Boston Private Financial Holdings, Inc. (Parent Company Only) Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015	[1]	Jun. 30, 2015	[1]	Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014	[1]	Jun. 30, 2014	[1]	Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Income Attributable to Parent	$ 15,002	[1]	$ 13,530		$ 17,610		$ 18,783	[1]	$ 12,177	[1]	$ 18,265		$ 21,332		$ 17,041	[1]	$ 64,925	$ 68,815	$ 70,535
Net income from discontinued operations	1,455	[1]	$ 1,316		$ 1,546		2,094	[1]	1,510	[1]	$ 1,272		$ 1,450		1,928	[1]	6,411	6,160	7,792
Net income from continuing operations																	62,921	67,405	66,691
Gain on repurchase of debt																	0	0	(620)
Deferred income tax expense/(benefit)																	(4,575)	5,058	10,313
Depreciation and amortization																	22,187	19,378	19,107
Net decrease/(increase) in other operating activities																	2,852	14,387	5,861
Net Cash Provided by (Used in) Operating Activities, Continuing Operations																	87,477	100,899	106,383
Cash Provided by (Used in) Operating Activities, Discontinued Operations																	6,411	6,160	7,792
Net Cash Provided by (Used in) Operating Activities																	93,888	107,059	114,175
Payments for (Proceeds from) Other Investing Activities																	0	1,601	224
Net Cash Provided by (Used in) Investing Activities, Continuing Operations																	(694,790)	(368,228)	(295,908)
Net cash provided by/(used in) investing activities - discontinued operations																	0	0	0
Net Cash Provided by (Used in) Investing Activities																	(694,790)	(368,228)	(295,908)
Repurchase of debt																	0	0	(35,536)
Proceeds from issuance of Series D preferred stock, net																	0	0	47,753
Repurchase of Series B preferred stock, including deemed dividend at repurchase																	0	0	(69,827)
Dividends paid to common share holders																	(29,608)	(25,829)	(19,129)
Dividends paid to preferred shareholders																	(3,475)	(3,475)	(2,660)
Tax savings/ (deficiency) from certain stock compensation awards																	(1,262)	1,294	(663)
Proceeds from stock option exercises																	1,206	1,807	2,332
Proceeds from issuance of common stock, net																	(515)	(353)	1,230
Other equity adjustments																	(199)	(1,669)	238
Net Cash Provided by (Used in) Financing Activities, Continuing Operations																	666,987	241,897	64,870
Net cash provided by/(used in) financing activities - discontinued operations																	0	0	0
Net Cash Provided by (Used in) Financing Activities																	666,987	241,897	64,870
Cash and Cash Equivalents, Period Increase (Decrease)																	66,085	(19,272)	(116,863)
Cash and cash equivalents at beginning of year							172,609								191,881		172,609	191,881	308,744
Cash and cash equivalents at end of period	238,694								172,609								238,694	172,609	191,881
Parent Company [Member]
Net Income Attributable to Parent																	46,187	40,330	46,572
Net income from discontinued operations																	6,411	6,160	7,792
Net income from continuing operations																	58,514	62,655	62,743
Gain on repurchase of debt																	0	0	(620)
Deferred income tax expense/(benefit)																	(4,575)	4,642	4,873
Depreciation and amortization																	5,097	1,743	3,187
Net decrease/(increase) in other operating activities																	2,167	(2,834)	(6,630)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations																	42,465	37,721	39,590
Cash Provided by (Used in) Operating Activities, Discontinued Operations																	6,411	6,160	7,792
Net Cash Provided by (Used in) Operating Activities																	48,876	43,881	47,382
Payments to Acquire Businesses, Net of Cash Acquired																	1,821	0	0
Proceeds from Divestiture of Businesses																	0	0	747
Payments for (Proceeds from) Other Investing Activities																	1	(98)	(115)
Net Cash Provided by (Used in) Investing Activities, Continuing Operations																	99	(30,602)	276
Net cash provided by/(used in) investing activities - discontinued operations																	0	0	0
Net Cash Provided by (Used in) Investing Activities																	99	(30,602)	276
Repurchase of debt																	0	0	(35,536)
Proceeds from issuance of Series D preferred stock, net																	0	0	47,753
Repurchase of Series B preferred stock, including deemed dividend at repurchase																	0	0	(69,827)
Dividends paid to common share holders																	(29,608)	(25,829)	(19,129)
Dividends paid to preferred shareholders																	(3,475)	(3,475)	(2,660)
Tax savings/ (deficiency) from certain stock compensation awards																	(1,262)	1,294	(663)
Proceeds from stock option exercises																	1,206	1,807	2,332
Proceeds from issuance of common stock, net																	160	32,387	4,583
Other equity adjustments																	(5,204)	(7,424)	(3,178)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations																	(38,183)	(1,240)	(76,325)
Net cash provided by/(used in) financing activities - discontinued operations																	0	0	0
Net Cash Provided by (Used in) Financing Activities																	(38,183)	(1,240)	(76,325)
Cash and Cash Equivalents, Period Increase (Decrease)																	10,792	12,039	(28,667)
Cash and cash equivalents at beginning of year							$ 44,593								$ 32,554		44,593	32,554	61,221
Cash and cash equivalents at end of period	$ 55,385								$ 44,593								55,385	44,593	32,554
Private Banking Segment [Member] | Parent Company [Member]
Net Income Attributable to Parent																	(57,201)	(62,491)	(64,628)
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries																	22,700	26,500	27,900
Non Banking Segments [Member] | Parent Company [Member]
Net Income Attributable to Parent																	(13,026)	(12,850)	(11,280)
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries																	28,789	20,356	24,045
Private Banking Segment [Member]
Net Income Attributable to Parent																	57,989	59,508	61,207
Net income from continuing operations																	57,989	59,508	61,207
Private Banking Segment [Member] | Parent Company [Member]
Payments of Distributions to Affiliates																	0	(29,007)	0
Non Banking Segments [Member] | Parent Company [Member]
Payments of Distributions to Affiliates																	$ (1,723)	$ (1,497)	$ (356)

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