Boston Private Financial Holdings, Inc. (Parent Company Only) Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 127,259	$ 120,541	$ 106,557	$ 238,694
Other assets	246,962	259,515
Total assets	8,494,625	8,311,744	7,970,474
Junior subordinated debentures	106,363	106,363
Other liabilities	143,540	135,880
Total liabilities	7,738,145	7,508,339
Redeemable Noncontrolling Interests	2,526	17,461
Total Shareholders’ Equity	753,954	780,758
Total liabilities, redeemable noncontrolling interests and shareholders’ equity	8,494,625	8,311,744
Parent Company
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	51,088	66,361	$ 54,694	$ 55,385
Investment in partnerships and trusts	6,340	6,340
Other assets	36,483	11,046
Total assets	896,553	926,418
Junior subordinated debentures	106,363	106,363
Deferred income taxes	12,968	5,322
Other liabilities	20,742	11,328
Total liabilities	140,073	123,013
Redeemable Noncontrolling Interests	2,526	22,647
Total Shareholders’ Equity	753,954	780,758
Total liabilities, redeemable noncontrolling interests and shareholders’ equity	896,553	926,418
Private Banking | Parent Company
Condensed Financial Statements, Captions [Line Items]
Investment in wholly-owned and majority-owned subsidiaries:	773,271	731,907
Non Banking Segments | Parent Company
Condensed Financial Statements, Captions [Line Items]
Investment in wholly-owned and majority-owned subsidiaries:	$ 29,371	$ 110,764