17,150 58,334 58,267 After five years through ten years 54,641 54,554 129,723 128,954 3,000 3,125 113,576 110,842 After ten years 78,663 78,515 122,718 122,004 11,259 11,316 186,208 183,362 Total $ 151,032 $ 151,032 $ 334,285 $ 332,467 $ 44,438 $ 45,097 $ 378,254 $ 372,580 Sales of investment securities and gross gains and losses are shown in the following table. (in thousands) 2017 2016 2015 Available-for-sale: Sales proceeds $ 55,408 $ 68,673 $ 2,099 Gross realized gains $ 46 $ 458 $ 7 Gross realized losses $ (231 ) $ (64 ) $ (1 ) Held-to-maturity: Sales proceeds $ — $ 1,265 $ 1,015 Gross realized gains $ — $ 32 $ 73 Gross realized losses $ — $ — $ — Pledged investment securities are shown in the following table: (in thousands) December 31, 2017 December 31, 2016 Pledged to the State of California: Secure public deposits in compliance with the Local Agency Security Program $ 107,829 $ 108,304 Collateral for trust deposits 761 822 Total investment securities pledged to the State of California $ 108,590 $ 109,126 Collateral for Wealth Management and Trust Services ("WMTS') checking account $ 2,026 $ 2,146 As part of our ongoing review of our investment securities portfolio, we reassessed the classification of certain MBS pass-through and CMOs securities issued by FHLMC and FNMA. During 2017, we transferred $129 million of these securities, which we intend and have the ability to hold to maturity, from available-for-sale securities to held-to-maturity at fair value. The net unrealized pre-tax losses of $3.0 million at the date of transfer remained in accumulated other comprehensive income and are amortized over the remaining lives of the securities. Amortization of the net unrealized pre-tax losses totaled $426 thousand in 2017, and $21 thousand and $61 thousand in 2016 and 2015, respectively, for securities transferred from available-for-sale to held-to-maturity in 2014. There were no securities transferred from available-for-sale to held to maturity in 2016 or 2015. Other-Than-Temporarily Impaired ("OTTI") Debt Securities We have evaluated the credit of our investment securities and their issuers and/or insurers. Based on our evaluation, Management has determined that no investment security in our investment portfolio is other-than-temporarily impaired as of December 31, 2017 . We do not have the intent and it is more likely than not that we will not have to sell the remaining securities temporarily impaired at December 31, 2017 before recovery of the amortized cost basis. There were 198 and 134 securities in unrealized loss positions at December 31, 2017 and 2016 , respectively. Those securities are summarized and classified according to the duration of the loss period in the tables below: December 31, 2017 < 12 continuous months ≥ 12 continuous months Total securities in a loss position (in thousands) Fair value Unrealized loss Fair value Unrealized loss Fair value Unrealized loss Held-to-maturity: MBS pass-through securities issued by FHLMC and FNMA $ 16,337 $ (143 ) $ 46,845 $ (371 ) $ 63,182 $ (514 ) Obligations of state and political subdivisions 3,648 (31 ) — — 3,648 (31 ) CMOs issued by FHLMC 11,066 (31 ) 13,824 (43 ) 24,890 (74 ) Total held-to-maturity 31,051 (205 ) 60,669 (414 ) 91,720 (619 ) Available-for-sale: MBS pass-through securities issued by FHLMC and FNMA 32,189 (121 ) 15,325 (302 ) 47,514 (423 ) SBA-backed securities 11,028 (53 ) 165 (2 ) 11,193 (55 ) CMOs issued by FNMA 26,401 (171 ) 5,440 (77 ) 31,841 (248 ) CMOs issued by FHLMC 69,276 (628 ) — — 69,276 (628 ) CMOs issued by GNMA 14,230 (194 ) — — 14,230 (194 ) Debentures of government-sponsored agencies 2,984 (5 ) — — 2,984 (5 ) Obligations of state and political subdivisions 52,197 (288 ) 19,548 (546 ) 71,745 (834 ) Corporate bonds 3,060 (3 ) 3,060 (3 ) Privately issued CMO's 1,310 (2 ) — — 1,310 (2 ) Total available-for-sale 212,675 (1,465 ) 40,478 (927 ) 253,153 (2,392 ) Total temporarily impaired securities $ 243,726 $ (1,670 ) $ 101,147 $ (1,341 ) $ 344,873 $ (3,011 ) December 31, 2016 < 12 continuous months > 12 continuous months Total securities in a loss position (in thousands) Fair value Unrealized loss Fair value Unrealized loss Fair value Unrealized loss Held-to-maturity: MBS pass-through securities issued by FHLMC and FNMA $ 2,250 $ (154 ) $ — $ — $ 2,250 $ (154 ) Obligations of state and political subdivisions 3,362 (6 ) — — 3,362 (6 ) Corporate bonds 3,518 (1 ) — — 3,518 (1 ) Total held-to-maturity 9,130 (161 ) — — 9,130 (161 ) Available-for-sale: MBS pass-through securities issued by FHLMC and FNMA 161,409 (3,570 ) — — 161,409 (3,570 ) SBA-backed securities 607 (7 ) — — 607 (7 ) CMOs issued by FNMA 9,498 (109 ) — — 9,498 (109 ) CMOs issued by FHLMC 31,545 (731 ) — — 31,545 (731 ) CMOs issued by GNMA 1,583 (1 ) — — 1,583 (1 ) Debentures of government- sponsored agencies 19,951 (38 ) 9,946 (52 ) 29,897 (90 ) Obligations of state and political subdivisions 59,567 (1,740 ) — — 59,567 (1,740 ) Corporate bonds 154 (1 ) — — 154 (1 ) Total available-for-sale 284,314 (6,197 ) 9,946 (52 ) 294,260 (6,249 ) Total temporarily impaired securities $ 293,444 $ (6,358 ) $ 9,946 $ (52 ) $ 303,390 $ (6,410 ) As of December 31, 2017 , fifty-five investment securities in our portfolio had been in a continuous loss position for twelve months or more. They consisted of thirty-two obligations of U.S. state and political subdivisions, four CMOs issued by FHLMC, three CMOs issued by FNMA and sixteen agency MBS securities. We have evaluated each issuer's financial information as well as credit enhancement and guarantees, and believe that the decline in fair value is primarily driven by factors other than credit. It is probable that we will be able to collect all amounts due according to the contractual terms and no other-than-temporary impairment exists on these securities. Based upon our assessment of the credit fundamentals, we concluded that these securities were not other-than-temporarily impaired at December 31, 2017 . There were one hundred forty-three investment securities in our portfolio that had been in temporary loss positions for less than twelve months as of December 31, 2017 , and their temporary loss positions mainly arose from changes in interest rates since purchase. They consisted of eighty-one obligations of U.S. state and political subdivisions, five corporate bonds, sixteen agency MBS securities, thirty-four agency CMOs, two privately issued CMOs and five debentures of government-sponsored agencies. Securities of government-sponsored agencies are supported by the U.S. Federal Government, which protects us from credit losses. Other temporarily impaired securities are deemed creditworthy after internal analysis of the issuers' latest financial information and credit enhancement. Additionally, all are rated as investment grade by at least one major rating agency. As a result of this impairment analysis, we concluded that these securities were not other-than-temporarily impaired at December 31, 2017 . Non-Marketable Securities As a member of the FHLB, we are required to maintain a minimum investment in FHLB capital stock determined by the Board of Directors of the FHLB. The minimum investment requirements can increase in the event we increase our total asset size or borrowings with the FHLB. Shares cannot be purchased or sold except between the FHLB and its members at the $100 per share par value. We held $11.1 million and $10.2 million of FHLB stock recorded at cost in other assets on the consolidated statements of condition at December 31, 2017 and 2016 , respectively. The carrying amounts of these investments are reasonable estimates of fair value because the securities are restricted to member banks and they do not have a readily determinable market value. Management does not believe that the FHLB stock is other-than-temporarily-impaired, due to FHLB's current financial position. On February 21, 2018, FHLB announced a cash dividend for the fourth quarter of 2017 at an annualized dividend rate of 7.00% to be distributed in mid-March 2018. Cash dividends paid on FHLB capital stock are recorded as non-interest income. As a member bank of Visa U.S.A., we hold 16,939 shares of Visa Inc. Class B common stock with a carrying value of zero , which is equal to our cost basis. These shares are restricted from resale until their conversion into Class A (voting) shares upon the termination of Visa Inc.'s Covered Litigation escrow account. As a result of the restriction, these shares are not considered available-for-sale and are not carried at fair value. When converting this Class B common stock to Class A common stock under the conversion rate of 1.6483 , as of the latest SEC Form 10-Q filed by Visa, Inc. on February 1, 2018, and the closing stock price of Class A shares, the value of our shares of Class B common stock would have been $3.2 million and $2.2 million at December 31, 2017 and 2016 , respectively. The conversion rate is subject to further reduction upon the final settlement of the covered litigation against Visa Inc. and its member banks. See Note 12, Commitments and Contingencies herein. We invest in low income housing tax credit funds as a limited partner, which totaled $2.1 million and $2.5 million recorded in other assets as of December 31, 2017 and 2016 , respectively. In 2017 , we recognized $332 thousand of low income housing tax credits and other tax benefits, net of $331 thousand of amortization expense of low income housing tax credit investment, as a component of income tax expense. As of December 31, 2017 , our unfunded commitments for these low income housing tax credit funds totaled $546 thousand . We did not recognize any impairment losses on these low income housing tax credit investments during 2017 or 2016 , as the value of the future tax benefits exceeds the carrying value of the investments. On December 22, 2017, the Tax Cuts and Jobs Act of 2017 was signed into law, which reduces the federal corporate income tax rate from 35% to 21% for tax years beginning 2018. Due to the tax rate change, we revised the amortization schedule according to the proportional amortization method for the tax deduction benefits on these low income housing tax credit investments starting in 2018 using the 21% federal tax rate and recorded a catch-up amortization expense of $67 thousand in 2017 as a component of income tax expense.

Loans and Allowance for Loan Lo

Loans and Allowance for Loan Losses	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Loans and Allowance for Loan Losses	Loans and Allowance for Loan Losses Credit Quality of Loans Virtually all of our loans are from customers located in California, primarily in Marin, Alameda, Sonoma, San Francisco and Napa counties. Approximately 87% and 85% of total loans were secured by real estate at December 31, 2017 and 2016 , respectively. At December 31, 2017 , 67% of our loans were for commercial real estate, 85% of which were secured by real estate located in Marin, Sonoma, Alameda, San Francisco and Napa counties (California). The following table shows outstanding loans by class and payment aging as of December 31, 2017 and 2016 . Loan Aging Analysis by Class (in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential 1 Installment and other consumer Total December 31, 2017 30-59 days past due $ — $ — $ — $ — $ 99 $ 255 $ 330 $ 684 60-89 days past due 1,340 — — — — — — 1,340 90 days or more past due — — — — 307 — — 307 Total past due 1,340 — — — 406 255 330 2,331 Current 234,495 300,963 822,984 63,828 132,061 95,271 27,080 1,676,682 Total loans 3 $ 235,835 $ 300,963 $ 822,984 $ 63,828 $ 132,467 $ 95,526 $ 27,410 $ 1,679,013 Non-accrual loans 2 $ — $ — $ — $ — $ 406 $ — $ — $ 406 December 31, 2016 30-59 days past due $ 283 $ — $ — $ — $ 77 $ — $ 2 $ 362 60-89 days past due — — — — — — 49 49 90 days or more past due — — — — 91 — — 91 Total past due 283 — — — 168 — 51 502 Current 218,332 247,713 724,228 74,809 117,039 78,549 25,444 1,486,114 Total loans 3 $ 218,615 $ 247,713 $ 724,228 $ 74,809 $ 117,207 $ 78,549 $ 25,495 $ 1,486,616 Non-accrual loans 2 $ — $ — $ — $ — $ 91 $ — $ 54 $ 145 1 Our residential loan portfolio does not include sub-prime loans, nor is it our practice to underwrite loans commonly referred to as "Alt-A mortgages," the characteristics of which are loans lacking full documentation, borrowers having low FICO scores or higher loan-to-value ratios. 2 There were three purchased credit impaired ("PCI") loans with unpaid balances totaling $131 thousand and no carrying values that had stopped accreting interest at December 31, 2017 . There were no PCI loans that had stopped accreting interest at December 31, 2016 . Amounts exclude accreting PCI loans of $2.1 million and $2.9 million at December 31, 2017 and 2016 , respectively, as we have a reasonable expectation about future cash flows to be collected and we continue to recognize accretable yield on these loans in interest income. There were no accruing loans past due more than ninety days at December 31, 2017 or 2016 . 3 Amounts include net deferred loan origination costs of $818 thousand and $883 thousand at December 31, 2017 and 2016 , respectively. Amounts are also net of unaccreted purchase discounts on non-PCI loans of $1.2 million and $1.8 million at December 31, 2017 and 2016 , respectively. Our commercial loans are generally made to established small and mid-sized businesses to provide financing for their growth and working capital needs, equipment purchases and acquisitions. Management examines historical, current, and projected cash flows to determine the ability of the borrower to repay obligations as agreed. Commercial loans are made based primarily on the identified cash flows of the borrower and secondarily on the underlying collateral and guarantor support. The cash flows of borrowers, however, may not occur as expected, and the collateral securing these loans may fluctuate in value. Most commercial and industrial loans are secured by the assets being financed, such as accounts receivable and inventory, and typically include a personal guarantee. We target stable businesses with guarantors who provide additional sources of repayment and have proven to be resilient in periods of economic stress. Commercial real estate loans are subject to underwriting standards and processes similar to commercial loans discussed above. We underwrite these loans to be repaid from cash flow and to be supported by real property collateral. Underwriting standards for commercial real estate loans include, but are not limited to, debt coverage and loan-to-value ratios. Furthermore, substantially all of our loans are guaranteed by the owners of the properties. Commercial real estate loans may be adversely affected by conditions in the real estate markets or in the general economy. In the event of a vacancy, guarantors are expected to carry the loans until a replacement tenant can be found. The owner's substantial equity investment provides a strong economic incentive to continue to support the commercial real estate projects. As such, we have generally experienced a relatively low level of loss and delinquencies in this portfolio. Construction loans are generally made to developers and builders to finance construction, renovation and occasionally land acquisitions in anticipation of near-term development. These loans are underwritten after evaluation of the borrower's financial strength, reputation, prior track record, and independent appraisals. The construction industry can be affected by significant events, including: the inherent volatility of real estate markets and vulnerability to delays due to weather, change orders, inability to obtain construction permits, labor or material shortages, and price changes. Estimates of construction costs and value associated with the completed project may be inaccurate. Repayment of construction loans is largely dependent on the ultimate success of the project. Consumer loans primarily consist of home equity lines of credit and other residential tenancy-in-common fractional interest loans ("TIC"), floating homes and mobile homes along with a small number of installment loans. We originate consumer loans utilizing credit score information, debt-to-income ratio and loan-to-value ratio analysis. Diversification among consumer loan types, coupled with relatively small loan amounts that are spread across many individual borrowers, mitigates risk. Our other residential loans include TIC units located almost entirely in San Francisco County. We use a risk rating system to evaluate asset quality, and to identify and monitor credit risk in individual loans, and in the loan portfolio. Definitions of loans that are risk graded “Special Mention” or worse are consistent with those used by the Federal Deposit Insurance Corporation ("FDIC"). Our internally assigned grades are as follows: Pass and Watch : Loans to borrowers of acceptable or better credit quality. Borrowers in this category demonstrate fundamentally sound financial positions, repayment capacity, credit history and management expertise. Loans in this category must have an identifiable and stable source of repayment and meet the Bank’s policy regarding debt service coverage ratios. These borrowers are capable of sustaining normal economic, market or operational setbacks without significant financial consequences. Negative external industry factors are generally not present. The loan may be secured, unsecured or supported by non-real estate collateral for which the value is more difficult to determine and/or marketability is more uncertain. This category also includes “Watch” loans, where the primary source of repayment has been delayed. “Watch” is intended to be a transitional grade, with either an upgrade or downgrade within a reasonable period. Special Mention : Potential weaknesses that deserve close attention. If left uncorrected, those potential weaknesses may result in deterioration of the payment prospects for the asset. Special Mention assets do not present sufficient risk to warrant adverse classification. Substandard : Inadequately protected by either the current sound worth and paying capacity of the obligor or the collateral pledged, if any. A Substandard asset has a well-defined weakness or weaknesses that jeopardize(s) the liquidation of the debt. Substandard assets are characterized by the distinct possibility that we will sustain some loss if such weaknesses or deficiencies are not corrected. Well-defined weaknesses include adverse trends or developments of the borrower’s financial condition, managerial weaknesses and/or significant collateral deficiencies. Doubtful : Critical weaknesses that make collection or liquidation in full improbable. There may be specific pending events that work to strengthen the asset; however, the amount or timing of the loss may not be determinable. Pending events generally occur within one year of the asset being classified as Doubtful. Examples include: merger, acquisition, or liquidation; capital injection; guarantee; perfecting liens on additional collateral; and refinancing. Such loans are placed on non-accrual status and usually are collateral-dependent. We regularly review our credits for accuracy of risk grades whenever new information is received. Borrowers are required to submit financial information at regular intervals. Generally, commercial borrowers with lines of credit are required to submit financial information with reporting intervals ranging from monthly to annually depending on credit size, risk and complexity. Investor commercial real estate borrowers are generally required to submit rent rolls or property income statements annually. Construction loans are monitored monthly, and reviewed on an ongoing basis. Home equity and other consumer loans are reviewed based on delinquency. Loans graded “Watch” or worse, regardless of loan type, are reviewed no less than quarterly. The following table represents an analysis of the carrying amount in loans, net of deferred fees and costs and purchase premiums or discounts, by internally assigned risk grades, including PCI loans, at December 31, 2017 and 2016 . Credit Risk Profile by Internally Assigned Risk Grade (in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Purchased credit-impaired Total December 31, 2017 Pass $ 214,636 $ 281,104 $ 818,570 $ 60,859 $ 130,558 $ 95,526 $ 27,287 $ 1,325 $ 1,629,865 Special Mention 9,318 9,284 1,850 — — — — 790 21,242 Substandard 11,816 9,409 1,774 2,969 1,815 — 123 — 27,906 Total loans $ 235,770 $ 299,797 $ 822,194 $ 63,828 $ 132,373 $ 95,526 $ 27,410 $ 2,115 $ 1,679,013 December 31, 2016 Pass $ 201,987 $ 234,849 $ 720,417 $ 71,564 $ 115,680 $ 78,549 $ 25,083 $ 2,920 $ 1,451,049 Special Mention 9,197 4,799 607 — 1,334 — — — 15,937 Substandard 7,391 6,993 1,498 3,245 91 — 412 — 19,630 Total loans $ 218,575 $ 246,641 $ 722,522 $ 74,809 $ 117,105 $ 78,549 $ 25,495 $ 2,920 $ 1,486,616 Troubled Debt Restructuring Our loan portfolio includes certain loans that have been modified in a troubled debt restructuring (“TDR”), where economic concessions have been granted to borrowers experiencing financial difficulties. These concessions typically result from our loss mitigation activities and could include reductions in the interest rate, payment extensions, forgiveness of principal, forbearance or other actions. TDRs on non-accrual status at the time of restructure may be returned to accruing status after Management considers the borrower’s sustained repayment performance for a reasonable period, generally six months, and obtains reasonable assurance of repayment and performance. A loan may no longer be reported as a TDR if all of the following conditions are met: • The loan is subsequently refinanced or restructured at current market interest rates and the new terms are consistent with the treatment of creditworthy borrowers under regular underwriting standards; • The borrower is no longer considered to be in financial difficulty; • Performance on the loan is reasonably assured, and; • Existing loan did not have any forgiveness of principal or interest. The removal of TDR status must be approved by the same Management level that approved the upgrading of the loan classification. There were no loans removed from TDR designation during 2017 or 2016. During 2015, five loans with a recorded investment totaling $1.6 million were removed from TDR designation, after meeting all of the conditions noted above. The following table summarizes the carrying amount of TDR loans by loan class as of December 31, 2017 and December 31, 2016 . (in thousands) As of Recorded investment in Troubled Debt Restructurings 1 December 31, 2017 December 31, 2016 Commercial and industrial $ 2,165 $ 2,207 Commercial real estate, owner-occupied 6,999 6,993 Commercial real estate, investor 2,171 2,256 Construction 2,969 3,245 Home equity 347 625 Other residential 1,148 1,965 Installment and other consumer 721 877 Total $ 16,520 $ 18,168 1 There were no TDR loans on non-accrual status at December 31, 2017 or December 31, 2016 . Includes no acquired TDR loans as of December 31, 2017 or December 31, 2016 . The following table presents information for loans modified in a TDR during the presented periods, including the number of contracts modified, the recorded investment in the loans prior to modification, and the recorded investment in the loans at period end after being restructured. The table excludes fully charged-off TDR loans and loans modified in a TDR and subsequently paid-off during the years presented. (dollars in thousands) Number of Contracts Modified Pre-Modification Outstanding Recorded Investment Post-Modification Outstanding Recorded Investment Post-Modification Outstanding Recorded Investment at Period End TDRs modified during 2017: Installment and other consumer 1 $ 50 $ 50 $ 47 TDRs modified during 2016: Commercial real estate, investor 2 $ 1,830 $ 1,826 $ 1,752 Home equity 1 1 87 222 245 Installment and other consumer 1 68 67 66 Total 4 $ 1,985 $ 2,115 $ 2,063 1 The home equity line of credit modified in 2016 included debt consolidation, which increased the post-modification balance. TDRs modified during 2015: Commercial and industrial 7 $ 3,271 $ 3,251 $ 2,811 The modifications during 2017 , 2016 and 2015 primarily involved maturity or payment extensions, interest rate concessions, renewals, and other changes to loan terms. During 2017 , 2016 and 2015 , there were no defaults on loans that had been modified in a TDR within the prior twelve-month period. We report defaulted TDRs based on a payment default definition of more than ninety days past due. Impaired Loans The following tables summarize information by class on impaired loans and their related allowances. Total impaired loans include non-accrual loans, accruing TDR loans and accreting PCI loans that have experienced post-acquisition declines in cash flows expected to be collected. (in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Total December 31, 2017 Recorded investment in impaired loans: With no specific allowance recorded $ 309 $ — $ — $ 2,689 $ 406 $ 995 $ 46 $ 4,445 With a specific allowance recorded 1,856 6,999 2,171 280 347 153 675 12,481 Total recorded investment in impaired loans $ 2,165 $ 6,999 $ 2,171 $ 2,969 $ 753 $ 1,148 $ 721 $ 16,926 Unpaid principal balance of impaired loans $ 2,278 $ 6,993 $ 2,168 $ 2,963 $ 750 $ 1,147 $ 720 $ 17,019 Specific allowance $ 50 $ 188 $ 159 $ 7 $ 6 $ 1 $ 102 $ 513 Average recorded investment in impaired loans during 2017 $ 2,113 $ 6,998 $ 2,842 $ 3,132 $ 679 $ 1,324 $ 841 $ 17,929 Interest income recognized on impaired loans during 2017 1 $ 202 $ 266 $ 87 $ 147 $ 24 $ 62 $ 37 $ 825 December 31, 2016 Recorded investment in impaired loans: With no specific allowance recorded $ 315 $ — $ — $ 2,692 $ 91 $ 1,008 $ 103 $ 4,209 With a specific allowance recorded 1,892 6,993 2,256 553 624 957 829 14,104 Total recorded investment in impaired loans $ 2,207 $ 6,993 $ 2,256 $ 3,245 $ 715 $ 1,965 $ 932 $ 18,313 Unpaid principal balance of impaired loans $ 2,177 $ 6,993 $ 2,252 $ 3,238 $ 713 $ 1,965 $ 932 $ 18,270 Specific allowance $ 285 $ 163 $ 375 $ 8 $ 7 $ 55 $ 98 $ 991 Average recorded investment in impaired loans during 2016 $ 3,514 $ 7,069 $ 2,950 $ 3,242 $ 945 $ 1,988 $ 1,127 $ 20,835 Interest income recognized on impaired loans during 2016 1 $ 175 $ 199 $ 1,514 $ 137 $ 60 $ 90 $ 48 $ 2,223 Average recorded investment in impaired loans during 2015 $ 4,237 $ 7,886 $ 2,833 $ 4,164 $ 602 $ 2,028 $ 1,523 $ 23,273 Interest income recognized on impaired loans during 2015 1 $ 238 $ 295 $ 33 $ 86 $ 18 $ 92 $ 64 $ 826 1 Interest income recognized on a cash basis totaled $100 thousand in 2017 and was primarily related to the pay-off of a commercial non-accrual PCI loan in the fourth quarter. Interest income recognized on a cash basis totaled $1.4 million in 2016 and was primarily related to the interest recovery upon the pay-off of a partially charged off non-accrual commercial real estate loan during the third quarter. No interest income on impaired loans was recognized on a cash basis in 2015. Management monitors delinquent loans continuously and identifies problem loans, generally loans graded substandard or worse, loans on non-accrual status and loans modified in a TDR, to be evaluated individually for impairment testing. Generally, the recorded investment in impaired loans is net of any charge-offs from estimated losses related to specifically-identified impaired loans when they are deemed uncollectible. There were no charged-off portions of impaired loans outstanding at December 31, 2017 and 2016 . In addition, the recorded investment in impaired loans is net of purchase discounts or premiums on acquired loans and deferred fees and costs. At December 31, 2017 and 2016 , outstanding commitments to extend credit on impaired loans, including performing loans to borrowers whose terms have been modified in TDRs, totaled $935 thousand and $1.6 million , respectively. The following tables disclose activity in the allowance for loan losses ("ALLL") and the recorded investment in loans by class, as well as the related ALLL disaggregated by impairment evaluation method. Allowance for Loan Losses Rollforward for the Year Ended (in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Unallocated Total Year ended December 31, 2017 Beginning balance $ 3,248 $ 1,753 $ 6,320 $ 781 $ 973 $ 454 $ 372 $ 1,541 $ 15,442 Provision (reversal) 584 541 155 (100 ) 58 82 3 (823 ) 500 Charge-offs (289 ) — — — — — (4 ) — (293 ) Recoveries 111 — — — — — 7 — 118 Ending balance $ 3,654 $ 2,294 $ 6,475 $ 681 $ 1,031 $ 536 $ 378 $ 718 $ 15,767 Year ended December 31, 2016 Beginning balance $ 3,023 $ 2,249 $ 6,178 $ 724 $ 910 $ 394 $ 425 $ 1,096 $ 14,999 Provision (reversal) 93 (476 ) (2,014 ) 57 60 60 (75 ) 445 (1,850 ) Charge-offs (11 ) (20 ) — — — — (5 ) — (36 ) Recoveries 143 — 2,156 — 3 — 27 — 2,329 Ending balance $ 3,248 $ 1,753 $ 6,320 $ 781 $ 973 $ 454 $ 372 $ 1,541 $ 15,442 Year ended December 31, 2015 Beginning balance $ 2,837 $ 1,924 $ 6,672 $ 839 $ 859 $ 433 $ 566 $ 969 $ 15,099 Provision (reversal) (45 ) 325 (517 ) 724 48 (39 ) (123 ) 127 500 Charge-offs (5 ) — — (839 ) — — (20 ) — (864 ) Recoveries 236 — 23 — 3 — 2 — 264 Ending balance $ 3,023 $ 2,249 $ 6,178 $ 724 $ 910 $ 394 $ 425 $ 1,096 $ 14,999 Allowance for Loan Losses and Recorded Investment In Loans (dollars in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Unallocated Total December 31, 2017 Ending ALLL related to loans collectively evaluated for impairment $ 3,604 $ 2,106 $ 6,316 $ 674 $ 1,025 $ 535 $ 276 $ 718 $ 15,254 Ending ALLL related to loans individually evaluated for impairment 50 188 159 7 6 1 102 — 513 Ending ALLL related to purchased credit-impaired loans — — — — — — — — — Ending balance $ 3,654 $ 2,294 $ 6,475 $ 681 $ 1,031 $ 536 $ 378 $ 718 $ 15,767 Recorded Investment: Collectively evaluated for impairment $ 233,605 $ 292,798 $ 820,023 $ 60,859 $ 131,620 $ 94,378 $ 26,689 $ — $ 1,659,972 Individually evaluated for impairment 2,165 6,999 2,171 2,969 753 1,148 721 — 16,926 Purchased credit-impaired 65 1,166 790 — 94 — — — 2,115 Total $ 235,835 $ 300,963 $ 822,984 $ 63,828 $ 132,467 $ 95,526 $ 27,410 $ — $ 1,679,013 Ratio of allowance for loan losses to total loans 1.55 % 0.76 % 0.79 % 1.07 % 0.78 % 0.56 % 1.38 % NM 0.94 % Allowance for loan losses to non-accrual loans NM NM NM NM 254 % NM NM NM 3,883 % NM - Not Meaningful Allowance for Loan Losses and Recorded Investment In Loans (dollars in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Unallocated Total December 31, 2016 Ending ALLL related to loans collectively evaluated for impairment $ 2,963 $ 1,590 $ 5,945 $ 773 $ 966 $ 399 $ 274 $ 1,541 $ 14,451 Ending ALLL related to loans individually evaluated for impairment 285 163 375 8 7 55 98 — 991 Ending ALLL related to purchased credit-impaired loans — — — — — — — — — Ending balance $ 3,248 $ 1,753 $ 6,320 $ 781 $ 973 $ 454 $ 372 $ 1,541 $ 15,442 Loans outstanding: Collectively evaluated for impairment $ 216,368 $ 239,648 $ 720,266 $ 71,564 $ 116,390 $ 76,584 $ 24,563 $ — $ 1,465,383 Individually evaluated for impairment 2,207 6,993 2,256 3,245 715 1,965 932 — 18,313 Purchased credit-impaired 40 1,072 1,706 — 102 — — — 2,920 Total $ 218,615 $ 247,713 $ 724,228 $ 74,809 $ 117,207 $ 78,549 $ 25,495 $ — $ 1,486,616 Ratio of allowance for loan losses to total loans 1.49 % 0.71 % 0.87 % 1.04 % 0.83 % 0.58 % 1.46 % NM 1.04 % Allowance for loan losses to non-accrual loans NM NM NM NM 1,071 % NM 683 % NM 10,650 % NM - Not Meaningful Purchased Credit-Impaired Loans Acquired loans are considered credit-impaired if there is evidence of significant deterioration of credit quality since origination and it is probable, at the acquisition date, that we will be unable to collect all contractually required payments receivable. Management has determined certain loans purchased in our two bank acquisitions to be PCI loans based on credit indicators such as nonaccrual status, past due status, loan risk grade, loan-to-value ratio, etc. Revolving credit agreements (e.g., home equity lines of credit and revolving commercial loans) are not considered PCI loans as cash flows cannot be reasonably estimated. The following table reflects the unpaid principal balance and related carrying value of PCI loans: PCI Loans December 31, 2017 December 31, 2016 (in thousands) Unpaid Principal Balance Carrying Value Unpaid Principal Balance Carrying Value Commercial and industrial $ 276 $ 65 $ 45 $ 40 Commercial real estate, owner occupied 1,297 1,166 1,344 1,072 Commercial real estate, investor 1,064 790 1,713 1,706 Construction — — — — Home equity 231 94 248 102 Total purchased credit-impaired loans $ 2,868 $ 2,115 $ 3,350 $ 2,920 The activities in the accretable yield, or income expected to be earned over the remaining lives of the PCI loans were as follows: Accretable Yield Years ended (in thousands) December 31, 2017 December 31, 2016 December 31, 2015 Balance at beginning of period $ 1,476 $ 2,618 $ 4,027 Additions 109 — — Removals 1 — (778 ) (914 ) Accretion (331 ) (364 ) (495 ) Balance at end of period $ 1,254 $ 1,476 $ 2,618 1 Represents the accretable difference that is relieved when a loan exits the PCI population due to payoff, full charge-off, or transfer to repossessed assets, etc. Pledged Loans Our FHLB line of credit is secured under terms of a blanket collateral agreement by a pledge of certain qualifying loans with unpaid principal balances of $887.9 million and $869.2 million at December 31, 2017 and 2016 , respectively. In addition, we pledge a certain residential loan portfolio, which totaled $67.6 million and $54.6 million at December 31, 2017 and 2016 , respectively, to secure our borrowing capacity with the Federal Reserve Bank of San Francisco ( “ FRBSF ” ). Also, see Note 7, Borrowings. Related Party Loans The Bank has, and expects to have in the future, banking transactions in the ordinary course of its business with directors, officers, principal shareholders and their businesses or associates. These transactions, including loans, are granted on substantially the same terms, including interest rates and collateral on loans, as those prevailing at the same time for comparable transactions with persons not related to us. Likewise, these transactions do not involve more than the normal risk of collectability or present other unfavorable features. During the first and fourth quarters of 2017, two new directors joined our Board of Directors resulting in the reclassification of existing loans to those directors and their businesses as related party status. An analysis of net loans to related parties for each of the three years ended December 31, 2017 , 2016 and 2015 is as follows: (in thousands) 2017 2016 2015 Balance at beginning of year $ 1,988 $ 2,562 $ 3,329 Additions 3,186 — — Advances 74 — 165 Repayments (128 ) (574 ) (390 ) Reclassified due to a change in borrower status 6,732 — (542 ) Balance at end of year $ 11,852 $ 1,988 $ 2,562 Undisbursed commitments to related parties totaled $9.1 million and $1.1 million as of December 31, 2017 and 2016 , respectively.

Bank Premises and Equipment

Bank Premises and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Bank Premises and Equipment	Bank Premises and Equipment A summary of Bank premises and equipment at December 31 follows: (in thousands) 2017 2016 Leasehold improvements $ 14,937 $ 13,883 Furniture and equipment 11,113 10,627 Subtotal 26,050 24,510 Accumulated depreciation and amortization (17,438 ) (15,990 ) Bank premises and equipment, net $ 8,612 $ 8,520 The amount of depreciation and amortization totaled $1.9 million , $1.8 million , and $2.0 million for the years ended December 31, 2017 , 2016 and 2015 , respectively.

Bank Owned Life Insurance

Bank Owned Life Insurance	12 Months Ended
	Dec. 31, 2017
Insurance [Abstract]
Bank Owned Life Insurance	Bank Owned Life Insurance We own life insurance policies on the lives of certain officers designated by the Board of Directors to fund our employee benefit programs, and death benefits provided under the specific terms of these insurance policies are estimated to be $81.9 million at December 31, 2017 . The benefits to employees' beneficiaries are limited to the employee's active service period. The investment in bank owned life insurance policies are reported in interest receivable and other assets at their cash surrender value of $38.1 million and $32.4 million at December 31, 2017 and 2016 , respectively. The cash surrender value includes both the original premiums paid for the life insurance policies and the accumulated accretion of policy income since inception of the policies. Income of $845 thousand , $844 thousand and $814 thousand was recognized on the life insurance policies in 2017 , 2016 and 2015 , respectively. We regularly monitor the credit ratings of our insurance carriers to ensure that they comply with our policy.

