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BORROWINGS (Trust Preferred Securities) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015
Debt Instrument [Line Items] |  |
Face Amount |  | $ 71.0
Junior Subordinated Debentures [Member] |  |
Debt Instrument [Line Items] |  |
Face Amount | $ 71.0 |
Junior Subordinated Debentures [Member] | Capital Trust V Preferred Securities Due in 2037 [Member] |  |
Debt Instrument [Line Items] |  |
Face Amount | $ 50.0 |
Fixed rate | 2.44% |
Junior Subordinated Debentures [Member] | Capital Trust V Preferred Securities Due in 2037 [Member] | LIBOR [Member] |  |
Debt Instrument [Line Items] |  |
Basis spread on variable rate | 1.48% |
Junior Subordinated Debentures [Member] | Slades Ferry Trust I Preferred Securities Due in 2034 [Member] |  |
Debt Instrument [Line Items] |  |
Face Amount | $ 10.0 |
Fixed rate | 3.78% |
Junior Subordinated Debentures [Member] | Slades Ferry Trust I Preferred Securities Due in 2034 [Member] | LIBOR [Member] |  |
Debt Instrument [Line Items] |  |
Basis spread on variable rate | 2.79% |
Junior Subordinated Debentures [Member] | Central Bancorp Capital Trust I Securities Due in 2034 [Member] |  |
Debt Instrument [Line Items] |  |
Face Amount | $ 5.1 |
Fixed rate | 3.40% |
Junior Subordinated Debentures [Member] | Central Bancorp Capital Trust I Securities Due in 2034 [Member] | LIBOR [Member] |  |
Debt Instrument [Line Items] |  |
Basis spread on variable rate | 2.44% |
Junior Subordinated Debentures [Member] | Central Bancorp Capital Trust II Securities Due in 2037 [Member] |  |
Debt Instrument [Line Items] |  |
Face Amount | $ 5.9 |
Fixed rate | 7.015% |
Junior Subordinated Debentures [Member] | Central Bancorp Capital Trust II Securities Due in 2037 [Member] | LIBOR [Member] |  |
Debt Instrument [Line Items] |  |
Basis spread on variable rate | 1.65% |
Subordinated Debt [Member] | Subordinated Debentures Due in October 2019 [Member] | LIBOR [Member] |  |
Debt Instrument [Line Items] |  |
Basis spread on variable rate | 3.00% |
Subordinated Debt [Member] | Subordinated Debentures Due in November 2019 [Member] [Domain] |  |
Debt Instrument [Line Items] |  |
Fixed rate | 4.75% |
Subordinated Debt [Member] | Subordinated Debentures Due in November 2019 [Member] [Domain] | LIBOR [Member] |  |
Debt Instrument [Line Items] |  |
Basis spread on variable rate | 2.98% |

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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399 + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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