CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income, Net of Taxes
Balance at Dec. 31, 2013	$ 180,887us-gaap_StockholdersEquity	$ 80,095	$ 101,464	$ (672)
Balance (in shares) at Dec. 31, 2013		5,877,524
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,771us-gaap_NetIncomeLoss		19,771
Other comprehensive income (loss)	1,760			1,760
Stock options exercised (in shares)		49,415
Stock options exercised	1,452	1,452
Excess tax benefit - stock-based compensation	172	172
Stock issued under employee stock purchase plan (in shares)		521
Stock issued under employee stock purchase plan	23	23
Restricted stock granted (in shares)		8,523
Restricted stock granted	0	0
Restricted stock forfeited/cancelled (in shares)		(2,067)
Restricted stock forfeited/cancelled	0	0
Stock-based compensation - stock options	200	200
Stock-based compensation - restricted stock	246	246
Cash dividends paid on common stock	(4,733)us-gaap_DividendsCommonStockCash		(4,733)
Stock purchased by directors under director stock plan (in shares)		260
Stock purchased by directors under director stock plan	12	12
Stock issued in payment of director fees (in shares)		5,306
Stock issued in payment of director fees	236bmrc_StockIssuedInPaymentOfDirectorFees	236
Balance at Dec. 31, 2014	200,026us-gaap_StockholdersEquity	82,436	116,502	1,088
Balance (in shares) at Dec. 31, 2014	5,939,482us-gaap_CommonStockSharesOutstanding	5,939,482
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,457us-gaap_NetIncomeLoss		4,457
Other comprehensive income (loss)	755			755
Stock options exercised (in shares)		9,371
Stock options exercised	312	312
Excess tax benefit - stock-based compensation	28	28
Stock issued under employee stock purchase plan (in shares)		96
Stock issued under employee stock purchase plan	5	5
Restricted stock granted (in shares)		15,970
Restricted stock granted	0	0
Stock-based compensation - stock options	36	36
Stock-based compensation - restricted stock	56	56
Cash dividends paid on common stock	(1,307)us-gaap_DividendsCommonStockCash		(1,307)
Stock issued in payment of director fees (in shares)		2,695
Stock issued in payment of director fees	138bmrc_StockIssuedInPaymentOfDirectorFees	138
Balance at Mar. 31, 2015	$ 204,506us-gaap_StockholdersEquity	$ 83,011	$ 119,652	$ 1,843
Balance (in shares) at Mar. 31, 2015	5,967,614us-gaap_CommonStockSharesOutstanding	5,967,614

Stock Issued During Period, Shares, Nonemployee Director Stock Purchase Plans

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Stock Issued During Period, Value, Nonemployee Director Stock Purchase Plans

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Dollar amount of common stock issued by an Entity to its directors in payment of services they render.

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Common stock issued by an Entity to its directors in payment of services they render in number of shares.

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Amount of equity-based compensation, related to restricted stock units or restricted stock awards, recognized as expense or an asset, if compensation is capitalized.

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This element represents the amount of recognized equity-based compensation related to stock options during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized).

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Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Number of shares related to Restricted Stock Award forfeited during the period.

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Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

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Number of share options (or share units) exercised during the current period.

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Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

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Value of stock related to Restricted Stock Awards forfeited during the period.

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Aggregate value of stock related to Restricted Stock Awards issued during the period.

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Value of stock issued as a result of the exercise of stock options.

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