Deposits

Deposits	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Deposits	Deposits A stratification of time deposits at December 31, 2017 and 2016 is presented in the following table: (in thousands) December 31, 2017 December 31, 2016 Time deposits of less than $100 thousand $ 39,361 $ 36,346 Time deposits of $100 thousand to $250 thousand 68,391 66,092 Time deposits of more than $250 thousand 52,364 49,025 Total time deposits $ 160,116 $ 151,463 Interest on time deposits was $576 thousand , $743 thousand and $853 thousand in 2017 , 2016 and 2015 , respectively. Scheduled maturities of time deposits at December 31, 2017 are presented as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Scheduled maturities of time deposits $ 108,352 $ 13,000 $ 10,511 $ 18,976 $ 9,276 $ 1 $ 160,116 As of December 31, 2017 , $107.8 million in securities held-to-maturity were pledged as collateral for our local agency deposits. Our deposit portfolio includes deposits offered through the Promontory Interfinancial Network that are comprised of Certificate of Deposit Account Registry Service ® ("CDARS") balances included in time deposits and Insured Cash Sweep ® ("ICS") balances included in money market deposits. In addition, in 2016, we began offering deposits through Reich & Tang Deposit Networks, LLC, comprised of Demand Deposit Marketplace SM ("DDM") balances, mostly in money market deposits. Through these two networks we are able to offer our customers access to FDIC-insured deposit products in aggregate amounts exceeding current insurance limits. When we place funds through CDARS, ICS and DDM, on behalf of a customer, we have the option of receiving matching deposits through the network's reciprocal deposit program. We consider the reciprocal deposits to be in-market deposits as distinguished from traditional out-of-market brokered deposits. We had $13.5 million and $15.1 million in CDARS and $41.0 million and $29.0 million in ICS balances in the reciprocal deposit program at December 31, 2017 and 2016 , respectively. In addition, we had $29.2 million and $36.4 million in DDM balances in the reciprocal deposit program at December 31, 2017 and 2016, respectively. We also have the ability to place deposits through the networks for which we receive no matching deposits ("one-way" deposits). One-way CDARS and ICS deposits totaled $4.2 million and $361 thousand at December 31, 2017 and 2016 , respectively. The aggregate amount of deposit overdrafts that have been reclassified as loan balances was $224 thousand and $229 thousand at December 31, 2017 and 2016 , respectively. Collectability of these overdrafts is subject to the same credit review process as other loans. The Bank accepts deposits from shareholders, directors and employees in the normal course of business, and the terms are comparable to those with non-affiliated parties. The total deposits from directors and their businesses, and executive officers were $29.9 million and $7.3 million at December 31, 2017 and 2016 , respectively.

Borrowings

Borrowings	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Borrowings	Borrowings Federal Funds Purchased – The Bank had unsecured lines of credit with correspondent banks for overnight borrowings totaling $100.4 million at December 31, 2017 (including $8.4 million assumed from Bank of Napa) and $92.0 million at December 31, 2016 . In general, interest rates on these lines approximate the federal funds target rate. We had no overnight borrowings under these credit facilities at December 31, 2017 and December 31, 2016 . Federal Home Loan Bank Borrowings – As of December 31, 2017 and 2016 , the Bank had lines of credit with the FHLB totaling $538.9 million and $513.7 million , respectively, based on eligible collateral of certain loans. There were no FHLB overnight borrowings at December 31, 2017 or 2016 . On February 5, 2008, the Bank entered into a ten -year borrowing agreement under the same FHLB line of credit for $15.0 million at a fixed rate of 2.07% . On June 15, 2016, the Bank repaid the $15.0 million early and incurred a prepayment fee of $312 thousand recorded in interest expense. At December 31, 2017 and 2016 , $538.9 million and $513.7 million , respectively, were remaining as available for borrowing from the FHLB. Federal Reserve Line of Credit – The Bank has a line of credit with the FRBSF secured by certain residential loans. At December 31, 2017 and 2016 , the Bank had borrowing capacity under this line totaling $52.1 million and $43.1 million , respectively, and had no outstanding borrowings with the FRBSF. As part of an acquisition, Bancorp assumed two subordinated debentures due to NorCal Community Bancorp Trusts I and II (the "Trusts"), established for the sole purpose of issuing trust preferred securities on September 22, 2003 and December 29, 2005, respectively. The subordinated debentures were recorded at fair values totaling $4.95 million at acquisition date with contractual values totaling $8.2 million . The difference between the contractual balance and the fair value at acquisition date is accreted into interest expense over the lives of the debentures. Accretion on the subordinated debentures totaled $153 thousand , $191 thousand and $210 thousand in 2017 , 2016 and 2015 , respectively. Bancorp has the option to defer payment of the interest on the subordinated debentures for a period of up to five years, as long as there is no default on the subordinated debentures. In the event of interest deferral, dividends to Bancorp common stockholders are prohibited. The trust preferred securities were sold and issued in private transactions pursuant to an exemption from registration under the Securities Act of 1933, as amended. Bancorp has guaranteed, on a subordinated basis, distributions and other payments due on trust preferred securities totaling $8.0 million issued by the Trusts, which have identical maturity, repricing and payment terms as the subordinated debentures. The following is a summary of the contractual terms of the subordinated debentures due to the Trusts as of December 31, 2017 : (in thousands) Subordinated debentures due to NorCal Community Bancorp Trust I on October 7, 2033 with interest payable quarterly, based on 3-month LIBOR plus 3.05%, repricing quarterly (4.41% as of December 31, 2017), redeemable, in whole or in part, on any interest payment date $ 4,124 Subordinated debentures due to NorCal Community Bancorp Trust II on March 15, 2036 with interest payable quarterly, based on 3-month LIBOR plus 1.40%, repricing quarterly (2.99% as of December 31, 2017), redeemable, in whole or in part, on any interest payment date 4,124 Total $ 8,248 Borrowings at December 31, 2017 and 2016 are summarized as follows: 2017 2016 (dollars in thousands) Carrying Value Average Balance Average Rate Carrying Value Average Balance Average Rate FHLB overnight borrowings $ — $ 1 1.75 % $ — $ 5,383 0.42 % FHLB fixed-rate advances $ — $ — — % $ — $ 6,803 6.59 % 1 Subordinated debentures $ 5,739 $ 5,664 7.65 % $ 5,586 $ 5,493 7.80 % 1 Average rate includes the impact of the $312 thousand prepayment fee in 2016 discussed above.

Stockholders' Equity and Stock

Stockholders' Equity and Stock Plans	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity and Stock Plans	Stockholders' Equity and Stock Plans Share-Based Awards On May 11, 2010, our shareholders approved the 2010 Director Stock Plan to pay director fees in shares of Bancorp common stock up to 150,000 shares. In addition to cash compensation, we issued 2,878 , 4,607 and 5,295 shares of common under the 2010 Director Stock Plan to directors in 2017 , 2016 and 2015 , respectively. As of December 31, 2017 , 110,433 shares were available for future grants under this plan. On September 27, 2017, the Board of Directors adopted the 2017 Employee Stock Purchase Plan, effective July 1, 2017, which replaced the 2007 Employee Stock Purchase Plan. Under the plan, our employees may purchase Bancorp common shares through payroll deductions of between one percent and fifteen percent of pay in each pay period. Shares are purchased quarterly at a five percent discount from the closing market price on the last day of the quarter. Of the 200,000 common shares set aside for employee purchases, there were 192,453 shares available for future grants under the plan as of December 31, 2017 . Shares purchased under the 2017 plan are restricted until the plan is approved by our shareholders. On March 17, 2017, the Board of Directors approved the 2017 Equity Plan, which was affirmed by Bancorp's shareholders on May 16, 2017 and replaced the 2007 Equity Plan. As of the 2017 Equity Plan's effective date, there were 118,668 shares of common stock available for future grants to employees, advisors and non-employee directors. As of December 31, 2017 , there were 108,981 shares available for future grants under the 2017 Equity Plan. The Compensation Committee of the Board of Directors has the discretion to determine which employees, advisors and non-employee directors will receive an award, the timing of awards, the vesting schedule for each award, the type of award to be granted, the number of shares of Bancorp stock to be subject to each option and restricted stock award, and any other terms and conditions. Options are issued at an exercise price equal to the fair value of the stock at the date of grant. Options and restricted stock awarded to officers and employees during 2006 through 2014 vest 20% on each anniversary of the grant date for five years and expire ten years from the grant date. Options granted to non-employee directors prior to 2016 vest 20% immediately and 20% on each anniversary of the grant date for four years and expire seven years from the grant date. In general, options granted after 2014 for employees and after 2015 for non-employee directors generally vest by one-third on each anniversary of the grant for three years and expire ten years from the grant date. Options issued as replacement awards in connection with the Bank of Napa acquisition were fully vested as part of the merger agreement with Bank of Napa. Stock options may be net settled by a reduction in the number of shares otherwise deliverable upon exercise in satisfaction of the exercise payment and applicable tax withholding requirements. During 2017, we withheld 12,208 shares totaling $801 thousand at a weighted-average price of $65.63 for cashless stock option exercises. There were no stock options exercised under net settlement arrangements in 2016 or 2015. Shares withheld under net settlement arrangements are available for future grants. Beginning in 2015, performance-based stock awards were issued to a selected group of employees. Stock award vesting is contingent upon the achievement of pre-established long-term performance goals set by the Compensation Committee of the Board of Directors. Performance is measured over a three -year period and cliff vested. These performance-based stock awards were granted at a maximum opportunity level, and based on the achievement of the pre-established goals, the actual payouts can range from 0% to 200% of the target award. For performance-based stock awards, an estimate is made of the number of shares expected to vest based on the probability that the performance criteria will be achieved to determine the amount of compensation expense to be recognized. The estimate is re-evaluated quarterly and total compensation expense is adjusted for any change in the current period. A summary of activity for stock options for the years ended December 31, 2017 , 2016 and 2015 is presented below. The intrinsic value of options outstanding and exercisable is calculated as the number of in-the-money options times the difference between the market price of our stock as of each year-end presented and the exercise prices of the in-the-money options. Number of Shares Weighted Average Exercise Price Aggregate Intrinsic Value (in thousands) Weighted Average Grant-Date Fair Value Weighted Average Remaining Contractual Term (in years) Options outstanding at December 31, 2014 194,672 $ 35.14 $ 3,398 4.48 Granted 28,320 50.70 $ 12.21 Cancelled, expired or forfeited (652 ) 48.38 Exercised (37,071 ) 30.72 755 Options outstanding at December 31, 2015 185,269 38.35 2,788 5.00 Exercisable (vested) at December 31, 2015 114,581 34.12 2,209 3.21 Options outstanding at December 31, 2015 185,269 38.35 2,788 5.00 Granted 32,637 49.37 10.11 Exercised (36,117 ) 33.98 661 Options outstanding at December 31, 2016 181,789 41.20 5,190 5.77 Exercisable (vested) at December 31, 2016 103,211 36.65 3,416 4.18 Options outstanding at December 31, 2016 181,789 41.20 5,190 5.77 Granted 1 100,664 39.78 32.61 Cancelled, expired or forfeited (2,011 ) 43.97 Exercised (21,474 ) 38.62 585 Options outstanding at December 31, 2017 258,968 40.84 7,075 5.34 Exercisable (vested) at December 31, 2017 192,172 35.69 6,212 4.42 1 Includes 70,145 replacement stock option awards issued in the Acquisition with a $27.20 weighted average exercise price and a $40.71 weighted average grant-date fair value. See Note 18, Acquisition. The following table summarizes non-vested restricted stock awards and changes during the years ended December 31, 2017 , 2016 and 2015 . Number of Shares Weighted Average Grant-Date Fair Value Non-vested awards at December 31, 2014 22,423 $ 41.25 Granted 15,970 50.75 Vested (6,555 ) 40.00 Forfeited (450 ) 48.45 Non-vested awards at December 31, 2015 31,388 46.24 Granted 16,910 49.65 Vested (8,599 ) 44.14 Non-vested awards at December 31, 2016 39,699 48.15 Granted 16,230 69.59 Vested (10,321 ) 45.78 Non-vested awards at December 31, 2017 45,608 56.31 A summary of the options outstanding and exercisable by price range as of December 31, 2017 is presented in the following table: Stock Options Outstanding as of December 31, 2017 Stock Options Exercisable as of December 31, 2017 Range of Exercise Prices Stock Options Outstanding Remaining Contractual Life (in years) Weighted Average Exercise Price Stock Options Exercisable Weighted Average Exercise Price $10.00 - $20.00 14,120 2.1 $ 17.74 14,120 $ 17.74 $20.01 - $30.00 51,731 1.1 26.05 51,731 26.05 $30.01 - $40.00 70,363 5.3 35.53 68,238 35.41 $40.01 - $50.00 64,511 7.1 46.14 33,224 44.73 $50.01 - $60.00 27,724 6.9 50.70 18,200 50.70 $60.01 - $70.00 30,519 9.3 68.68 6,659 65.46 258,968 192,172 We determine the fair value of stock options at the grant date using the Black-Scholes pricing model that takes into account the stock price at the grant date, the exercise price, and the following assumptions (weighted-average shown). Years ended December 31, 2017 2016 2015 Risk-free interest rate 1.66 % 1.37 % 1.67 % Expected dividend yield on common stock 1.70 % 2.02 % 1.75 % Expected life in years 2.4 6.0 6.0 Expected price volatility 25.58 % 25.56 % 28.06 % The fair value of stock options on the grant date is recorded as a stock-based compensation expense in the consolidated statements of comprehensive income over the requisite service period with a corresponding increase in common stock. Stock-based compensation also includes compensation expense related to the issuance of restricted stock awards. The grant-date fair value of the restricted stock awards, which equals intrinsic value on that date, is being recorded as compensation expense over the requisite service period. Total compensation cost for these share-based payment arrangements was $1.3 million , $994 thousand and $636 thousand during 2017 , 2016 and 2015 , respectively, and the total recognized deferred tax benefits related thereto were $293 thousand , $318 thousand and $194 thousand , respectively. As of December 31, 2017 , there was $1.5 million of total unrecognized compensation expense related to non-vested stock options and restricted stock awards. This cost is expected to be recognized over a weighted-average period of approximately 2.1 years. The total grant-date fair value of stock options vested during the years ended December 31, 2017 , 2016 and 2015 was $449 thousand , $282 thousand and $202 thousand , respectively. The total grant-date fair value of restricted stock awards vested during 2017 , 2016 and 2015 was $473 thousand , $380 thousand and $262 thousand , respectively. We adopted ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting effective January 1, 2017 as discussed in Note 1 , which requires us to record excess tax benefits (deficiencies) resulting from the exercise of non-qualified stock options, the disqualifying disposition of incentive stock options and vesting of restricted stock awards as income tax benefits (expense) in the consolidated statements of comprehensive income with a corresponding decrease (increase) to current taxes payable. For the year ended December 31, 2017 , we recognized $214 thousand in excess tax benefits recorded as a reduction to income tax expense related to these types of transactions. Prior to the adoption of this ASU, excess tax benefits (deficiencies) were recognized as an increase (decrease) to common stock in the consolidated statements of changes in stockholders' equity. The tax benefits realized from disqualifying dispositions of incentive stock options were recognized in tax expense to the extent of the book compensation cost recorded. Total tax benefits from disqualifying dispositions of incentive stock options recognized during 2016 and 2015 were $70 thousand and $49 thousand , respectively. Dividends Presented below is a summary of cash dividends paid to common shareholders, recorded as a reduction of retained earnings. On January 19, 2018, the Board of Directors declared a cash dividend of $0.29 per share, payable on February 9, 2018 to shareholders of record at the close of business on February 2, 2018. Years ended December 31, (in thousands except per share data) 2017 2016 2015 Cash dividends to common stockholders $ 6,896 $ 6,223 $ 5,390 Cash dividends per common share $ 1.12 $ 1.02 $ 0.90 The holders of unvested restricted stock awards and performance-based stock awards are entitled to dividends on the same per-share ratio as holders of common stock. Upon the adoption of ASU No. 2016-09, tax benefits on dividends paid on unvested restricted stock awards are recorded as tax benefits in the consolidated statements of comprehensive income with a corresponding decrease to current taxes payable. Dividends on forfeited awards are included in stock-based compensation expense. Prior to the adoption of ASU No. 2016-09, tax benefits on dividends were recognized as an increase to common stock in the consolidated statements of changes in stockholders' equity. Under the California Corporations Code, payment of dividends by Bancorp to its shareholders is restricted to the amount of retained earnings immediately prior to the distribution or the amount of assets that exceeds the total liabilities immediately after the distribution. As of December 31, 2017 , Bancorp's retained earnings and the amount of assets that exceeds the total liabilities were $155.5 million and $297.0 million , respectively. Under the California Financial Code, payment of dividends by the Bank to Bancorp is restricted to the lesser of retained earnings or the amount of undistributed net profits of the Bank from the three most recent fiscal years. Under this restriction, approximately $39.9 million of the Bank's retained earnings balance was available for payment of dividends to Bancorp as of December 31, 2017 . Bancorp held $3.2 million in cash at December 31, 2017 . This cash, combined with the $39.9 million dividends available to be distributed from the Bank, is expected to be adequate to cover Bancorp's estimated operational needs and cash dividends to shareholders for 2018. Preferred Stock and Shareholder Rights Plan On July 6, 2017, Bancorp adopted a new shareholder rights agreement (“Rights Agreement”), which replaced the existing Rights Agreement that expired on July 23, 2017. The Rights Agreement, which expires on July 23, 2022, is designed to discourage takeovers that involve abusive tactics or do not provide fair value to shareholders. The Rights Agreement defines the percentage of share ownership of an "acquiring person" as 10% of the outstanding common shares. Each right entitles the registered holder to purchase from Bancorp one one-hundredth of a share of Series A Junior Participating Preferred Stock, no par value, of Bancorp at an initial price of $90 per one one-hundredth of a preferred share, subject to adjustment upon the occurrence of certain events. As of December 31, 2017, Bancorp was authorized to issue five million shares of preferred stock with no par value, one million shares of which have been designated as Series A Junior Participating Preferred Stock, with no par value under the Rights Agreement. In the event of a proposed merger, tender offer or other attempt to gain control of Bancorp that the Board of Directors does not approve, the Board of Directors may authorize the issuance of shares of common or preferred stock that would impede the completion of such a transaction. An effect of the possible issuance of common or preferred stock, therefore, may be to deter a future takeover attempt. The Board of Directors has no present plans or understandings for the issuance of any common or preferred stock in connection with the Rights Agreement. Warrant Under the United States Department of the Treasury Capital Purchase Program (the “TCPP”), Bancorp issued to the U.S. Treasury a warrant to purchase 154,242 shares of common stock at a per share exercise price of $27.23 . The warrant was immediately exercisable and was subsequently auctioned to two institutional investors in November 2011. The warrant, as adjusted, represented the right to purchase 157,711 shares of common stock at $26.63 per share when it was exercised in September 2015 and the cashless exercise resulted in the issuance of 70,591 shares of common stock.

Fair Value of Assets and Liabil

Fair Value of Assets and Liabilities	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value of Assets and Liabilities	Fair Value of Assets and Liabilities Fair Value Hierarchy and Fair Value Measurement We group our assets and liabilities that are measured at fair value in three levels within the fair value hierarchy, based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. These levels are: Level 1: Valuations are based on unadjusted quoted prices in active markets for identical assets or liabilities. Level 2: Valuations are based on quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuations for which all significant assumptions are observable or can be corroborated by observable market data. Level 3: Valuations are based on unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Values are determined using pricing models and discounted cash flow models and may include significant Management judgment and estimation. Transfers between levels of the fair value hierarchy are recognized through our monthly and/or quarterly valuation process in the reporting period during which the event or circumstances that caused the transfer occurred. The following table summarizes our assets and liabilities that were required to be recorded at fair value on a recurring basis. (in thousands) Description of Financial Instruments Carrying Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2017 Securities available for sale: Mortgage-backed securities and collateralized mortgage obligations issued by U.S. government agencies $ 188,061 $ — $ 188,061 $ — SBA-backed securities $ 25,982 $ — $ 25,817 $ 165 Debentures of government sponsored agencies $ 12,938 $ — $ 12,938 $ — Privately-issued collateralized mortgage obligations $ 1,431 $ — $ 1,431 $ — Obligations of state and political subdivisions $ 97,491 $ — $ 97,491 $ — Corporate bonds $ 6,564 $ — $ 6,564 $ — Derivative financial assets (interest rate contracts) $ 74 $ — $ 74 $ — Derivative financial liabilities (interest rate contracts) $ 740 $ — $ 740 $ — December 31, 2016 Securities available for sale: Mortgage-backed securities and collateralized mortgage obligations issued by U.S. government agencies $ 253,434 $ — $ 253,434 $ — SBA-backed securities $ 607 $ — $ — $ 607 Debentures of government sponsored agencies $ 35,403 $ — $ 35,403 $ — Privately-issued collateralized mortgage obligations $ 419 $ — $ 419 $ — Obligations of state and political subdivisions $ 77,701 $ — $ 77,701 $ — Corporate bonds $ 5,016 $ — $ 5,016 $ — Derivative financial assets (interest rate contracts) $ 55 $ — $ 55 $ — Derivative financial liabilities (interest rate contracts) $ 933 $ — $ 933 $ — Securities available-for-sale are recorded at fair value on a recurring basis. When available, quoted market prices (Level 1) are used to determine the fair value of securities available-for-sale. If quoted market prices are not available, we obtain pricing information from a reputable third-party service provider, who may utilize valuation techniques that use current market-based or independently sourced parameters, such as bid/ask prices, dealer-quoted prices, interest rates, benchmark yield curves, prepayment speeds, probability of default, loss severity and credit spreads (Level 2). Level 2 securities include obligations of state and political subdivisions, U.S. agencies or government-sponsored agencies' debt securities, mortgage-backed securities, government agency-issued, privately-issued collateralized mortgage obligations and corporate bonds. As of December 31, 2017 and 2016 , there were no securities that were considered Level 1 securities. As of December 31, 2017 , we have one available-for-sale security that is considered a Level 3 security. The security is a U.S. government agency obligation collateralized by a small number of business equipment loans guaranteed by the Small Business Administration ("SBA") program. This security is not actively traded and is owned only by a few investors. The significant unobservable data that is reflected in the fair value measurement include dealer quotes, projected prepayment speeds/average life and credit information, among other things. The unrealized loss on this SBA-guaranteed security decreased by $6 thousand in 2017 recorded as part of other comprehensive income. Securities held-to-maturity may be written down to fair value (determined using the same techniques discussed above for securities available-for-sale) as a result of an other-than-temporary impairment, and we did not record any write-downs during 2017 or 2016 . On a recurring basis, derivative financial instruments are recorded at fair value, which is based on the income approach using observable Level 2 market inputs, reflecting market expectations of future interest rates as of the measurement date. Standard valuation techniques are used to calculate the present value of the future expected cash flows assuming an orderly transaction. Valuation adjustments may be made to reflect both our own credit risk and the counterparties’ credit risk in determining the fair value of the derivatives. Level 2 inputs for the valuations are limited to observable market prices for London Interbank Offered Rate (“LIBOR”) and Overnight Index Swap ("OIS") rates (for the very short term), quoted prices for LIBOR futures contracts, observable market prices for LIBOR and OIS swap rates, and one-month and three-month LIBOR basis spreads at commonly quoted intervals. Mid-market pricing of the inputs is used as a practical expedient in the fair value measurements. We project spot rates at reset days specified by each swap contract to determine future cash flows, then discount to present value using either LIBOR or OIS curves depending on whether the swap positions are fully collateralized as of the measurement date. When the value of any collateral placed with counterparties is less than the interest rate derivative liability, a credit valuation adjustment ("CVA") is applied to reflect the credit risk we pose to counterparties. We have used the spread between the Standard & Poor's BBB rated U.S. Bank Composite rate and LIBOR for the closest maturity term corresponding to the duration of the swaps to derive the CVA. A similar credit risk adjustment, correlated to the credit standing of the counterparty, is made when collateral posted by the counterparty does not fully cover their liability to the Bank. For further discussion on our methodology in valuing our derivative financial instruments, refer to Note 14, Derivative Financial Instruments and Hedging Activities . Certain financial assets may be measured at fair value on a non-recurring basis. These assets can be subject to fair value adjustments that result from the application of the lower of cost or fair value accounting or write-downs of individual assets, such as impaired loans and other real estate owned ("OREO"). In addition, assets acquired or liabilities assumed from business combinations are measured at fair value at the date of acquisition. Refer to Note 18 for details of fair value measurement used in association with business combinations. The following table presents the carrying value of assets and liabilities measured at fair value on a non-recurring basis and that were held in the consolidated statements of condition at each respective period end, by level within the fair value hierarchy as of December 31, 2017 and 2016 . (in thousands) Description of Financial Instruments Carrying Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2017 None $ — $ — $ — $ — December 31, 2016 Other real estate $ 408 $ — $ — $ 408 When a loan is identified as impaired, it is reported at the lower of cost or fair value, measured based on the loan's observable market price (Level 1) or the current net realizable value of the underlying collateral securing the loan, if the loan is collateral dependent (Level 3). Net realizable value of the underlying collateral is the fair value of the collateral less estimated selling costs and any prior liens. Appraisals, recent comparable sales, offers and listing prices are factored in when valuing the collateral. We review and verify the qualifications and licenses of the certified general appraisers used for appraising commercial properties or certified residential appraisers for residential properties. Real estate appraisals may utilize a combination of approaches including replacement cost, sales comparison and the income approach. Comparable sales and income data are analyzed by the appraisers and adjusted to reflect differences between them and the subject property such as property characteristics, leasing status and physical condition. When appraisals are received, Management reviews the underlying assumptions and methodology utilized, as well as the overall resulting value in conjunction with independent data sources such as recent market data and industry-wide statistics. We generally use a 6% discount for selling costs which is applied to all properties, regardless of size. Appraised values may be adjusted to reflect changes in market conditions that have occurred subsequent to the appraisal date, or for revised estimates regarding the timing or cost of the property sale. These adjustments are based on qualitative judgments made by Management on a case-by-case basis and are generally unobservable valuation inputs as they are specific to the underlying collateral. There have been no significant changes in the valuation techniques during 2017 . OREO represents collateral acquired through foreclosure and is initially recorded at fair value as established by a current appraisal, adjusted for disposition costs. Subsequently, OREO is measured at lower of cost or fair value. OREO values are reviewed on an ongoing basis and any subsequent decline in fair value is recorded as a foreclosed asset expense in the current period. The value of OREO is determined based on independent appraisals, similar to the process used for impaired loans, discussed above, and is classified as Level 3. All OREO had been acquired through business combinations and were sold as of December 31, 2017. Disclosures about Fair Value of Financial Instruments The table below is a summary of fair value estimates for financial instruments as of December 31, 2017 and 2016 , excluding financial instruments recorded at fair value on a recurring basis (summarized in the first table in this note). The carrying amounts in the following table are recorded in the consolidated statements of condition under the indicated captions. Further, we have not disclosed the fair value of financial instruments specifically excluded from disclosure requirements of the Financial Instruments Topic of the Codification (ASC 825-10-50-8), such as BOLI. Additionally, we hold shares of FHLB stock and Visa Inc. Class B common stock at cost. These shares are restricted from resale and their values were discussed in Note 2, Investment Securities , above. December 31, 2017 December 31, 2016 (in thousands) Carrying Amounts Fair Value Fair Value Hierarchy Carrying Amounts Fair Value Fair Value Hierarchy Financial assets: Cash and cash equivalents $ 203,545 $ 203,545 Level 1 $ 48,804 $ 48,804 Level 1 Investment securities held-to-maturity 151,032 151,032 Level 2 44,438 45,097 Level 2 Loans, net 1,663,246 1,650,198 Level 3 1,471,174 1,473,360 Level 3 Interest receivable 7,501 7,501 Level 2 6,319 6,319 Level 2 Financial liabilities: Deposits 2,148,670 2,148,050 Level 2 1,772,700 1,773,102 Level 2 Subordinated debentures 5,739 5,118 Level 3 5,586 5,083 Level 3 Interest payable 191 191 Level 2 134 134 Level 2 Following is a description of methods and assumptions used to estimate the fair value of each class of financial instrument not recorded at fair value but required for disclosure purposes: Cash and Cash Equivalents - The carrying amounts of cash and cash equivalents approximate their fair value because of the short-term nature of these instruments. Held-to-maturity Securities - Held-to-maturity securities, which generally consist of obligations of state and political subdivisions and corporate bonds, are recorded at their amortized cost. Their fair value for disclosure purposes is determined using methodologies similar to those described above for available-for-sale securities using Level 2 inputs. If Level 2 inputs are not available, we may utilize pricing models that incorporate unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities (Level 3). As of December 31, 2017 and 2016 , we did not hold any held-to-maturity securities whose fair value was measured using significant unobservable inputs. Loans - The fair value of loans with variable interest rates approximates their current carrying value, because their rates are regularly adjusted to current market rates. The fair value of fixed rate loans or variable loans at negotiated interest rate floors or ceilings with remaining maturities in excess of one year is estimated by discounting the future cash flows using current market rates at which similar loans would be made to borrowers with similar creditworthiness and similar remaining maturities. The allowance for loan losses (“ALLL”) is considered to be a reasonable estimate of the portion of loan discount attributable to credit risks. Interest Receivable and Payable - The interest receivable and payable balances approximate their fair value due to the short-term nature of their settlement dates. Deposits - The fair value of deposits without stated maturity, such as transaction accounts, savings accounts and money market accounts, is the amount payable on demand at the reporting date. The fair value of time deposits is estimated by discounting the future cash flows using current rates offered for deposits of similar remaining maturities. Subordinated Debentures - The fair values of the subordinated debentures were estimated by discounting the future cash flows (interest payment at a rate of three-month LIBOR plus 3.05% and 1.40% ) to their present values using current market rates at which similar bonds would be issued with similar credit ratings as ours and similar remaining maturities. Each interest payment was discounted at the spot rate of the corresponding term, determined based on the yields and terms of comparable trust preferred securities, plus a liquidity premium. In July 2010, the Dodd-Frank Act was signed into law and limits the ability of certain bank holding companies to treat trust preferred security debt issuances as Tier 1 capital. This law effectively closed the trust-preferred securities markets for new issuances and led to the absence of observable or comparable transactions in the market place. Due to the use of unobservable inputs of trust preferred securities, we consider the fair value to be a Level 3 measurement. See Note 7, Borrowings for further information. Commitments - The value of unrecognized financial instruments is estimated based on the fee income associated with the commitments which, in the absence of credit exposure, is considered to approximate their settlement value. The fair value of commitment fees was not material as of December 31, 2017 and 2016 , respectively.

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Benefit Plans	Benefit Plans In 2003, we established a Deferred Compensation Plan that allows certain key Management personnel designated by the Board of Directors of the Bank to defer up to 80% of their salary and 100% of their annual bonus. The plan was amended in 2007 in order to comply with the most recent Internal Revenue Code Section 409A changes. Under the amended plan, amounts deferred earn interest that is equal to the prime rate as published in the Wall Street Journal, on the first business day of the year, which was 3.75% on January 1, 2017, 3.50% on January 1, 2016 and 3.25% on January 1, 2015. Our deferred compensation obligation totaled $3.4 million and $3.2 million at December 31, 2017 and 2016 , respectively, and is included in interest payable and other liabilities. Our 401(k) Defined Contribution Plan (the “401(k) Plan”) commenced in May 1990 and is available to all regular employees at least eighteen years of age who complete ninety days of service, and enter the plan during one of the four open enrollment dates (January 1, April 1, July 1, and October 1) of each year. Under the 401(k) Plan, employees can defer between 1% and 50% of their eligible compensation, up to the maximum amount allowed by the Internal Revenue Code. Contributions to the 401(k) Plan for the employer match are vested at a rate of 20% per year over a five year period. In 2015 and 2016, the Bank matched 60% of each participant's contribution, with a maximum of $4 thousand of matching contribution per participant per year. In 2017, the Bank increased the match to 70% of each participant's contribution, with a maximum of $5 thousand of matching contribution per participant per year. Employer contributions totaled $765 thousand , $589 thousand and $555 thousand for the years ended December 31, 2017 , 2016 and 2015 , respectively. In 1999, the 401(k) Plan was amended to include an employee stock ownership component and was renamed the Bank of Marin Employee Stock Ownership and Savings Plan (the “Plan”). Under the terms of the Plan, as amended, the Board of Directors determines a specific portion of the Bank's profits to be contributed to the employee stock ownership each year either in common stock or in cash for the purchase of Bancorp stock to be allocated to all eligible employees based on a percentage of their salaries, regardless of whether an employee is participating in the 401(k) plan or not. In January 2010, the Bank of Marin Employee Stock Ownership and Savings Plan was split into two plans: Bank of Marin 401(k) Plan and Bank of Marin Employee Stock Ownership Plan ("ESOP"). The same eligibility criteria apply under the ESOP, while employees' contributions are not permitted. For all participants, employer contributions vest over a five year period of service. After five years of service, all employer contributions vest immediately. The Bank of Marin 401(k) Plan was amended in early 2016 to incorporate recent changes in the pension laws, and was amended again in November 2016 to include a Roth 401(k) option. The Bank contributed cash in the amount of $1.2 million in 2016 and $1.1 million in 2015 to the ESOP, which purchased Bancorp stock at market prices. Starting in 2017, Bancorp issued shares of common stock and contributed them to the ESOP and recognized $1.2 million in expense, based on the quoted market price on the date of contribution. Cash dividends paid on Bancorp stock held by the ESOP are used to purchase additional shares in the open market. All shares of Bancorp stock held by the ESOP are included in the calculations of basic and diluted earnings per share. The employer contributions to the ESOP and the 401(k) Plan are included in salaries and benefits expense. On January 1, 2011, we established a Salary Continuation Plan for a select group of Executive Management, who will receive twenty-five percent of their estimated salary at retirement as salary continuation benefit payments upon retirement. Each participant will need to participate in this plan for five years before vesting begins. After five years, the participant will vest ratably in the benefit over the remaining period until age 65 . This Plan is unfunded and nonqualified for tax purposes and for purposes of Title I of the Employee Retirement Income Security Act of 1974. As part of the acquisition of Bank of Napa in November 2017, we assumed the salary continuation agreements for four former executive officers of Bank of Napa. Under these agreements, fixed annual retirement benefit payments will be made for ten years beginning the first day of the month following the executive reaching the age of 65 . At December 31, 2017 and 2016 , respectively, our liability under the Salary Continuation Plan was $2.5 million (including $1.2 million assumed from Bank of Napa) and $1.0 million recorded in interest payable and other liabilities.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The current and deferred components of the income tax provision for each of the three years ended December 31 are as follows: (in thousands) 2017 2016 2015 Current tax provision Federal $ 5,379 $ 9,710 $ 7,097 State 2,623 3,794 2,931 Total current 8,002 13,504 10,028 Deferred tax provision (benefit) Federal 4,444 (206 ) 382 State 416 48 80 Total deferred 4,860 (158 ) 462 Total income tax provision $ 12,862 $ 13,346 $ 10,490 On December 22, 2017, the Tax Cuts and Jobs Act of 2017 was signed into law. The law reduces the federal corporate income tax rate to 21% for tax years beginning on or after January 1, 2018. Due to the enactment of the Tax Cuts and Jobs Act of 2017, the Bank has valued all of its deferred tax assets and liabilities at the 21% rate. The adjustment to the net deferred tax assets valuation as of December 22, 2017 was $3.0 million and has been recorded in the provision for income taxes in the fourth quarter of 2017. The following table shows the tax effect of our cumulative temporary differences as of December 31: (in thousands) 2017 2016 Deferred tax assets: Allowance for loan losses and off-balance sheet credit commitments $ 4,945 $ 6,871 Net operating loss carryforwards 2,629 3,582 Net unrealized loss on securities available-for-sale 1,405 2,543 Deferred compensation plan and salary continuation plan 1,744 1,773 State franchise tax 557 1,300 Accrued but unpaid expenses 212 1,251 Fair value adjustment on acquired loans 570 799 Deferred rent and other lease incentives 328 547 Depreciation and disposals on premises and equipment 632 528 Other real estate owned — 448 Stock-based compensation 463 398 Interest received on non-accrual loans 130 185 Other 266 196 Total gross deferred tax assets 13,881 20,421 Deferred tax liabilities: Deferred loan origination costs and fees (2,153 ) (2,784 ) Unaccreted discount on subordinated debentures (742 ) (1,119 ) Core deposit intangible asset (1,919 ) (1,085 ) Accretion on investment securities (56 ) (54 ) Other (221 ) (42 ) Total gross deferred tax liabilities (5,091 ) (5,084 ) Net deferred tax assets $ 8,790 $ 15,337 As of December 31, 2017 , federal and California net operating loss carryforwards ("NOLs") of $5.1 million and $18.1 million , respectively, corresponded to the total $2.6 million deferred tax asset above. If not fully utilized, the federal NOLs will begin to expire in 2030, and the California NOLs will begin to expire in 2028. Based upon the level of historical taxable income and projections for future taxable income over the periods during which the deferred tax assets are expected to be deductible, Management believes it is more likely than not we will realize the benefit of the remaining deferred tax assets. Accordingly, no valuation allowance has been established as of December 31, 2017 or 2016 . The effective tax rate for 2017 , 2016 and 2015 differs from the current federal statutory income tax rate as follows: 2017 2016 2015 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % Increase (decrease) due to: California franchise tax, net of federal tax benefit 6.9 % 6.8 % 6.8 % Write down of federal deferred tax assets, net 1 10.5 % — % — % Tax exempt interest on municipal securities and loans (6.1 )% (4.0 )% (4.2 )% Tax exempt earnings on bank owned life insurance (1.0 )% (0.8 )% (1.0 )% Non-deductible acquisition related expenses 0.8 % — % — % Low income housing and qualified zone academy bond tax credits (0.4 )% (0.3 )% (0.2 )% Stock-based compensation excess tax benefit 2 (0.3 )% — % — % Other (0.8 )% (0.1 )% (0.1 )% Effective Tax Rate 44.6 % 36.6 % 36.3 % 1 Due to the enactment of the Tax Cuts and Jobs Act of 2017, which reduces the federal corporate income tax rate to 21% for tax years beginning on or after January 1, 2018, we wrote down net deferred tax assets as of December 22, 2017 by $3.0 million and has been recorded in income tax expense in 2017. 2 Due to the adoption of ASU 2016-09 in 2017, all excess (or deficient) tax benefits associated with stock-based compensation awards are recognized as income tax benefit (expense). Bancorp and the Bank have entered into a tax allocation agreement, which provides that income taxes shall be allocated between the parties on a separate entity basis. The intent of this agreement is that each member of the consolidated group will incur no greater tax liability than it would have incurred on a stand-alone basis. We file a consolidated return in the U.S. Federal tax jurisdiction and a combined return in the State of California tax jurisdiction. There were no ongoing federal or state income tax examinations at the issuance of this report. We are no longer subject to examinations by tax authorities for years before 2014 for federal income tax and before 2013 for California. At December 31, 2017 and 2016, there were no unrecognized tax benefits, and neither the Bank nor Bancorp had accruals for interest and penalties related to unrecognized tax benefits.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies We rent certain premises under long-term, non-cancelable operating leases expiring at various dates through the year 2032. Most of the leases contain certain renewal options and escalation clauses. At December 31, 2017 , the approximate minimum future commitments payable under non-cancelable contracts for leased premises are as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Operating leases 1 $ 4,444 $ 4,198 $ 3,758 $ 2,138 $ 1,330 $ 2,904 $ 18,772 1 Minimum payments have not been reduced by minimum sublease rentals of $51 thousand due in the future under non-cancelable subleases. Rent expense included in occupancy expense totaled $4.1 million in 2017 and $3.9 million in 2016 and $4.2 million 2015 . Litigation Matters We may be party to legal actions, which arise from time to time as part of the normal course of our business. We believe, after consultation with legal counsel, that we have meritorious defenses in these actions, and that litigation contingent liability, if any, will not have a material adverse effect on our financial position, results of operations, or cash flows. We are responsible for our proportionate share of certain litigation indemnifications provided to Visa U.S.A. ("Visa") by its member banks in connection with lawsuits related to anti-trust charges and interchange fees ("Covered Litigation"). In 2012, Visa had reached a $4.0 billion interchange multidistrict litigation class settlement agreement for which it maintains an escrow account to be used for settlements or judgments in the Covered Litigation. At December 31, 2017 , according to Visa's Form 10-Q filed on February 1, 2018, the escrow account balance was $828 million . While the accrued liability related to the Covered Litigation could be higher or lower than the litigation escrow account balance, Visa did not record an additional accrual for the Covered Litigation during 2017. In 2017, a number of class plaintiffs filed amended complaints for damages or filed new class complaints against Visa for injunctive relief. In addition, Wal-Mart Stores, Inc. entered into a new, unconditional settlement agreement with Visa in October 2017. As of the date of Visa's filing, it had reached settlement agreements with individual merchants representing 51% of the Visa-branded payment card sales volume of merchants who opted out of the 2012 settlement agreement. Litigation is ongoing and until the appeal process is complete, Visa is uncertain whether it will resolve the claims as contemplated by the settlement agreement and additional lawsuits may arise. The conversion rate of Visa Class B common stock held by us to Class A common stock (as discussed in Note 2, Investment Securities) may decrease if Visa makes more Covered Litigation settlement payments in the future, and the full effect on member banks is still uncertain. However, we are not aware of significant future cash settlement payments required by us on the Covered Litigation.

