Reportable Segments (Details) (USD $)	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	$ 43,541,000	[1]	$ 42,302,000	[1]	$ 43,899,000	[1]	$ 44,276,000	[1]	$ 45,546,000	[1]	$ 46,366,000	[1]	$ 46,596,000	[1]	$ 44,768,000	[1]	$ 174,018,000		$ 183,276,000		$ 178,954,000
Noninterest Income	34,345,000	[1]	30,251,000	[1]	41,006,000	[1]	30,739,000	[1]	30,446,000	[1]	28,769,000	[1]	28,153,000	[1]	27,598,000	[1]	136,341,000		114,966,000		118,911,000
Revenues																	310,359,000		298,242,000		297,865,000
Noninterest Expense	55,705,000	[1]	52,110,000	[1]	56,838,000	[1]	56,707,000	[1]	62,889,000	[1]	58,315,000	[1]	55,479,000	[1]	55,771,000	[1]	221,360,000		232,454,000		234,324,000	[2]
Income tax expense	7,303,000	[1]	8,557,000	[1]	10,551,000	[1]	5,897,000	[1]	6,115,000	[1]	5,124,000	[1]	5,240,000	[1]	3,851,000	[1]	32,308,000	[3]	20,330,000	[3]	14,280,000	[3]
Net income from continuing operations																	66,691,000		48,758,000		36,101,000
Net Income (Loss) Attributable to Noncontrolling Interest	1,178,000	[1]	871,000	[1]	969,000	[1]	930,000	[1]	715,000	[1]	855,000	[1]	759,000	[1]	793,000	[1]	3,948,000		3,122,000		3,148,000
Net income attributable to the Company	17,668,000	[1]	18,336,000	[1]	21,328,000	[1]	13,203,000	[1]	13,092,000	[1]	16,513,000	[1]	14,161,000	[1]	9,505,000	[1]	70,535,000		53,271,000		39,137,000
Amortization of Intangible Assets																	4,327,000		4,369,000		4,800,000
Depreciation																	6,235,000		6,570,000		6,236,000
Assets	6,437,109,000								6,465,005,000								6,437,109,000		6,465,005,000		6,049,372,000
Assets under Management, Carrying Amount	24,280,000,000								20,417,000,000								24,280,000,000		20,417,000,000		18,140,000,000
Private Banking Segment [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net																	178,199,000		189,260,000		186,006,000	[4]
Noninterest Income																	49,001,000	[5]	34,368,000		39,208,000	[4]
Revenues																	227,200,000		223,628,000		225,214,000	[4]
Noninterest Expense																	139,876,000		149,815,000	[2]	152,238,000	[2],[4]
Income tax expense																	32,696,000	[3]	25,901,000	[3]	19,697,000	[3],[4]
Net income from continuing operations																	64,628,000		51,212,000		40,119,000	[4]
Net Income (Loss) Attributable to Noncontrolling Interest																	0		0		0	[4]
Net income attributable to the Company																	64,628,000		51,212,000		40,119,000	[4]
Amortization of Intangible Assets																	277,000		133,000		404,000	[4]
Depreciation																	5,456,000		5,772,000		5,438,000	[4]
Assets	6,251,087,000								6,269,390,000								6,251,087,000		6,269,390,000		5,843,089,000	[4]
Assets under Management, Carrying Amount	4,565,000,000								3,941,000,000								4,565,000,000		3,941,000,000		3,571,000,000	[4]
Investment Managers Segment [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net																	20,000		31,000		74,000
Noninterest Income																	43,875,000		39,201,000		39,802,000
Revenues																	43,895,000		39,232,000		39,876,000
Noninterest Expense																	33,195,000		31,359,000		31,181,000
Income tax expense																	3,493,000	[3]	2,688,000	[3]	2,803,000	[3]
Net income from continuing operations																	7,207,000		5,185,000		5,892,000
Net Income (Loss) Attributable to Noncontrolling Interest																	2,164,000		1,599,000		1,727,000
Net income attributable to the Company																	5,043,000		3,586,000		4,165,000
Amortization of Intangible Assets																	3,058,000		3,201,000		3,319,000
Depreciation																	221,000		247,000		250,000
Assets	100,609,000								102,843,000								100,609,000		102,843,000		105,629,000
Assets under Management, Carrying Amount	10,401,000,000								8,444,000,000								10,401,000,000		8,444,000,000		7,594,000,000
Wealth Advisors Segment [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net																	66,000		26,000		27,000	[6]
Noninterest Income																	42,350,000		37,647,000		34,553,000	[6]
Revenues																	42,416,000		37,673,000		34,580,000	[6]
Noninterest Expense																	29,588,000		28,001,000		25,193,000	[6]
Income tax expense																	4,807,000	[3]	3,561,000	[3]	3,439,000	[3],[6]
Net income from continuing operations																	8,021,000		6,111,000		5,948,000	[6]
Net Income (Loss) Attributable to Noncontrolling Interest																	1,784,000		1,523,000		1,421,000	[6]
Net income attributable to the Company																	6,237,000		4,588,000		4,527,000	[6]
Amortization of Intangible Assets																	992,000		1,035,000		1,077,000	[6]
Depreciation																	363,000		360,000		358,000	[6]
Assets	73,972,000								66,869,000								73,972,000		66,869,000		70,086,000	[6]
Assets under Management, Carrying Amount	9,336,000,000								8,052,000,000								9,336,000,000		8,052,000,000		6,994,000,000	[6]
Operating Segments [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net																	178,285,000		189,317,000		186,107,000
Noninterest Income																	135,226,000		111,216,000		113,563,000
Revenues																	313,511,000		300,533,000		299,670,000
Noninterest Expense																	202,659,000		209,175,000		208,612,000
Income tax expense																	40,996,000	[3]	32,150,000	[3]	25,939,000	[3]
Net income from continuing operations																	79,856,000		62,508,000		51,959,000
Net Income (Loss) Attributable to Noncontrolling Interest																	3,948,000		3,122,000		3,148,000
Net income attributable to the Company																	75,908,000		59,386,000		48,811,000
Amortization of Intangible Assets																	4,327,000		4,369,000		4,800,000
Depreciation																	6,040,000		6,379,000		6,046,000
Assets	6,425,668,000								6,439,102,000								6,425,668,000		6,439,102,000		6,018,804,000
Assets under Management, Carrying Amount	24,302,000,000								20,437,000,000								24,302,000,000		20,437,000,000		18,159,000,000
Holding Company and Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net																	(4,267,000)		(6,041,000)		(7,153,000)
Noninterest Income																	1,115,000		3,750,000		5,348,000
Revenues																	(3,152,000)		(2,291,000)		(1,805,000)
Noninterest Expense																	18,701,000		23,279,000	[2]	25,712,000	[2]
Income tax expense																	(8,688,000)	[3]	(11,820,000)	[3]	(11,659,000)	[3]
Net income from continuing operations																	(13,165,000)		(13,750,000)		(15,858,000)
Net Income (Loss) Attributable to Noncontrolling Interest																	0		0		0
Net income attributable to the Company																	(5,373,000)	[7]	(6,115,000)	[7]	(9,674,000)	[7]
Amortization of Intangible Assets																	0		0		0
Depreciation																	195,000		191,000		190,000
Assets	11,441,000								25,903,000								11,441,000		25,903,000		30,568,000
Assets under Management, Carrying Amount	$ (22,000,000)								$ (20,000,000)								$ (22,000,000)		$ (20,000,000)		$ (19,000,000)

