3. FAIR VALUE MEASUREMENTS - Carrying amounts and estimated fair values (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financial assets:
Cash and due from banks	$ 22,449us-gaap_CashAndDueFromBanks	$ 17,948us-gaap_CashAndDueFromBanks
Interest-bearing deposits in banks	1,000us-gaap_InterestBearingDepositsInBanks	1,000us-gaap_InterestBearingDepositsInBanks
Available-for-sale securities	289,064us-gaap_AvailableForSaleSecurities	272,791us-gaap_AvailableForSaleSecurities
Held-to-maturity securities	922	1,263
FHLB stock	3,686us-gaap_FederalHomeLoanBankStock	3,248us-gaap_FederalHomeLoanBankStock
Loans and leases, net	261,421	249,931
Accrued interest receivable	1,858	1,930
Financial liabilities:
Noninterest-bearing	155,698	145,516
Savings	58,820us-gaap_DepositsSavingsDeposits	51,733us-gaap_DepositsSavingsDeposits
Money market	147,625us-gaap_DepositsMoneyMarketDeposits	135,169us-gaap_DepositsMoneyMarketDeposits
NOW accounts	60,862amrb_NowAccountsFairValueDisclosure	59,042amrb_NowAccountsFairValueDisclosure
Time, $100,000 or more	66,203us-gaap_TimeDeposits100000OrMore	69,763us-gaap_TimeDeposits100000OrMore
Other time	22,282amrb_OtherTimeFairValueDisclosure	23,426amrb_OtherTimeFairValueDisclosure
Short-term borrowings	3,500us-gaap_ShorttermDebtFairValue	8,000us-gaap_ShorttermDebtFairValue
Long-term borrowings	7,567us-gaap_LongTermDebtFairValue	8,110us-gaap_LongTermDebtFairValue
Accrued interest payable	59	125
Level 1
Financial assets:
Cash and due from banks	22,449	17,948
Interest-bearing deposits in banks
Available-for-sale securities	28	70
Held-to-maturity securities
FHLB stock
Loans and leases, net
Accrued interest receivable
Financial liabilities:
Noninterest-bearing	155,698	145,516
Savings	58,820	51,733
Money market	147,625	135,169
NOW accounts	60,862	59,042
Time, $100,000 or more
Other time
Short-term borrowings	3,500	8,000
Long-term borrowings
Accrued interest payable
Level 2
Financial assets:
Cash and due from banks
Interest-bearing deposits in banks	1,002	1,000
Available-for-sale securities	289,036	272,721
Held-to-maturity securities	922	1,263
FHLB stock
Loans and leases, net
Accrued interest receivable	1,150	1,170
Financial liabilities:
Noninterest-bearing
Savings
Money market
NOW accounts
Time, $100,000 or more	66,203	69,763
Other time	22,282	23,426
Short-term borrowings
Long-term borrowings	7,567	8,110
Accrued interest payable	59	125
Level 3
Financial assets:
Cash and due from banks
Interest-bearing deposits in banks
Available-for-sale securities
Held-to-maturity securities
FHLB stock
Loans and leases, net	261,421	249,931
Accrued interest receivable	708	760
Financial liabilities:
Noninterest-bearing
Savings
Money market
NOW accounts
Time, $100,000 or more
Other time
Short-term borrowings
Long-term borrowings
Accrued interest payable
Carrying Amount
Financial assets:
Cash and due from banks	22,449	17,948
Interest-bearing deposits in banks	1,000	1,000
Available-for-sale securities	289,064	272,791
Held-to-maturity securities	862	1,185
FHLB stock	3,686	3,248
Loans and leases, net	258,057	251,747
Accrued interest receivable	1,858	1,930
Financial liabilities:
Noninterest-bearing	155,698	145,516
Savings	58,820	51,733
Money market	147,625	135,169
NOW accounts	60,862	59,042
Time, $100,000 or more	65,569	68,990
Other time	22,119	23,240
Short-term borrowings	3,500	8,000
Long-term borrowings	7,500	8,000
Accrued interest payable	$ 59	$ 125

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Accrued Interest Receivable Fair Value Disclosure

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Custom Element.

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Custom Element.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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For banks and other depository institutions: Includes cash on hand (currency and coin), cash items in process of collection, noninterest bearing deposits due from other financial institutions (including corporate credit unions), and noninterest bearing balances with the Federal Reserve Banks, Federal Home Loan Banks and central banks.

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Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts.

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Amount of interest bearing deposits with no stated maturity, which may include passbook and statement savings accounts and money-market deposit accounts (MMDAs).

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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Fair value of investments in debt securities classified as held-to-maturity.

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For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing deposits in other financial institutions for relatively short periods of time including, for example, certificates of deposits, which are presented separately from cash on the balance sheet.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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The aggregate amount of all domestic and foreign noninterest-bearing deposits liabilities held by the entity.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

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The aggregate amount of domestic and foreign time deposit liabilities (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $100,000 or more.

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