Concentrations of Credit Risk

Concentrations of Credit Risk	12 Months Ended
	Dec. 31, 2017
Risks and Uncertainties [Abstract]
Concentrations of Credit Risk	Concentrations of Credit Risk Concentration of credit risk is the risk associated with a lack of diversification, such as having substantial investments in a few individual issuers, thereby exposing us to greater risks resulting from adverse economic, political, regulatory, geographic, industrial or credit developments. Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash and cash equivalents, investment securities and loans. Our cash in correspondent bank accounts, at times, may exceed FDIC insured limits. We place cash and cash equivalents with high quality financial institutions, periodically monitor their credit worthiness and limit the amount of credit exposure with any one institution according to regulations. Concentrations of credit risk with respect to investment securities are limited to the U.S. Government, its agencies and Government Sponsored Enterprises ("GSEs") and was $358.4 million , or 74% of our total investment portfolio at December 31, 2017 and $299.5 million , or 72% at December 31, 2016 . We also manage our credit exposure related to our loan portfolio to avoid the risk of undue concentration of credits in a particular industry by reducing significant exposure to highly leveraged transactions or to any individual customer or counterparty, and by obtaining collateral as appropriate. No individual borrower accounts for more than 2% of loans held in the portfolio. The largest loan concentration group by industry of the borrowers is real estate, which accounts for 81% and 79% of our loan portfolio at December 31, 2017 and 2016 , respectively.

Derivative Financial Instrument

Derivative Financial Instruments and Hedging Activities	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments and Hedging Activities	Derivative Financial Instruments and Hedging Activities We have entered into interest rate swap agreements, primarily as an asset/liability management strategy, in order to mitigate the changes in the fair value of specified long-term fixed-rate loans (or firm commitments to enter into long-term fixed-rate loans) caused by changes in interest rates. These hedges allow us to offer long-term fixed rate loans to customers without assuming the interest rate risk of a long-term asset. Converting our fixed-rate interest payments to floating-rate interest payments, generally benchmarked to the one-month U.S. dollar LIBOR index, protects us against changes in the fair value of our loans associated with fluctuating interest rates. Our credit exposure, if any, on interest rate swap asset positions is limited to the fair value (net of any collateral pledged to us) and interest payments of all swaps by each counterparty. Conversely, when an interest rate swap is in a liability position exceeding a certain threshold, we may be required to post collateral to the counterparty in an amount determined by the agreements. Collateral levels are monitored and adjusted on a regular basis for changes in interest rate swap values. As of December 31, 2017 , we had five interest rate swap agreements, which are scheduled to mature in June 2031, October 2031, July 2032, August 2037 and October 2037. All of our derivatives are accounted for as fair value hedges. The notional amounts of the interest rate contracts are equal to the notional amounts of the hedged loans. Our interest rate swap payments are settled monthly with counterparties. Accrued interest on the swaps totaled $8 thousand and $13 thousand as of December 31, 2017 and 2016 , respectively. Information on our derivatives follows: Asset derivatives Liability derivatives (in thousands) December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 Fair value hedges: Interest rate contracts notional amount $ 4,019 $ 4,217 $ 14,810 $ 15,495 Interest rate contracts fair value 1 $ 74 $ 55 $ 740 $ 933 Years ended December 31, (in thousands) 2017 2016 2015 Increase in value of designated interest rate swaps due to LIBOR interest rate movements recognized in interest income $ 212 $ 778 $ 280 Payment on interest rate swaps recorded in interest income (333 ) (556 ) (918 ) Decrease in value of hedged loans recognized in interest income (166 ) (571 ) (308 ) Decrease in value of yield maintenance agreement recognized against interest income (15 ) (94 ) (52 ) Net loss on derivatives recognized against interest income 2 $ (302 ) $ (443 ) $ (998 ) 1 See Note 9, Fair Value of Assets and Liabilities for valuation methodology. 2 Includes hedge ineffectiveness gain of $31 thousand , gain of $113 thousand and loss of $80 thousand for the years December 31, 2017 , 2016 and 2015 , respectively. Changes in value of swaps were included in the assessment of hedge effectiveness. Hedge ineffectiveness is the measure of the extent to which the change in the fair value of the hedging instruments does not exactly offset the change in the fair value of the hedged items from period to period. Our derivative transactions with counterparties are under International Swaps and Derivative Association (“ISDA”) master agreements that include “right of set-off” provisions. “Right of set-off” provisions are legally enforceable rights to offset recognized amounts and there may be an intention to settle such amounts on a net basis. We do not offset such financial instruments for financial reporting purposes. Information on financial instruments that are eligible for offset in the consolidated statements of condition follows: Offsetting of Financial Assets and Derivative Assets Gross Amounts Not Offset in the Statements of Condition Gross Amounts Net Amounts Gross Amounts Offset in the of Assets Presented of Recognized Statements of in the Statements Financial Cash Collateral (in thousands) Assets 1 Condition of Condition 1 Instruments Received Net Amount December 31, 2017 Derivatives by Counterparty: Counterparty A $ 74 $ 74 $ (74 ) $ — Total $ 74 $ — $ 74 $ (74 ) $ — $ — December 31, 2016 Derivatives by Counterparty: Counterparty A $ 55 $ — $ 55 $ (55 ) $ — $ — Total $ 55 $ — $ 55 $ (55 ) $ — $ — 1 Amounts exclude accrued interest totaling $0.3 thousand and $1 thousand at December 31, 2017 and December 31, 2016 , respectively. Offsetting of Financial Liabilities and Derivative Liabilities Gross Amounts Not Offset in the Statements of Condition Gross Amounts Net Amounts of Gross Amounts Offset in the Liabilities Presented of Recognized Statements of in the Statements of Financial Cash Collateral (in thousands) Liabilities 2 Condition Condition 2 Instruments Pledged Net Amount December 31, 2017 Derivatives by Counterparty: Counterparty A $ 740 $ 740 $ (74 ) (666 ) $ — Total $ 740 $ — $ 740 $ (74 ) $ (666 ) $ — December 31, 2016 Derivatives by Counterparty: Counterparty A $ 933 $ — $ 933 $ (55 ) $ (878 ) $ — Total $ 933 $ — $ 933 $ (55 ) $ (878 ) $ — 2 Amounts exclude accrued interest totaling $8 thousand and $12 thousand at December 31, 2017 and December 31, 2016 , respectively.

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Regulatory Matters	Regulatory Matters We are subject to various regulatory capital requirements administered by the federal banking agencies. Failure to meet minimum capital requirements as set forth in the tables below can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a material effect on our consolidated financial statements. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, we must meet specific capital guidelines that involve quantitative measures of our assets, liabilities, and certain off-balance sheet items as calculated under regulatory accounting practices. The capital amounts and the Bank’s prompt corrective action classification are also subject to qualitative judgments by the regulators about components of capital, risk weightings and other factors. Capital ratios are reviewed by Management on a regular basis to ensure that capital exceeds the prescribed regulatory minimums and is adequate to meet our anticipated future needs. For all periods presented, the Bank’s ratios exceed the regulatory definition of “well capitalized” under the regulatory framework for prompt corrective action and Bancorp’s ratios exceed the required minimum ratios to be considered a well capitalized bank holding company. In addition, the most recent notification from the FDIC categorized the Bank as well capitalized under the regulatory framework for prompt corrective action as of December 31, 2017. There are no conditions or events since that notification that Management believes have changed the Bank’s categories and we expect the Bank to remain well capitalized for prompt corrective action purposes. In July 2013, the Board of Governors of the Federal Reserve System, the Federal Deposit Insurance Corporation and the Office of the Comptroller of the Currency ("Agencies") finalized regulatory capital rules known as “Basel III.” The rules became effective beginning January 2015, and will be fully phased-in by January 2019. The guidelines, among other things, changed the minimum capital requirements of banks and bank holding companies, by increasing the Tier 1 capital to risk-weighted assets ratio to 6% , and introduced a new requirement to maintain a minimum ratio of common equity Tier 1 capital to risk-weighted assets of 4.5% . By 2019, when fully phased in, the rules will require further increases to certain minimum capital requirements and a capital conservation buffer of an additional 2.5% of risk-weighted assets. In August 2017, the Agencies published a final rule ("transitions NPR") halting the phase-in of certain Basel III capital rules for banks not using the Basel advanced approaches. The rule extends the regulatory capital treatment applicable during 2017 under the regulatory capital rules for certain items. These items include regulatory capital deductions, risk weights, and certain minority interest limitations. This effectively pauses the full transition to the Basel III treatment of mortgage servicing assets, certain deferred tax assets, investments in the capital of unconsolidated financial institutions and minority interests while the Agencies pursue more extensive rulemaking to simplify the treatment of assets. The transitions NPR that was effective January 1, 2018 does not apply to Bank of Marin. We have modeled our ratios under fully phased-in Basel III rules and, based on present facts, we do not expect that we will be required to raise additional capital as a result of the fully phased-in rules. The Bancorp’s and Bank's capital adequacy ratios as of December 31, 2017 and 2016 are presented in the following tables. Bancorp's Tier 1 capital includes the subordinated debentures, which are not included at the Bank level. We continued to build capital in 2017 through stock issued in the Bank of Napa acquisition and the accumulation of net income. Capital Ratios for Bancorp (dollars in thousands) Actual Ratio Adequately Capitalized Threshold 1 Ratio to be a Well Capitalized Bank Holding Company December 31, 2017 Amount Ratio Amount Ratio Amount Ratio Total Capital (to risk-weighted assets) $ 287,435 14.91 % ≥ $ 178,323 ≥ 9.250 % ≥ $ 192,782 ≥ 10.000 % Tier 1 Capital (to risk-weighted assets) $ 270,710 14.04 % ≥ $ 139,767 ≥ 7.250 % ≥ $ 154,225 ≥ 8.000 % Tier 1 Capital (to average assets) $ 270,710 12.13 % ≥ $ 89,285 ≥ 4.000 % ≥ $ 111,607 ≥ 5.000 % Common Equity Tier 1 (to risk-weighted assets) $ 265,119 13.75 % ≥ $ 110,849 ≥ 5.750 % ≥ $ 125,308 ≥ 6.500 % December 31, 2016 Total Capital (to risk-weighted assets) $ 247,453 14.32 % ≥ $ 149,039 ≥ 8.625 % ≥ $ 172,799 ≥ 10.000 % Tier 1 Capital (to risk-weighted assets) $ 231,111 13.37 % ≥ $ 114,479 ≥ 6.625 % ≥ $ 138,239 ≥ 8.000 % Tier 1 Capital (to average assets) $ 231,111 11.39 % ≥ $ 81,189 ≥ 4.000 % ≥ $ 101,486 ≥ 5.000 % Common Equity Tier 1 (to risk-weighted assets) $ 225,925 13.07 % ≥ $ 88,559 ≥ 5.125 % ≥ $ 112,319 ≥ 6.500 % 1 The 2017 and 2016 adequately capitalized thresholds include the capital conservation buffer that was effective January 1, 2016 and January 1, 2017, respectively. These ratios are not reflected on a fully phased-in basis. Capital Ratios for the Bank (dollars in thousands) Actual Ratio Adequately Capitalized Threshold 1 Ratio to be Well Capitalized under Prompt Corrective Action Provisions December 31, 2017 Amount Ratio Amount Ratio Amount Ratio Total Capital (to risk-weighted assets) $ 283,885 14.73 % ≥ $ 178,281 ≥ 9.250 % ≥ $ 192,737 ≥ 10.000 % Tier 1 Capital (to risk-weighted assets) $ 267,160 13.86 % ≥ $ 139,734 ≥ 7.250 % ≥ $ 154,189 ≥ 8.000 % Tier 1 Capital (to average assets) $ 267,160 11.97 % ≥ $ 89,275 ≥ 4.000 % ≥ $ 111,593 ≥ 5.000 % Common Equity Tier 1 (to risk-weighted assets) $ 267,160 13.86 % ≥ $ 110,824 ≥ 5.750 % ≥ $ 125,279 ≥ 6.500 % December 31, 2016 Total Capital (to risk-weighted assets) $ 243,468 14.09 % ≥ $ 149,016 ≥ 8.625 % ≥ $ 172,772 ≥ 10.000 % Tier 1 Capital (to risk-weighted assets) $ 222,127 13.15 % ≥ $ 114,462 ≥ 6.625 % ≥ $ 138,218 ≥ 8.000 % Tier 1 Capital (to average assets) $ 222,127 11.19 % ≥ $ 81,176 ≥ 4.000 % ≥ $ 101,469 ≥ 5.000 % Common Equity Tier 1 (to risk-weighted assets) $ 222,127 13.15 % ≥ $ 88,546 ≥ 5.125 % ≥ $ 112,302 ≥ 6.500 % 1 The 2017 and 2016 adequately capitalized thresholds include the capital conservation buffer that was effective January 1, 2016 and January 1, 2017, respectively. These ratios are not reflected on a fully phased-in basis.

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Financial Instruments with Off-Balance Sheet Risk	Financial Instruments with Off-Balance Sheet Risk We make commitments to extend credit in the normal course of business to meet the financing needs of our customers. These financial instruments include commitments to extend credit in the form of loans or through standby letters of credit. Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. Because various commitments will expire without being fully drawn upon, the total commitment amount does not necessarily represent future cash requirements. We are exposed to credit loss equal to the contractual amount of the commitment in the event of nonperformance by the borrower. We use the same credit underwriting criteria for all credit exposure. The amount of collateral obtained, if deemed necessary by us, is based on Management's credit evaluation of the borrower. Collateral types pledged may include accounts receivable, inventory, other personal property and real property. The contractual amount of undrawn loan commitments and standby letters of credit not reflected on the consolidated statements of condition are as follows: (in thousands) December 31, 2017 December 31, 2016 Commercial lines of credit $ 224,370 $ 216,774 Revolving home equity lines 177,678 148,143 Undisbursed construction loans 35,322 44,798 Personal and other lines of credit 11,758 10,635 Standby letters of credit 4,074 1,939 Total commitments and standby letters of credit $ 453,202 $ 422,289 We record an allowance for losses on these off-balance sheet commitments based on an estimate of probabilities of these commitments being drawn upon according to the historical utilization experience on different types of commitments and expected loss. We set aside an allowance for losses on off-balance sheet commitments in the amount of $958 thousand and $899 thousand as of December 31, 2017 and 2016 , respectively, which is recorded in interest payable and other liabilities on the consolidated statements of condition. Approximately 44% of the commitments expire in 2018, approximately 41% expire between 2019 and 2025 and approximately 15% expire thereafter.

Condensed Bank of Marin Bancorp

Condensed Bank of Marin Bancorp Parent Only Financial Statements	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Bank of Marin Bancorp Parent Only Financial Statements	Condensed Bank of Marin Bancorp Parent Only Financial Statements Presented below is financial information for Bank of Marin Bancorp, parent holding company only. CONDENSED UNCONSOLIDATED STATEMENTS OF CONDITION December 31, 2017 and 2016 (in thousands) 2017 2016 Assets Cash and due from Bank of Marin $ 3,246 $ 3,568 Investment in bank subsidiary 299,486 232,431 Other assets 586 670 Total assets $ 303,318 $ 236,669 Liabilities and Stockholders' Equity Subordinated debentures $ 5,739 $ 5,586 Accrued expenses payable 146 96 Other liabilities 408 424 Total liabilities 6,293 6,106 Stockholders' equity 297,025 230,563 Total liabilities and stockholders' equity $ 303,318 $ 236,669 CONDENSED UNCONSOLIDATED STATEMENTS OF INCOME Years ended December 31, 2017, 2016 and 2015 (in thousands) 2017 2016 2015 Income Dividends from bank subsidiary $ 8,000 $ 6,400 $ 6,500 Miscellaneous Income 8 7 6 Total income 8,008 6,407 6,506 Expense Interest expense 439 435 420 Non-interest expense 2,087 984 973 Total expense 2,526 1,419 1,393 Income (loss) before income taxes and equity in undistributed net income of subsidiary 5,482 4,988 5,113 Income tax benefit 876 594 583 Income (loss) before equity in undistributed net income of subsidiary 6,358 5,582 5,696 Earnings of bank subsidiary greater (less) than dividends received from bank subsidiary 9,618 17,552 12,745 Net income $ 15,976 $ 23,134 $ 18,441 CONDENSED UNCONSOLIDATED STATEMENTS OF CASH FLOWS Years ended December 31, 2017, 2016 and 2015 (in thousands) 2017 2016 2015 Cash Flows from Operating Activities: Net income $ 15,976 $ 23,134 $ 18,441 Adjustments to reconcile net income to net cash provided by (used in) operating activities: Earnings of bank subsidiary greater than dividends received from bank subsidiary (9,618 ) (17,552 ) (12,745 ) Net change in operating assets and liabilities: Accretion of discount on subordinated debentures 153 191 210 Other assets 92 353 (298 ) Intercompany receivable (40 ) 171 (18 ) Other liabilities 51 (302 ) 368 Noncash director compensation expense - common stock 20 — — Net cash provided by operating activities 6,634 5,995 5,958 Cash Flows from Investing Activities: Capital contribution to subsidiary (853 ) (1,285 ) (1,156 ) Net cash used in investing activities (853 ) (1,285 ) (1,156 ) Cash Flows from Financing Activities: Proceeds from stock options exercised and stock issued under employee and director stock purchase plans and ESOP 853 1,285 1,156 Payment of tax withholdings for stock options exercised (60 ) — — Dividends paid on common stock (6,896 ) (6,223 ) (5,390 ) Net cash used by financing activities (6,103 ) (4,938 ) (4,234 ) Net (decrease) increase in cash and cash equivalents (322 ) (228 ) 568 Cash and cash equivalents at beginning of period 3,568 3,796 3,228 Cash and cash equivalents at end of period $ 3,246 $ 3,568 $ 3,796 Supplemental schedule of non-cash investing and financing activities: Stock issued in payment of director fees $ 188 $ 234 $ 275

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisition	Acquisition On November 21, 2017, we completed the merger of Bank of Napa, N.A. (OTCQB: BNNP), to enhance our market presence in Napa, California. Bank of Napa was a national bank with two branch offices serving Napa. The acquisition added $134.7 million in loans, $249.9 million in deposits and $75.5 million in investment securities to Bank of Marin as of the acquisition date. Bank of Napa shareholders received 0.307 shares of Bancorp common stock for each share of Bank of Napa common stock outstanding. The acquisition of Bank of Napa constituted a business combination and has been accounted for using the acquisition method of accounting. The assets acquired and liabilities assumed, both tangible and intangible, were recorded at their fair values as of the acquisition date in accordance with ASC 805, Business Combinations . The acquisition was treated as a "reorganization" within the definition of section 368(a) of the Internal Revenue Code and is generally considered tax-free for U.S. federal income tax purposes. The following table reflects the estimated fair values of the assets acquired and liabilities assumed related to the acquisition: (dollars in thousands) Acquisition Date November 21, 2017 Assets: Cash and cash equivalents $ 59,779 Investment securities 75,469 Loans 134,720 Core deposit intangible 4,441 Goodwill 23,705 Bank premises and equipment 599 Other assets 6,408 Total assets acquired $ 305,121 Liabilities: Deposits: Non-interest bearing $ 77,266 Interest bearing Transaction accounts 50,080 Savings accounts 12,157 Money market accounts 85,045 Other time accounts 25,338 Total deposits 249,886 Other liabilities 2,050 Total liabilities assumed $ 251,936 Merger consideration of $53,185 (735,264 common shares and 70,145 shares of replacement stock options issued by Bank of Marin Bancorp). $ 53,185 The following table presents the net assets acquired from Bank of Napa, consideration paid and the estimated fair value adjustments: (dollars in thousands) Acquisition Date November 21, 2017 Book value of net assets acquired from Bank of Napa $ 26,152 Fair value adjustments: Loans 1,301 Core deposit intangible asset 4,441 Total purchase accounting adjustments 5,742 Deferred tax liabilities (tax effect of purchase accounting adjustments at 42.05%) (2,414 ) Fair value of net assets acquired from Bank of Napa $ 29,480 Merger consideration $ 53,185 Less: fair value of net assets acquired (29,480 ) Goodwill $ 23,705 Goodwill As a result of the Bank of Napa acquisition, we recorded $23.7 million in goodwill, which represents the excess of the total purchase price paid over the fair value of the assets acquired, net of the fair values of liabilities assumed. Goodwill mainly reflects expected value created through the combined operations of Bank of Napa and Bank of Marin. It is evaluated for impairment annually. We determined that the fair value of our traditional community banking activities (provided through our branch network) exceeded the carrying amount of the bank-level reporting unit. Therefore, no impairment on goodwill was recorded in 2017 . The goodwill is not deductible for tax purposes. The following is a description of the methods used to determine the fair values of significant assets and liabilities whose fair values are different from their carrying amounts on Bank of Napa's books at acquisition date presented above. Loans The fair values for acquired loans were developed based upon the present values of the expected cash flows utilizing market-derived discount rates. Expected cash flows for each acquired loan were projected based on contractual cash flows adjusted for expected prepayment, expected default (i.e. probability of default and loss severity), and principal recovery. Prepayment rates were applied to the principal outstanding based on the type of loan, where appropriate. Prepayments were based on a constant prepayment rate (“CPR”) applied across the life of a loan. For performing loans, we used annual CPRs between 5 percent and 27 percent , depending on the characteristics of the loan pool (e.g. construction, commercial real estate, etc.). For classified loans, no prepayment was assumed and applied. Non-PCI loans were valued on a loan-by-loan basis when applying the discount rate on the expected cash flows. The discount rates used were based on current market rates for new originations of comparable loans, where available, and include adjustments for credit and illiquidity premium. To the extent comparable market rates are not readily available, a discount rate was derived based on the assumptions of a market participant's cost of funds, capital charge, servicing costs, and return requirements for comparable risk assets. PCI loans were also valued on an individual basis. The following table presents the fair value of loans acquired from Bank of Napa for PCI loans as of the acquisition date (November 21, 2017): (in thousands) PCI loans Contractually required payments including interest $ 1,769 Less: contractual cash flows not expected to be collected (nonaccretable difference) 805 Cash flows expected to be collected (undiscounted) 964 Less: interest component of cash flows expected to be collected (accretable yield) 109 Fair value of PCI loans $ 855 The following table presents the fair value of loans acquired from Bank of Napa for non-PCI loans as of the acquisition date (November 21, 2017): (in thousands) Non-PCI loans Contractually required payments including interest $ 183,833 Contractual cash flows not expected to be collected $ 14,227 Fair value of non-PCI loans $ 133,865 The following table reflects the outstanding balance and related fair value of PCI loans as of the acquisition date: PCI Loans (in thousands) Unpaid principal balance Fair value Commercial $ 417 $ 70 Commercial real estate 1,070 785 Total purchased credit-impaired loans $ 1,487 $ 855 Core Deposit Intangible The core deposit intangible represents the estimated future benefits of acquired deposits and is booked separately from the related deposits. The value of the core deposit intangible asset was determined using a discounted cash flow approach to arrive at the cost differential between the core deposits (non-maturity deposits such as transaction, savings and money market accounts) and alternative funding sources. It was calculated as the present value of the difference in cash flows between maintaining the core deposits (interest and net maintenance costs) and the cost of an equal amount of funds with a similar term from an alternative source. The core deposit intangible is amortized on an accelerated basis over an estimated ten -year life, and is evaluated periodically for impairment. No impairment loss was recognized in 2017 . We recorded a core deposit intangible asset of $4.4 million at acquisition, of which $56 thousand was amortized in 2017 . At December 31, 2017 , the future estimated amortization expense on the CDI from the Bank of Napa acquisition is as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Core deposit intangible amortization $ 508 $ 499 $ 488 $ 475 $ 460 $ 1,955 $ 4,385 Pro Forma Results of Operations The first column of the following table presents the former Bank of Napa's operations and its actual contribution to our net interest income and net income included in our consolidated statement of comprehensive income from the acquisition date (November 21, 2017) through December 31, 2017. The table also presents pro forma information of the combined entity as if the acquisition occurred on January 1, 2016. The pro forma information does not necessarily reflect the results of operations that would have resulted had the acquisition been completed at the beginning of the periods presented, nor is it indicative of the results of operations in future periods. Furthermore, cost savings and other business synergies related to the acquisition are not reflected in the pro forma amounts. Pro Forma Revenue and Earnings (in thousands) Actual from acquisition date through December 31, 2017 2017 2016 Net interest income $ 913 $ 82,802 $ 80,898 Net (loss) Income $ (576 ) 1 $ 18,898 2 $ 21,559 2 1 Bank of Napa's net loss from November 21, 2017 through December 31, 2017 includes acquisition-related costs, accretion of the discount on acquired loans and core deposit intangible amortization. 2 2017 pro forma combined net income was adjusted to exclude acquisition related costs of $2.2 million incurred by Bank of Marin Bancorp and $2.5 million incurred by Bank of Napa. 2016 pro forma combined earnings were adjusted to include these acquisition related costs as if the merger occurred on January 1, 2016. Acquisition-related expenses are recognized as incurred and continue until all systems have been converted and operational functions become fully integrated. Bank of Marin Bancorp incurred acquisition-related expenses in the consolidated statements of comprehensive income in 2017 for the Bank of Napa acquisition as follows: (in thousands) Year Ended December 31, 2017 Data processing 1 $ 1,108 Professional services 952 Personnel severance 35 Other 114 Total $ 2,209 1 Primarily relates to Bank of Napa's core processing system contract termination and deconversion fees.

