ACQUISITIONS (Details Textual) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended						12 Months Ended
	Apr. 01, 2019	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Acquisition Related Costs		$ 0	$ 0	$ 0	$ 705	$ 24,696	$ 1,032	$ 0	$ 26,433	$ 11,168
Business Combination, Pro Forma Information [Abstract]
Business Combination, Acquired Receivable, Fair Value	$ 23,200
Blue Hills Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Equity Interest Issued or Issuable Shareholders Option To Receive, Cash Per Share	$ 5.25
Number of shares of company stock issued for each share of Central common stock (in shares)	0.2308
Business transaction value	$ 661,300
Cost of acquired entity, cash paid	$ 161,600
Increase in acquirer outstanding shares	6,166,010
Acquisition Related Costs								26,000
Loans acquired	$ 2,073,714
Combination of INDB and Blue Hills Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Acquisition Related Costs								$ 57,300