Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2017

REGULATORY MATTERS [Abstract]

Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block]

	Actual				For capital adequacy purposes (at least)				To be well capitalized under prompt corrective action provisions (at least)				Basel III minimum capital ratio with capital conservation buffer (1)
	Amount		Ratio		Amount		Ratio		Amount		Ratio
	(In thousands)
As of December 31, 2017
Common equity tier 1 risk-based capital
Company	$	607,800	10.32	%	$	265,153	4.5	%	n/a		n/a		7.0	%
Boston Private Bank	694,201		11.83		264,028		4.5		$	381,373	6.5	%	7.0
Tier 1 risk-based capital
Company	758,089		12.87		353,537		6.0		n/a		n/a		8.5
Boston Private Bank	694,201		11.83		352,037		6.0		469,382		8.0		8.5
Total risk-based capital
Company	832,182		14.12		471,383		8.0		n/a		n/a		10.5
Boston Private Bank	767,576		13.08		469,382		8.0		586,728		10.0		10.5
Tier 1 leverage capital
Company	758,089		9.34		324,725		4.0		n/a		n/a		4.0
Boston Private Bank	694,201		8.63		321,920		4.0		402,400		5.0		4.0
As of December 31, 2016
Common equity tier 1 risk-based capital
Company	$	571,663	10.00	%	$	257,222	4.5	%	n/a		n/a		7.0	%
Boston Private Bank	661,991		11.64		256,030		4.5		$	369,822	6.5%		7.0
Tier 1 risk-based capital
Company	722,674		12.64		342,962		6.0		n/a		n/a		8.5
Boston Private Bank	661,991		11.64		341,374		6.0		455,165		8.0		8.5
Total risk-based capital
Company	794,584		13.90		457,283		8.0		n/a		n/a		10.5
Boston Private Bank	733,214		12.89		455,165		8.0		568,956		10.0		10.5
Tier 1 leverage capital
Company	722,674		9.42		306,848		4.0		n/a		n/a		4.0
Boston Private Bank	661,991		8.70		304,510		4.0		380,637		5.0		4.0

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n/a = not applicable

(1) Required capital ratios under the Basel III capital rules with the fully phased-in capital conservation buffer added to the minimum risk-based capital ratios. The fully phased-in ratios are effective for 2019, with lower requirements during the transition years 2016 through 2018.