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation : The consolidated financial statements include the accounts of Bank of Marin Bancorp (“Bancorp”), a bank holding company, and its wholly-owned bank subsidiary, Bank of Marin (the “Bank”), a California state-chartered commercial bank. References to “we,” “our,” “us” mean Bancorp and the Bank that are consolidated for financial reporting purposes. All material intercompany transactions have been eliminated. We have evaluated subsequent events through the date of filing with the Securities and Exchange Commission (“SEC”) and have determined that there are no subsequent events that require additional recognition or disclosure. The NorCal Community Bancorp Trusts I and II, respectively (the "Trusts"), were formed for the sole purpose of issuing trust preferred securities. Bancorp is not considered the primary beneficiary of the Trusts (variable interest entities), therefore the Trusts are not consolidated in our consolidated financial statements, but rather the subordinated debentures are shown as a liability on our consolidated statements of condition (See Note 7, Borrowings). Bancorp's investment in the securities of the Trusts is accounted for under the equity method and is included in interest receivable and other assets on the consolidated statements of condition.
Cash and Cash Equivalents	Cash and Cash Equivalents include cash, due from banks, federal funds sold and other short-term investments with maturity less than three months at the time of origination.
Investment Securities	Investment Securities are classified as "held-to-maturity," "trading securities" or "available-for-sale." Investments classified as held-to-maturity are those that we have the ability and intent to hold until maturity and are reported at cost, adjusted for the amortization or accretion of premiums or discounts. Investments held for resale in anticipation of short-term market movements are classified as trading securities and are reported at fair value, with unrealized gains and losses included in earnings. Investments that are neither held-to-maturity nor trading are classified as available-for-sale and are reported at fair value. Unrealized gains and losses for available-for-sale securities, net of related tax, are reported as a separate component of comprehensive income and included in stockholders' equity until realized. For discussion of our methodology in determining fair value, see Note 9, Fair Value of Assets and Liabilities. Securities transferred from the available-for-sale category to the held-to-maturity category are recorded at fair value at the date of transfer. Unrealized holding gains or losses associated with the transfer of securities from available-for-sale to held-to-maturity are included in the balance of accumulated other comprehensive income (loss), net of tax, in the consolidated balance sheets. These unrealized holding gains or losses are amortized over the remaining life of the security as a yield adjustment in a manner consistent with the amortization or accretion of the original purchase premium or discount on the associated security. At each financial statement date, we assess whether declines in the fair value of held-to-maturity and available-for-sale securities below their costs are deemed to be other-than-temporary. We consider, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer, and (iii) our intent and ability to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value. Evidence evaluated includes, but is not limited to, the remaining payment terms of the instrument and economic factors that are relevant to the collectability of the instrument, such as: current prepayment speeds, the current financial condition of the issuer(s), industry analyst reports, credit ratings, credit default rates, interest rate trends, the quality of any credit enhancement and the value of any underlying collateral. For each security in an unrealized loss position ("impaired security"), we assess whether we intend to sell the security or if it is more likely than not that we will be required to sell the security before recovery of its amortized cost basis. If we intend to sell the security or it is more likely than not we will be required to sell the security before recovery of its amortized cost basis, the entire difference between the investment’s amortized cost basis and its fair value at the balance sheet date is recognized against earnings. For impaired securities that are not intended for sale and will not be required to be sold prior to recovery of our amortized cost basis, we determine if the impairment has a credit loss component. For both held-to-maturity and available-for-sale securities, if the amount of cash flows expected to be collected are less than the amortized cost, an other-than-temporary impairment shall be considered to have occurred and the credit loss component is recognized against earnings as the difference between present value of the expected future cash flows and the amortized cost. In determining the present value of the expected cash flows, we discount the expected cash flows at the effective interest rate implicit in the security at the date of purchase. The remaining difference between the fair value and the amortized basis is deemed to be due to factors that are not credit related and is recognized in other comprehensive income, net of applicable taxes. For held-to-maturity securities, if there is no credit loss component, no impairment is recognized. The portion of other-than-temporary impairment recognized in other comprehensive income for credit impaired debt securities classified as held-to-maturity is accreted from other comprehensive income to the amortized cost of the debt security over the remaining life of the debt security in a prospective manner on the basis of the amount and timing of future estimated cash flows. Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the effective interest method. In March 2017, the Financial Accounting Standards Board ("FASB") issued ASU No. 2017-08, Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities . The amendments in this ASU shorten the amortization period for certain callable debt securities purchased at a premium and require the premium to be amortized to the earliest call date. The ASU is effective for annual periods beginning after December 15, 2018, including interim periods within those periods. We early adopted this ASU effective January 1, 2017, which did not have a material impact on our financial condition and results of operations. Dividend and interest income are recognized when earned. Realized gains and losses on the sale of securities and credit losses related to other-than-temporary impairment on available-for-sale and held-to-maturity securities are included in non-interest income as gains (losses) on investment securities, net. The specific identification method is used to calculate realized gains and losses on sales of securities.
Originated Loans	Originated Loans are reported at the principal amount outstanding net of deferred fees (costs), charge-offs and the allowance for loan losses (“ALLL”). Interest income is accrued daily using the simple interest method. Loans are placed on non-accrual status when Management believes that there is doubt as to the collection of principal or interest, generally when they become contractually past due by ninety days or more with respect to principal or interest, except for loans that are well-secured and in the process of collection. When loans are placed on non-accrual status, any accrued but uncollected interest is reversed from current-period interest income. Non-accrual loans may be returned to accrual status when one of the following occurs: • The borrower has resumed paying the full amount of the principal and interest and we are satisfied with the borrower's financial position. In order to meet this test, we must have received repayment of all past due principal and interest unless the amounts contractually due are reasonably assured of repayment within a reasonable period of time, and there has been a sustained period of repayment performance (generally, six consecutive monthly payments), according to the original contractual terms or modified terms for loans whose contractual terms have been restructured in a manner which grants a concession to a borrower experiencing financial difficulties (“troubled debt restructuring”). • The loan has become well secured and is in the process of collection. Loan origination fees and commitment fees, offset by certain direct loan origination costs, are deferred and amortized as yield adjustments over the contractual lives of the related loans.
Loan Charge-Off Policy	Loan Charge-Off Policy: For all loan types excluding overdraft accounts, we generally make a charge-off determination at or before 90 days past due. A collateral-dependent loan is partially charged down to the fair value of collateral securing it if: (1) it is deemed uncollectable, or (2) it has been classified as a loss by either our internal loan review process or external examiners. A non-collateral-dependent loan is partially charged down to its net realizable value under the same circumstances. Overdraft accounts are generally charged off when they exceed 60 days past due.
Acquired Loans	Acquired Loans : Acquired loans are recorded at their estimated fair values at acquisition date in accordance with Accounting Standards Code ("ASC") 805, Business Combinations , factoring in credit losses expected to be incurred over the life of the loan. Accordingly, an allowance for loan losses is not carried over or recorded for acquired loans as of the acquisition date. We estimated the fair value of acquired loans at the acquisition date based on a discounted cash flow methodology that considered factors including the type of loan and related collateral, risk classification, fixed or variable interest rate, term of loan, whether or not the loan was amortizing, and current discount rates. Loans, except for purchased credit impaired ("PCI") loans, were grouped together according to similar risk characteristics and treated in the aggregate when applying various valuation techniques. Expected cash flows incorporated our best estimate of key assumptions at the time, such as property values, default rates, loss severity and prepayment speeds. Discount rates were based on market rates for new originations of comparable loans, where available, and included adjustments for liquidity factors. To the extent comparable market rates were not readily available, a discount rate was derived based on the assumptions of market participants' cost of funds, servicing costs and return requirements for comparable risk assets. In either case, the discount rate did not include a factor for credit losses, as that had been considered in estimating the cash flows. The process of calculating fair values of acquired loans, including estimates of losses expected to be incurred over the estimated remaining lives of the loans at acquisition date and ongoing updates to Management's expectation of future cash flows, requires significant subjective judgments and assumptions. The economic environment and lack of market liquidity and transparency are factors that have influenced, and may continue to affect, these assumptions and estimates. We acquired loans with evidence of significant credit quality deterioration subsequent to their origination and for which it was probable, at acquisition, that we would be unable to collect all contractually required payments. Management applied significant subjective judgment in determining which loans were PCI loans. Evidence of credit quality deterioration as of the purchase date may include data such as past due and nonaccrual status, risk grades and charge-off history. The difference between the undiscounted expected cash flows expected to be collected and the fair value at acquisition date ("accretable difference") is accreted into interest income at a level yield of return over the estimated remaining life of the PCI loan, provided that the timing and amount of future cash flows is reasonably estimable. The accretable yield is affected by: • Changes in interest rate indices for variable rate loans – Expected future cash flows are based on the variable rates in effect at the time of the regular evaluations of cash flows expected to be collected; • Changes in prepayment assumptions – Prepayments affect the estimated life of the loans which may change the amount of interest income, and possibly principal, expected to be collected; and • Changes in the expected principal and interest payments over the estimated life – Updates to expected cash flows are driven by the credit outlook and actions taken with borrowers. Changes in expected future cash flows from loan modifications are included in the regular evaluations of cash flows expected to be collected. The cash flows expected to be collected are updated each quarter based on current assumptions regarding default rates, loss severities, and other factors that are reflective of current financial conditions of the borrowers and the market conditions. Probable decreases in expected cash flows after acquisition result in impairment recorded as a specific allowance for loan losses or a charge-off to the allowance. Impairment is calculated as the present value of the expected future cash flows on the PCI loan, discounted at the loan's effective interest rate implicit in the loan. The nonaccretable difference on the date of acquisition is defined as the difference between the contractually required payments and the cash flows expected to be collected, considering the result of prepayments, and is not recorded. For purposes of accounting for the PCI loans from past business combinations, we elected not to apply the pooling method but to account for these loans individually. Disposals of loans, which may include sales of loans to third parties, receipt of payments in full by the borrower, or foreclosure of the collateral, result in removal of the loan from the PCI loan portfolio at its carrying amount. If a PCI loan pays off earlier than expected, a gain is recorded as interest income when the payoff amount exceeds the recorded investment. For acquired loans not considered credit impaired ("non-PCI"), we recognize the entire fair value discount accretion to interest income, based on contractual cash flows using an effective interest rate method for term loans, and on a straight line basis for revolving lines. When a non-PCI loan is placed on non-accrual status subsequent to acquisition, accretion stops until the loan is returned to accrual status. The level of accretion on non-PCI loans varies from period to period due to maturities and early pay-offs of these loans during the reporting periods. Subsequent to acquisition, if the probable and estimable losses for non-PCI loans exceed the amount of the remaining unaccreted discount, the excess is established as an allowance for loan losses. For further information regarding our acquired loans, see Note 3, Loans and Allowance for Loan Losses.
Allowance for Loan Losses	Allowance for Loan Losses is based upon estimates of loan losses and is maintained at a level considered adequate to provide for probable losses inherent in the loan portfolio. The allowance is increased by provisions for loan losses charged against earnings and reduced by charge-offs, net of recoveries. In periodic evaluations of the adequacy of the allowance balance, Management considers current economic conditions, known and inherent risks in the portfolio, adverse situations that may affect the borrower's ability to repay, the estimated value of any underlying collateral, our past loan loss experience and other factors. The ALLL is based on estimates, and ultimate losses may vary from current estimates. Our Board of Directors' Asset/Liability Management Committee (“ALCO”) reviews the adequacy of the ALLL at least quarterly. The overall allowance consists of 1) specific allowances for individually identified impaired loans ("ASC 310-10") and 2) general allowances for pools of loans ("ASC 450-20"), which incorporate quantitative (e.g., historical loan loss rates) and qualitative risk factors (e.g., portfolio growth and trends, credit concentrations, economic and regulatory factors, etc.). The first component, specific allowances, results from the analysis of identified problem credits and the evaluation of sources of repayment including collateral, as applicable. Through Management's ongoing loan grading and credit monitoring process, individual loans are identified that have conditions indicating the borrower may be unable to pay all amounts due in accordance with the contractual terms. These loans are evaluated for impairment individually by Management. Management considers an originated loan to be impaired when it is probable we will be unable to collect all amounts due according to the contractual terms of the loan agreement. When the fair value of the impaired loan is less than the recorded investment in the loan, the difference is recorded as an impairment through the establishment of a specific allowance. For loans determined to be impaired, the extent of the impairment is measured based on the present value of expected future cash flows discounted at the loan's effective interest rate at origination (for originated loans), based on the loan's observable market price, or based on the fair value of the collateral if the loan is collateral dependent or if foreclosure is imminent. Generally, with problem credits that are collateral dependent, we obtain appraisals of the collateral at least annually. We may obtain appraisals more frequently if we believe the collateral value is subject to market volatility, if a specific event has occurred to the collateral, or if we believe foreclosure is imminent. The second component is an estimate of the probable inherent losses in each loan pool with similar characteristics. This analysis encompasses the entire loan portfolio, excluding individually identified impaired loans and acquired loans whose purchase discount has not been fully accreted. Under our allowance model, loans are evaluated on a pool basis by federal regulatory reporting codes ("CALL codes" or "segments"), which are further delineated by assigned credit risk ratings, as described in Note 3, Loans and Allowance for Loan Losses. Segments include the following: • Loans secured by real estate: - 1-4 family residential construction loans - Other construction loans and all land development and other land loans - Secured by farmland (including residential and other improvements) - Revolving, open-end loans secured by 1-4 family residential properties and extended under lines of credit - Closed-end loans secured by 1-4 family residential properties, secured by first liens - Closed-end loans secured by 1-4 family residential properties, secured by junior liens - Secured by multifamily (5 or more) residential properties - Loans secured by owner-occupied non-farm nonresidential properties - Loans secured by other non-farm nonresidential properties • Loans to finance agricultural production and other loans to farmers • Commercial and industrial loans • Loans to individuals for household, family and other personal expenditures (i.e., consumer loans) • Other loans The model determines general allowances by loan segment based on quantitative (loss history) and qualitative risk factors. Qualitative internal and external risk factors include, but are not limited to, the following: • Changes in the nature and volume of the loan portfolio. • Changes in the volume and severity of past due loans, the volume of non-accruals loans, and the volume and severity of adversely classified or graded loans. • The existence and effect of individual loan and loan segment concentrations. • Changes in lending policies and procedures, including changes in underwriting standards and collection, charge-off, and recovery practices not considered elsewhere. • Changes in the experience, ability, and depth of lending management and other relevant staff. • Changes in the quality of our systematic loan review processes. • Changes in economic and business conditions, and developments that affect the collectability of the portfolio. • Changes in the value of underlying collateral, where applicable. • The effect of other external factors such as legal and regulatory requirements on the level of estimated credit losses in the portfolio. • The effect of acquisitions of other loan portfolios on our infrastructure, including risk associated with entering new geographic areas as a result of such acquisitions. • The presence of specialized lending segments in the portfolio. Beginning with the quarter ended March 31, 2016, Management enhanced its methodology for determining the quantitative and qualitative risk factors assigned to unimpaired loans in order to capture historical loss information at the loan level, track loss migration through risk grade deterioration, increase efficiencies related to performing the calculations, and refine how we incorporate environmental and other unique risk elements into our estimation of credit losses. The changes in methodology did not result in a material difference in general allowances. Prior to March 31, 2016, under the Bank's allowance model, each segment was assigned a quantitative loss factor that was primarily based on a rolling twenty-quarter look-back at our historical losses for that particular segment, as well as a number of other assumptions. Under the current methodology, the quantitative risk factor for each segment utilizes the greater of either the historical loss method or migration analysis loss method based on loss history beginning March 2010. Under the historical loss method, quarterly loss rates are calculated for each segment by dividing annualized net charge-offs during each quarter by the quarter's average segment balances. The quarterly loss rates are averaged over the entire loss history period. Under the migration analysis method, loss rates are calculated at the risk grade and segment levels by dividing the net charge-off amount by the total segment balance at the beginning of each migration period where the charged-off loan in question was present. Migration loss rates are averaged for each risk grade and segment for the entire loss history period. For each segment, the loss rates that result in the larger of the migration loss reserves or segment historical loss reserves are applied to the current loan balances. Qualitative factors are combined with these quantitative factors at the segment level to arrive at the overall general allowances. We establish specific allowances to account for credit deterioration for probable decreases in cash flows for PCI loans subsequent to acquisition. The estimated cash flows expected to be collected on PCI loans is updated quarterly and requires the use of key assumptions and estimates based on factors such as the current economic environment, changes in collateral values, loan workout plans, changes in the probability of default, loss severities, and prepayments. Probable decreases in expected cash flows after acquisition result in impairment recorded as a specific allowance for loan losses or a charge-off to the allowance. Impairment is calculated as the present value of the expected future cash flows on the PCI loan, discounted at the loan's effective interest rate implicit in the loan. While we believe we use the best information available to determine the allowance for loan losses, our results of operations could be significantly affected if circumstances differ substantially from the assumptions used in determining the allowance. A decline in local and national economic conditions, or significant changes in other assumptions, could result in a material increase in the allowance for loan losses and may adversely affect our financial condition and results of operations. In addition, the determination of the amount of the allowance for loan losses is subject to review by bank regulators as part of their routine examination process, which may result in the establishment of additional allowance for loan losses based upon their judgment of information available to them at the time of their examination. For further information regarding the allowance for loan losses, see Note 3, Loans and Allowance for Loan Losses.
Allowance for Losses on Off-Balance-Sheet Commitments	Allowance for Losses on Off-Balance Sheet Commitments : We make commitments to extend credit to meet the financing needs of our customers in the form of loans or standby letters of credit. We are exposed to credit loss in the event that a decline in credit quality of the borrower leads to nonperformance. We record an allowance for losses on these off-balance sheet commitments based on estimates of probability that these commitments will be drawn upon according to our historical utilization experience on different types of commitments and expected loss severity. This allowance is included in interest payable and other liabilities on the consolidated statements of condition.
Transfers of Financial Assets	Transfers of Financial Assets : We have entered into certain participation agreements with other organizations. We account for these transfers of financial assets as sales when control over the transferred financial assets has been surrendered. Control over transferred assets is deemed to be surrendered when (1) the assets and liabilities have been isolated from us, (2) the transferee has the right to pledge or exchange the assets (or beneficial interests) it received, free of conditions that constrain it from taking advantage of that right, beyond a trivial benefit and (3) we do not maintain effective control over the transferred financial assets or third-party beneficial interests related to those transferred assets.
Premises and Equipment	Premises and Equipment : Premises and equipment consist of leasehold improvements, furniture, fixtures, software and equipment and are stated at cost, less accumulated depreciation and amortization, which are calculated on a straight-line basis. Furniture and fixtures are depreciated over eight years and equipment is generally depreciated over three to twenty years. Leasehold improvements are amortized over the lesser of their estimated useful lives or the terms of the leases. When assets are sold or otherwise disposed of, the cost and related accumulated depreciation or amortization are removed from the accounts and any resulting gain or loss is recognized in income for the period. The cost of maintenance and repairs is charged to expense as incurred.
Business Combinations	Business Combinations : Business combinations are accounted for under the acquisition method of accounting in accordance with ASC 805, Business Combinations . Under the acquisition method the acquiring entity in a business combination recognizes the acquired assets and assumed liabilities at their estimated fair values as of the date of acquisition. Any excess of the purchase price over the fair value of net assets and other identifiable intangible assets acquired is recorded as goodwill. To the extent the fair value of net assets acquired, including other identifiable assets, exceed the purchase price, a bargain purchase gain is recognized. Assets acquired and liabilities assumed from contingencies must also be recognized at fair value, if the fair value can be determined during the measurement period. Results of operations of an acquired business are included in the consolidated statements of operations from the date of acquisition. Acquisition-related costs, including conversion and restructuring charges, are expensed as incurred.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets : Goodwill is determined as the excess of the fair value of the consideration transferred, plus the fair value of any noncontrolling interests in the acquiree, over the fair value of the net assets acquired and liabilities assumed as of the acquisition date. Goodwill that arises from a business combination is periodically evaluated for impairment at the reporting unit level, at least annually. Intangible assets with definite useful lives are amortized over their estimated useful lives to their estimated residual values. Core deposit intangible ("CDI") represents the estimated future benefit of deposits related to an acquisition and is booked separately from the related deposits and evaluated periodically for impairment. The CDI asset is amortized on an accelerated method over its estimated useful life of ten years. We make a qualitative assessment of whether it is more likely than not that the fair value of a reporting unit where goodwill is assigned is less than its carrying amount. If we conclude that it is more likely than not that the fair value is more than its carrying amount, no impairment is recorded. Goodwill is tested for impairment on an interim basis if circumstances change or an event occurs between annual tests that would more likely than not reduce the fair value of the reporting unit below its carrying amount. The qualitative assessment includes adverse events or circumstances identified that could negatively affect the reporting units’ fair value as well as positive and mitigating events. Such indicators may include, among others, a significant change in legal factors or in the general business climate, significant change in our stock price and market capitalization, unanticipated competition, and an action or assessment by a regulator. If the fair value of a reporting unit is less than its carrying amount, an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value is recognized. The loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. In January 2017, the FASB issued ASU No. 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment . The ASU is effective for fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. We early adopted this ASU effective January 1, 2017, which did not have a material impact on our financial condition and results of operations.
Other Real Estate Owned (OREO)	Other Real Estate Owned ("OREO") : OREO is comprised of property acquired through foreclosure, in substance repossession or acceptance of deeds-in-lieu of foreclosure when the related loan receivable is de-recognized. OREO is recorded at fair value of the collateral less estimated costs to sell, establishing a new cost basis, and subsequently accounted for at the lower of cost or fair value less estimated costs to sell. Any shortfall of collateral value from the recorded investment of the related loan is recognized as loss at the time of foreclosure and is charged against the allowance for loan losses. Fair value of collateral is generally based on an independent appraisal of the property. Revenues and expenses associated with OREO, and subsequent adjustments to the fair value of the property and to the estimated costs of disposal, are realized and reported as a component of non-interest income and expense when incurred.
Bank Owned Life Insurance	Bank Owned Life Insurance ("BOLI") : The Bank owns life insurance policies on certain key current and former officers. BOLI is recorded in interest receivable and other assets on the consolidated statements of condition at the amount that can be realized under the insurance contract at the period end, which is the cash surrender value adjusted for other charges or amounts due that are probable at settlement.
Federal Home Loan Bank of San Francisco (FHLB) Stock	Federal Home Loan Bank of San Francisco ("FHLB") Stock : The Bank is a member of the FHLB. Members are required to own a certain amount of stock based on the level of borrowings and other factors. Our investment in FHLB stock is carried at cost and is included as part of interest receivable and other assets on the consolidated statements of condition. We periodically evaluate FHLB stock for impairment based on ultimate recovery of par value. Both cash and stock dividends are reported as non-interest income.
Investments in Low Income Housing Tax Credit Funds	Investments in Low Income Housing Tax Credit Funds : We have invested in limited partnerships that were formed to develop and operate affordable housing projects for low or moderate-income tenants throughout California. Our ownership in each limited partnership is less than two percent . We account for the investments in qualified affordable housing tax credit funds using the proportional amortization method, where the initial cost of the investment is amortized in proportion to the tax credits and other tax benefits received and the net investment performance is recognized as part of income tax expense (benefit). Each of the partnerships must meet the regulatory minimum requirements for affordable housing for a minimum 15-year compliance period to fully utilize the tax credits. If the partnerships cease to qualify during the compliance period, the credit may be denied for any period in which the project is not in compliance and a portion of the credit previously taken is subject to recapture with interest. We record an impairment charge if the value of the future tax benefits is less than the carrying value of the investments.
Employee Stock Ownership Plan (ESOP)	Employee Stock Ownership Plan (“ESOP”) : We recognize compensation cost of the ESOP contribution when funds become committed for the purchase of Bancorp's common shares into the ESOP in the year in which the employees render service entitling them to the contribution. If we contribute stock, the compensation cost is the fair value of the shares when they are committed to be released (i.e., when the number of shares becomes known and formally approved). In 2017 , the Bank made only stock contributions to the ESOP. In 2016 and 2015 , the Bank made only cash contributions to the ESOP without leveraging.
Income Taxes	Income Taxes : Income taxes reported in the consolidated financial statements are computed based on an asset and liability approach. We recognize the amount of taxes payable or refundable for the current year and we record deferred tax assets and liabilities for future tax consequences attributable to differences between the financial statement carrying amount of existing assets and liabilities and their respective tax bases using enacted tax rates in effect for the year in which the temporary differences are expected to reverse. We record net deferred tax assets to the extent it is more likely than not that they will be realized. In evaluating our ability to recover the deferred tax assets and the need to establish a valuation allowance against the deferred tax assets, Management considers all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, and tax planning strategies. In projecting future taxable income, Management develops assumptions including the amount of future state and federal pretax operating income, the reversal of temporary differences, and the implementation of feasible and prudent tax planning strategies. These assumptions require significant judgment about the forecasts of future taxable income and are consistent with the plans and estimates being used to manage the underlying business. Bancorp files consolidated federal and combined state income tax returns. We recognize the financial statement effect of a tax position when it is more likely than not, based on the technical merits and all available evidence, that the position will be sustained upon examination, including the resolution through protests, appeals or litigation processes. For tax positions that meet the more-likely-than-not threshold, we measure and record the largest amount of tax benefit that is greater than fifty percent likely of being realized upon ultimate settlement with the taxing authority. The remainder of the benefits associated with tax positions taken is recorded as unrecognized tax benefits, along with any related interest and penalties. Interest and penalties related to unrecognized tax benefits are recorded in tax expense. In deciding whether or not our tax positions taken meet the more-likely-than-not recognition threshold, we must make judgments and interpretations about the application of inherently complex state and federal tax laws. To the extent tax authorities disagree with tax positions taken by us, our effective tax rates could be materially affected in the period of settlement with the taxing authorities. Revision of our estimate of accrued income taxes also may result from our own income tax planning, which may affect effective tax rates and results of operations for any reporting period. We present an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating loss ("NOL") carryforward, or similar tax loss or tax credit carryforward, rather than as a liability, when (1) the uncertain tax position would reduce the NOL or other carryforward under the tax law of the applicable jurisdiction and (2) we intend to and are able to use the deferred tax asset for that purpose. Otherwise, the unrecognized tax benefit is presented as a liability instead of being netted with deferred tax assets.
Earnings per share (EPS)	Earnings per share (“EPS”) are based upon the weighted average number of common shares outstanding during each year. The following table shows: 1) weighted average basic shares, 2) potentially dilutive weighted average common shares related to stock options, unvested restricted stock awards and stock warrant, and 3) weighted average diluted shares. Basic EPS are calculated by dividing net income by the weighted average number of common shares outstanding during each annual period, excluding unvested restricted stock awards. Diluted EPS are calculated using the weighted average number of potentially dilutive common shares. The number of potentially dilutive common shares included in year-to-date diluted EPS is a year-to-date weighted average of potentially dilutive common shares included in each quarterly diluted EPS computation. In computing diluted EPS, we exclude anti-dilutive shares such as options whose exercise prices exceed the current common stock price as they would not reduce EPS under the treasury method. We have two forms of our outstanding common stock: common stock and unvested restricted stock awards. Holders of unvested restricted stock awards receive non-forfeitable dividends at the same rate as common shareholders and they both share equally in undistributed earnings. Under the two-class method, the difference in EPS is nominal for these participating securities.
Share-Based Compensation	Share-Based Compensation : All share-based payments, including stock options and restricted stock, are recognized as stock-based compensation expense in the statements of comprehensive income based on the grant-date fair value of the award with a corresponding increase in common stock. The grant-date fair value of the award is amortized on a straight-line basis over the requisite service period, which is generally the vesting period. The stock-based compensation expense excludes stock grants to directors as compensation for their services, which are recognized as director expenses separately based on the grant-date value of the stock. See Note 8, Stockholders' Equity and Stock Option Plans for further discussion. We determine fair value of stock options at the grant date using a Black-Scholes pricing model that takes into account the stock price at the grant date, the exercise price, the expected life of the option, the volatility of the underlying stock, the expected dividend yield and the risk-free interest rate over the expected life of the option. The expected term of options granted is derived from historical data on employee exercises and post-vesting employment termination behavior. The risk-free rate for periods within the expected life of the option is based on the U.S. Treasury yield curve in effect at the time of the grant. Expected volatility is based on the historical volatility of the common stock over the most recent period that is generally commensurate with the expected life of the options. The Black-Scholes option valuation model requires the input of highly subjective assumptions, including the expected life of the stock-based award and stock price volatility. The assumptions used represent Management's best estimates based on historical information, but these estimates involve inherent uncertainties and the application of Management's judgment. As a result, if other assumptions had been used, the recorded stock-based compensation expense could have been materially different from that recorded in the consolidated financial statements. The fair value of restricted stock is based on the stock price on grant date. In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09"). This ASU identifies areas for simplification involving several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as equity or liabilities, forfeiture accounting, and classifications on the statement of cash flows. We adopted the requirements of this ASU effective January 1, 2017, which impacted the following areas: Forfeiture rates: We have elected to account for forfeitures as they occur. Previously, we accounted for forfeitures based on an estimate of the number of awards expected to vest. The policy change was applied using a modified retrospective approach and did not have a material effect on our financial condition or results of operations. Income taxes: We have recorded excess tax benefits (deficiencies) resulting from the exercise of non-qualified stock options, the disqualifying disposition of incentive stock options and vesting of restricted stock awards as tax benefits (expense) in the consolidated statements of comprehensive income with a corresponding decrease (increase) to current taxes payable. Prior to the adoption of this ASU, excess tax benefits (deficiencies) were recognized as an increase (decrease) to common stock in the consolidated statements of changes in stockholders' equity. In addition, we have reflected excess tax benefits as an operating activity in the consolidated statements of cash flows. Prior to the adoption of this ASU, excess tax benefits were reflected as a financing activity. We applied the amendment prospectively and did not reclassify cash flows from operating and financing activities in the prior period consolidated financial statements. For the year ended December 31, 2017 , we recognized $214 thousand in excess tax benefits recorded as a reduction to income tax expense. Statutory tax withholding: Cash paid for tax withholdings when shares are surrendered in a cashless stock option exchange has been classified as a financing activity in the consolidated statements of cash flows. There were no shares surrendered for tax withholdings prior to the adoption of ASU 2016-09.
Derivative Financial Instruments and Hedging Activities	Derivative Financial Instruments and Hedging Activities - Fair Value Hedges : All of our interest rate swap contracts are designated and qualified as fair value hedges. The terms of our interest rate swap contracts are closely aligned to the terms of the designated fixed-rate loans. The hedging relationships are tested for effectiveness on a quarterly basis. The interest rate swaps are carried on the consolidated statements of condition at their fair value in other assets (when the fair value is positive) or in other liabilities (when the fair value is negative). The changes in the fair value of the interest rate swaps are recorded in interest income. The unrealized gains or losses due to changes in fair value of the hedged fixed-rate loans are recorded as an adjustment to the hedged loans and offset in interest income. For derivative instruments executed with the same counterparty under a master netting arrangement, we do not offset fair value amounts of interest rate swaps in liability positions with the ones in asset positions. From time to time, we make firm commitments to enter into long-term fixed-rate loans with borrowers backed by yield maintenance agreements and simultaneously enter into forward interest rate swap agreements with correspondent banks to mitigate the change in fair value of the yield maintenance agreement. Prior to loan funding, yield maintenance agreements with net settlement features that meet the definition of a derivative are considered as non-designated hedges and are carried on the consolidated statements of condition at their fair value in other assets (when the fair value is positive) or in other liabilities (when the fair value is negative). The offsetting changes in the fair value of the forward swap and the yield maintenance agreement are recorded in interest income. When the fixed-rate loans are originated, the forward swaps are designated to offset the change in fair value in the loans. Subsequent to the point of the swap designations, the fair value of the related yield maintenance agreements at the designation date was recorded in other assets and is amortized using the effective yield method over the life of the respective designated loans. The net effect of the change in fair value of interest rate swaps, the amortization of the yield maintenance agreement and the change in the fair value of the hedged loans result in an insignificant amount of hedge ineffectiveness recognized in interest income. For further detail, see Note 14, Derivative Financial Instruments and Hedging Activities.
Advertising Costs	Advertising Costs are expensed as incurred.
Comprehensive Income	Comprehensive Income includes net income, changes in the unrealized gains or losses on available-for-sale investment securities, and amortization of net unrealized gains or losses on securities transferred from available-for-sale to held-to-maturity, net of related taxes, reported on the consolidated statements of comprehensive income and as components of stockholders' equity.
Fair Value Measurements	Fair Value Measurements : We use fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures. We base our fair values on 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. Securities available-for-sale and derivatives are recorded at fair value on a recurring basis. Additionally, from time to time, we may be required to record certain assets and liabilities at fair value on a non-recurring basis, such as purchased loans and acquired deposits recorded at acquisition date, certain impaired loans, other real estate owned and securities held-to-maturity that are other-than-temporarily impaired. These non-recurring fair value adjustments typically involve write-downs of individual assets due to application of lower-of-cost or market accounting. When we develop our fair value measurement process, we maximize the use of observable inputs. Whenever there is no readily available market data, we use our best estimates and assumptions in determining fair value, but these estimates involve inherent uncertainties and the application of Management's judgment. As a result, if other assumptions had been used, our recorded earnings or disclosures could have been materially different from those reflected in these consolidated financial statements. For detailed information on our use of fair value measurements and our related valuation methodologies, see Note 9, Fair Value of Assets and Liabilities.
Use of Estimates	Use of Estimates : The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America requires Management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Significant accounting estimates reflected in the consolidated financial statements include ALLL, other-than-temporary impairment of investment securities, accrued liabilities, accounting for income taxes and fair value measurements (including fair values of acquired assets and assumed liabilities at acquisition dates) as discussed in the Notes herein.
Recently Adopted and Issued Accounting Standards	Recently Issued Accounting Standards In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606). This ASU is a converged standard involving FASB and International Financial Reporting Standards that provides a single comprehensive revenue recognition model for all contracts with customers across transactions and industries. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount and at a time that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Subsequent updates related to Revenue from Contracts with Customers (Topic 606) are as follows: • August 2015 ASU No. 2015-14 - Deferral of the Effective Date , institutes a one-year deferral of the effective date of this amendment to interim and annual reporting periods beginning after December 15, 2017. Early application is permitted only as of annual periods beginning after December 15, 2016, including interim reporting periods within that reporting period. • March 2016 ASU No. 2016-08 - Principal versus Agent Considerations (Reporting Revenue Gross versus Net), clarifies the implementation guidance on principal versus agent considerations and on the use of indicators that assist an entity in determining whether it controls a specified good or service before it is transferred to the customer. • April 2016 ASU No. 2016-10 - Identifying Performance Obligations and Licensing, provides guidance in determining performance obligations in a contract with a customer and clarifies whether a promise to grant a license provides a right to access or the right to use intellectual property. • May 2016 ASU No. 2016-12 - Narrow Scope Improvements and Practical Expedients , gives further guidance on assessing collectability, presentation of sales taxes, noncash consideration, and completed contracts and contract modifications at transition. • December 2016 ASU No. 2016-20 - Technical Corrections and Improvements to Topic 606 , further clarifies specific aspects of previously issued guidance or corrects unintended application of the guidance. Our revenue is mainly comprised of interest income on financial instruments, which is explicitly excluded from the scope of ASU 2014-09. We have identified applicable sources of non-interest income and are gathering and reviewing related contracts and evaluating their potential impact to our revenue recognition under the new standards. While the recognition of certain components of our non-interest income may be affected by the ASU, we do not expect it to have a material impact on our financial condition and results of operations. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . The amendments in this ASU make improvements to accounting standards related to financial instruments, including the following: • Requires equity investments, except for those accounted for under the equity method of accounting or those that result in consolidation of the investee, to be measured at fair value with changes in fair value recognized in net income. However, an entity may choose to measure equity investments that do not have readily determinable fair values at cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. • Simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment. When impairment exists, an entity is required to measure the investment at fair value. • Eliminates the requirement to disclose the method(s) and significant assumptions used to estimate the fair value that is currently required to be disclosed for financial instruments measured at amortized cost on the consolidated balance sheet. • Requires public companies to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes. • Requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset (i.e., securities or loans and receivables) on the balance sheet or the accompanying notes to the financial statements. • Clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity's other deferred tax assets. ASU 2016-01 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. This ASU may affect our financial statement presentation and related footnotes, but we do not expect it to have a material impact on our financial condition or results of operations. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) . The amendments in this ASU intend to increase transparency and comparability among organizations by recognizing an asset, which represents the right to use the asset for the lease term, and a lease liability, which is a lessee's obligation to make lease payments measured on a discounted basis. This ASU generally applies to leasing arrangements exceeding a twelve month term. ASU 2016-02 is effective for annual periods, including interim periods within those annual periods beginning after December 15, 2018 and requires a modified retrospective method of adoption. Early application of the amendments is permitted. We intend to adopt this ASU during the first quarter of 2019, as required, and are continuing to evaluate our lease agreements and potential accounting software solutions as they become available. As of December 31, 2017 , our undiscounted operating lease obligations that were off-balance sheet totaled $18.8 million (See Note 12, Commitments and Contingencies). Upon adoption of this ASU, the present values of leases currently classified as operating leases will be recognized as lease assets and liabilities on our consolidated balance sheets. Additional disclosures of key information about our leasing arrangements will also be required. We do not expect that the ASU will have a material impact on our capital ratios or return on average assets when adopted and we are currently evaluating the effect that the ASU will have on other components of our financial condition and results of operations. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . Under the new guidance, entities will be required to measure expected credit losses by utilizing forward-looking information to assess an entity's allowance for credit losses. The measurement of expected credit losses will be based on historical experience, current conditions and reasonable and supportable forecasts that affect the collectability of a credit over its remaining life. In addition, the ASU amends the accounting for potential credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. ASU 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. We have formed an internal Current Expected Credit Loss ("CECL") committee and are working with our third party vendor to determine the appropriate methodologies and resources to utilize in preparation for transition to the new accounting standards. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments . This ASU provides guidance on how to present and classify eight specific cash flow topics in the statement of cash flows. The ASU is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The amendments should be applied using a retrospective transition method to each period presented, if practical. This ASU may affect our presentation of certain cash flows and their categorization as operating, investing or financing activities in the consolidated statements of cash flows, but we do not expect it to have a material impact on our financial condition or results of operations. In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business . The amendments are intended to help companies evaluate whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses and provide a more robust framework to use in determining when a set of assets and activities is a business. The amendments are effective for annual periods after December 31, 2017, including interim periods within those periods. The amendments will be adopted prospectively. We will consider these amendments in our evaluation of the accounting for any future business acquisitions or asset disposals. In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting . This ASU applies to entities that change the terms or conditions of a share-based payment award. The FASB adopted this ASU to provide clarity in what constitutes a modification and to reduce diversity in practice in applying Topic 718. In order for a change to a share-based arrangement to not require Topic 718 modification accounting treatment, all of the following must be met: no change in fair value, no change in vesting conditions and no change in the balance sheet classification of the modified award. The ASU is effective for fiscal years beginning after December 15, 2017, including interim periods within those periods. Early adoption is permitted, including adoption in an interim period. The amendments should be applied prospectively to an award modified on or after the adoption date. We do not expect this ASU to have a material impact on our financial condition or results of operations. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities . This amendment changes both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. It is intended to more closely align hedge accounting with companies' risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. The ASU is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The amended presentation and disclosure guidance will be required prospectively. We expect this amendment to affect the presentation of our hedging activities, but we do not expect it to have a material impact on our financial condition or results of operations. In February 2018, the FASB issued ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income . This amendment helps organizations address certain stranded income tax effects in accumulated other comprehensive income (AOCI) resulting from the enactment of the Tax Cuts and Jobs Act of 2017. The ASU requires financial statement preparers to disclose a description of the accounting policy for releasing income tax effects from AOCI, whether they elect to reclassify the stranded income tax effects from the Tax Cuts and Jobs Act of 2017 and information about the other income tax effects that are reclassified. The amendments are effective for all organizations for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted. The amendments in this ASU should be applied either in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate tax rate in the Tax Cuts and Jobs Act of 2017 is recognized. We are early adopting this ASU in the first quarter of 2018 by reclassifying $637 thousand from AOCI to retained earnings. This amount represents the stranded income tax effects related to the unrealized loss on available-for-sale securities in AOCI on the date of the enactment of the Tax Cuts and Jobs Act of 2017.

