Unaudited Consolidated Statements of Changes in Equity - USD ($) $ in Thousands		Total		Total Brookline Bancorp, Inc. Stockholders’ Equity		Common Stock	Additional Paid-in Capital	Retained Earnings		Accumulated Other Comprehensive (Loss) Income	Treasury Stock	Unallocated Common Stock Held by ESOP	Noncontrolling Interest in Subsidiary
Balance at Dec. 31, 2014		$ 646,605	[1]	$ 641,818	[1]	$ 757	$ 617,475	$ 84,860	[1]	$ (1,622)	$ (58,282)	$ (1,370)	$ 4,787
Increase (Decrease) in Stockholders' Equity
Net income attributable to Brookline Bancorp, Inc.	[1]	36,456		36,456				36,456
Net income attributable to noncontrolling interest in subsidiary		1,857	[1]										1,857
Issuance of noncontrolling units		65	[1]										65
Other comprehensive income		2,813	[1]	2,813	[1]					2,813
Common stock dividends per share	[1]	(18,632)		(18,632)				(18,632)
Dividend to owners of noncontrolling interest in subsidiary		(1,437)	[1]										(1,437)
Compensation under recognition and retention plans		767	[1]	767	[1]		(1,313)				2,080
Common stock held by ESOP committed to be released		246	[1]	246	[1]		90					156
Balance at Sep. 30, 2015		668,740	[1]	663,468	[1]	757	616,252	102,684	[1]	1,191	(56,202)	(1,214)	5,272
Balance at Dec. 31, 2015		673,486		667,485		757	616,899	109,675		(2,476)	(56,208)	(1,162)	6,001
Increase (Decrease) in Stockholders' Equity
Net income attributable to Brookline Bancorp, Inc.		39,083		39,083				39,083
Net income attributable to noncontrolling interest in subsidiary		2,203											2,203
Issuance of noncontrolling units		76											76
Other comprehensive income		7,372		7,372						7,372
Common stock dividends per share		(19,018)		(19,018)				(19,018)
Dividend to owners of noncontrolling interest in subsidiary		(1,734)											(1,734)
Compensation under recognition and retention plans		1,034		1,034			(1,023)				2,057
Common stock held by ESOP committed to be released		415		415			266					149
Balance at Sep. 30, 2016		$ 702,917		$ 696,371		$ 757	$ 616,142	$ 129,740		$ 4,896	$ (54,151)	$ (1,013)	$ 6,546

[1] Previously reported amounts prior to January 1, 2015 have been restated to reflect a retrospective change in accounting principle for investments in qualified affordable housing projects, in accordance with ASU 2014-01. Refer to Note 8, "Investments in Qualified Affordable Projects".