Boston Private Financial Holdings, Inc. (Parent Company Only) Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015	[1]	Jun. 30, 2015	[1]	Mar. 31, 2015		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Net Income Attributable to Parent	$ 17,552	[1]	$ 19,636		$ 16,398		$ 18,041	[1]	$ 15,002	[1]	$ 13,530		$ 17,610		$ 18,783	[1]	$ 71,628		$ 64,925		$ 68,815
Net income from discontinued operations	1,184	[1]	$ 1,047		$ 1,245		2,065	[1]	1,455	[1]	$ 1,316		$ 1,546		2,094	[1]	5,541	[2]	6,411	[2]	6,160	[2]
Net income from continuing operations																	70,244		62,921		67,405
Deferred income tax expense/(benefit)																	2,777		(4,575)		5,058
Depreciation and amortization																	23,441		22,187		19,378
Net decrease/(increase) in other operating activities																	(817)		2,852		14,387
Net Cash Provided by (Used in) Operating Activities, Continuing Operations																	100,606		87,477		100,899
Cash Provided by (Used in) Operating Activities, Discontinued Operations																	5,541		6,411		6,160
Net Cash Provided by (Used in) Operating Activities																	106,147		93,888		107,059
Payments for (Proceeds from) Other Investing Activities																	0		0		1,601
Net Cash Provided by (Used in) Investing Activities, Continuing Operations																	(692,780)		(694,790)		(368,228)
Net cash provided by/(used in) investing activities - discontinued operations																	0		0		0
Net Cash Provided by (Used in) Investing Activities																	(692,780)		(694,790)		(368,228)
Repurchase of common stock																	(9,323)		0		0
Dividends paid to common share holders																	(33,110)		(29,608)		(25,829)
Dividends paid to preferred shareholders																	(3,475)		(3,475)		(3,475)
Tax savings/ (deficiency) from certain stock compensation awards																	(620)		(1,262)		1,294
Proceeds from stock option exercises																	1,725		1,206		1,807
Proceeds from issuance of common stock, net																	842		(515)		(353)
Other equity adjustments																	(82)		(199)		(1,669)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations																	454,496		666,987		241,897
Net cash provided by/(used in) financing activities - discontinued operations																	0		0		0
Net Cash Provided by (Used in) Financing Activities																	454,496		666,987		241,897
Cash and Cash Equivalents, Period Increase (Decrease)																	(132,137)		66,085		(19,272)
Cash and cash equivalents at beginning of year							238,694								172,609		238,694		172,609		191,881
Cash and cash equivalents at end of period	106,557								238,694								106,557		238,694		172,609
Parent Company [Member]
Net Income Attributable to Parent																	46,711		46,187		40,330
Net income from discontinued operations																	5,541		6,411		6,160
Net income from continuing operations																	66,087		58,514		62,655
Deferred income tax expense/(benefit)																	10,000		(4,575)		4,642
Depreciation and amortization																	(738)		5,097		1,743
Net decrease/(increase) in other operating activities																	(16,633)		2,167		(2,834)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations																	33,799		42,465		37,721
Cash Provided by (Used in) Operating Activities, Discontinued Operations																	5,541		6,411		6,160
Net Cash Provided by (Used in) Operating Activities																	39,340		48,876		43,881
Payments to Acquire Businesses, Net of Cash Acquired																	1,890		1,821		0
Payments for (Proceeds from) Other Investing Activities																	1		1		(98)
Net Cash Provided by (Used in) Investing Activities, Continuing Operations																	671		99		(30,602)
Net cash provided by/(used in) investing activities - discontinued operations																	0		0		0
Net Cash Provided by (Used in) Investing Activities																	671		99		(30,602)
Repurchase of common stock																	9,323		0		0
Dividends paid to common share holders																	(33,110)		(29,608)		(25,829)
Dividends paid to preferred shareholders																	(3,475)		(3,475)		(3,475)
Tax savings/ (deficiency) from certain stock compensation awards																	(620)		(1,262)		1,294
Proceeds from stock option exercises																	1,725		1,206		1,807
Proceeds from issuance of common stock, net																	7,786		160		32,387
Other equity adjustments																	(3,685)		(5,204)		(7,424)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations																	(40,702)		(38,183)		(1,240)
Net cash provided by/(used in) financing activities - discontinued operations																	0		0		0
Net Cash Provided by (Used in) Financing Activities																	(40,702)		(38,183)		(1,240)
Cash and Cash Equivalents, Period Increase (Decrease)																	(691)		10,792		12,039
Cash and cash equivalents at beginning of year							$ 55,385								$ 44,593		55,385		44,593		32,554
Cash and cash equivalents at end of period	$ 54,694								$ 55,385								54,694		55,385		44,593
Private Banking Segment [Member] | Parent Company [Member]
Net Income Attributable to Parent																	(58,184)		(57,201)		(62,491)
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries																	22,700		22,700		26,500
Non Banking Segments [Member] | Parent Company [Member]
Net Income Attributable to Parent																	(13,477)		(13,026)		(12,850)
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries																	24,044		28,789		20,356
Private Banking Segment [Member]
Net Income Attributable to Parent																	70,348		57,989		59,508
Net income from continuing operations																	70,348		57,989		59,508
Private Banking Segment [Member] | Parent Company [Member]
Payments of Distributions to Affiliates																	0		0		(29,007)
Non Banking Segments [Member] | Parent Company [Member]
Payments of Distributions to Affiliates																	$ (1,220)		$ (1,723)		$ (1,497)

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

[2] The Company presents its EPS based on the treasury stock method. The Company reverted to the treasury stock presentation from the two-class presentation due to the immaterial number of participating shares outstanding as of March 31, 2016. If the EPS presentation had been based on the two-class method, the following adjustments would have been made to the presentation of EPS for the year ended December 31, 2016. Net income attributable to common shareholders would have been reduced by an additional $4 thousand, for the year ended December 31, 2016. The allocation of net income to participating securities would have been $8 thousand for the year ended December 31, 2016, reducing net income attributable to common shareholders by a total of $12 thousand for the same period. Basic EPS would not change. Weighted average diluted shared outstanding would have been reduced by 7,185 shares for the year ended December 31, 2016. Diluted EPS would not change. If the EPS presentation had been based on the two-class method, the following adjustments would have been made to the presentation of EPS for the year ended December 31, 2015. Net income attributable to common shareholders would have been reduced by an additional $90 thousand for the year ended December 31, 2015, and the allocation of net income to participating securities would have been $92 thousand for the same period, reducing net income attributable to common shareholders by a total of $182 thousand, for the same period. Total basic EPS and basic EPS from continuing operations would each decrease by $0.01 per share for the year ended December 31, 2015. Weighted average diluted shares outstanding would have been reduced by 167,937 shares for the same period. Diluted EPS would not change.If the EPS presentation had been based on the two-class method, the following adjustments would have been made to the presentation of EPS for the year ended December 31, 2014. Net income attributable to common shareholders would have been reduced by an additional$228 thousand for the year ended December 31, 2014, and the allocation of net income to participating securities would have been $335 thousand for the same period, reducing net income attributable to common shareholders by a total of $563 thousand, for the same period. Total basic EPS and basic EPS from continuing operations would each decrease by $0.01 per share for the year ended December 31, 2014. Weighted average diluted shares outstanding would have been reduced by 428,913 shares for the same period. Total diluted EPS and diluted EPS from discontinued operations would each decrease by $0.01 per share.