Summary of Significant Accoun27

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	At December 31, 2017, the future estimated amortization expense for the CDI arising from our past acquisitions is as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Core deposit intangible amortization $ 921 $ 887 $ 853 $ 818 $ 782 $ 2,231 $ 6,492 At December 31, 2017 , the future estimated amortization expense on the CDI from the Bank of Napa acquisition is as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Core deposit intangible amortization $ 508 $ 499 $ 488 $ 475 $ 460 $ 1,955 $ 4,385
Schedule of Earnings Per Share Reconciliation	The following table shows: 1) weighted average basic shares, 2) potentially dilutive weighted average common shares related to stock options, unvested restricted stock awards and stock warrant, and 3) weighted average diluted shares. Basic EPS are calculated by dividing net income by the weighted average number of common shares outstanding during each annual period, excluding unvested restricted stock awards. Diluted EPS are calculated using the weighted average number of potentially dilutive common shares. The number of potentially dilutive common shares included in year-to-date diluted EPS is a year-to-date weighted average of potentially dilutive common shares included in each quarterly diluted EPS computation. In computing diluted EPS, we exclude anti-dilutive shares such as options whose exercise prices exceed the current common stock price as they would not reduce EPS under the treasury method. We have two forms of our outstanding common stock: common stock and unvested restricted stock awards. Holders of unvested restricted stock awards receive non-forfeitable dividends at the same rate as common shareholders and they both share equally in undistributed earnings. Under the two-class method, the difference in EPS is nominal for these participating securities. (in thousands, except per share data) 2017 2016 2015 Weighted average basic shares outstanding 6,196 6,073 5,966 Potentially dilutive common shares related to: Stock options 62 34 41 Unvested restricted stock awards 15 8 5 Warrant — — 53 Weighted average diluted shares outstanding 6,273 6,115 6,065 Net income $ 15,976 $ 23,134 $ 18,441 Basic EPS $ 2.58 $ 3.81 $ 3.09 Diluted EPS $ 2.55 $ 3.78 $ 3.04 Weighted average anti-dilutive shares not included in the calculation of diluted EPS 21 64 36

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Schedule of Available-for-sale Securities and Held-to-maturity Securities Reconciliation	Our investment securities portfolio consists of obligations of state and political subdivisions, corporate bonds, U.S. government agency securities, including mortgage-backed securities (“MBS”) and collateralized mortgage obligations (“CMOs”) issued or guaranteed by Federal National Mortgage Association ("FNMA"), Federal Home Loan Mortgage Corporation ("FHLMC"), or Government National Mortgage Association ("GNMA"), Small Business Administration ("SBA") backed securities, debentures issued by government-sponsored agencies such as FNMA, Federal Farm Credit Bureau, FHLB and FHLMC, as well as privately issued CMOs, as reflected in the table below: December 31, 2017 December 31, 2016 Amortized Fair Gross Unrealized Amortized Fair Gross Unrealized (in thousands) Cost Value Gains (Losses) Cost Value Gains (Losses) Held-to-maturity: Obligations of state and political subdivisions $ 19,646 $ 19,998 $ 383 $ (31 ) $ 30,856 $ 31,544 $ 694 $ (6 ) Corporate bonds — — — — 3,519 3,518 — (1 ) MBS pass-through securities issued by FHLMC and FNMA 100,376 100,096 234 (514 ) 10,063 10,035 126 (154 ) CMOs issued by FHLMC 31,010 30,938 2 (74 ) — — — — Total held-to-maturity 151,032 151,032 619 (619 ) 44,438 45,097 820 (161 ) Available-for-sale: Securities of U.S. government agencies: MBS pass-through securities issued by FHLMC and FNMA 65,559 65,262 126 (423 ) 193,384 189,959 145 (3,570 ) SBA-backed securities 25,979 25,982 58 (55 ) 614 607 — (7 ) CMOs issued by FNMA 35,340 35,125 33 (248 ) 13,790 13,772 91 (109 ) CMOs issued by FHLMC 70,514 69,889 3 (628 ) 43,452 42,758 37 (731 ) CMOs issued by GNMA 17,953 17,785 26 (194 ) 6,844 6,945 102 (1 ) Debentures of government- sponsored agencies 12,940 12,938 3 (5 ) 35,486 35,403 7 (90 ) Privately issued CMOs 1,432 1,431 1 (2 ) 419 419 1 (1 ) Obligations of state and political subdivisions 98,027 97,491 298 (834 ) 79,306 77,701 135 (1,740 ) Corporate bonds 6,541 6,564 26 (3 ) 4,959 5,016 57 — Total available-for-sale 334,285 332,467 574 (2,392 ) 378,254 372,580 575 (6,249 ) Total investment securities $ 485,317 $ 483,499 $ 1,193 $ (3,011 ) $ 422,692 $ 417,677 $ 1,395 $ (6,410 )
Investments Classified by Contractual Maturity Date	The amortized cost and fair value of investment debt securities by contractual maturity at December 31, 2017 are shown below. Expected maturities may differ from contractual maturities if the issuers of the securities have the right to call or prepay obligations with or without call or prepayment penalties. December 31, 2017 December 31, 2016 Held-to-Maturity Available-for-Sale Held-to-Maturity Available-for-Sale (in thousands) Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Within one year $ 2,151 $ 2,172 $ 10,268 $ 10,272 $ 13,473 $ 13,506 $ 20,136 $ 20,109 After one but within five years 15,577 15,791 71,576 71,237 16,706 17,150 58,334 58,267 After five years through ten years 54,641 54,554 129,723 128,954 3,000 3,125 113,576 110,842 After ten years 78,663 78,515 122,718 122,004 11,259 11,316 186,208 183,362 Total $ 151,032 $ 151,032 $ 334,285 $ 332,467 $ 44,438 $ 45,097 $ 378,254 $ 372,580
Gain (Loss) on Investments	Sales of investment securities and gross gains and losses are shown in the following table. (in thousands) 2017 2016 2015 Available-for-sale: Sales proceeds $ 55,408 $ 68,673 $ 2,099 Gross realized gains $ 46 $ 458 $ 7 Gross realized losses $ (231 ) $ (64 ) $ (1 ) Held-to-maturity: Sales proceeds $ — $ 1,265 $ 1,015 Gross realized gains $ — $ 32 $ 73 Gross realized losses $ — $ — $ —
Schedule of Financial Instruments Owned and Pledged as Collateral	Pledged investment securities are shown in the following table: (in thousands) December 31, 2017 December 31, 2016 Pledged to the State of California: Secure public deposits in compliance with the Local Agency Security Program $ 107,829 $ 108,304 Collateral for trust deposits 761 822 Total investment securities pledged to the State of California $ 108,590 $ 109,126 Collateral for Wealth Management and Trust Services ("WMTS') checking account $ 2,026 $ 2,146
Schedule of Unrealized Loss on Investments	Those securities are summarized and classified according to the duration of the loss period in the tables below: December 31, 2017 < 12 continuous months ≥ 12 continuous months Total securities in a loss position (in thousands) Fair value Unrealized loss Fair value Unrealized loss Fair value Unrealized loss Held-to-maturity: MBS pass-through securities issued by FHLMC and FNMA $ 16,337 $ (143 ) $ 46,845 $ (371 ) $ 63,182 $ (514 ) Obligations of state and political subdivisions 3,648 (31 ) — — 3,648 (31 ) CMOs issued by FHLMC 11,066 (31 ) 13,824 (43 ) 24,890 (74 ) Total held-to-maturity 31,051 (205 ) 60,669 (414 ) 91,720 (619 ) Available-for-sale: MBS pass-through securities issued by FHLMC and FNMA 32,189 (121 ) 15,325 (302 ) 47,514 (423 ) SBA-backed securities 11,028 (53 ) 165 (2 ) 11,193 (55 ) CMOs issued by FNMA 26,401 (171 ) 5,440 (77 ) 31,841 (248 ) CMOs issued by FHLMC 69,276 (628 ) — — 69,276 (628 ) CMOs issued by GNMA 14,230 (194 ) — — 14,230 (194 ) Debentures of government-sponsored agencies 2,984 (5 ) — — 2,984 (5 ) Obligations of state and political subdivisions 52,197 (288 ) 19,548 (546 ) 71,745 (834 ) Corporate bonds 3,060 (3 ) 3,060 (3 ) Privately issued CMO's 1,310 (2 ) — — 1,310 (2 ) Total available-for-sale 212,675 (1,465 ) 40,478 (927 ) 253,153 (2,392 ) Total temporarily impaired securities $ 243,726 $ (1,670 ) $ 101,147 $ (1,341 ) $ 344,873 $ (3,011 ) December 31, 2016 < 12 continuous months > 12 continuous months Total securities in a loss position (in thousands) Fair value Unrealized loss Fair value Unrealized loss Fair value Unrealized loss Held-to-maturity: MBS pass-through securities issued by FHLMC and FNMA $ 2,250 $ (154 ) $ — $ — $ 2,250 $ (154 ) Obligations of state and political subdivisions 3,362 (6 ) — — 3,362 (6 ) Corporate bonds 3,518 (1 ) — — 3,518 (1 ) Total held-to-maturity 9,130 (161 ) — — 9,130 (161 ) Available-for-sale: MBS pass-through securities issued by FHLMC and FNMA 161,409 (3,570 ) — — 161,409 (3,570 ) SBA-backed securities 607 (7 ) — — 607 (7 ) CMOs issued by FNMA 9,498 (109 ) — — 9,498 (109 ) CMOs issued by FHLMC 31,545 (731 ) — — 31,545 (731 ) CMOs issued by GNMA 1,583 (1 ) — — 1,583 (1 ) Debentures of government- sponsored agencies 19,951 (38 ) 9,946 (52 ) 29,897 (90 ) Obligations of state and political subdivisions 59,567 (1,740 ) — — 59,567 (1,740 ) Corporate bonds 154 (1 ) — — 154 (1 ) Total available-for-sale 284,314 (6,197 ) 9,946 (52 ) 294,260 (6,249 ) Total temporarily impaired securities $ 293,444 $ (6,358 ) $ 9,946 $ (52 ) $ 303,390 $ (6,410 )

Loans and Allowance for Loan 29

Loans and Allowance for Loan Losses (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Past Due Financing Receivables	The following table shows outstanding loans by class and payment aging as of December 31, 2017 and 2016 . Loan Aging Analysis by Class (in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential 1 Installment and other consumer Total December 31, 2017 30-59 days past due $ — $ — $ — $ — $ 99 $ 255 $ 330 $ 684 60-89 days past due 1,340 — — — — — — 1,340 90 days or more past due — — — — 307 — — 307 Total past due 1,340 — — — 406 255 330 2,331 Current 234,495 300,963 822,984 63,828 132,061 95,271 27,080 1,676,682 Total loans 3 $ 235,835 $ 300,963 $ 822,984 $ 63,828 $ 132,467 $ 95,526 $ 27,410 $ 1,679,013 Non-accrual loans 2 $ — $ — $ — $ — $ 406 $ — $ — $ 406 December 31, 2016 30-59 days past due $ 283 $ — $ — $ — $ 77 $ — $ 2 $ 362 60-89 days past due — — — — — — 49 49 90 days or more past due — — — — 91 — — 91 Total past due 283 — — — 168 — 51 502 Current 218,332 247,713 724,228 74,809 117,039 78,549 25,444 1,486,114 Total loans 3 $ 218,615 $ 247,713 $ 724,228 $ 74,809 $ 117,207 $ 78,549 $ 25,495 $ 1,486,616 Non-accrual loans 2 $ — $ — $ — $ — $ 91 $ — $ 54 $ 145 1 Our residential loan portfolio does not include sub-prime loans, nor is it our practice to underwrite loans commonly referred to as "Alt-A mortgages," the characteristics of which are loans lacking full documentation, borrowers having low FICO scores or higher loan-to-value ratios. 2 There were three purchased credit impaired ("PCI") loans with unpaid balances totaling $131 thousand and no carrying values that had stopped accreting interest at December 31, 2017 . There were no PCI loans that had stopped accreting interest at December 31, 2016 . Amounts exclude accreting PCI loans of $2.1 million and $2.9 million at December 31, 2017 and 2016 , respectively, as we have a reasonable expectation about future cash flows to be collected and we continue to recognize accretable yield on these loans in interest income. There were no accruing loans past due more than ninety days at December 31, 2017 or 2016 . 3 Amounts include net deferred loan origination costs of $818 thousand and $883 thousand at December 31, 2017 and 2016 , respectively. Amounts are also net of unaccreted purchase discounts on non-PCI loans of $1.2 million and $1.8 million at December 31, 2017 and 2016 , respectively.
Financing Receivable Credit Quality Indicators	The following table represents an analysis of the carrying amount in loans, net of deferred fees and costs and purchase premiums or discounts, by internally assigned risk grades, including PCI loans, at December 31, 2017 and 2016 . Credit Risk Profile by Internally Assigned Risk Grade (in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Purchased credit-impaired Total December 31, 2017 Pass $ 214,636 $ 281,104 $ 818,570 $ 60,859 $ 130,558 $ 95,526 $ 27,287 $ 1,325 $ 1,629,865 Special Mention 9,318 9,284 1,850 — — — — 790 21,242 Substandard 11,816 9,409 1,774 2,969 1,815 — 123 — 27,906 Total loans $ 235,770 $ 299,797 $ 822,194 $ 63,828 $ 132,373 $ 95,526 $ 27,410 $ 2,115 $ 1,679,013 December 31, 2016 Pass $ 201,987 $ 234,849 $ 720,417 $ 71,564 $ 115,680 $ 78,549 $ 25,083 $ 2,920 $ 1,451,049 Special Mention 9,197 4,799 607 — 1,334 — — — 15,937 Substandard 7,391 6,993 1,498 3,245 91 — 412 — 19,630 Total loans $ 218,575 $ 246,641 $ 722,522 $ 74,809 $ 117,105 $ 78,549 $ 25,495 $ 2,920 $ 1,486,616
Troubled Debt Restructurings on Financing Receivables	The following table summarizes the carrying amount of TDR loans by loan class as of December 31, 2017 and December 31, 2016 . (in thousands) As of Recorded investment in Troubled Debt Restructurings 1 December 31, 2017 December 31, 2016 Commercial and industrial $ 2,165 $ 2,207 Commercial real estate, owner-occupied 6,999 6,993 Commercial real estate, investor 2,171 2,256 Construction 2,969 3,245 Home equity 347 625 Other residential 1,148 1,965 Installment and other consumer 721 877 Total $ 16,520 $ 18,168 1 There were no TDR loans on non-accrual status at December 31, 2017 or December 31, 2016 . Includes no acquired TDR loans as of December 31, 2017 or December 31, 2016 . The following table presents information for loans modified in a TDR during the presented periods, including the number of contracts modified, the recorded investment in the loans prior to modification, and the recorded investment in the loans at period end after being restructured. The table excludes fully charged-off TDR loans and loans modified in a TDR and subsequently paid-off during the years presented. (dollars in thousands) Number of Contracts Modified Pre-Modification Outstanding Recorded Investment Post-Modification Outstanding Recorded Investment Post-Modification Outstanding Recorded Investment at Period End TDRs modified during 2017: Installment and other consumer 1 $ 50 $ 50 $ 47 TDRs modified during 2016: Commercial real estate, investor 2 $ 1,830 $ 1,826 $ 1,752 Home equity 1 1 87 222 245 Installment and other consumer 1 68 67 66 Total 4 $ 1,985 $ 2,115 $ 2,063 1 The home equity line of credit modified in 2016 included debt consolidation, which increased the post-modification balance. TDRs modified during 2015: Commercial and industrial 7 $ 3,271 $ 3,251 $ 2,811
Impaired Financing Receivables	The following tables summarize information by class on impaired loans and their related allowances. Total impaired loans include non-accrual loans, accruing TDR loans and accreting PCI loans that have experienced post-acquisition declines in cash flows expected to be collected. (in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Total December 31, 2017 Recorded investment in impaired loans: With no specific allowance recorded $ 309 $ — $ — $ 2,689 $ 406 $ 995 $ 46 $ 4,445 With a specific allowance recorded 1,856 6,999 2,171 280 347 153 675 12,481 Total recorded investment in impaired loans $ 2,165 $ 6,999 $ 2,171 $ 2,969 $ 753 $ 1,148 $ 721 $ 16,926 Unpaid principal balance of impaired loans $ 2,278 $ 6,993 $ 2,168 $ 2,963 $ 750 $ 1,147 $ 720 $ 17,019 Specific allowance $ 50 $ 188 $ 159 $ 7 $ 6 $ 1 $ 102 $ 513 Average recorded investment in impaired loans during 2017 $ 2,113 $ 6,998 $ 2,842 $ 3,132 $ 679 $ 1,324 $ 841 $ 17,929 Interest income recognized on impaired loans during 2017 1 $ 202 $ 266 $ 87 $ 147 $ 24 $ 62 $ 37 $ 825 December 31, 2016 Recorded investment in impaired loans: With no specific allowance recorded $ 315 $ — $ — $ 2,692 $ 91 $ 1,008 $ 103 $ 4,209 With a specific allowance recorded 1,892 6,993 2,256 553 624 957 829 14,104 Total recorded investment in impaired loans $ 2,207 $ 6,993 $ 2,256 $ 3,245 $ 715 $ 1,965 $ 932 $ 18,313 Unpaid principal balance of impaired loans $ 2,177 $ 6,993 $ 2,252 $ 3,238 $ 713 $ 1,965 $ 932 $ 18,270 Specific allowance $ 285 $ 163 $ 375 $ 8 $ 7 $ 55 $ 98 $ 991 Average recorded investment in impaired loans during 2016 $ 3,514 $ 7,069 $ 2,950 $ 3,242 $ 945 $ 1,988 $ 1,127 $ 20,835 Interest income recognized on impaired loans during 2016 1 $ 175 $ 199 $ 1,514 $ 137 $ 60 $ 90 $ 48 $ 2,223 Average recorded investment in impaired loans during 2015 $ 4,237 $ 7,886 $ 2,833 $ 4,164 $ 602 $ 2,028 $ 1,523 $ 23,273 Interest income recognized on impaired loans during 2015 1 $ 238 $ 295 $ 33 $ 86 $ 18 $ 92 $ 64 $ 826 1 Interest income recognized on a cash basis totaled $100 thousand in 2017 and was primarily related to the pay-off of a commercial non-accrual PCI loan in the fourth quarter. Interest income recognized on a cash basis totaled $1.4 million in 2016 and was primarily related to the interest recovery upon the pay-off of a partially charged off non-accrual commercial real estate loan during the third quarter. No interest income on impaired loans was recognized on a cash basis in 2015.
Allowance for Credit Losses on Financing Receivables	The following tables disclose activity in the allowance for loan losses ("ALLL") and the recorded investment in loans by class, as well as the related ALLL disaggregated by impairment evaluation method. Allowance for Loan Losses Rollforward for the Year Ended (in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Unallocated Total Year ended December 31, 2017 Beginning balance $ 3,248 $ 1,753 $ 6,320 $ 781 $ 973 $ 454 $ 372 $ 1,541 $ 15,442 Provision (reversal) 584 541 155 (100 ) 58 82 3 (823 ) 500 Charge-offs (289 ) — — — — — (4 ) — (293 ) Recoveries 111 — — — — — 7 — 118 Ending balance $ 3,654 $ 2,294 $ 6,475 $ 681 $ 1,031 $ 536 $ 378 $ 718 $ 15,767 Year ended December 31, 2016 Beginning balance $ 3,023 $ 2,249 $ 6,178 $ 724 $ 910 $ 394 $ 425 $ 1,096 $ 14,999 Provision (reversal) 93 (476 ) (2,014 ) 57 60 60 (75 ) 445 (1,850 ) Charge-offs (11 ) (20 ) — — — — (5 ) — (36 ) Recoveries 143 — 2,156 — 3 — 27 — 2,329 Ending balance $ 3,248 $ 1,753 $ 6,320 $ 781 $ 973 $ 454 $ 372 $ 1,541 $ 15,442 Year ended December 31, 2015 Beginning balance $ 2,837 $ 1,924 $ 6,672 $ 839 $ 859 $ 433 $ 566 $ 969 $ 15,099 Provision (reversal) (45 ) 325 (517 ) 724 48 (39 ) (123 ) 127 500 Charge-offs (5 ) — — (839 ) — — (20 ) — (864 ) Recoveries 236 — 23 — 3 — 2 — 264 Ending balance $ 3,023 $ 2,249 $ 6,178 $ 724 $ 910 $ 394 $ 425 $ 1,096 $ 14,999 Allowance for Loan Losses and Recorded Investment In Loans (dollars in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Unallocated Total December 31, 2017 Ending ALLL related to loans collectively evaluated for impairment $ 3,604 $ 2,106 $ 6,316 $ 674 $ 1,025 $ 535 $ 276 $ 718 $ 15,254 Ending ALLL related to loans individually evaluated for impairment 50 188 159 7 6 1 102 — 513 Ending ALLL related to purchased credit-impaired loans — — — — — — — — — Ending balance $ 3,654 $ 2,294 $ 6,475 $ 681 $ 1,031 $ 536 $ 378 $ 718 $ 15,767 Recorded Investment: Collectively evaluated for impairment $ 233,605 $ 292,798 $ 820,023 $ 60,859 $ 131,620 $ 94,378 $ 26,689 $ — $ 1,659,972 Individually evaluated for impairment 2,165 6,999 2,171 2,969 753 1,148 721 — 16,926 Purchased credit-impaired 65 1,166 790 — 94 — — — 2,115 Total $ 235,835 $ 300,963 $ 822,984 $ 63,828 $ 132,467 $ 95,526 $ 27,410 $ — $ 1,679,013 Ratio of allowance for loan losses to total loans 1.55 % 0.76 % 0.79 % 1.07 % 0.78 % 0.56 % 1.38 % NM 0.94 % Allowance for loan losses to non-accrual loans NM NM NM NM 254 % NM NM NM 3,883 % NM - Not Meaningful Allowance for Loan Losses and Recorded Investment In Loans (dollars in thousands) Commercial and industrial Commercial real estate, owner-occupied Commercial real estate, investor Construction Home equity Other residential Installment and other consumer Unallocated Total December 31, 2016 Ending ALLL related to loans collectively evaluated for impairment $ 2,963 $ 1,590 $ 5,945 $ 773 $ 966 $ 399 $ 274 $ 1,541 $ 14,451 Ending ALLL related to loans individually evaluated for impairment 285 163 375 8 7 55 98 — 991 Ending ALLL related to purchased credit-impaired loans — — — — — — — — — Ending balance $ 3,248 $ 1,753 $ 6,320 $ 781 $ 973 $ 454 $ 372 $ 1,541 $ 15,442 Loans outstanding: Collectively evaluated for impairment $ 216,368 $ 239,648 $ 720,266 $ 71,564 $ 116,390 $ 76,584 $ 24,563 $ — $ 1,465,383 Individually evaluated for impairment 2,207 6,993 2,256 3,245 715 1,965 932 — 18,313 Purchased credit-impaired 40 1,072 1,706 — 102 — — — 2,920 Total $ 218,615 $ 247,713 $ 724,228 $ 74,809 $ 117,207 $ 78,549 $ 25,495 $ — $ 1,486,616 Ratio of allowance for loan losses to total loans 1.49 % 0.71 % 0.87 % 1.04 % 0.83 % 0.58 % 1.46 % NM 1.04 % Allowance for loan losses to non-accrual loans NM NM NM NM 1,071 % NM 683 % NM 10,650 % NM - Not Meaningful
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period	The following table reflects the unpaid principal balance and related carrying value of PCI loans: PCI Loans December 31, 2017 December 31, 2016 (in thousands) Unpaid Principal Balance Carrying Value Unpaid Principal Balance Carrying Value Commercial and industrial $ 276 $ 65 $ 45 $ 40 Commercial real estate, owner occupied 1,297 1,166 1,344 1,072 Commercial real estate, investor 1,064 790 1,713 1,706 Construction — — — — Home equity 231 94 248 102 Total purchased credit-impaired loans $ 2,868 $ 2,115 $ 3,350 $ 2,920 The following table presents the fair value of loans acquired from Bank of Napa for PCI loans as of the acquisition date (November 21, 2017): (in thousands) PCI loans Contractually required payments including interest $ 1,769 Less: contractual cash flows not expected to be collected (nonaccretable difference) 805 Cash flows expected to be collected (undiscounted) 964 Less: interest component of cash flows expected to be collected (accretable yield) 109 Fair value of PCI loans $ 855 The following table presents the fair value of loans acquired from Bank of Napa for non-PCI loans as of the acquisition date (November 21, 2017): (in thousands) Non-PCI loans Contractually required payments including interest $ 183,833 Contractual cash flows not expected to be collected $ 14,227 Fair value of non-PCI loans $ 133,865 The following table reflects the outstanding balance and related fair value of PCI loans as of the acquisition date: PCI Loans (in thousands) Unpaid principal balance Fair value Commercial $ 417 $ 70 Commercial real estate 1,070 785 Total purchased credit-impaired loans $ 1,487 $ 855
Accretable Yield Activity	The activities in the accretable yield, or income expected to be earned over the remaining lives of the PCI loans were as follows: Accretable Yield Years ended (in thousands) December 31, 2017 December 31, 2016 December 31, 2015 Balance at beginning of period $ 1,476 $ 2,618 $ 4,027 Additions 109 — — Removals 1 — (778 ) (914 ) Accretion (331 ) (364 ) (495 ) Balance at end of period $ 1,254 $ 1,476 $ 2,618 1 Represents the accretable difference that is relieved when a loan exits the PCI population due to payoff, full charge-off, or transfer to repossessed assets, etc.
Schedule of Related Party Transactions	An analysis of net loans to related parties for each of the three years ended December 31, 2017 , 2016 and 2015 is as follows: (in thousands) 2017 2016 2015 Balance at beginning of year $ 1,988 $ 2,562 $ 3,329 Additions 3,186 — — Advances 74 — 165 Repayments (128 ) (574 ) (390 ) Reclassified due to a change in borrower status 6,732 — (542 ) Balance at end of year $ 11,852 $ 1,988 $ 2,562

Bank Premises and Equipment (Ta

Bank Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of Bank Premises and Equipment	A summary of Bank premises and equipment at December 31 follows: (in thousands) 2017 2016 Leasehold improvements $ 14,937 $ 13,883 Furniture and equipment 11,113 10,627 Subtotal 26,050 24,510 Accumulated depreciation and amortization (17,438 ) (15,990 ) Bank premises and equipment, net $ 8,612 $ 8,520

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Schedule of Time Deposits	A stratification of time deposits at December 31, 2017 and 2016 is presented in the following table: (in thousands) December 31, 2017 December 31, 2016 Time deposits of less than $100 thousand $ 39,361 $ 36,346 Time deposits of $100 thousand to $250 thousand 68,391 66,092 Time deposits of more than $250 thousand 52,364 49,025 Total time deposits $ 160,116 $ 151,463
Schedule of Maturities for Time Deposits	Scheduled maturities of time deposits at December 31, 2017 are presented as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Scheduled maturities of time deposits $ 108,352 $ 13,000 $ 10,511 $ 18,976 $ 9,276 $ 1 $ 160,116

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Subordinated Debentures	The following is a summary of the contractual terms of the subordinated debentures due to the Trusts as of December 31, 2017 : (in thousands) Subordinated debentures due to NorCal Community Bancorp Trust I on October 7, 2033 with interest payable quarterly, based on 3-month LIBOR plus 3.05%, repricing quarterly (4.41% as of December 31, 2017), redeemable, in whole or in part, on any interest payment date $ 4,124 Subordinated debentures due to NorCal Community Bancorp Trust II on March 15, 2036 with interest payable quarterly, based on 3-month LIBOR plus 1.40%, repricing quarterly (2.99% as of December 31, 2017), redeemable, in whole or in part, on any interest payment date 4,124 Total $ 8,248
Schedule of Borrowings	Borrowings at December 31, 2017 and 2016 are summarized as follows: 2017 2016 (dollars in thousands) Carrying Value Average Balance Average Rate Carrying Value Average Balance Average Rate FHLB overnight borrowings $ — $ 1 1.75 % $ — $ 5,383 0.42 % FHLB fixed-rate advances $ — $ — — % $ — $ 6,803 6.59 % 1 Subordinated debentures $ 5,739 $ 5,664 7.65 % $ 5,586 $ 5,493 7.80 % 1 Average rate includes the impact of the $312 thousand prepayment fee in 2016 discussed above.

Stockholders' Equity and Stoc33

Stockholders' Equity and Stock Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Share-based Compensation, Stock Options, Activity	A summary of activity for stock options for the years ended December 31, 2017 , 2016 and 2015 is presented below. The intrinsic value of options outstanding and exercisable is calculated as the number of in-the-money options times the difference between the market price of our stock as of each year-end presented and the exercise prices of the in-the-money options. Number of Shares Weighted Average Exercise Price Aggregate Intrinsic Value (in thousands) Weighted Average Grant-Date Fair Value Weighted Average Remaining Contractual Term (in years) Options outstanding at December 31, 2014 194,672 $ 35.14 $ 3,398 4.48 Granted 28,320 50.70 $ 12.21 Cancelled, expired or forfeited (652 ) 48.38 Exercised (37,071 ) 30.72 755 Options outstanding at December 31, 2015 185,269 38.35 2,788 5.00 Exercisable (vested) at December 31, 2015 114,581 34.12 2,209 3.21 Options outstanding at December 31, 2015 185,269 38.35 2,788 5.00 Granted 32,637 49.37 10.11 Exercised (36,117 ) 33.98 661 Options outstanding at December 31, 2016 181,789 41.20 5,190 5.77 Exercisable (vested) at December 31, 2016 103,211 36.65 3,416 4.18 Options outstanding at December 31, 2016 181,789 41.20 5,190 5.77 Granted 1 100,664 39.78 32.61 Cancelled, expired or forfeited (2,011 ) 43.97 Exercised (21,474 ) 38.62 585 Options outstanding at December 31, 2017 258,968 40.84 7,075 5.34 Exercisable (vested) at December 31, 2017 192,172 35.69 6,212 4.42 1 Includes 70,145 replacement stock option awards issued in the Acquisition with a $27.20 weighted average exercise price and a $40.71 weighted average grant-date fair value. See Note 18, Acquisition.
Schedule of Unrecognized Compensation Cost, Nonvested Awards	The following table summarizes non-vested restricted stock awards and changes during the years ended December 31, 2017 , 2016 and 2015 . Number of Shares Weighted Average Grant-Date Fair Value Non-vested awards at December 31, 2014 22,423 $ 41.25 Granted 15,970 50.75 Vested (6,555 ) 40.00 Forfeited (450 ) 48.45 Non-vested awards at December 31, 2015 31,388 46.24 Granted 16,910 49.65 Vested (8,599 ) 44.14 Non-vested awards at December 31, 2016 39,699 48.15 Granted 16,230 69.59 Vested (10,321 ) 45.78 Non-vested awards at December 31, 2017 45,608 56.31
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range	A summary of the options outstanding and exercisable by price range as of December 31, 2017 is presented in the following table: Stock Options Outstanding as of December 31, 2017 Stock Options Exercisable as of December 31, 2017 Range of Exercise Prices Stock Options Outstanding Remaining Contractual Life (in years) Weighted Average Exercise Price Stock Options Exercisable Weighted Average Exercise Price $10.00 - $20.00 14,120 2.1 $ 17.74 14,120 $ 17.74 $20.01 - $30.00 51,731 1.1 26.05 51,731 26.05 $30.01 - $40.00 70,363 5.3 35.53 68,238 35.41 $40.01 - $50.00 64,511 7.1 46.14 33,224 44.73 $50.01 - $60.00 27,724 6.9 50.70 18,200 50.70 $60.01 - $70.00 30,519 9.3 68.68 6,659 65.46 258,968 192,172
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	We determine the fair value of stock options at the grant date using the Black-Scholes pricing model that takes into account the stock price at the grant date, the exercise price, and the following assumptions (weighted-average shown). Years ended December 31, 2017 2016 2015 Risk-free interest rate 1.66 % 1.37 % 1.67 % Expected dividend yield on common stock 1.70 % 2.02 % 1.75 % Expected life in years 2.4 6.0 6.0 Expected price volatility 25.58 % 25.56 % 28.06 %
Summary of Cash Dividends Paid to Common Shareholders	Presented below is a summary of cash dividends paid to common shareholders, recorded as a reduction of retained earnings. On January 19, 2018, the Board of Directors declared a cash dividend of $0.29 per share, payable on February 9, 2018 to shareholders of record at the close of business on February 2, 2018. Years ended December 31, (in thousands except per share data) 2017 2016 2015 Cash dividends to common stockholders $ 6,896 $ 6,223 $ 5,390 Cash dividends per common share $ 1.12 $ 1.02 $ 0.90

Fair Value of Assets and Liab34

Fair Value of Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following table summarizes our assets and liabilities that were required to be recorded at fair value on a recurring basis. (in thousands) Description of Financial Instruments Carrying Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2017 Securities available for sale: Mortgage-backed securities and collateralized mortgage obligations issued by U.S. government agencies $ 188,061 $ — $ 188,061 $ — SBA-backed securities $ 25,982 $ — $ 25,817 $ 165 Debentures of government sponsored agencies $ 12,938 $ — $ 12,938 $ — Privately-issued collateralized mortgage obligations $ 1,431 $ — $ 1,431 $ — Obligations of state and political subdivisions $ 97,491 $ — $ 97,491 $ — Corporate bonds $ 6,564 $ — $ 6,564 $ — Derivative financial assets (interest rate contracts) $ 74 $ — $ 74 $ — Derivative financial liabilities (interest rate contracts) $ 740 $ — $ 740 $ — December 31, 2016 Securities available for sale: Mortgage-backed securities and collateralized mortgage obligations issued by U.S. government agencies $ 253,434 $ — $ 253,434 $ — SBA-backed securities $ 607 $ — $ — $ 607 Debentures of government sponsored agencies $ 35,403 $ — $ 35,403 $ — Privately-issued collateralized mortgage obligations $ 419 $ — $ 419 $ — Obligations of state and political subdivisions $ 77,701 $ — $ 77,701 $ — Corporate bonds $ 5,016 $ — $ 5,016 $ — Derivative financial assets (interest rate contracts) $ 55 $ — $ 55 $ — Derivative financial liabilities (interest rate contracts) $ 933 $ — $ 933 $ —
Fair Value Measurements, Nonrecurring	The following table presents the carrying value of assets and liabilities measured at fair value on a non-recurring basis and that were held in the consolidated statements of condition at each respective period end, by level within the fair value hierarchy as of December 31, 2017 and 2016 . (in thousands) Description of Financial Instruments Carrying Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2017 None $ — $ — $ — $ — December 31, 2016 Other real estate $ 408 $ — $ — $ 408
Fair Value, by Balance Sheet Grouping	The table below is a summary of fair value estimates for financial instruments as of December 31, 2017 and 2016 , excluding financial instruments recorded at fair value on a recurring basis (summarized in the first table in this note). The carrying amounts in the following table are recorded in the consolidated statements of condition under the indicated captions. Further, we have not disclosed the fair value of financial instruments specifically excluded from disclosure requirements of the Financial Instruments Topic of the Codification (ASC 825-10-50-8), such as BOLI. Additionally, we hold shares of FHLB stock and Visa Inc. Class B common stock at cost. These shares are restricted from resale and their values were discussed in Note 2, Investment Securities , above. December 31, 2017 December 31, 2016 (in thousands) Carrying Amounts Fair Value Fair Value Hierarchy Carrying Amounts Fair Value Fair Value Hierarchy Financial assets: Cash and cash equivalents $ 203,545 $ 203,545 Level 1 $ 48,804 $ 48,804 Level 1 Investment securities held-to-maturity 151,032 151,032 Level 2 44,438 45,097 Level 2 Loans, net 1,663,246 1,650,198 Level 3 1,471,174 1,473,360 Level 3 Interest receivable 7,501 7,501 Level 2 6,319 6,319 Level 2 Financial liabilities: Deposits 2,148,670 2,148,050 Level 2 1,772,700 1,773,102 Level 2 Subordinated debentures 5,739 5,118 Level 3 5,586 5,083 Level 3 Interest payable 191 191 Level 2 134 134 Level 2

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The current and deferred components of the income tax provision for each of the three years ended December 31 are as follows: (in thousands) 2017 2016 2015 Current tax provision Federal $ 5,379 $ 9,710 $ 7,097 State 2,623 3,794 2,931 Total current 8,002 13,504 10,028 Deferred tax provision (benefit) Federal 4,444 (206 ) 382 State 416 48 80 Total deferred 4,860 (158 ) 462 Total income tax provision $ 12,862 $ 13,346 $ 10,490
Schedule of Deferred Tax Assets and Liabilities	The following table shows the tax effect of our cumulative temporary differences as of December 31: (in thousands) 2017 2016 Deferred tax assets: Allowance for loan losses and off-balance sheet credit commitments $ 4,945 $ 6,871 Net operating loss carryforwards 2,629 3,582 Net unrealized loss on securities available-for-sale 1,405 2,543 Deferred compensation plan and salary continuation plan 1,744 1,773 State franchise tax 557 1,300 Accrued but unpaid expenses 212 1,251 Fair value adjustment on acquired loans 570 799 Deferred rent and other lease incentives 328 547 Depreciation and disposals on premises and equipment 632 528 Other real estate owned — 448 Stock-based compensation 463 398 Interest received on non-accrual loans 130 185 Other 266 196 Total gross deferred tax assets 13,881 20,421 Deferred tax liabilities: Deferred loan origination costs and fees (2,153 ) (2,784 ) Unaccreted discount on subordinated debentures (742 ) (1,119 ) Core deposit intangible asset (1,919 ) (1,085 ) Accretion on investment securities (56 ) (54 ) Other (221 ) (42 ) Total gross deferred tax liabilities (5,091 ) (5,084 ) Net deferred tax assets $ 8,790 $ 15,337
Schedule of Effective Income Tax Rate Reconciliation	The effective tax rate for 2017 , 2016 and 2015 differs from the current federal statutory income tax rate as follows: 2017 2016 2015 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % Increase (decrease) due to: California franchise tax, net of federal tax benefit 6.9 % 6.8 % 6.8 % Write down of federal deferred tax assets, net 1 10.5 % — % — % Tax exempt interest on municipal securities and loans (6.1 )% (4.0 )% (4.2 )% Tax exempt earnings on bank owned life insurance (1.0 )% (0.8 )% (1.0 )% Non-deductible acquisition related expenses 0.8 % — % — % Low income housing and qualified zone academy bond tax credits (0.4 )% (0.3 )% (0.2 )% Stock-based compensation excess tax benefit 2 (0.3 )% — % — % Other (0.8 )% (0.1 )% (0.1 )% Effective Tax Rate 44.6 % 36.6 % 36.3 % 1 Due to the enactment of the Tax Cuts and Jobs Act of 2017, which reduces the federal corporate income tax rate to 21% for tax years beginning on or after January 1, 2018, we wrote down net deferred tax assets as of December 22, 2017 by $3.0 million and has been recorded in income tax expense in 2017. 2 Due to the adoption of ASU 2016-09 in 2017, all excess (or deficient) tax benefits associated with stock-based compensation awards are recognized as income tax benefit (expense).

