ACQUISITIONS (Additional Information) (Details) $ in Thousands			12 Months Ended
	Dec. 21, 2018 USD ($) branch shares	Jan. 04, 2018 USD ($) branch shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2019 USD ($)
Business Acquisition [Line Items]
Time deposit discount	$ 1,000	$ 965
Bank-owned life insurance			$ 35,778		$ 36,008
Community Bank of Bergen County Merger
Business Acquisition [Line Items]
Branches | branch		3
Entity shares issued per acquiree share (in shares) | shares		0.97
Number of shares issued (in shares) | shares		1,873,028
Value of common stock issued		$ 51,900
Cash paid for fractional shares		2
Stock options total payment		140
Merger expenses			4,000	$ 1,200
Fair value adjustment		261
Gross amortized cost basis of acquired loans		$ 242,471
Amortization period		3 years 6 months
Interest rate fair value adjustment on general pooled loans		$ 324
Credit fair value adjustment on general pooled loans		$ 4,100
Expected term of acquired loans		4 years
Premium		$ 3,500
Amortization period		40 years
Life of deposits		22 months 15 days
Bank-owned life insurance		$ 7,963
Acquired borrowings carrying value		$ 12,000
Community Bank of Bergen County Merger | Weighted Average
Business Acquisition [Line Items]
Life of deposits		16 months 15 days
Community Bank of Bergen County Merger | Core deposits
Business Acquisition [Line Items]
Useful life		10 years
Intangibles		$ 1,300	1,300
Enterprise Bank N.J.
Business Acquisition [Line Items]
Branches | branch	4
Entity shares issued per acquiree share (in shares) | shares	0.4538
Number of shares issued (in shares) | shares	1,573,454
Value of common stock issued	$ 32,400
Cash paid for fractional shares	1
Stock options total payment	1,600
Merger expenses			1,800
Fair value adjustment	100
Gross amortized cost basis of acquired loans	262,126
Interest rate fair value adjustment on general pooled loans	(1,100)
Credit fair value adjustment on general pooled loans	$ 3,900
Amortization period	3 years
Life of deposits	11 months 12 days
Acquired borrowings carrying value	$ 47,300
Acquired at a discount	$ 282
Weighted average interest rate	2.23%
Fair value adjustment	$ 149
Enterprise Bank N.J. | Weighted Average
Business Acquisition [Line Items]
Life of deposits	11 months 12 days
Enterprise Bank N.J. | Core deposits
Business Acquisition [Line Items]
Useful life	10 years
Intangibles	$ 1,000		$ 1,100