ACQUISITIONS (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended							12 Months Ended
	Nov. 16, 2018	May 12, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Acquisition Related Costs			$ 8,046	$ 2,688	$ 434	$ 0	$ 0	$ 2,909	$ 484	$ 11,168	$ 3,393	$ 5,455
Blue Hills Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Equity Interest Issued or Issuable Shareholders Option To Receive, Cash Per Share			$ 5.25							$ 5.25
Number of shares of company stock issued for each share of Central common stock (in shares)			0.2308							0.2308
MNB Bancorp [Member]
Business Acquisition [Line Items]
Equity Interest Issued or Issuable Shareholders Option To Receive, Cash Per Share	$ 275
Number of shares of company stock issued for each share of Central common stock (in shares)	3.55
Value of shares of company stock issued for each share of acquiree stock (in dollars per share)	$ 285.38
Company's closing price per share (in dollars per share)	$ 80.39
Business transaction value	$ 56,100
Cost of acquired entity, percentage cash	25.00%
Business Acquisition, Cost of Acquired Entity, Percentage Stock Consideration	75.00%
Cost of acquired entity, cash paid	$ 13,600
Consideration Transferred, Equity Interests Issued and Issuable	$ 42,500
Increase in acquirer outstanding shares	528,353
Acquisition Related Costs										$ 8,800
Loans acquired	$ 293,498
Combination of INDB and MNB Bancorp [Member]
Business Acquisition [Line Items]
Acquisition Related Costs										$ 7,500
Island Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Equity Interest Issued or Issuable Shareholders Option To Receive, Cash Per Share		$ 500
Number of shares of company stock issued for each share of Central common stock (in shares)		9.525
Value of shares of company stock issued for each share of acquiree stock (in dollars per share)		$ 605.31
Company's closing price per share (in dollars per share)		$ 63.55
Business transaction value		$ 28,300
Cost of acquired entity, percentage cash		20.00%
Business Acquisition, Cost of Acquired Entity, Percentage Stock Consideration		80.00%
Cost of acquired entity, cash paid		$ 4,800
Consideration Transferred, Equity Interests Issued and Issuable		$ 23,500
Increase in acquirer outstanding shares		369,286
Acquisition Related Costs											3,200
Loans acquired		$ 155,551
Combination of INDB and Island Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Acquisition Related Costs											$ 2,600