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	At December 31, 2017 , the approximate minimum future commitments payable under non-cancelable contracts for leased premises are as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Operating leases 1 $ 4,444 $ 4,198 $ 3,758 $ 2,138 $ 1,330 $ 2,904 $ 18,772 1 Minimum payments have not been reduced by minimum sublease rentals of $51 thousand due in the future under non-cancelable subleases.

Derivative Financial Instrume37

Derivative Financial Instruments and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	Information on our derivatives follows: Asset derivatives Liability derivatives (in thousands) December 31, 2017 December 31, 2016 December 31, 2017 December 31, 2016 Fair value hedges: Interest rate contracts notional amount $ 4,019 $ 4,217 $ 14,810 $ 15,495 Interest rate contracts fair value 1 $ 74 $ 55 $ 740 $ 933
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance	Years ended December 31, (in thousands) 2017 2016 2015 Increase in value of designated interest rate swaps due to LIBOR interest rate movements recognized in interest income $ 212 $ 778 $ 280 Payment on interest rate swaps recorded in interest income (333 ) (556 ) (918 ) Decrease in value of hedged loans recognized in interest income (166 ) (571 ) (308 ) Decrease in value of yield maintenance agreement recognized against interest income (15 ) (94 ) (52 ) Net loss on derivatives recognized against interest income 2 $ (302 ) $ (443 ) $ (998 ) 1 See Note 9, Fair Value of Assets and Liabilities for valuation methodology. 2 Includes hedge ineffectiveness gain of $31 thousand , gain of $113 thousand and loss of $80 thousand for the years December 31, 2017 , 2016 and 2015 , respectively. Changes in value of swaps were included in the assessment of hedge effectiveness. Hedge ineffectiveness is the measure of the extent to which the change in the fair value of the hedging instruments does not exactly offset the change in the fair value of the hedged items from period to period.
Offsetting Assets	Information on financial instruments that are eligible for offset in the consolidated statements of condition follows: Offsetting of Financial Assets and Derivative Assets Gross Amounts Not Offset in the Statements of Condition Gross Amounts Net Amounts Gross Amounts Offset in the of Assets Presented of Recognized Statements of in the Statements Financial Cash Collateral (in thousands) Assets 1 Condition of Condition 1 Instruments Received Net Amount December 31, 2017 Derivatives by Counterparty: Counterparty A $ 74 $ 74 $ (74 ) $ — Total $ 74 $ — $ 74 $ (74 ) $ — $ — December 31, 2016 Derivatives by Counterparty: Counterparty A $ 55 $ — $ 55 $ (55 ) $ — $ — Total $ 55 $ — $ 55 $ (55 ) $ — $ — 1 Amounts exclude accrued interest totaling $0.3 thousand and $1 thousand at December 31, 2017 and December 31, 2016 , respectively. Offsetting of Financial Liabilities and Derivative Liabilities Gross Amounts Not Offset in the Statements of Condition Gross Amounts Net Amounts of Gross Amounts Offset in the Liabilities Presented of Recognized Statements of in the Statements of Financial Cash Collateral (in thousands) Liabilities 2 Condition Condition 2 Instruments Pledged Net Amount December 31, 2017 Derivatives by Counterparty: Counterparty A $ 740 $ 740 $ (74 ) (666 ) $ — Total $ 740 $ — $ 740 $ (74 ) $ (666 ) $ — December 31, 2016 Derivatives by Counterparty: Counterparty A $ 933 $ — $ 933 $ (55 ) $ (878 ) $ — Total $ 933 $ — $ 933 $ (55 ) $ (878 ) $ —
Offsetting Liabilities	Offsetting of Financial Liabilities and Derivative Liabilities Gross Amounts Not Offset in the Statements of Condition Gross Amounts Net Amounts of Gross Amounts Offset in the Liabilities Presented of Recognized Statements of in the Statements of Financial Cash Collateral (in thousands) Liabilities 2 Condition Condition 2 Instruments Pledged Net Amount December 31, 2017 Derivatives by Counterparty: Counterparty A $ 740 $ 740 $ (74 ) (666 ) $ — Total $ 740 $ — $ 740 $ (74 ) $ (666 ) $ — December 31, 2016 Derivatives by Counterparty: Counterparty A $ 933 $ — $ 933 $ (55 ) $ (878 ) $ — Total $ 933 $ — $ 933 $ (55 ) $ (878 ) $ — 2 Amounts exclude accrued interest totaling $8 thousand and $12 thousand at December 31, 2017 and December 31, 2016 , respectively.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Schedule of Capital Adequacy Ratios	The Bancorp’s and Bank's capital adequacy ratios as of December 31, 2017 and 2016 are presented in the following tables. Bancorp's Tier 1 capital includes the subordinated debentures, which are not included at the Bank level. We continued to build capital in 2017 through stock issued in the Bank of Napa acquisition and the accumulation of net income. Capital Ratios for Bancorp (dollars in thousands) Actual Ratio Adequately Capitalized Threshold 1 Ratio to be a Well Capitalized Bank Holding Company December 31, 2017 Amount Ratio Amount Ratio Amount Ratio Total Capital (to risk-weighted assets) $ 287,435 14.91 % ≥ $ 178,323 ≥ 9.250 % ≥ $ 192,782 ≥ 10.000 % Tier 1 Capital (to risk-weighted assets) $ 270,710 14.04 % ≥ $ 139,767 ≥ 7.250 % ≥ $ 154,225 ≥ 8.000 % Tier 1 Capital (to average assets) $ 270,710 12.13 % ≥ $ 89,285 ≥ 4.000 % ≥ $ 111,607 ≥ 5.000 % Common Equity Tier 1 (to risk-weighted assets) $ 265,119 13.75 % ≥ $ 110,849 ≥ 5.750 % ≥ $ 125,308 ≥ 6.500 % December 31, 2016 Total Capital (to risk-weighted assets) $ 247,453 14.32 % ≥ $ 149,039 ≥ 8.625 % ≥ $ 172,799 ≥ 10.000 % Tier 1 Capital (to risk-weighted assets) $ 231,111 13.37 % ≥ $ 114,479 ≥ 6.625 % ≥ $ 138,239 ≥ 8.000 % Tier 1 Capital (to average assets) $ 231,111 11.39 % ≥ $ 81,189 ≥ 4.000 % ≥ $ 101,486 ≥ 5.000 % Common Equity Tier 1 (to risk-weighted assets) $ 225,925 13.07 % ≥ $ 88,559 ≥ 5.125 % ≥ $ 112,319 ≥ 6.500 % 1 The 2017 and 2016 adequately capitalized thresholds include the capital conservation buffer that was effective January 1, 2016 and January 1, 2017, respectively. These ratios are not reflected on a fully phased-in basis. Capital Ratios for the Bank (dollars in thousands) Actual Ratio Adequately Capitalized Threshold 1 Ratio to be Well Capitalized under Prompt Corrective Action Provisions December 31, 2017 Amount Ratio Amount Ratio Amount Ratio Total Capital (to risk-weighted assets) $ 283,885 14.73 % ≥ $ 178,281 ≥ 9.250 % ≥ $ 192,737 ≥ 10.000 % Tier 1 Capital (to risk-weighted assets) $ 267,160 13.86 % ≥ $ 139,734 ≥ 7.250 % ≥ $ 154,189 ≥ 8.000 % Tier 1 Capital (to average assets) $ 267,160 11.97 % ≥ $ 89,275 ≥ 4.000 % ≥ $ 111,593 ≥ 5.000 % Common Equity Tier 1 (to risk-weighted assets) $ 267,160 13.86 % ≥ $ 110,824 ≥ 5.750 % ≥ $ 125,279 ≥ 6.500 % December 31, 2016 Total Capital (to risk-weighted assets) $ 243,468 14.09 % ≥ $ 149,016 ≥ 8.625 % ≥ $ 172,772 ≥ 10.000 % Tier 1 Capital (to risk-weighted assets) $ 222,127 13.15 % ≥ $ 114,462 ≥ 6.625 % ≥ $ 138,218 ≥ 8.000 % Tier 1 Capital (to average assets) $ 222,127 11.19 % ≥ $ 81,176 ≥ 4.000 % ≥ $ 101,469 ≥ 5.000 % Common Equity Tier 1 (to risk-weighted assets) $ 222,127 13.15 % ≥ $ 88,546 ≥ 5.125 % ≥ $ 112,302 ≥ 6.500 % 1 The 2017 and 2016 adequately capitalized thresholds include the capital conservation buffer that was effective January 1, 2016 and January 1, 2017, respectively. These ratios are not reflected on a fully phased-in basis.

Financial Instruments with Of39

Financial Instruments with Off-Balance Sheet Risk (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Contractual Amount, Off-Balance Sheet Risks	The contractual amount of undrawn loan commitments and standby letters of credit not reflected on the consolidated statements of condition are as follows: (in thousands) December 31, 2017 December 31, 2016 Commercial lines of credit $ 224,370 $ 216,774 Revolving home equity lines 177,678 148,143 Undisbursed construction loans 35,322 44,798 Personal and other lines of credit 11,758 10,635 Standby letters of credit 4,074 1,939 Total commitments and standby letters of credit $ 453,202 $ 422,289

Condensed Bank of Marin Banco40

Condensed Bank of Marin Bancorp Parent Only Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule of Condensed Balance Sheet	Presented below is financial information for Bank of Marin Bancorp, parent holding company only. CONDENSED UNCONSOLIDATED STATEMENTS OF CONDITION December 31, 2017 and 2016 (in thousands) 2017 2016 Assets Cash and due from Bank of Marin $ 3,246 $ 3,568 Investment in bank subsidiary 299,486 232,431 Other assets 586 670 Total assets $ 303,318 $ 236,669 Liabilities and Stockholders' Equity Subordinated debentures $ 5,739 $ 5,586 Accrued expenses payable 146 96 Other liabilities 408 424 Total liabilities 6,293 6,106 Stockholders' equity 297,025 230,563 Total liabilities and stockholders' equity $ 303,318 $ 236,669
Schedule of Condensed Income Statement	CONDENSED UNCONSOLIDATED STATEMENTS OF INCOME Years ended December 31, 2017, 2016 and 2015 (in thousands) 2017 2016 2015 Income Dividends from bank subsidiary $ 8,000 $ 6,400 $ 6,500 Miscellaneous Income 8 7 6 Total income 8,008 6,407 6,506 Expense Interest expense 439 435 420 Non-interest expense 2,087 984 973 Total expense 2,526 1,419 1,393 Income (loss) before income taxes and equity in undistributed net income of subsidiary 5,482 4,988 5,113 Income tax benefit 876 594 583 Income (loss) before equity in undistributed net income of subsidiary 6,358 5,582 5,696 Earnings of bank subsidiary greater (less) than dividends received from bank subsidiary 9,618 17,552 12,745 Net income $ 15,976 $ 23,134 $ 18,441
Schedule of Condensed Cash Flow Statement	CONDENSED UNCONSOLIDATED STATEMENTS OF CASH FLOWS Years ended December 31, 2017, 2016 and 2015 (in thousands) 2017 2016 2015 Cash Flows from Operating Activities: Net income $ 15,976 $ 23,134 $ 18,441 Adjustments to reconcile net income to net cash provided by (used in) operating activities: Earnings of bank subsidiary greater than dividends received from bank subsidiary (9,618 ) (17,552 ) (12,745 ) Net change in operating assets and liabilities: Accretion of discount on subordinated debentures 153 191 210 Other assets 92 353 (298 ) Intercompany receivable (40 ) 171 (18 ) Other liabilities 51 (302 ) 368 Noncash director compensation expense - common stock 20 — — Net cash provided by operating activities 6,634 5,995 5,958 Cash Flows from Investing Activities: Capital contribution to subsidiary (853 ) (1,285 ) (1,156 ) Net cash used in investing activities (853 ) (1,285 ) (1,156 ) Cash Flows from Financing Activities: Proceeds from stock options exercised and stock issued under employee and director stock purchase plans and ESOP 853 1,285 1,156 Payment of tax withholdings for stock options exercised (60 ) — — Dividends paid on common stock (6,896 ) (6,223 ) (5,390 ) Net cash used by financing activities (6,103 ) (4,938 ) (4,234 ) Net (decrease) increase in cash and cash equivalents (322 ) (228 ) 568 Cash and cash equivalents at beginning of period 3,568 3,796 3,228 Cash and cash equivalents at end of period $ 3,246 $ 3,568 $ 3,796 Supplemental schedule of non-cash investing and financing activities: Stock issued in payment of director fees $ 188 $ 234 $ 275

Acquisition (Tables)

Acquisition (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table reflects the estimated fair values of the assets acquired and liabilities assumed related to the acquisition: (dollars in thousands) Acquisition Date November 21, 2017 Assets: Cash and cash equivalents $ 59,779 Investment securities 75,469 Loans 134,720 Core deposit intangible 4,441 Goodwill 23,705 Bank premises and equipment 599 Other assets 6,408 Total assets acquired $ 305,121 Liabilities: Deposits: Non-interest bearing $ 77,266 Interest bearing Transaction accounts 50,080 Savings accounts 12,157 Money market accounts 85,045 Other time accounts 25,338 Total deposits 249,886 Other liabilities 2,050 Total liabilities assumed $ 251,936 Merger consideration of $53,185 (735,264 common shares and 70,145 shares of replacement stock options issued by Bank of Marin Bancorp). $ 53,185 The following table presents the net assets acquired from Bank of Napa, consideration paid and the estimated fair value adjustments: (dollars in thousands) Acquisition Date November 21, 2017 Book value of net assets acquired from Bank of Napa $ 26,152 Fair value adjustments: Loans 1,301 Core deposit intangible asset 4,441 Total purchase accounting adjustments 5,742 Deferred tax liabilities (tax effect of purchase accounting adjustments at 42.05%) (2,414 ) Fair value of net assets acquired from Bank of Napa $ 29,480 Merger consideration $ 53,185 Less: fair value of net assets acquired (29,480 ) Goodwill $ 23,705
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period	The following table reflects the unpaid principal balance and related carrying value of PCI loans: PCI Loans December 31, 2017 December 31, 2016 (in thousands) Unpaid Principal Balance Carrying Value Unpaid Principal Balance Carrying Value Commercial and industrial $ 276 $ 65 $ 45 $ 40 Commercial real estate, owner occupied 1,297 1,166 1,344 1,072 Commercial real estate, investor 1,064 790 1,713 1,706 Construction — — — — Home equity 231 94 248 102 Total purchased credit-impaired loans $ 2,868 $ 2,115 $ 3,350 $ 2,920 The following table presents the fair value of loans acquired from Bank of Napa for PCI loans as of the acquisition date (November 21, 2017): (in thousands) PCI loans Contractually required payments including interest $ 1,769 Less: contractual cash flows not expected to be collected (nonaccretable difference) 805 Cash flows expected to be collected (undiscounted) 964 Less: interest component of cash flows expected to be collected (accretable yield) 109 Fair value of PCI loans $ 855 The following table presents the fair value of loans acquired from Bank of Napa for non-PCI loans as of the acquisition date (November 21, 2017): (in thousands) Non-PCI loans Contractually required payments including interest $ 183,833 Contractual cash flows not expected to be collected $ 14,227 Fair value of non-PCI loans $ 133,865 The following table reflects the outstanding balance and related fair value of PCI loans as of the acquisition date: PCI Loans (in thousands) Unpaid principal balance Fair value Commercial $ 417 $ 70 Commercial real estate 1,070 785 Total purchased credit-impaired loans $ 1,487 $ 855
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	At December 31, 2017, the future estimated amortization expense for the CDI arising from our past acquisitions is as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Core deposit intangible amortization $ 921 $ 887 $ 853 $ 818 $ 782 $ 2,231 $ 6,492 At December 31, 2017 , the future estimated amortization expense on the CDI from the Bank of Napa acquisition is as follows: (in thousands) 2018 2019 2020 2021 2022 Thereafter Total Core deposit intangible amortization $ 508 $ 499 $ 488 $ 475 $ 460 $ 1,955 $ 4,385
Business Acquisition, Pro Forma Information	The first column of the following table presents the former Bank of Napa's operations and its actual contribution to our net interest income and net income included in our consolidated statement of comprehensive income from the acquisition date (November 21, 2017) through December 31, 2017. The table also presents pro forma information of the combined entity as if the acquisition occurred on January 1, 2016. The pro forma information does not necessarily reflect the results of operations that would have resulted had the acquisition been completed at the beginning of the periods presented, nor is it indicative of the results of operations in future periods. Furthermore, cost savings and other business synergies related to the acquisition are not reflected in the pro forma amounts. Pro Forma Revenue and Earnings (in thousands) Actual from acquisition date through December 31, 2017 2017 2016 Net interest income $ 913 $ 82,802 $ 80,898 Net (loss) Income $ (576 ) 1 $ 18,898 2 $ 21,559 2 1 Bank of Napa's net loss from November 21, 2017 through December 31, 2017 includes acquisition-related costs, accretion of the discount on acquired loans and core deposit intangible amortization. 2 2017 pro forma combined net income was adjusted to exclude acquisition related costs of $2.2 million incurred by Bank of Marin Bancorp and $2.5 million incurred by Bank of Napa. 2016 pro forma combined earnings were adjusted to include these acquisition related costs as if the merger occurred on January 1, 2016.
Schedule Of Acquisition-Related Expenses	Bancorp incurred acquisition-related expenses in the consolidated statements of comprehensive income in 2017 for the Bank of Napa acquisition as follows: (in thousands) Year Ended December 31, 2017 Data processing 1 $ 1,108 Professional services 952 Personnel severance 35 Other 114 Total $ 2,209 1 Primarily relates to Bank of Napa's core processing system contract termination and deconversion fees.

Summary of Significant Accoun42

Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)paymentbranch	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Entity Location [Line Items]
Number of consecutive payments considered sustained repayment performance | payment		6
Threshold period a past due loan is charged off		90 days
Threshold period a past due overdraft account is charged off		60 days
Ownership interest in each limited partnerships formed for affordable housing projects (less than)		2.00%
Advertising costs | $		$ 567	$ 565	$ 334
Excess tax benefits recorded as a reduction to income tax expense | $		214
Commitments under operating leases | $		$ 18,772
Marin County
Entity Location [Line Items]
Number of branches		10
Napa County
Entity Location [Line Items]
Number of branches		3
San Francisco
Entity Location [Line Items]
Number of branches		1
Sonoma County
Entity Location [Line Items]
Number of branches		6
Alameda County
Entity Location [Line Items]
Number of branches		3
Scenario, Forecast [Member]
Entity Location [Line Items]
Amount reclassified from AOCI to retained earnings representing stranded tax income effects | $	$ 637

Summary of Significant Accoun43

Summary of Significant Accounting Policies - Premises and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Furniture and equipment
Property, Plant and Equipment [Line Items]
Premises and equipment useful life	8 years
Minimum | Equipment
Property, Plant and Equipment [Line Items]
Premises and equipment useful life	3 years
Maximum | Equipment
Property, Plant and Equipment [Line Items]
Premises and equipment useful life	20 years

Summary of Significant Accoun44

Summary of Significant Accounting Policies - Future Amortization Expense of Core Deposits (Details) - Core deposit intangible $ in Thousands	Dec. 31, 2017USD ($)
Finite-Lived Intangible Assets [Line Items]
2,018	$ 921
2,019	887
2,020	853
2,021	818
2,022	782
Thereafter	2,231
Total core deposit intangible amortization	$ 6,492

Summary of Significant Accoun45

Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share, Basic and Diluted [Abstract]
Weighted average basic shares outstanding (in shares)	6,196	6,073	5,966
Potential common shares related to stock options (in shares)	62	34	41
Potential common shares related to unvested restricted stock awards (in shares)	15	8	5
Potential common shares related to warrants (in shares)	0	0	53
Weighted average diluted shares outstanding (in shares)	6,273	6,115	6,065
Net income	$ 15,976	$ 23,134	$ 18,441
Basic EPS (in dollars per share)	$ 2.58	$ 3.81	$ 3.09
Diluted EPS (in dollars per share)	$ 2.55	$ 3.78	$ 3.04
Weighted average anti-dilutive shares not included in the calculation of diluted EPS (in shares)	21	64	36

Investment Securities - Amortiz

Investment Securities - Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	$ 151,032	$ 44,438
Held-to-maturity, Fair Value	151,032	45,097
Held-to-maturity, Gross Unrealized Gains	619	820
Held-to-maturity, Gross Unrealized (Losses)	(619)	(161)
Available for sale, Amortized Cost	334,285	378,254
Available-for-sale, at fair value	332,467	372,580
Available-for-sale, Gross Unrealized Gains	574	575
Available-for-sale, Gross Unrealized (Losses)	(2,392)	(6,249)
Total investment securities, Amortized Cost	485,317	422,692
Total investment securities, Fair Value	483,499	417,677
Total investment securities, Gross Unrealized Gains	1,193	1,395
Total investment securities, Gross Unrealized (Losses)	(3,011)	(6,410)
MBS pass-through securities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Available for sale, Amortized Cost	65,559	193,384
Available-for-sale, at fair value	65,262	189,959
Available-for-sale, Gross Unrealized Gains	126	145
Available-for-sale, Gross Unrealized (Losses)	(423)	(3,570)
SBA-backed securities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Available for sale, Amortized Cost	25,979	614
Available-for-sale, at fair value	25,982	607
Available-for-sale, Gross Unrealized Gains	58	0
Available-for-sale, Gross Unrealized (Losses)	(55)	(7)
CMOs issued by FNMA
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Available for sale, Amortized Cost	35,340	13,790
Available-for-sale, at fair value	35,125	13,772
Available-for-sale, Gross Unrealized Gains	33	91
Available-for-sale, Gross Unrealized (Losses)	(248)	(109)
CMOs issued by FHLMC
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Available for sale, Amortized Cost	70,514	43,452
Available-for-sale, at fair value	69,889	42,758
Available-for-sale, Gross Unrealized Gains	3	37
Available-for-sale, Gross Unrealized (Losses)	(628)	(731)
CMOs issued by GNMA
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Available for sale, Amortized Cost	17,953	6,844
Available-for-sale, at fair value	17,785	6,945
Available-for-sale, Gross Unrealized Gains	26	102
Available-for-sale, Gross Unrealized (Losses)	(194)	(1)
Debentures of government- sponsored agencies
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Available for sale, Amortized Cost	12,940	35,486
Available-for-sale, at fair value	12,938	35,403
Available-for-sale, Gross Unrealized Gains	3	7
Available-for-sale, Gross Unrealized (Losses)	(5)	(90)
Privately issued CMOs
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Available for sale, Amortized Cost	1,432	419
Available-for-sale, at fair value	1,431	419
Available-for-sale, Gross Unrealized Gains	1	1
Available-for-sale, Gross Unrealized (Losses)	(2)	(1)
Obligations of state and political subdivisions
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	19,646	30,856
Held-to-maturity, Fair Value	19,998	31,544
Held-to-maturity, Gross Unrealized Gains	383	694
Held-to-maturity, Gross Unrealized (Losses)	(31)	(6)
Available for sale, Amortized Cost	98,027	79,306
Available-for-sale, at fair value	97,491	77,701
Available-for-sale, Gross Unrealized Gains	298	135
Available-for-sale, Gross Unrealized (Losses)	(834)	(1,740)
Corporate bonds
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	0	3,519
Held-to-maturity, Fair Value	0	3,518
Held-to-maturity, Gross Unrealized Gains	0	0
Held-to-maturity, Gross Unrealized (Losses)	0	(1)
Available for sale, Amortized Cost	6,541	4,959
Available-for-sale, at fair value	6,564	5,016
Available-for-sale, Gross Unrealized Gains	26	57
Available-for-sale, Gross Unrealized (Losses)	(3)	0
MBS pass-through securities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	100,376	10,063
Held-to-maturity, Fair Value	100,096	10,035
Held-to-maturity, Gross Unrealized Gains	234	126
Held-to-maturity, Gross Unrealized (Losses)	(514)	(154)
CMOs issued by FHLMC
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	31,010	0
Held-to-maturity, Fair Value	30,938	0
Held-to-maturity, Gross Unrealized Gains	2	0
Held-to-maturity, Gross Unrealized (Losses)	$ (74)	$ 0

Investment Securities - Maturit

Investment Securities - Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Held to Maturity, Amortized Cost, Within one year	$ 2,151	$ 13,473
Held to Maturity, Fair Value, Within one year	2,172	13,506
Available for Sale Securities, Amortized Cost, Within one year	10,268	20,136
Available for Sale Securities, Debt Maturities, Fair Value, Within one year	10,272	20,109
Held to Maturity, Amortized Cost, After one but within five years	15,577	16,706
Held to Maturity, Fair Value, After one but within five years	15,791	17,150
Available for Sale, Amortized Cost, After one but within five years	71,576	58,334
Available for Sale, Fair Value, After one but within five years	71,237	58,267
Held to Maturity, Amortized Cost, After five years through ten years	54,641	3,000
Held to Maturity, Fair Value, After five years through ten years	54,554	3,125
Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis	129,723	113,576
Available for Sale, Fair Value, After five years through ten years	128,954	110,842
Held to Maturity, Amortized Cost, After ten years	78,663	11,259
Held to Maturity, Fair Value, After ten years	78,515	11,316
Available for Sale, Amortized Cost, After five years through ten years	122,718	186,208
Available for Sale, Fair Value, After ten years	122,004	183,362
Held to Maturity, Amortized Cost, Total	151,032	44,438
Held-to-Maturity, Fair Value, Total	151,032	45,097
Available for Sale, Amortized Cost, Total	334,285	378,254
Available for Sale, Fair Value, Total	$ 332,467	$ 372,580

Investment Securities - Securit

Investment Securities - Securities Sold, Pledged as Collateral and Transfers (Details) - USD ($) $ in Thousands	Feb. 24, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale:
Sales proceeds		$ 55,408	$ 68,673	$ 2,099
Gross realized gains		46	458	7
Gross realized losses		(231)	(64)	(1)
Held-to-maturity:
Sales proceeds		0	1,265	1,015
Gross realized gains		0	32	73
Gross realized losses		0	0	0
Securities transferred from available-for-sale to held-to-maturity	$ 129,000	128,965	0	0
Unrealized pre-tax loss from transfer of available-for-sale securities to held-to-maturity	$ 3,000
Amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity		426	21	$ 61
State of California
Available-for-sale:
Available-for-sale securities pledged as collateral		108,590	109,126
Public Deposits
Available-for-sale:
Available-for-sale securities pledged as collateral		107,829	108,304
Trust Deposits
Available-for-sale:
Available-for-sale securities pledged as collateral		761	822
Internal checking account
Available-for-sale:
Available-for-sale securities pledged as collateral		$ 2,026	$ 2,146

Investment Securities - Other T

Investment Securities - Other Than Temporarily Impaired Debt Securities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)security	Dec. 31, 2016USD ($)security	Dec. 31, 2015USD ($)
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Number of securities considered other than temporarily impaired | security	0
Number of investment securities in unrealized loss positions | security	198	134
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held-to-maturity, Less than 12 continuous months, Fair value	$ 31,051	$ 9,130
Held-to-maturity, Less than 12 continuous months, Unrealized loss	(205)	(161)
Held-to-maturity, Greater than 12 continuous months, Fair value	60,669	0
Held-to-maturity, Greater than 12 continuous months, Unrealized loss	(414)	0
Held-to-maturity, Total securities in a loss position, Fair value	91,720	9,130
Held-to-maturity, Total securities in a loss position, Unrealized loss	(619)	(161)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	212,675	284,314
Available-for-sale, Less than 12 continuous months, Unrealized loss	(1,465)	(6,197)
Available-for-sale, Greater than 12 continuous months, Fair value	40,478	9,946
Available-for-sale, Greater than 12 continuous months, Unrealized loss	(927)	(52)
Available-for-sale, Total securities in a loss position, Fair value	253,153	294,260
Available-for-sale, Total securities in a loss position, Unrealized loss	(2,392)	(6,249)
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract]
Total temporarily impaired securities, Less than 12 continuous months, Fair value	243,726	293,444
Total temporarily impaired securities, Less than 12 continuous months, Unrealized loss	(1,670)	(6,358)
Total temporarily impaired securities, Greater than 12 continuous months, Fair value	101,147	9,946
Total temporarily impaired securities, Greater than 12 continuous months, Unrealized loss	(1,341)	(52)
Total temporarily impaired securities, Total securities in a loss position, Fair value	344,873	303,390
Total temporarily impaired securities, Total securities in a loss position, Unrealized loss	$ (3,011)	(6,410)
Number of securities in continuous loss position for more than 12 months | security	55
Number of securities in continuous loss position for less than 12 months | security	143
Net loss on sale of available for sale securities sold	$ 231	64	$ 1
MBS pass-through securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	32,189	161,409
Available-for-sale, Less than 12 continuous months, Unrealized loss	(121)	(3,570)
Available-for-sale, Greater than 12 continuous months, Fair value	15,325	0
Available-for-sale, Greater than 12 continuous months, Unrealized loss	(302)	0
Available-for-sale, Total securities in a loss position, Fair value	47,514	161,409
Available-for-sale, Total securities in a loss position, Unrealized loss	$ (423)	(3,570)
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract]
Number of securities in continuous loss position for more than 12 months | security	16
Number of securities in continuous loss position for less than 12 months | security	16
SBA-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	$ 11,028	607
Available-for-sale, Less than 12 continuous months, Unrealized loss	(53)	(7)
Available-for-sale, Greater than 12 continuous months, Fair value	165	0
Available-for-sale, Greater than 12 continuous months, Unrealized loss	(2)	0
Available-for-sale, Total securities in a loss position, Fair value	11,193	607
Available-for-sale, Total securities in a loss position, Unrealized loss	$ (55)	(7)
Collateralized Mortgage Obligations
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract]
Number of securities in continuous loss position for less than 12 months | security	34
CMOs issued by FNMA
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	$ 26,401	9,498
Available-for-sale, Less than 12 continuous months, Unrealized loss	(171)	(109)
Available-for-sale, Greater than 12 continuous months, Fair value	5,440	0
Available-for-sale, Greater than 12 continuous months, Unrealized loss	(77)	0
Available-for-sale, Total securities in a loss position, Fair value	31,841	9,498
Available-for-sale, Total securities in a loss position, Unrealized loss	$ (248)	(109)
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract]
Number of securities in continuous loss position for more than 12 months | security	3
CMOs issued by FHLMC
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	$ 69,276	31,545
Available-for-sale, Less than 12 continuous months, Unrealized loss	(628)	(731)
Available-for-sale, Greater than 12 continuous months, Fair value	0	0
Available-for-sale, Greater than 12 continuous months, Unrealized loss	0	0
Available-for-sale, Total securities in a loss position, Fair value	69,276	31,545
Available-for-sale, Total securities in a loss position, Unrealized loss	$ (628)	(731)
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract]
Number of securities in continuous loss position for more than 12 months | security	4
CMOs issued by GNMA
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	$ 14,230	1,583
Available-for-sale, Less than 12 continuous months, Unrealized loss	(194)	(1)
Available-for-sale, Greater than 12 continuous months, Fair value	0	0
Available-for-sale, Greater than 12 continuous months, Unrealized loss	0	0
Available-for-sale, Total securities in a loss position, Fair value	14,230	1,583
Available-for-sale, Total securities in a loss position, Unrealized loss	(194)	(1)
Debentures of government- sponsored agencies
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	2,984	19,951
Available-for-sale, Less than 12 continuous months, Unrealized loss	(5)	(38)
Available-for-sale, Greater than 12 continuous months, Fair value	0	9,946
Available-for-sale, Greater than 12 continuous months, Unrealized loss	0	(52)
Available-for-sale, Total securities in a loss position, Fair value	2,984	29,897
Available-for-sale, Total securities in a loss position, Unrealized loss	$ (5)	(90)
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract]
Number of securities in continuous loss position for less than 12 months | security	5
Obligations of state and political subdivisions
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	$ 52,197	59,567
Available-for-sale, Less than 12 continuous months, Unrealized loss	(288)	(1,740)
Available-for-sale, Greater than 12 continuous months, Fair value	19,548	0
Available-for-sale, Greater than 12 continuous months, Unrealized loss	(546)	0
Available-for-sale, Total securities in a loss position, Fair value	71,745	59,567
Available-for-sale, Total securities in a loss position, Unrealized loss	$ (834)	(1,740)
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract]
Number of securities in continuous loss position for more than 12 months | security	32
Number of securities in continuous loss position for less than 12 months | security	81
Corporate bonds
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	$ 3,060	154
Available-for-sale, Less than 12 continuous months, Unrealized loss	(3)	(1)
Available-for-sale, Greater than 12 continuous months, Fair value		0
Available-for-sale, Greater than 12 continuous months, Unrealized loss		0
Available-for-sale, Total securities in a loss position, Fair value	3,060	154
Available-for-sale, Total securities in a loss position, Unrealized loss	$ (3)	(1)
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract]
Number of securities in continuous loss position for less than 12 months | security	5
Privately issued CMOs
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available-for-sale, Less than 12 continuous months, Fair value	$ 1,310
Available-for-sale, Less than 12 continuous months, Unrealized loss	(2)
Available-for-sale, Greater than 12 continuous months, Fair value	0
Available-for-sale, Greater than 12 continuous months, Unrealized loss	0
Available-for-sale, Total securities in a loss position, Fair value	1,310
Available-for-sale, Total securities in a loss position, Unrealized loss	$ (2)
Available-for-sale and Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract] [Abstract]
Number of securities in continuous loss position for less than 12 months | security	2
MBS pass-through securities
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held-to-maturity, Less than 12 continuous months, Fair value	$ 16,337	2,250
Held-to-maturity, Less than 12 continuous months, Unrealized loss	(143)	(154)
Held-to-maturity, Greater than 12 continuous months, Fair value	46,845	0
Held-to-maturity, Greater than 12 continuous months, Unrealized loss	(371)	0
Held-to-maturity, Total securities in a loss position, Fair value	63,182	2,250
Held-to-maturity, Total securities in a loss position, Unrealized loss	(514)	(154)
Obligations of state and political subdivisions
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held-to-maturity, Less than 12 continuous months, Fair value	3,648	3,362
Held-to-maturity, Less than 12 continuous months, Unrealized loss	(31)	(6)
Held-to-maturity, Greater than 12 continuous months, Fair value	0	0
Held-to-maturity, Greater than 12 continuous months, Unrealized loss	0	0
Held-to-maturity, Total securities in a loss position, Fair value	3,648	3,362
Held-to-maturity, Total securities in a loss position, Unrealized loss	(31)	(6)
CMOs issued by FHLMC
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held-to-maturity, Less than 12 continuous months, Fair value	11,066
Held-to-maturity, Less than 12 continuous months, Unrealized loss	(31)
Held-to-maturity, Greater than 12 continuous months, Fair value	13,824
Held-to-maturity, Greater than 12 continuous months, Unrealized loss	(43)
Held-to-maturity, Total securities in a loss position, Fair value	24,890
Held-to-maturity, Total securities in a loss position, Unrealized loss	(74)	0
Corporate bonds
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held-to-maturity, Less than 12 continuous months, Fair value		3,518
Held-to-maturity, Less than 12 continuous months, Unrealized loss		(1)
Held-to-maturity, Greater than 12 continuous months, Fair value		0
Held-to-maturity, Greater than 12 continuous months, Unrealized loss		0
Held-to-maturity, Total securities in a loss position, Fair value		3,518
Held-to-maturity, Total securities in a loss position, Unrealized loss	$ 0	$ (1)

