Regulatory Matters (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital	$ 689,767	$ 676,206
Capital to Risk Weighted Assets	14.77%	14.61%
Capital Required for Capital Adequacy	373,483	370,223
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Capital Required to be Well Capitalized	466,854	462,779
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Tier One Risk Based Capital	631,041	617,965
Tier One Risk Based Capital to Risk Weighted Assets	13.52%	13.35%
Tier One Risk Based Capital Required for Capital Adequacy	186,741	185,112
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.00%	4.00%
Tier One Risk Based Capital Required to be Well Capitalized	280,112	277,667
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%	6.00%
Tier One Leverage Capital	631,041	617,965
Tier One Leverage Capital to Average Assets	10.09%	9.94%
Tier One Leverage Capital Required for Capital Adequacy	250,085	248,692
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%	4.00%
Tier One Leverage Capital Required to be Well Capitalized	312,606	310,865
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Boston Private Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital	631,510	594,422
Capital to Risk Weighted Assets	13.63%	12.94%
Capital Required for Capital Adequacy	354,285	367,522
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Capital Required to be Well Capitalized	442,856	459,402
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Tier One Risk Based Capital	573,340	536,649
Tier One Risk Based Capital to Risk Weighted Assets	12.37%	11.68%
Tier One Risk Based Capital Required for Capital Adequacy	177,112	183,761
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.00%	4.00%
Tier One Risk Based Capital Required to be Well Capitalized	265,714	275,641
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.00%	6.00%
Tier One Leverage Capital	573,340	536,649
Tier One Leverage Capital to Average Assets	9.27%	8.73%
Tier One Leverage Capital Required for Capital Adequacy	239,663	245,755
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%	4.00%
Tier One Leverage Capital Required to be Well Capitalized	$ 299,579	$ 307,194
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%