Unaudited Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income before noncontrolling interest in subsidiary	$ 14,272	$ 13,449	$ 41,286	$ 38,313
Investment securities available-for-sale:
Unrealized securities holding (losses) gains	(1,672)	4,608	11,486	4,495
Income tax expense (benefit)	599	(1,642)	(4,114)	(1,682)
Net unrealized securities holding (losses) gains	(1,073)	2,966	7,372	2,813
Postretirement benefits:
Adjustment of accumulated obligation for postretirement benefits	0	0	0	0
Income tax expense	0	0	0	0
Net adjustment of accumulated obligation for postretirement benefits	0	0	0	0
Other comprehensive (loss) income, net of taxes	(1,073)	2,966	7,372	2,813	[1]
Comprehensive income	13,199	16,415	48,658	41,126
Net income attributable to noncontrolling interest in subsidiary	655	561	2,203	1,857
Comprehensive income attributable to Brookline Bancorp, Inc.	$ 12,544	$ 15,854	$ 46,455	$ 39,269

[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".