Investment Securities - Non-mar

Investment Securities - Non-marketable Securities (Details)	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares	Feb. 21, 2018	Dec. 31, 2016USD ($)
Schedule of Cost-method Investments [Line Items]
Federal Home Loan Bank stock, par value (usd per share) | $ / shares	$ 100
Investments in low income housing tax credit funds	$ 2,100,000		$ 2,500,000
Low income housing tax credits and other tax benefits	332,000
Low income housing amortization expense	331,000
Unfunded commitments for low income housing tax credit funds	546,000
Catch-up amortization expense due to tax reduction	$ 67,000
Subsequent event
Schedule of Cost-method Investments [Line Items]
Federal Home Loan Bank, dividend rate percentage		7.00%
Visa Inc. Class B common stock
Schedule of Cost-method Investments [Line Items]
Number of shares of securities carried at cost | shares	16,939
Carrying value of securities carried at cost	$ 0
Fair value of Class B common stock	$ 3,200,000		2,200,000
Conversion ratio for common stock	1.6483
Other assets
Schedule of Cost-method Investments [Line Items]
Federal Home Loan Bank stock	$ 11,100,000		$ 10,200,000

Loans and Allowance for Loan 51

Loans and Allowance for Loan Losses - Percentage of Loans Geographically and by Collateral (Details)	Dec. 31, 2017	Dec. 31, 2016
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans by class to all loans	67.00%
Commercial real estate | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans by class and geographic location	85.00%
Loans secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans by class to all loans	87.00%	85.00%

Loans and Allowance for Loan 52

Loans and Allowance for Loan Losses - Loans Outstanding and Aging Analysis (Details)	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	$ 2,331,000	$ 502,000
Current	1,676,682,000	1,486,114,000
Total loans	1,679,013,000	1,486,616,000
Non-accrual loans	$ 406,000	145,000
Number of purchase credit impaired (PCI) loans with unpaid balances | loan	3
Unpaid balances on purchase credit impaired (PCI) loans	$ 131,000
Purchased Credit Impaired (PCI) loans no longer accreting interest	0	0
Purchased Credit-impaired (PCI) loans accreting interest	2,100,000	2,900,000
Deferred loan fees	818,000	883,000
Unaccreted purchase discounts on non-PCI loans	1,200,000	1,800,000
30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	684,000	362,000
60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	1,340,000	49,000
90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	307,000	91,000
Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	1,340,000	283,000
Current	234,495,000	218,332,000
Total loans	235,835,000	218,615,000
Non-accrual loans	0	0
Commercial | Commercial and industrial | 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	283,000
Commercial | Commercial and industrial | 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	1,340,000	0
Commercial | Commercial and industrial | 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Commercial real estate | Commercial real estate, owner-occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Current	300,963,000	247,713,000
Total loans	300,963,000	247,713,000
Non-accrual loans	0	0
Commercial real estate | Commercial real estate, owner-occupied | 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Commercial real estate | Commercial real estate, owner-occupied | 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Commercial real estate | Commercial real estate, owner-occupied | 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Commercial real estate | Commercial real estate, investor
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Current	822,984,000	724,228,000
Total loans	822,984,000	724,228,000
Non-accrual loans	0	0
Commercial real estate | Commercial real estate, investor | 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Commercial real estate | Commercial real estate, investor | 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Commercial real estate | Commercial real estate, investor | 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Current	63,828,000	74,809,000
Total loans	63,828,000	74,809,000
Non-accrual loans	0	0
Commercial real estate | Construction | 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Commercial real estate | Construction | 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Commercial real estate | Construction | 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Residential loans | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	406,000	168,000
Current	132,061,000	117,039,000
Total loans	132,467,000	117,207,000
Non-accrual loans	406,000	91,000
Residential loans | Home equity | 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	99,000	77,000
Residential loans | Home equity | 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Residential loans | Home equity | 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	307,000	91,000
Residential loans | Other residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	255,000	0
Current	95,271,000	78,549,000
Total loans	95,526,000	78,549,000
Non-accrual loans	0	0
Residential loans | Other residential | 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	255,000	0
Residential loans | Other residential | 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Residential loans | Other residential | 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	0
Consumer loans | Installment and other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	330,000	51,000
Current	27,080,000	25,444,000
Total loans	27,410,000	25,495,000
Non-accrual loans	0	54,000
Consumer loans | Installment and other consumer | 30-59 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	330,000	2,000
Consumer loans | Installment and other consumer | 60-89 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	0	49,000
Consumer loans | Installment and other consumer | 90 days or more past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	$ 0	$ 0

Loans and Allowance for Loan 53

Loans and Allowance for Loan Losses - Credit Risk Profile by Internally Assigned Risk Grade (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,679,013	$ 1,486,616
Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,629,865	1,451,049
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,242	15,937
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	27,906	19,630
Commercial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	235,770	218,575
Total loans	235,835	218,615
Commercial | Pass | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	214,636	201,987
Commercial | Special Mention | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	9,318	9,197
Commercial | Substandard | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	11,816	7,391
Commercial real estate | Commercial real estate, owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	299,797	246,641
Total loans	300,963	247,713
Commercial real estate | Commercial real estate, investor
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	822,194	722,522
Total loans	822,984	724,228
Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	63,828	74,809
Total loans	63,828	74,809
Commercial real estate | Pass | Commercial real estate, owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	281,104	234,849
Commercial real estate | Pass | Commercial real estate, investor
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	818,570	720,417
Commercial real estate | Pass | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	60,859	71,564
Commercial real estate | Special Mention | Commercial real estate, owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	9,284	4,799
Commercial real estate | Special Mention | Commercial real estate, investor
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	1,850	607
Commercial real estate | Special Mention | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	0	0
Commercial real estate | Substandard | Commercial real estate, owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	9,409	6,993
Commercial real estate | Substandard | Commercial real estate, investor
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	1,774	1,498
Commercial real estate | Substandard | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	2,969	3,245
Residential loans | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	132,373	117,105
Total loans	132,467	117,207
Residential loans | Other residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	95,526	78,549
Residential loans | Pass | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	130,558	115,680
Residential loans | Pass | Other residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	95,526	78,549
Residential loans | Special Mention | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	0	1,334
Residential loans | Special Mention | Other residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Residential loans | Substandard | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans excluding purchased credit-impaired loans	1,815	91
Residential loans | Substandard | Other residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer loans | Installment and other consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	27,410	25,495
Consumer loans | Pass | Installment and other consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	27,287	25,083
Consumer loans | Special Mention | Installment and other consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer loans | Substandard | Installment and other consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	123	412
Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	2,115	2,920
Receivables Acquired with Deteriorated Credit Quality | Pass
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	1,325	2,920
Receivables Acquired with Deteriorated Credit Quality | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	790	0
Receivables Acquired with Deteriorated Credit Quality | Substandard
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	0	0
Receivables Acquired with Deteriorated Credit Quality | Commercial | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	65	40
Receivables Acquired with Deteriorated Credit Quality | Commercial real estate | Commercial real estate, owner-occupied
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	1,166	1,072
Receivables Acquired with Deteriorated Credit Quality | Commercial real estate | Commercial real estate, investor
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	790	1,706
Receivables Acquired with Deteriorated Credit Quality | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	0	0
Receivables Acquired with Deteriorated Credit Quality | Residential loans | Home equity
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	94	102
Receivables Acquired with Deteriorated Credit Quality | Residential loans | Other residential
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	0	0
Receivables Acquired with Deteriorated Credit Quality | Consumer loans | Installment and other consumer
Financing Receivable, Recorded Investment [Line Items]
Purchased credit-impaired	$ 0	$ 0

Loans and Allowance for Loan 54

Loans and Allowance for Loan Losses - Troubled Debt Restructuring by Class (Details)	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan	Dec. 31, 2015USD ($)loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans removed from TDR resignation | loan	0	0	5
Recorded investment of loans removed from TDR resignation			$ 1,600,000
Recorded investment in Troubled Debt Restructurings	$ 16,520,000	$ 18,168,000
TDR loans accruing interest as of period end	0
Acquired loans included in TDR	0
Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment in Troubled Debt Restructurings	2,165,000	2,207,000
Commercial real estate | Commercial real estate, owner-occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment in Troubled Debt Restructurings	6,999,000	6,993,000
Commercial real estate | Commercial real estate, investor
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment in Troubled Debt Restructurings	2,171,000	2,256,000
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment in Troubled Debt Restructurings	2,969,000	3,245,000
Residential loans | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment in Troubled Debt Restructurings	347,000	625,000
Residential loans | Other residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment in Troubled Debt Restructurings	1,148,000	1,965,000
Consumer loans | Installment and other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment in Troubled Debt Restructurings	$ 721,000	$ 877,000

Loans and Allowance for Loan 55

Loans and Allowance for Loan Losses - Troubled Debt Restructuring Modifications (Details)	12 Months Ended
	Dec. 31, 2017USD ($)contract	Dec. 31, 2016USD ($)contract	Dec. 31, 2015USD ($)contract
Financing Receivable, Modifications [Line Items]
Number of Contracts Modified | contract		4
Pre-Modification Outstanding Recorded Investment		$ 1,985,000
Post-Modification Outstanding Recorded Investment		2,115,000
Post-Modification Outstanding Recorded Investment at Period End		2,063,000
Total of TDR loans charged-off within previous 12 months	$ 0	$ 0	$ 0
Consumer loans | Installment and other consumer
Financing Receivable, Modifications [Line Items]
Number of Contracts Modified | contract	1	1
Pre-Modification Outstanding Recorded Investment	$ 50,000	$ 68,000
Post-Modification Outstanding Recorded Investment	50,000	67,000
Post-Modification Outstanding Recorded Investment at Period End	$ 47,000	$ 66,000
Commercial | Commercial real estate, investor
Financing Receivable, Modifications [Line Items]
Number of Contracts Modified | contract		2
Pre-Modification Outstanding Recorded Investment		$ 1,830,000
Post-Modification Outstanding Recorded Investment		1,826,000
Post-Modification Outstanding Recorded Investment at Period End		$ 1,752,000
Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Number of Contracts Modified | contract			7
Pre-Modification Outstanding Recorded Investment			$ 3,271,000
Post-Modification Outstanding Recorded Investment			3,251,000
Post-Modification Outstanding Recorded Investment at Period End			$ 2,811,000
Residential loans | Home equity
Financing Receivable, Modifications [Line Items]
Number of Contracts Modified | contract		1
Pre-Modification Outstanding Recorded Investment		$ 87,000
Post-Modification Outstanding Recorded Investment		222,000
Post-Modification Outstanding Recorded Investment at Period End		$ 245,000

Loans and Allowance for Loan 56

Loans and Allowance for Loan Losses - Impaired Loans and Related Allowance (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Recorded investment in impaired loans:
With no specific allowance recorded	$ 4,445,000	$ 4,209,000
With a specific allowance recorded	12,481,000	14,104,000
Total recorded investment in impaired loans	16,926,000	18,313,000
Unpaid principal balance of impaired loans:
Total unpaid principal balance of impaired loans	17,019,000	18,270,000
Specific valuation	513,000	991,000
Average recorded investment in impaired loans during the period	17,929,000	20,835,000	$ 23,273,000
Interest income recognized on impaired loans	825,000	2,223,000	826,000
Charged-off portion of impaired loans	0	0
Outstanding commitments to extend credit on impaired loans	935,000	1,600,000
Interest income recognized on impaired loans during the period ended, cash basis	100,000	1,400,000	0
Commercial | Commercial and industrial
Recorded investment in impaired loans:
With no specific allowance recorded	309,000	315,000
With a specific allowance recorded	1,856,000	1,892,000
Total recorded investment in impaired loans	2,165,000	2,207,000
Unpaid principal balance of impaired loans:
Total unpaid principal balance of impaired loans	2,278,000	2,177,000
Specific valuation	50,000	285,000
Average recorded investment in impaired loans during the period	2,113,000	3,514,000	4,237,000
Interest income recognized on impaired loans	202,000	175,000	238,000
Commercial real estate | Commercial real estate, owner-occupied
Recorded investment in impaired loans:
With no specific allowance recorded	0	0
With a specific allowance recorded	6,999,000	6,993,000
Total recorded investment in impaired loans	6,999,000	6,993,000
Unpaid principal balance of impaired loans:
Total unpaid principal balance of impaired loans	6,993,000	6,993,000
Specific valuation	188,000	163,000
Average recorded investment in impaired loans during the period	6,998,000	7,069,000	7,886,000
Interest income recognized on impaired loans	266,000	199,000	295,000
Commercial real estate | Commercial real estate, investor
Recorded investment in impaired loans:
With no specific allowance recorded	0	0
With a specific allowance recorded	2,171,000	2,256,000
Total recorded investment in impaired loans	2,171,000	2,256,000
Unpaid principal balance of impaired loans:
Total unpaid principal balance of impaired loans	2,168,000	2,252,000
Specific valuation	159,000	375,000
Average recorded investment in impaired loans during the period	2,842,000	2,950,000	2,833,000
Interest income recognized on impaired loans	87,000	1,514,000	33,000
Commercial real estate | Construction
Recorded investment in impaired loans:
With no specific allowance recorded	2,689,000	2,692,000
With a specific allowance recorded	280,000	553,000
Total recorded investment in impaired loans	2,969,000	3,245,000
Unpaid principal balance of impaired loans:
Total unpaid principal balance of impaired loans	2,963,000	3,238,000
Specific valuation	7,000	8,000
Average recorded investment in impaired loans during the period	3,132,000	3,242,000	4,164,000
Interest income recognized on impaired loans	147,000	137,000	86,000
Residential loans | Home equity
Recorded investment in impaired loans:
With no specific allowance recorded	406,000	91,000
With a specific allowance recorded	347,000	624,000
Total recorded investment in impaired loans	753,000	715,000
Unpaid principal balance of impaired loans:
Total unpaid principal balance of impaired loans	750,000	713,000
Specific valuation	6,000	7,000
Average recorded investment in impaired loans during the period	679,000	945,000	602,000
Interest income recognized on impaired loans	24,000	60,000	18,000
Residential loans | Other residential
Recorded investment in impaired loans:
With no specific allowance recorded	995,000	1,008,000
With a specific allowance recorded	153,000	957,000
Total recorded investment in impaired loans	1,148,000	1,965,000
Unpaid principal balance of impaired loans:
Total unpaid principal balance of impaired loans	1,147,000	1,965,000
Specific valuation	1,000	55,000
Average recorded investment in impaired loans during the period	1,324,000	1,988,000	2,028,000
Interest income recognized on impaired loans	62,000	90,000	92,000
Consumer loans | Installment and other consumer
Recorded investment in impaired loans:
With no specific allowance recorded	46,000	103,000
With a specific allowance recorded	675,000	829,000
Total recorded investment in impaired loans	721,000	932,000
Unpaid principal balance of impaired loans:
Total unpaid principal balance of impaired loans	720,000	932,000
Specific valuation	102,000	98,000
Average recorded investment in impaired loans during the period	841,000	1,127,000	1,523,000
Interest income recognized on impaired loans	$ 37,000	$ 48,000	$ 64,000

Loans and Allowance for Loan 57

Loans and Allowance for Loan Losses - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 15,442	$ 14,999	$ 15,099
Provision (reversal)	500	(1,850)	500
Charge-offs	(293)	(36)	(864)
Recoveries	118	2,329	264
Ending balance	15,767	15,442	14,999
Ending ALLL related to loans collectively evaluated for impairment	15,254	14,451
Ending ALLL related to loans individually evaluated for impairment	513	991
Ending ALLL	15,767	15,442
Recorded Investment:
Collectively evaluated for impairment	1,659,972	1,465,383
Individually evaluated for impairment	16,926	18,313
Total loans	$ 1,679,013	$ 1,486,616
Ratio of allowance for loan losses to total loans	0.94%	1.04%
Allowance for loan losses to non-accrual loans	3883.00%	10650.00%
Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	2,115	2,920
Commercial | Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,248	3,023	2,837
Provision (reversal)	584	93	(45)
Charge-offs	(289)	(11)	(5)
Recoveries	111	143	236
Ending balance		3,248	3,023
Ending ALLL related to loans collectively evaluated for impairment	3,604	2,963
Ending ALLL related to loans individually evaluated for impairment	50	285
Ending ALLL	3,654	3,248
Recorded Investment:
Collectively evaluated for impairment	233,605	216,368
Individually evaluated for impairment	2,165	2,207
Total loans	$ 235,835	$ 218,615
Ratio of allowance for loan losses to total loans	1.55%	1.49%
Commercial | Commercial and industrial | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	65	40
Commercial real estate | Commercial real estate, owner-occupied
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,753	2,249	1,924
Provision (reversal)	541	(476)	325
Charge-offs	0	(20)	0
Recoveries	0	0	0
Ending balance		1,753	2,249
Ending ALLL related to loans collectively evaluated for impairment	2,106	1,590
Ending ALLL related to loans individually evaluated for impairment	188	163
Ending ALLL	2,294	1,753
Recorded Investment:
Collectively evaluated for impairment	292,798	239,648
Individually evaluated for impairment	6,999	6,993
Total loans	$ 300,963	$ 247,713
Ratio of allowance for loan losses to total loans	0.76%	0.71%
Commercial real estate | Commercial real estate, owner-occupied | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	1,166	1,072
Commercial real estate | Commercial real estate, investor
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	6,320	6,178	6,672
Provision (reversal)	155	(2,014)	(517)
Charge-offs	0	0	0
Recoveries	0	2,156	23
Ending balance		6,320	6,178
Ending ALLL related to loans collectively evaluated for impairment	6,316	5,945
Ending ALLL related to loans individually evaluated for impairment	159	375
Ending ALLL	6,475	6,320
Recorded Investment:
Collectively evaluated for impairment	820,023	720,266
Individually evaluated for impairment	2,171	2,256
Total loans	$ 822,984	$ 724,228
Ratio of allowance for loan losses to total loans	0.79%	0.87%
Commercial real estate | Commercial real estate, investor | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	790	1,706
Commercial real estate | Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	781	724	839
Provision (reversal)	(100)	57	724
Charge-offs	0	0	(839)
Recoveries	0	0	0
Ending balance		781	724
Ending ALLL related to loans collectively evaluated for impairment	674	773
Ending ALLL related to loans individually evaluated for impairment	7	8
Ending ALLL	681	781
Recorded Investment:
Collectively evaluated for impairment	60,859	71,564
Individually evaluated for impairment	2,969	3,245
Total loans	$ 63,828	$ 74,809
Ratio of allowance for loan losses to total loans	1.07%	1.04%
Commercial real estate | Construction | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	0	0
Residential loans | Home equity
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	973	910	859
Provision (reversal)	58	60	48
Charge-offs	0	0	0
Recoveries	0	3	3
Ending balance		973	910
Ending ALLL related to loans collectively evaluated for impairment	1,025	966
Ending ALLL related to loans individually evaluated for impairment	6	7
Ending ALLL	1,031	973
Recorded Investment:
Collectively evaluated for impairment	131,620	116,390
Individually evaluated for impairment	753	715
Total loans	$ 132,467	$ 117,207
Ratio of allowance for loan losses to total loans	0.78%	0.83%
Allowance for loan losses to non-accrual loans	254.00%	1071.00%
Residential loans | Home equity | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	94	102
Residential loans | Other residential
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	454	394	433
Provision (reversal)	82	60	(39)
Charge-offs	0	0	0
Recoveries	0	0	0
Ending balance		454	394
Ending ALLL related to loans collectively evaluated for impairment	535	399
Ending ALLL related to loans individually evaluated for impairment	1	55
Ending ALLL	536	454
Recorded Investment:
Collectively evaluated for impairment	94,378	76,584
Individually evaluated for impairment	1,148	1,965
Total loans	$ 95,526	$ 78,549
Ratio of allowance for loan losses to total loans	0.56%	0.58%
Residential loans | Other residential | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	0	0
Consumer loans | Installment and other consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	372	425	566
Provision (reversal)	3	(75)	(123)
Charge-offs	(4)	(5)	(20)
Recoveries	7	27	2
Ending balance		372	425
Ending ALLL related to loans collectively evaluated for impairment	276	274
Ending ALLL related to loans individually evaluated for impairment	102	98
Ending ALLL	378	372
Recorded Investment:
Collectively evaluated for impairment	26,689	24,563
Individually evaluated for impairment	721	932
Total loans	$ 27,410	$ 25,495
Ratio of allowance for loan losses to total loans	1.38%	1.46%
Allowance for loan losses to non-accrual loans		683.00%
Consumer loans | Installment and other consumer | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	$ 0	$ 0
Recorded Investment:
Purchased credit-impaired	0	0
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,541	1,096	969
Provision (reversal)	(823)	445	127
Charge-offs	0	0	0
Recoveries	0	0	0
Ending balance		1,541	$ 1,096
Ending ALLL related to loans collectively evaluated for impairment	718	1,541
Ending ALLL related to loans individually evaluated for impairment	0	0
Ending ALLL	718	1,541
Recorded Investment:
Collectively evaluated for impairment	0	0
Individually evaluated for impairment	0	0
Total loans		0
Unallocated | Receivables Acquired with Deteriorated Credit Quality
Allowance for Loan and Lease Losses [Roll Forward]
Ending ALLL	0	0
Recorded Investment:
Purchased credit-impaired	$ 0	$ 0

Loans and Allowance for Loan 58

Loans and Allowance for Loan Losses - Purchased Credit-Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
PCI Loans, Carrying Value [Abstract]
Unpaid Principal Balance	$ 2,868	$ 3,350
Carrying Value	2,115	2,920
Accretable Yield [Roll Forward]
Balance at beginning of period	1,476	2,618	$ 4,027
Additions	109	0	0
Removals	0	(778)	(914)
Accretion	(331)	(364)	(495)
Balance at end of period	1,254	1,476	$ 2,618
Commercial | Commercial and industrial
PCI Loans, Carrying Value [Abstract]
Unpaid Principal Balance	276	45
Carrying Value	65	40
Commercial real estate | Commercial real estate, owner-occupied
PCI Loans, Carrying Value [Abstract]
Unpaid Principal Balance	1,297	1,344
Carrying Value	1,166	1,072
Commercial real estate | Commercial real estate, investor
PCI Loans, Carrying Value [Abstract]
Unpaid Principal Balance	1,064	1,713
Carrying Value	790	1,706
Commercial real estate | Construction
PCI Loans, Carrying Value [Abstract]
Unpaid Principal Balance	0	0
Carrying Value	0	0
Residential loans | Home equity
PCI Loans, Carrying Value [Abstract]
Unpaid Principal Balance	231	248
Carrying Value	$ 94	$ 102

Loans and Allowance for Loan 59

Loans and Allowance for Loan Losses - Pledged Loans (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financial Instruments Owned and Pledged as Collateral [Line Items]
Certain qualifying loans pledged for FHLB line of credit	$ 887.9	$ 869.2
Other residential
Financial Instruments Owned and Pledged as Collateral [Line Items]
Residential loans pledged for FRB borrowings	$ 67.6	$ 54.6

Loans and Allowance for Loan 60

Loans and Allowance for Loan Losses - Related Party Loans (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2017USD ($)director	Jun. 30, 2017director	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Loans and Leases Receivable, Related Parties [Roll Forward]
Balance at beginning of year			$ 1,988	$ 2,562	$ 3,329
Additions			3,186	0	0
Advances			74	0	165
Repayments			(128)	(574)	(390)
Reclassified due to a change in borrower status			6,732	0	(542)
Balance at end of year	$ 11,852		11,852	1,988	$ 2,562
Related Party Transaction [Line Items]
Number of new board of directors | director	1,000	1,000
Directors, Officers, Principal Shareholders and Associates
Related Party Transaction [Line Items]
Undisbursed commitment to related parties	$ 9,100		$ 9,100	$ 1,100

Bank Premises and Equipment (De

Bank Premises and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	$ 26,050	$ 24,510
Accumulated depreciation and amortization	(17,438)	(15,990)
Bank premises and equipment, net	8,612	8,520
Depreciation and amortization	1,900	1,800	$ 2,000
Leasehold improvements
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	14,937	13,883
Furniture and equipment
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	$ 11,113	$ 10,627

Bank Owned Life Insurance (Deta

Bank Owned Life Insurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance [Abstract]
Estimated death benefits	$ 81,900
Death benefits provided under terms of the programs	38,100	$ 32,400
Earnings on bank-owned life Insurance	$ 845	$ 844	$ 814

Deposits - Stratification of Ti

Deposits - Stratification of Time Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Banking and Thrift [Abstract]
Time deposits of less than $100 thousand	$ 39,361	$ 36,346
Time deposits of $100 thousand to $250 thousand	68,391	66,092
Time deposits of more than $250 thousand	52,364	49,025
Total time deposits	$ 160,116	$ 151,463

Deposits - Narrative (Details)

Deposits - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Banking and Thrift [Abstract]
Interest on time accounts	$ 576	$ 743	$ 853
Held-to-maturity securities pledged as collateral	107,800
CDARS balance in reciprocal deposit program	13,500	15,100
ICS balance in reciprocal deposit program	41,000	29,000
DDM balance in reciprocal deposit program	29,200	36,400
One-way CDARS deposits	4,200	361
Deposit overdrafts reclassified as loan balances	224	229
Related party deposit liabilities	$ 29,900	$ 7,300

Deposits - Time Deposit Maturit

Deposits - Time Deposit Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Scheduled maturities of time deposits
2,018	$ 108,352
2,019	13,000
2,020	10,511
2,021	18,976
2,022	9,276
Thereafter	1
Total time deposits	$ 160,116	$ 151,463

Borrowings - Lines of Credit an

Borrowings - Lines of Credit and Borrowing Agreements (Details) - Line of Credit - USD ($)	Jun. 15, 2016	Feb. 05, 2008	Dec. 31, 2017	Dec. 31, 2016
Federal Home Loan Bank Borrowings
Line of Credit Facility [Line Items]
Term of FHLB borrowing agreements		10 years
Principal amount of borrowing agreements with FHLB		$ 15,000,000
Fixed interest rate of FHLB borrowing agreement		2.07%
Amount of FHLB borrowings outstanding			$ 0	$ 0
Federal Home Loan Bank
Line of Credit Facility [Line Items]
Lines of credit			538,900,000	513,700,000
Remaining available line of credit from FHLB			538,900,000	513,700,000
Federal Home Loan Bank Borrowings
Line of Credit Facility [Line Items]
Amount of debt repaid	$ 15,000,000
Federal Home Loan Bank Borrowings | Interest expense
Line of Credit Facility [Line Items]
Prepayment fee on debt repaid	$ 312,000
Federal Funds Purchased
Line of Credit Facility [Line Items]
Lines of credit			100,400,000	92,000,000
Short-term Debt			0	0
Federal Funds Purchased | Bank of Napa, N.A. (Napa)
Line of Credit Facility [Line Items]
Lines of credit				8,400,000
Federal Home Loan Bank Overnight Borrowings
Line of Credit Facility [Line Items]
Short-term Debt			0
Federal Home Loan Bank Borrowings
Line of Credit Facility [Line Items]
Short-term Debt			0	0
Federal Reserve Line of Credit
Line of Credit Facility [Line Items]
Lines of credit			52,100,000	43,100,000
Amount of FHLB borrowings outstanding			$ 0	$ 0

Borrowings - Subordinated Debt

Borrowings - Subordinated Debt (Details) $ in Thousands	Nov. 29, 2013USD ($)debenture	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Debt Instrument [Line Items]
Number of subordinated debentures acquired | debenture	2
Accretion of discount on subordinated debentures		$ 153	$ 191	$ 210
Amount guaranteed, on subordinated basis, distributions and other payments on trust preferred securities		8,000
Subordinated debentures		5,739	5,586
Subordinated debenture
Debt Instrument [Line Items]
Subordinated debenture	$ 4,950
Long-term Debt, Gross	$ 8,200	8,248
Accretion of discount on subordinated debentures		153	191	$ 210
Subordinated debentures		5,739	$ 5,586
Subordinated debenture | NorCal Community Bancorp Trust I
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 4,124
Effective interest rate		4.41%
Basis spread on subordinated debenture		3.05%
Subordinated debenture | NorCal Community Bancorp Trust II
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 4,124
Effective interest rate		2.99%
Basis spread on subordinated debenture		1.40%
Subordinated debenture | Maximum
Debt Instrument [Line Items]
Debenture distribution deferral period	5 years

Borrowings - Schedule of Borrow

Borrowings - Schedule of Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Subordinated debenture, Carrying Value	$ 5,739	$ 5,586
Subordinated debenture
Debt Instrument [Line Items]
Subordinated debenture, Carrying Value	5,739	5,586
Subordinated debenture, Average Balance	$ 5,664	$ 5,493
Borrowings, Average Rate	7.65%	7.80%
Line of Credit | Federal Home Loan Bank Borrowings
Debt Instrument [Line Items]
FHLB overnight borrowings and advances, Carrying Value	$ 0	$ 0
FHLB overnight borrowings and advances, Average Balance	$ 0	$ 6,803
Borrowings, Average Rate	0.00%	6.59%
Federal Home Loan Bank Borrowings | Line of Credit
Debt Instrument [Line Items]
Short-term Debt	$ 0	$ 0
FHLB overnight borrowings and advances, Average Balance	$ 1	$ 5,383
Borrowings, Average Rate	1.75%	0.42%

Stockholders' Equity and Stoc69

Stockholders' Equity and Stock Plans - Narrative (Details) $ / shares in Units, $ in Thousands

Jan. 19, 2018$ / shares

Sep. 30, 2015$ / sharesshares

Nov. 30, 2011investor

Dec. 31, 2017USD ($)$ / sharesshares

Dec. 31, 2016USD ($)$ / sharesshares

Dec. 31, 2015USD ($)shares

Jul. 23, 2017$ / sharesshares

Jul. 06, 2017

May 16, 2017shares

Nov. 01, 2011$ / sharesshares

May 11, 2010shares

Jul. 01, 2007shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shares withheld for tax withholding and exercise of options

12,208

0

0

Value of shares withheld for tax withholding and exercise of options | $

$ 801

Shares withheld for tax withholding and exercise of options, weighted average price (usd per share) | $ / shares

$ 65.63

Total compensation cost for share-based payment arrangements | $

$ 1,300

$ 994

$ 636

Share-based compensation income tax benefit recognized | $

293

318

194

Unrecognized compensation expense | $

$ 1,500

Period for recognizing unrecognized compensation expense

2 years 1 month 6 days

Excess tax benefits recorded as a reduction to income tax expense | $

$ 214

Tax benefit realized from disqualifying dispositions of incentive stock options | $

$ 70

49

Percentage of share ownership defining an acquiring person

10.00%

Preferred stock, no par value (in dollars per share) | $ / shares

$ 0

$ 0

Preferred stock, authorized (in shares)

5,000,000

5,000,000

Number of common stock shares authorized to be purchased by warrant

157,711

154,242

Number of institutional investors that purchased warrant | investor

2

Net issuance of shares of common stock from cashless exercise (in shares)

70,591

Subsequent event

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Dividends declared per common share (usd per share) | $ / shares

$ 0.29

Stock options

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Total grant-date fair value of option shares vested | $

$ 449

$ 282

202

Stock options | During 2006 through 2014

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

5 years

Expiration period of grants

10 years

Stock options | During 2006 through 2014 | Vesting Rate, Year One

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | During 2006 through 2014 | Vesting Rate, Year Two

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | During 2006 through 2014 | Vesting Rate, Year Three

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | During 2006 through 2014 | Vesting Rate Year Four

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | During 2006 through 2014 | Vesting Rate Year Five

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | Prior to 2016

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

4 years

Expiration period of grants

7 years

Stock options | Prior to 2016 | Immediately Upon Grant

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | Prior to 2016 | Vesting Rate, Year One

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | Prior to 2016 | Vesting Rate, Year Two

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | Prior to 2016 | Vesting Rate, Year Three

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | Prior to 2016 | Vesting Rate Year Four

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Stock options | After 2014

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

33.00%

Award vesting period

3 years

Expiration period of grants

10 years

Stock options | During 2016

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

33.00%

Award vesting period

3 years

Expiration period of grants

10 years

Restricted stock award

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Total grant-date fair value of option shares vested | $

$ 473

$ 380

$ 262

Restricted stock award | During 2006 through 2014

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

5 years

Expiration period of grants

10 years

Restricted stock award | During 2006 through 2014 | Vesting Rate, Year One

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Restricted stock award | During 2006 through 2014 | Vesting Rate, Year Two

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Restricted stock award | During 2006 through 2014 | Vesting Rate, Year Three

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Restricted stock award | During 2006 through 2014 | Vesting Rate Year Four

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Restricted stock award | During 2006 through 2014 | Vesting Rate Year Five

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

20.00%

Performance shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Award vesting period

3 years

Minimum | Performance shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

0.00%

Maximum | Performance shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Vesting percentage

200.00%

Director Stock Plan, 2010

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shares approved to be issued in common stock

150,000

Number of shares available for future grants under plan

110,433

Employee Stock Purchase Plan, 2007

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shares approved to be issued in common stock

200,000

Number of shares available for future grants under plan

192,453

Discount from closing market price at end of each quarter

500.00%

Employee Stock Purchase Plan, 2007 | Minimum

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Approved payroll deduction to purchase shares, percentage

100.00%

Employee Stock Purchase Plan, 2007 | Maximum

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Approved payroll deduction to purchase shares, percentage

1500.00%

The 2017 Equity Plan

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of shares available for future grants under plan

108,981

118,668

Common Stock

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Exercise price of warrant to purchase common stock (in shares) | $ / shares

$ 26.63

Common Stock | U.S. Treasury Capital Purchase Program (TCPP)

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Exercise price of warrant to purchase common stock (in shares) | $ / shares

$ 27.23

Common Stock | Director Stock Plan, 2010

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shares awarded in period from plan

2,878

4,607

5,295

Series A Junior Participating Preferred Stock

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Preferred stock, no par value (in dollars per share) | $ / shares

$ 0

Preferred stock, authorized (in shares)

1,000,000

Exercise price of warrant to purchase common stock (in shares) | $ / shares

$ 9,000

Number of shares each right entitles holder to purchase

0.01

Stockholders' Equity and Stoc70

Stockholders' Equity and Stock Plans - Options Outstanding Rollforward (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 21, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of Shares
Options outstanding, beginning balance (in shares)		181,789	185,269	194,672
Granted (in shares)		100,664	32,637	28,320
Cancelled, expired or forfeited (in shares)		(2,011)		(652)
Exercised (in shares)		(21,474)	(36,117)	(37,071)
Options outstanding, ending balance (in shares)		258,968	181,789	185,269	194,672
Exercisable (vested), ending balance (in shares)		192,172	103,211	114,581
Weighted Average Exercise Price
Options outstanding, beginning balance (usd per share)		$ 41.20	$ 38.35	$ 35.14
Granted (usd per share)		39.78	49.37	50.70
Cancelled, expired or forfeited (usd per share)		43.97		48.38
Exercised (usd per share)		38.62	33.98	30.72
Options outstanding, ending balance (usd per share)		40.84	41.20	38.35	$ 35.14
Exercisable (vested), ending balance (usd per share)		35.69	36.65	34.12
Weighted Average Grant-Date Fair Value
Granted (usd per share)		$ 32.61	$ 10.11	$ 12.21
Weighted Average Remaining Contractual Term
Options outstanding		5 years 4 months 2 days	5 years 9 months 7 days	5 years	4 years 5 months 23 days
Exercisable (vested)		4 years 5 months 1 day	4 years 2 months 4 days	3 years 2 months 15 days
Aggregate Intrinsic Value
Options outstanding, beginning balance		$ 5,190	$ 2,788	$ 3,398
Exercised		585	661	755
Options outstanding, ending balance		7,075	5,190	2,788	$ 3,398
Exercisable (vested) at year end		$ 6,212	$ 3,416	$ 2,209
Bank of Napa, N.A. (Napa)
Business Acquisition [Line Items]
Number of options issued in merger	70,145	70,145
Weighted Average Exercise Price
Options outstanding, ending balance (usd per share)		$ 27.20
Weighted Average Grant-Date Fair Value
Granted (usd per share)		$ 40.71

Stockholders' Equity and Stoc71

Stockholders' Equity and Stock Plans - Non-vested Awards Activity (Details) - Restricted Stock Awards - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Non-vested awards, beginning balance (in shares)	39,699	31,388	22,423
Granted (in shares)	16,230	16,910	15,970
Vested (in shares)	(10,321)	(8,599)	(6,555)
Forfeited (in shares)			(450)
Non-vested awards, ending balance (in shares)	45,608	39,699	31,388
Weighted Average Grant-Date Fair Value
Non-vested awards, beginning balance (usd per share)	$ 48.15	$ 46.24	$ 41.25
Granted (usd per share)	69.59	49.65	50.75
Vested (usd per share)	45.78	44.14	40
Forfeited (usd per share)			48.45
Non-vested awards, ending balance (usd per share)	$ 56.31	$ 48.15	$ 46.24

