Regulatory Matters (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Risk Based Capital	$ 571,663	$ 534,241
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	10.00%	9.80%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy	$ 257,222	$ 245,216
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Tier One Risk Based Capital	$ 722,674	$ 686,160
Tier One Risk Based Capital to Risk Weighted Assets	12.64%	12.59%
Tier One Risk Based Capital Required for Capital Adequacy	$ 342,962	$ 326,954
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%	6.00%
Capital	$ 794,584	$ 754,758
Capital to Risk Weighted Assets	13.90%	13.85%
Capital Required for Capital Adequacy	$ 457,283	$ 435,939
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Tier One Leverage Capital	$ 722,674	$ 686,160
Tier One Leverage Capital to Average Assets	9.42%	9.50%
Tier One Leverage Capital Required for Capital Adequacy	$ 306,848	$ 289,059
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%	4.00%
Basel III Minimum with Capital Conservation Buffer [Domain]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	7.00%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	8.50%
Capital Required for Capital Adequacy to Risk Weighted Assets	10.50%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%
Boston Private Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Risk Based Capital	$ 661,991	$ 621,668
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	11.64%	11.49%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy	$ 256,030	$ 243,407
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Common Equity Tier One Risk Based Capital Required to be Well Capitalized	$ 369,822	$ 351,588
Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier One Risk Based Capital	$ 661,991	$ 621,668
Tier One Risk Based Capital to Risk Weighted Assets	11.64%	11.49%
Tier One Risk Based Capital Required for Capital Adequacy	$ 341,374	$ 324,543
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%	6.00%
Tier One Risk Based Capital Required to be Well Capitalized	$ 455,165	$ 432,723
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	8.00%
Capital	$ 733,214	$ 689,437
Capital to Risk Weighted Assets	12.89%	12.75%
Capital Required for Capital Adequacy	$ 455,165	$ 432,723
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Capital Required to be Well Capitalized	$ 568,956	$ 540,904
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Tier One Leverage Capital	$ 661,991	$ 621,668
Tier One Leverage Capital to Average Assets	8.70%	8.68%
Tier One Leverage Capital Required for Capital Adequacy	$ 304,510	$ 286,461
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%	4.00%
Tier One Leverage Capital Required to be Well Capitalized	$ 380,637	$ 358,077
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Boston Private Bank [Member] \| Basel III Minimum with Capital Conservation Buffer [Domain]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	7.00%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	8.50%
Capital Required for Capital Adequacy to Risk Weighted Assets	10.50%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%

Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets

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Common Equity Tier One Risk Based Capital Required to be Well Capitalized

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Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets

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Common Equity Tier One Risk Based Capital to Risk Weighted Assets

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The amount of total capital as defined in the regulations.

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The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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