Boston Private Financial Holdings, Inc. (Parent Company Only) Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017	[1]	Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Noninterest Income, Other Operating Income																	$ 2,098		$ 3,410		$ 3,722
Revenues																	378,652		359,225		346,939
Salaries and employee benefits																	178,406		163,767		159,401
Professional services																	13,763		11,576		12,861
Interest Expense, Junior Subordinated Debentures																	2,919		2,427		3,875
Other																	14,569		13,437		14,561
Income before income taxes	$ 3,400		$ 27,980		$ 33,456		$ 21,549		$ 24,762		$ 28,351		$ 23,768		$ 24,325		86,385		101,207		93,313
Income tax benefit	21,391		8,289		9,963		6,553		7,247		8,652		7,626		7,438		46,196	[2]	30,963	[2]	30,392	[2]
Income from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	989		1,186		1,063		1,632		1,184		1,047		1,245		2,065		4,870	[3]	5,541	[3]	6,411	[3]
Net income attributable to the Company	$ (18,280)		$ 19,803		$ 23,406		$ 15,662		$ 17,552		$ 19,636		$ 16,398		$ 18,041		40,591		71,628		64,925
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Interest Income, Operating																	180		130		116
Noninterest Income, Other Operating Income																	(1,071)		310		236
Revenues																	48,425		47,184		51,841
Salaries and employee benefits																	4,061		4,620		10,320
Professional services																	1,369		1,337		2,007
Interest Expense, Junior Subordinated Debentures																	2,919		2,427		3,875
Other																	1,424		1,381		2,740
Operating Expenses																	9,773		9,765		18,942
Income before income taxes																	38,652		37,419		32,899
Income tax benefit																	(6,880)		(3,751)		(6,877)
Income from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest																	4,870		5,541		6,411
Net income attributable to the Company																	50,402		46,711		46,187
Parent Company [Member] | Private Banking Segment [Member]
Condensed Financial Statements, Captions [Line Items]
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries																	25,200		22,700		22,700
Net income attributable to the Company																	(50,476)		(58,184)		(57,201)
Parent Company [Member] | Non Banking Segments [Member]
Condensed Financial Statements, Captions [Line Items]
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries																	24,116		24,044		28,789
Net income attributable to the Company																	11,150		(13,477)		(13,026)
Private Banking, Wealth Management and Trust, Investment Management, and Wealth Advisory Segments [Member] | Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income attributable to the Company																	$ (9,811)		$ 24,917		$ 18,738

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

[2] The Company’s effective tax rate for 2017, 2016, and 2015 is not consistent due to the re-measurement of the deferred tax assets, impairment of goodwill not deductible for tax purposes, 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 2017, 2016, and 2015. See Part II. Item 8. “Financial Statements and Supplementary Data - Note 17: Income Taxes” for additional details.

[3] The Holding Company and Eliminations calculation of Net Income attributable to the Company includes net income from Discontinued Operations for the years ended December 31, 2017, 2016 and 2015 of $4.9 million, $5.5 million, and $6.4 million, respectively