Stockholders' Equity and Stoc72

Stockholders' Equity and Stock Plans - Options Outstanding by Price Range (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding (in shares)	258,968	181,789	185,269	194,672
Stock Options Outstanding, Remaining Contractual Life	5 years 4 months 2 days	5 years 9 months 7 days	5 years	4 years 5 months 23 days
Weighted Average Exercise Price (usd per share)	$ 40.84	$ 41.20	$ 38.35	$ 35.14
$10.00 - $20.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit (usd per share)	10
Range of Exercise Prices, Upper Limit (usd per share)	20
$20.01 - $30.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit (usd per share)	20.01
Range of Exercise Prices, Upper Limit (usd per share)	30
$30.01 - $40.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit (usd per share)	30.01
Range of Exercise Prices, Upper Limit (usd per share)	40
$40.01 - $50.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit (usd per share)	40.01
Range of Exercise Prices, Upper Limit (usd per share)	50
$50.01 - $60.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit (usd per share)	50.01
Range of Exercise Prices, Upper Limit (usd per share)	60
$60.01 - $70.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Exercise Prices, Lower Limit (usd per share)	60.01
Range of Exercise Prices, Upper Limit (usd per share)	$ 70
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding (in shares)	258,968
Stock Options Outstanding, Remaining Contractual Life
Stock Options Exercisable (in shares)	192,172
Stock options | $10.00 - $20.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding (in shares)	14,120
Stock Options Outstanding, Remaining Contractual Life	2 years 1 month 6 days
Weighted Average Exercise Price (usd per share)	$ 17.74
Stock Options Exercisable (in shares)	14,120
Stock Options Exercisable, Weighted Average Exercise Price (usd per share)	$ 17.74
Stock options | $20.01 - $30.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding (in shares)	51,731
Stock Options Outstanding, Remaining Contractual Life	1 year 1 month 6 days
Weighted Average Exercise Price (usd per share)	$ 26.05
Stock Options Exercisable (in shares)	51,731
Stock Options Exercisable, Weighted Average Exercise Price (usd per share)	$ 26.05
Stock options | $30.01 - $40.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding (in shares)	70,363
Stock Options Outstanding, Remaining Contractual Life	5 years 3 months 18 days
Weighted Average Exercise Price (usd per share)	$ 35.53
Stock Options Exercisable (in shares)	68,238
Stock Options Exercisable, Weighted Average Exercise Price (usd per share)	$ 35.41
Stock options | $40.01 - $50.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding (in shares)	64,511
Stock Options Outstanding, Remaining Contractual Life	7 years 1 month 6 days
Weighted Average Exercise Price (usd per share)	$ 46.14
Stock Options Exercisable (in shares)	33,224
Stock Options Exercisable, Weighted Average Exercise Price (usd per share)	$ 44.73
Stock options | $50.01 - $60.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding (in shares)	27,724
Stock Options Outstanding, Remaining Contractual Life	6 years 10 months 24 days
Weighted Average Exercise Price (usd per share)	$ 50.70
Stock Options Exercisable (in shares)	18,200
Stock Options Exercisable, Weighted Average Exercise Price (usd per share)	$ 50.70
Stock options | $60.01 - $70.00
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Outstanding (in shares)	30,519
Stock Options Outstanding, Remaining Contractual Life	9 years 3 months 18 days
Weighted Average Exercise Price (usd per share)	$ 68.68
Stock Options Exercisable (in shares)	6,659
Stock Options Exercisable, Weighted Average Exercise Price (usd per share)	$ 65.46

Stockholders' Equity and Stoc73

Stockholders' Equity and Stock Plans - Valuation Assumptions (Details) - Stock options	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.66%	1.37%	1.67%
Expected dividend yield on common stock	1.70%	2.02%	1.75%
Expected life in years	2 years 4 months 24 days	6 years	6 years
Expected price volatility	25.58%	25.56%	28.06%

Stockholders' Equity and Stoc74

Stockholders' Equity and Stock Plans - Dividends (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Cash dividends to common stockholders	$ 6,896	$ 6,223	$ 5,390
Cash dividends per common share (usd per share)	$ 1.12	$ 1.02	$ 0.90
Retained earnings	$ 155,544	$ 146,464
Stockholders' equity	$ 297,025	$ 230,563	$ 214,473	$ 200,026
Period used to determine amount available for payment of dividends based on restriction (in years)	3 years
Amount of retained earnings available for payment of dividends based on restriction	$ 39,900
Cash held	$ 3,200

Fair Value of Assets and Liab75

Fair Value of Assets and Liabilities - Recorded on a Recurring Basis (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)security	Dec. 31, 2016USD ($)security
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	$ 332,467	$ 372,580
Derivative financial assets (interest rate contracts)	74	55
Derivative financial liabilities (interest rate contracts)	$ 740	$ 933
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities | security	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities | security	1
Assets and liabilities at fair value measured on a recurring basis | Carrying Value | Interest rate contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets (interest rate contracts)	$ 74	$ 55
Derivative financial liabilities (interest rate contracts)	740	933
Assets and liabilities at fair value measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets (interest rate contracts)	0	0
Derivative financial liabilities (interest rate contracts)	0	0
Assets and liabilities at fair value measured on a recurring basis | Significant Other Observable Inputs (Level 2) | Interest rate contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets (interest rate contracts)	74	55
Derivative financial liabilities (interest rate contracts)	740	933
Assets and liabilities at fair value measured on a recurring basis | Significant Unobservable Inputs (Level 3) | Interest rate contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative financial assets (interest rate contracts)	0	0
Derivative financial liabilities (interest rate contracts)	0	0
Mortgage-backed securities and collateralized mortgage obligations issued by U.S. government agencies | Assets and liabilities at fair value measured on a recurring basis | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	188,061	253,434
Mortgage-backed securities and collateralized mortgage obligations issued by U.S. government agencies | Assets and liabilities at fair value measured on a 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]
Securities available for sale	0	0
Mortgage-backed securities and collateralized mortgage obligations issued by U.S. government agencies | Assets and liabilities at fair value measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	188,061	253,434
Mortgage-backed securities and collateralized mortgage obligations issued by U.S. government agencies | Assets and liabilities at fair value measured on a recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
SBA-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	25,982	607
SBA-backed securities | Assets and liabilities at fair value measured on a recurring basis | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	25,982	607
SBA-backed securities | Assets and liabilities at fair value measured on a 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]
Securities available for sale	0	0
SBA-backed securities | Assets and liabilities at fair value measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	25,817	0
SBA-backed securities | Assets and liabilities at fair value measured on a recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	165	607
Debentures of government sponsored agencies | Assets and liabilities at fair value measured on a recurring basis | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	12,938	35,403
Debentures of government sponsored agencies | Assets and liabilities at fair value measured on a 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]
Securities available for sale	0	0
Debentures of government sponsored agencies | Assets and liabilities at fair value measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	12,938	35,403
Debentures of government sponsored agencies | Assets and liabilities at fair value measured on a recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
Privately issued CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,431	419
Privately issued CMOs | Assets and liabilities at fair value measured on a recurring basis | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,431	419
Privately issued CMOs | Assets and liabilities at fair value measured on a 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]
Securities available for sale	0	0
Privately issued CMOs | Assets and liabilities at fair value measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	1,431	419
Privately issued CMOs | Assets and liabilities at fair value measured on a recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
Obligations of state and political subdivisions | Assets and liabilities at fair value measured on a recurring basis | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	97,491	77,701
Obligations of state and political subdivisions | Assets and liabilities at fair value measured on a 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]
Securities available for sale	0	0
Obligations of state and political subdivisions | Assets and liabilities at fair value measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	97,491	77,701
Obligations of state and political subdivisions | Assets and liabilities at fair value measured on a recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	0
Corporate bonds | Assets and liabilities at fair value measured on a recurring basis | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	6,564	5,016
Corporate bonds | Assets and liabilities at fair value measured on a 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]
Securities available for sale	0	0
Corporate bonds | Assets and liabilities at fair value measured on a recurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	6,564	5,016
Corporate bonds | Assets and liabilities at fair value measured on a recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale	0	$ 0
U.S. government agency obligation collateralized by loans guaranteed by SBA program
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Decrease in unrealized gain (loss) due to transfers to Level 3	$ 6

Fair Value of Assets and Liab76

Fair Value of Assets and Liabilities - Recorded on Nonrecurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate for selling costs applied to all properties	6.00%
Financial instruments at fair value measured on a nonrecurring basis | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets recorded on nonrecurring basis	$ 0
Other real estate		$ 408
Financial instruments at fair value measured on a nonrecurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets recorded on nonrecurring basis	0
Other real estate		408
Financial instruments at fair value measured on a nonrecurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets recorded on nonrecurring basis	0
Other real estate		0
Financial instruments at fair value measured on a nonrecurring basis | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets recorded on nonrecurring basis	$ 0
Other real estate		$ 0

Fair Value of Assets and Liab77

Fair Value of Assets and Liabilities - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Nov. 29, 2013
Financial assets:
Investment securities held-to-maturity	$ 151,032	$ 45,097
Subordinated debenture
Financial liabilities:
Subordinated debentures			$ 4,950
Subordinated debenture | NorCal Community Bancorp Trust I
Financial liabilities:
Basis spread on subordinated debenture	3.05%
Subordinated debenture | NorCal Community Bancorp Trust II
Financial liabilities:
Basis spread on subordinated debenture	1.40%
Fair Value Hierarcy (Level 1) | Carrying Value
Financial assets:
Cash and cash equivalents	$ 203,545	48,804
Fair Value Hierarcy (Level 1) | Fair Value
Financial assets:
Cash and cash equivalents	203,545	48,804
Fair Value Hierarchy (Level 2) | Carrying Value
Financial assets:
Investment securities held-to-maturity	151,032	44,438
Interest receivable	7,501	6,319
Financial liabilities:
Deposits	2,148,670	1,772,700
Interest payable	191	134
Fair Value Hierarchy (Level 2) | Fair Value
Financial assets:
Investment securities held-to-maturity	151,032	45,097
Interest receivable	7,501	6,319
Financial liabilities:
Deposits	2,148,050	1,773,102
Interest payable	191	134
Fair Value Hierarchy (Level 3) | Carrying Value
Financial assets:
Loans, net	1,663,246	1,471,174
Financial liabilities:
Subordinated debentures	5,739	5,586
Fair Value Hierarchy (Level 3) | Fair Value
Financial assets:
Loans, net	1,650,198	1,473,360
Financial liabilities:
Subordinated debentures	$ 5,118	$ 5,083

Benefit Plans - Deferred Compen

Benefit Plans - Deferred Compensation Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Jan. 01, 2017	Dec. 31, 2016	Jan. 01, 2016	Jan. 01, 2015
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Interest rate earned on deferred amounts, prime rate first business day of year		3.75%		3.50%	3.25%
Deferred compensation obligation	$ 3.4		$ 3.2
Annual Salary | Management
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Maximum percentage of compensation allowed to be deferred	80.00%
Deferred Bonus | Management
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Maximum percentage of compensation allowed to be deferred	100.00%

Benefit Plans - Defined Contrib

Benefit Plans - Defined Contribution Plan (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)date	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Bank of Marin Employee Stock Ownership and Savings Plan (the Plan)
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, number of years to be fully vested	5 years
Cash contributed to the ESOP	$ 1,200	$ 1,200	$ 1,100
Defined Contribution Plan (the 401k Plan)
Defined Contribution Plan Disclosure [Line Items]
Minimum age of eligible employee for 401(k) plan	18 years
Minimum employment period to qualify for 401(k) plan	90 days
Number of open enrollment dates for 401(k) plan | date	4
Minimum annual contribution per employee, percent of eligible compensation	1.00%
Maximum annual contribution per employee, percent of eligible compensation	50.00%
Annual vesting percentage	20.00%
Defined contribution plan, number of years to be fully vested	5 years
Employer matching contribution percentage	70.00%	60.00%
Employer matching contribution maximum amount	$ 5	$ 4
Employer contributions	$ 765	$ 589	$ 555

Benefit Plans - Salary Continua

Benefit Plans - Salary Continuation Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Percentage of salary paid upon retirement	25.00%
Period before ratable vesting begins	5 years
Age ratable vesting ends	65 years
Liability under the Salary Continuation Plan	$ 2.5	$ 1
Bank of Napa, N.A. (Napa)
Defined Benefit Plan Disclosure [Line Items]
Liability under the Salary Continuation Plan	$ 1.2

Income Taxes - Components of In

Income Taxes - Components of Income Tax Provision (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current tax provision
Federal		$ 5,379	$ 9,710	$ 7,097
State		2,623	3,794	2,931
Total current		8,002	13,504	10,028
Deferred tax provision (benefit)
Federal		4,444	(206)	382
State		416	48	80
Total deferred		4,860	(158)	462
Total income tax provision		12,862	$ 13,346	$ 10,490
Write-down to net deferred tax assets recorded as income tax expense	$ 3,000	$ 3,000

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Asset and Liability (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Allowance for loan losses and off-balance sheet credit commitments	$ 4,945,000	$ 6,871,000
Net operating loss carryforwards	2,629,000	3,582,000
Net unrealized loss on securities available-for-sale	1,405,000	2,543,000
Deferred compensation plan and salary continuation plan	1,744,000	1,773,000
State franchise tax	557,000	1,300,000
Accrued but unpaid expenses	212,000	1,251,000
Fair value adjustment on acquired loans	570,000	799,000
Deferred rent and other lease incentives	328,000	547,000
Depreciation and disposals on premises and equipment	632,000	528,000
Other real estate owned	0	448,000
Stock-based compensation	463,000	398,000
Interest received on non-accrual loans	130,000	185,000
Other	266,000	196,000
Total gross deferred tax assets	13,881,000	20,421,000
Deferred tax liabilities:
Deferred loan origination costs and fees	(2,153,000)	(2,784,000)
Unaccreted discount on subordinated debentures	(742,000)	(1,119,000)
Core deposit intangible asset	(1,919,000)	(1,085,000)
Accretion on investment securities	(56,000)	(54,000)
Other	(221,000)	(42,000)
Total gross deferred tax liabilities	(5,091,000)	(5,084,000)
Net deferred tax assets	8,790,000	15,337,000
Valuation allowance of deferred tax assets	0	$ 0
Federal
Deferred tax liabilities:
Net operating loss carryforwards expected to expire	5,100,000
California
Deferred tax liabilities:
Net operating loss carryforwards expected to expire	$ 18,100,000

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent
Federal statutory income tax rate		35.00%	35.00%	35.00%
California franchise tax, net of federal tax benefit		6.90%	6.80%	6.80%
Write down of federal deferred tax assets, net		10.50%	0.00%	0.00%
Tax exempt interest on municipal securities and loans		(6.10%)	(4.00%)	(4.20%)
Tax exempt earnings on bank owned life insurance		(1.00%)	(0.80%)	(1.00%)
Non-deductible acquisition related expenses		0.80%	0.00%	0.00%
Low income housing and qualified zone academy bond tax credits		(0.40%)	(0.30%)	(0.20%)
Stock-based compensation excess tax benefit		(0.30%)	0.00%	0.00%
Other		(0.80%)	(0.10%)	(0.10%)
Effective Tax Rate		44.60%	36.60%	36.30%
Write-down to net deferred tax assets recorded as income tax expense	$ 3	$ 3

Commitments and Contingencies84

Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leases
2,018	$ 4,444
2,019	4,198
2,020	3,758
2,021	2,138
2,022	1,330
Thereafter	2,904
Total	18,772
Minimum payments due on minimum sublease rentals under non-cancelable subleases	51
Rent expense included in occupancy expense	4,100	$ 3,900	$ 4,200
Visa Inc.
Loss Contingencies [Line Items]
Estimated amount due to class plaintiffs in Visa litigation	4,000,000
Balance of escrow account for legal settlements maintained by Visa	$ 828,000
Pending Litigation [Member] | Visa Inc.
Loss Contingencies [Line Items]
Settlements reached by percentage of sales volume of merchants who opted out in Visa litigation, percent	51.00%

Concentrations of Credit Risk (

Concentrations of Credit Risk (Details) - Credit concentration risk $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)customer	Dec. 31, 2016USD ($)
U.S. Government, its agencies and Government Sponsored Enterprises (GSEs)
Concentration Risk [Line Items]
Concentration risk amount | $	$ 358.4	$ 299.5
Concentration risk percentage	74.00%	72.00%
Loans portfolio
Concentration Risk [Line Items]
Number of major borrowers | customer	0
Concentration risk, threshold for major borrower, percentage	2.00%
Loans on real estate
Concentration Risk [Line Items]
Concentration risk percentage	81.00%	79.00%

Derivative Financial Instrume86

Derivative Financial Instruments and Hedging Activities - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)derivative	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Fair value hedges:
Interest rate contracts fair value, Asset derivatives	$ 74	$ 55
Interest rate contracts fair value, Liability derivatives	740	933
Fair value hedge
Fair value hedges:
Net hedge ineffectiveness gain (loss), derivatives	31	113	$ (80)
Fair value hedge | Interest income
Fair value hedges:
Increase in value of designated interest rate swaps due to LIBOR interest rate movements recognized in interest income	212	778	280
Payment on interest rate swaps recorded in interest income	(333)	(556)	(918)
Decrease in value of hedged loans recognized in interest income	(166)	(571)	(308)
Decrease in value of yield maintenance agreement recognized against interest income	(15)	(94)	(52)
Net loss on derivatives recognized against interest income	(302)	(443)	$ (998)
Fair value hedge | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Derivatives, accrued interest, interest rate swaps	$ 8	13
Interest rate swap | Fair value hedge | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Number of derivative instruments | derivative	5
Interest rate swap | Fair value hedge | Designated as hedging instrument | Other assets
Fair value hedges:
Interest rate contracts notional amounts, Asset derivatives	$ 4,019	4,217
Interest rate swap | Fair value hedge | Designated as hedging instrument | Other liabilities
Fair value hedges:
Interest rate contracts notional amount, Liability derivatives	14,810	15,495
Interest rate contract | Fair value hedge | Designated as hedging instrument | Other assets
Fair value hedges:
Interest rate contracts fair value, Asset derivatives	74	55
Interest rate contract | Fair value hedge | Designated as hedging instrument | Other liabilities
Fair value hedges:
Interest rate contracts fair value, Liability derivatives	$ 740	$ 933

Derivative Financial Instrume87

Derivative Financial Instruments and Hedging Activities - Offsetting of Assets (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	$ 74,000	$ 55,000
Offset in the Statements of Condition	0	0
Net Amounts of Assets Presented in the Statements of Condition	74,000	55,000
Derivative, Collateral, Obligation to Return Securities	(74,000)	(55,000)
Gross Amounts Not Offset in the Statements of Condition, Cash Collateral Received	0	0
Net Amount	0	0
Other assets | Interest rate swap
Offsetting Assets [Line Items]
Derivative assets, accrued interest, interest rate swaps	300	1,000
Counterparty A
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	74,000	55,000
Offset in the Statements of Condition		0
Net Amounts of Assets Presented in the Statements of Condition	74,000	55,000
Derivative, Collateral, Obligation to Return Securities	(74,000)	(55,000)
Gross Amounts Not Offset in the Statements of Condition, Cash Collateral Received		0
Net Amount	$ 0	$ 0

Derivative Financial Instrume88

Derivative Financial Instruments and Hedging Activities - Offsetting of Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	$ 740	$ 933
Gross Amounts Offset in the Statements of Condition	0	0
Net Amounts of Liabilities Presented in the Statements of Condition	740	933
Gross Amounts Not Offset in the Statements of Condition, Financial Instruments	(74)	(55)
Gross Amounts Not Offset in the Statements of Condition, Cash Collateral Pledged	(666)	(878)
Net Amount	0	0
Other liabilities | Interest rate swap
Offsetting Liabilities [Line Items]
Derivative liabilities, accrued interest, interest rate swaps	8	12
Counterparty A
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	740	933
Gross Amounts Offset in the Statements of Condition		0
Net Amounts of Liabilities Presented in the Statements of Condition	740	933
Gross Amounts Not Offset in the Statements of Condition, Financial Instruments	(74)	(55)
Gross Amounts Not Offset in the Statements of Condition, Cash Collateral Pledged	(666)	(878)
Net Amount	$ 0	$ 0

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Bancorp
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital, Actual, Amount	$ 287,435	$ 247,453
Total Capital (to risk-weighted assets), Actual, Ratio	14.91%	14.32%
Total Capital, Minimum Capital for Capital Adequacy Purposes, Amount	$ 178,323	$ 149,039
Total Capital (to risk-weighted assets), Minimum Capital for Capital Adequacy Purposes, Ratio	9.25%	8.625%
Total Capital, Minimum Capital to be Well Capitalized, Amount	$ 192,782	$ 172,799
Total Capital (to risk-weighted assets), Minimum to be Well Capitalized, Ratio	10.00%	10.00%
Tier 1 Risk Based Capital, Actual, Amount	$ 270,710	$ 231,111
Tier 1 Risk Based Capital (to risk-weighted assets), Actual, Ratio	14.04%	13.37%
Tier 1 Capital, Minimum Capital for Capital Adequacy Purposes, Amount	$ 139,767	$ 114,479
Tier 1 Risk Based Capital (to risk-weighted assets), Minimum Capital for Capital Adequacy Purposes, Ratio	7.25%	6.625%
Tier 1 Risk Based Capital, Minimum Capital to be Well Capitalized, Amount	$ 154,225	$ 138,239
Tier 1 Risk Based Capital (to risk-weighted assets), Minimum Capital to be Well Capitalized, Ratio	8.00%	8.00%
Tier 1 Leverage Capital, Amount, Actual	$ 270,710	$ 231,111
Tier 1 Leverage Capital (to average assets), Actual, Ratio	12.13%	11.39%
Tier 1 Leverage Capital, Minimum Capital for Capital Adequacy Purposes, Amount	$ 89,285	$ 81,189
Tier 1 Leverage Capital (to average assets), Minimum Capital for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Tier 1 Leverage Capital, Actual, Amount	$ 111,607	$ 101,486
Tier 1 Leverage Capital (to average assets), Minimum Capital to be Well Capitalized, Ratio	5.00%	5.00%
Tier 1 Common Equity	$ 265,119	$ 225,925
Tier 1 Common Equity To Average Assets	13.75%	13.07%
Tier 1 Common Equity Required for Capital Adequacy	$ 110,849	$ 88,559
Tier 1 Common Equity Required for Capital Adequacy to Average Assets	5.75%	5.125%
Tier 1 Common Equity Required to be Well Capitalized	$ 125,308	$ 112,319
Tier 1 Common Equity Required to be Well Capitalized to Average Assets	6.50%	6.50%
The Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital, Actual, Amount	$ 283,885	$ 243,468
Total Capital (to risk-weighted assets), Actual, Ratio	14.73%	14.09%
Total Capital, Minimum Capital for Capital Adequacy Purposes, Amount	$ 178,281	$ 149,016
Total Capital (to risk-weighted assets), Minimum Capital for Capital Adequacy Purposes, Ratio	9.25%	8.625%
Total Capital, Minimum Capital to be Well Capitalized, Amount	$ 192,737	$ 172,772
Total Capital (to risk-weighted assets), Minimum to be Well Capitalized, Ratio	10.00%	10.00%
Tier 1 Risk Based Capital, Actual, Amount	$ 267,160	$ 222,127
Tier 1 Risk Based Capital (to risk-weighted assets), Actual, Ratio	13.86%	13.15%
Tier 1 Capital, Minimum Capital for Capital Adequacy Purposes, Amount	$ 139,734	$ 114,462
Tier 1 Risk Based Capital (to risk-weighted assets), Minimum Capital for Capital Adequacy Purposes, Ratio	7.25%	6.625%
Tier 1 Risk Based Capital, Minimum Capital to be Well Capitalized, Amount	$ 154,189	$ 138,218
Tier 1 Risk Based Capital (to risk-weighted assets), Minimum Capital to be Well Capitalized, Ratio	8.00%	8.00%
Tier 1 Leverage Capital, Amount, Actual	$ 267,160	$ 222,127
Tier 1 Leverage Capital (to average assets), Actual, Ratio	11.97%	11.19%
Tier 1 Leverage Capital, Minimum Capital for Capital Adequacy Purposes, Amount	$ 89,275	$ 81,176
Tier 1 Leverage Capital (to average assets), Minimum Capital for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Tier 1 Leverage Capital, Actual, Amount	$ 111,593	$ 101,469
Tier 1 Leverage Capital (to average assets), Minimum Capital to be Well Capitalized, Ratio	5.00%	5.00%
Tier 1 Common Equity	$ 267,160	$ 222,127
Tier 1 Common Equity To Average Assets	13.86%	13.15%
Tier 1 Common Equity Required for Capital Adequacy	$ 110,824	$ 88,546
Tier 1 Common Equity Required for Capital Adequacy to Average Assets	5.75%	5.125%
Tier 1 Common Equity Required to be Well Capitalized	$ 125,279	$ 112,302
Tier 1 Common Equity Required to be Well Capitalized to Average Assets	6.50%	6.50%

Financial Instruments with Of90

Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Commercial lines of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	$ 224,370	$ 216,774
Revolving home equity lines
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	177,678	148,143
Undisbursed construction loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	35,322	44,798
Personal and other lines of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	11,758	10,635
Standby letters of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	4,074	1,939
Total commitments and standby letters of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loan commitments and standby letters of credit, off-balance sheet	$ 453,202	422,289
Percentage of commitments expiring in 2018	44.00%
Percentage of commitments expiring between 2019 and 2025	41.00%
Percentage of commitments expiring 2026 and thereafter	15.00%
Total commitments and standby letters of credit | Interest Payable and Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowance for off-balance sheet commitments	$ 958	$ 899

Condensed Bank of Marin Banco91

Condensed Bank of Marin Bancorp Parent Only Financial Statements - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Other assets	$ 72,620	$ 68,961
Total assets	2,468,154	2,023,493
Subordinated debentures	5,739	5,586
Other liabilities	16,720	14,644
Total liabilities	2,171,129	1,792,930
Stockholders' equity	297,025	230,563	$ 214,473	$ 200,026
Total liabilities and stockholders' equity	2,468,154	2,023,493
Bancorp
Condensed Financial Statements, Captions [Line Items]
Cash and due from Bank of Marin	3,246	3,568
Investment in bank subsidiary	299,486	232,431
Other assets	586	670
Total assets	303,318	236,669
Subordinated debentures	5,739	5,586
Accrued expenses payable	146	96
Other liabilities	408	424
Total liabilities	6,293	6,106
Stockholders' equity	297,025	230,563
Total liabilities and stockholders' equity	$ 303,318	$ 236,669

Condensed Bank of Marin Banco92

Condensed Bank of Marin Bancorp Parent Only Financial Statements - Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Interest expense	$ 1,744	$ 2,269	$ 2,251
Non-interest expense	53,782	47,692	46,949
Income tax benefit	(12,862)	(13,346)	(10,490)
Net income	15,976	23,134	18,441
Bancorp
Condensed Financial Statements, Captions [Line Items]
Dividends from bank subsidiary	8,000	6,400	6,500
Miscellaneous Income	8	7	6
Total income	8,008	6,407	6,506
Interest expense	439	435	420
Non-interest expense	2,087	984	973
Total expense	2,526	1,419	1,393
Income (loss) before income taxes and equity in undistributed net income of subsidiary	5,482	4,988	5,113
Income tax benefit	876	594	583
Income (loss) before equity in undistributed net income of subsidiary	6,358	5,582	5,696
Earnings of bank subsidiary greater (less) than dividends received from bank subsidiary	9,618	17,552	12,745
Net income	$ 15,976	$ 23,134	$ 18,441

Condensed Bank of Marin Banco93

Condensed Bank of Marin Bancorp Parent Only Financial Statements - Cash Flow Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net income	$ 15,976	$ 23,134	$ 18,441
Accretion of discount on subordinated debentures	153	191	210
Other assets	(278)	581	347
Other liabilities	1,035	(324)	1,142
Noncash director compensation expense-common stock	197	180	274
Net cash provided by operating activities	26,947	25,446	23,682
Net cash used in investing activities	7,813	24,318	(263,278)
Payment of tax withholding for stock options exercised	(60)	0	0
Dividends paid on common stock	(6,896)	(6,223)	(5,390)
Net cash provided by (used in) financing activities	119,981	(27,303)	224,572
Net (decrease) increase in cash and cash equivalents	154,741	22,461	(15,024)
Stock issued in payment of director fees	188	234	275
Bancorp
Condensed Financial Statements, Captions [Line Items]
Net income	15,976	23,134	18,441
Earnings of bank subsidiary greater than dividends received from bank subsidiary	(9,618)	(17,552)	(12,745)
Accretion of discount on subordinated debentures	153	191	210
Other assets	92	353	(298)
Intercompany receivable	(40)	171	(18)
Other liabilities	51	(302)	368
Noncash director compensation expense-common stock	20	0	0
Net cash provided by operating activities	6,634	5,995	5,958
Capital contribution to subsidiary	(853)	(1,285)	(1,156)
Net cash used in investing activities	(853)	(1,285)	(1,156)
Proceeds from stock options exercised and stock issued under employee and director stock purchase plans and ESOP	853	1,285	1,156
Payment of tax withholding for stock options exercised	(60)	0	0
Dividends paid on common stock	(6,896)	(6,223)	(5,390)
Net cash provided by (used in) financing activities	(6,103)	(4,938)	(4,234)
Net (decrease) increase in cash and cash equivalents	(322)	(228)	568
Cash and cash equivalents at beginning of period	3,568	3,796	3,228
Cash and cash equivalents at end of period	3,246	3,568	3,796
Stock issued in payment of director fees	$ 188	$ 234	$ 275

Acquisition - Narrative (Detail

Acquisition - Narrative (Details)	12 Months Ended
	Dec. 31, 2017USD ($)	Nov. 21, 2017USD ($)branch	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Goodwill	$ 30,140,000		$ 6,436,000
Impairment on goodwill	$ 0
Minimum
Business Acquisition [Line Items]
Constant prepayment rate (CPR)	5.00%
Maximum
Business Acquisition [Line Items]
Constant prepayment rate (CPR)	27.00%
Bank of Napa, N.A. (Napa)
Business Acquisition [Line Items]
Loans acquired		$ 134,700,000
Deposits assumed		249,886,000
Investment securities acquired		$ 75,469,000
Number of branch offices | branch		2
Shares received by Napa shareholders in merger per acquiree share		0.307
Goodwill		$ 23,705,000

Acquisition - Estimated Fair Va

Acquisition - Estimated Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Nov. 21, 2017	Dec. 31, 2017	Dec. 31, 2016
Assets:
Goodwill		$ 30,140	$ 6,436
Bank of Napa, N.A. (Napa)
Assets:
Cash and cash equivalents	$ 59,779
Investment securities	75,469
Loans	134,720
Core deposit intangible	4,441
Goodwill	23,705
Bank premises and equipment	599
Other assets	6,408
Total assets acquired	305,121
Liabilities:
Deposits	249,886
Other liabilities	2,050
Total liabilities assumed	251,936
Merger consideration	53,185
Consideration transferred:
Merger consideration	$ 53,185
Number of shares issued in merger	735,264
Number of options issued in merger	70,145	70,145
Bank of Napa, N.A. (Napa) | Non-interest bearing
Liabilities:
Deposits	$ 77,266
Bank of Napa, N.A. (Napa) | Transaction accounts
Liabilities:
Deposits	50,080
Bank of Napa, N.A. (Napa) | Savings accounts
Liabilities:
Deposits	12,157
Bank of Napa, N.A. (Napa) | Money market accounts
Liabilities:
Deposits	85,045
Bank of Napa, N.A. (Napa) | Other time accounts
Liabilities:
Deposits	$ 25,338

Acquisition - Net Assets Acquir

Acquisition - Net Assets Acquired, Consideration Paid and Estimated Fair Value Adjustments (Details) - USD ($) $ in Thousands	Nov. 21, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Fair value of net assets acquired from Bank of Napa	$ 29,480
Fair value of net assets acquired from Bank of Napa	$ (29,480)
Goodwill		$ 30,140	$ 6,436
Tax rate on purchase accounting adjustments	42.05%
Bank of Napa, N.A. (Napa)
Business Acquisition [Line Items]
Book value of net assets acquired from Bank of Napa	$ 26,152
Fair value adjustment, loans	1,301
Fair value adjustment, core deposit intangible	4,441
Total purchase accounting adjustments	5,742
Deferred tax liabilities (tax effect of purchase accounting adjustments at 42.05%)	(2,414)
Fair value of net assets acquired from Bank of Napa	29,480
Merger consideration	53,185
Fair value of net assets acquired from Bank of Napa	(29,480)
Goodwill	$ 23,705

Acquisition - PCI and Non-PCI L

Acquisition - PCI and Non-PCI Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Nov. 21, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
PCI loans
Less: interest component of cash flows expected to be collected (accretable yield)	$ 1,254		$ 1,476	$ 2,618	$ 4,027
Bank of Napa, N.A. (Napa)
Non-PCI loans
Contractually required payments including interest		$ 183,833
Contractual cash flows not expected to be collected		14,227
Fair value of non-PCI loans		133,865
Bank of Napa, N.A. (Napa) | Receivables Acquired with Deteriorated Credit Quality
PCI loans
Contractually required payments including interest		1,769
Less: contractual cash flows not expected to be collected (nonaccretable difference)		805
Cash flows expected to be collected (undiscounted)		964
Less: interest component of cash flows expected to be collected (accretable yield)		109
Fair value of PCI loans		$ 855

Acquisition - Outstanding Balan

Acquisition - Outstanding Balance and Related Carrying Value of PCI Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Nov. 21, 2017	Dec. 31, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Unpaid Principal Balance	$ 2,868		$ 3,350
Bank of Napa, N.A. (Napa) | Receivables Acquired with Deteriorated Credit Quality
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Unpaid Principal Balance		$ 1,487
Fair value		855
Bank of Napa, N.A. (Napa) | Commercial | Receivables Acquired with Deteriorated Credit Quality
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Unpaid Principal Balance		417
Fair value		70
Bank of Napa, N.A. (Napa) | Commercial real estate | Receivables Acquired with Deteriorated Credit Quality
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Unpaid Principal Balance		1,070
Fair value		$ 785

Acquisition - Core Deposit Inta

Acquisition - Core Deposit Intangible (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization of core deposit intangible	$ 529	$ 533	$ 619
Core deposit intangible
Future Amortization Expense:
2,018	921
2,019	887
2,020	853
2,021	818
2,022	782
Thereafter	2,231
Total	$ 6,492
Bank of Napa, N.A. (Napa) | Core deposit intangible
Acquired Finite-Lived Intangible Assets [Line Items]
Core deposit intangible useful life	10 years
Amortization of core deposit intangible	$ 56
Future Amortization Expense:
2,018	508
2,019	499
2,020	488
2,021	475
2,022	460
Thereafter	1,955
Total	$ 4,385

Acquisition - Pro Forma Revenue

Acquisition - Pro Forma Revenue and Earnings (Details) - Bank of Napa, N.A. (Napa) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Net interest income, Actual from acquisition date through December 31, 2017	$ 913
Net interest income, Unaudited Pro Forma		$ 82,802	$ 80,898
Net (loss) Income, Actual from acquisition date through December 31, 2017	$ (576)
Net (loss) Income, Unaudited Pro Forma		18,898	21,559
One-time acquisition related costs		2,209
Bank of Napa, N.A. (Napa)
Business Acquisition [Line Items]
One-time acquisition related costs			$ 2,500
Bancorp
Business Acquisition [Line Items]
One-time acquisition related costs		$ 2,200

Acquisition - Acquisition-Relat

Acquisition - Acquisition-Related Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Data processing	$ 4,906	$ 3,625	$ 3,318
Professional services	2,858	2,044	2,121
Other	6,435	$ 6,067	$ 5,984
Bank of Napa, N.A. (Napa)
Business Acquisition [Line Items]
Data processing	1,108
Professional services	952
Personnel severance	35
Other	114
Total	$ 2,209