BORROWINGS (Details Textual) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Repayments of Subordinated Debt									$ 0	$ 30,000,000
Subordinated Debt	$ 34,635,000				$ 34,589,000				34,635,000	34,589,000
Customer Repurchase Agreements					134,000,000					134,000,000
Interest Expense, Long-term Debt									5,800,000	6,600,000	$ 6,400,000
Gains (Losses) on Extinguishment of Debt	0	$ 0	$ 0	$ (437,000)	0	$ 0	$ 0	$ (122,000)	(437,000)	(122,000)	0
Loans Pledged as Collateral	$ 1,400,000,000				$ 1,432,820,000				$ 1,400,000,000	$ 1,432,820,000
Federal Home Loan Bank Advances Weighted Average Interest Rate inclusive of Swaps	3.42%				2.60%				3.42%	2.60%
Repayments of Debt									$ 49,000,000	$ 13,000,000
Customer Repurchase Agreements and other short-term borrowings	$ 176,913,000				$ 133,958,000				176,913,000	133,958,000
Interest expense on short-term borrowings									208,000	210,000	$ 200,000
Total Long-Term Borrowings	107,742,000				107,895,000				107,742,000	107,895,000
Parent Company [Member]
Debt Instrument [Line Items]
Subordinated Debt	35,000,000				35,000,000				35,000,000	35,000,000
Capital Trust V Preferred Securities Due in 2037 [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Total Long-Term Borrowings	$ 51,500,000				51,497,000				$ 51,500,000	51,497,000
Fixed rate	2.44%								2.44%
Debt Instrument, interest rate, stated rate inclusive of interest rate swap - expired	6.52%								6.52%
Debt Instrument, interest rate, stated rate inclusive of interest rate swap - forward starting	2.84%								2.84%
Capital Trust V Preferred Securities Due in 2037 [Member] | Junior Subordinated Debt [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate									1.48%
Subordinated Debentures Due in October 2019 [Member] | Subordinated Debentures [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate									3.00%
Subordinated Debentures Due in November 2019 [Member] [Domain] | Subordinated Debentures [Member]
Debt Instrument [Line Items]
Fixed rate	4.75%								4.75%
Subordinated Debentures Due in November 2019 [Member] [Domain] | Subordinated Debentures [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate									2.98%
Slades Ferry Trust I Preferred Securities Due in 2034 [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Total Long-Term Borrowings	$ 10,224,000				10,219,000				$ 10,224,000	10,219,000
Fixed rate	3.78%								3.78%
Slades Ferry Trust I Preferred Securities Due in 2034 [Member] | Junior Subordinated Debt [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate									2.79%
Central Bancorp Capital Trust I Securities Due in 2034 [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Total Long-Term Borrowings	$ 5,302,000				5,516,000				$ 5,302,000	5,516,000
Fixed rate	3.40%								3.40%
Central Bancorp Capital Trust I Securities Due in 2034 [Member] | Junior Subordinated Debt [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate									2.44%
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Federal home loan bank unused remaining available borrowing capacity	$ 793,100,000				777,500,000				$ 793,100,000	777,500,000
Line of credit maximum borrowing capacity	5,000,000								5,000,000
Swap [Member] | Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
FHLB advances amount hedged	$ 25,000,000				$ 25,000,000				$ 25,000,000	$ 25,000,000
Derivative weighted average interest rate	2.85%				3.25%				2.85%	3.25%