ACQUISITIONS (Details Textual) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
	May 12, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 10, 2016
Business Acquisition [Line Items]
Acquisition Related Costs		$ 0	$ 0	$ 2,909	$ 484	$ 4,764	$ 151	$ 206	$ 334	$ 3,393	$ 5,455	$ 10,501
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
New England Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Number of shares of company stock issued for each share of Central common stock (in shares)													0.25
Value of shares of company stock issued for each share of acquiree stock (in dollars per share)													$ 15.14
Company's closing price per share (in dollars per share)													$ 60.55
Business transaction value													$ 41,700
Increase in acquirer outstanding shares													672,665
Acquisition Related Costs										$ 5,000
Loans acquired													$ 225,731
Combination of INDB and New England Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Acquisition Related Costs											$ 6,300