Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-35070
Entity Registrant Name	BOSTON PRIVATE FINANCIAL HOLDINGS, INC
Entity Incorporation, State or Country Code	MA
Entity Tax Identification Number	04-2976299
Entity Address, Address Line One	Ten Post Office Square
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02109
City Area Code	617
Local Phone Number	912-1900
Title of 12(b) Security	Common Stock
Trading Symbol	BPFH
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		82,464,321
Entity Central Index Key	0000821127
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false