[1] Due to rounding, the sum of the four quarters may not add to the year to date total.

[2] Non-interest expense for 2013 includes no restructuring expenses. Non-interest expense for 2012 includes $5.9 million of restructuring expenses; restructuring expenses incurred by the Private Banking segment amounted to $4.0 million, with the remaining $1.9 million incurred by the Holding Company. Non-interest expense for 2011 includes $8.1 million of restructuring expenses; restructuring expenses incurred by the Private Banking segment amounted to $5.5 million, with the remaining $2.6 million incurred by the Holding Company.

[3] The Company’s effective tax rate for 2013, 2012, and 2011 are not consistent due to earnings from tax-exempt investments, non-deductible compensation, state and local taxes, income tax credits and income attributable to noncontrolling interests having a different impact on the effective tax rate due primarily to the different levels of income before taxes in years 2013, 2012, and 2011. See Part II. Item 8. “Financial Statements and Supplementary Data - Note 17: Income Taxes” for additional details.

[4] In the second quarter of 2011, the Company merged its four Private Banking affiliates into one bank operating under the charter of Boston Private Bank. See Part II. Item 8. “Financial Statements and Supplementary Data-Note 2: Restructuring” for additional details.

[5] Included in Private Banking non-interest income for the year ended December 31, 2013 is the $10.6 million gain on sale of the Bank’s three offices in the Pacific Northwest

[6] In the second quarter of 2012, the Company sold its Wealth Advisory affiliate, DTC. Accordingly, current and prior period results for DTC have been reclassified into discontinued operations and are included with Holding Company and Eliminations in the tables above.

[7] Net income from discontinued operations for the years ended December 31, 2013, 2012 and 2011 of $7.8 million, $7.6 million, and $6.2 million, respectively, are included in Holding Company and Eliminations in the calculation of net income attributable to the Company.