SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2018 USD ($) $ / shares		Sep. 30, 2018 USD ($) $ / shares		Jun. 30, 2018 USD ($) $ / shares		Mar. 31, 2018 USD ($) $ / shares		Dec. 31, 2017 USD ($) $ / shares		Sep. 30, 2017 USD ($) $ / shares		Jun. 30, 2017 USD ($) $ / shares		Mar. 31, 2017 USD ($) $ / shares		Dec. 31, 2018 USD ($) Segment Customer $ / shares shares	Dec. 31, 2017 USD ($) Customer $ / shares shares	Dec. 31, 2016 USD ($) Customer $ / shares shares
Loans [Abstract]
Number of months for which borrower is required to demonstrate performance in accordance with the loan terms and conditions prior to returning a loan to accrual status																		6 months
Accounting for Goodwill and Other Intangible Assets [Abstract]
Impairment of goodwill																		$ 0	$ 0
Numerator [Abstract]
Net Income per the Consolidated Statements of Operations		$ 12,440		$ 11,782		$ 12,321		$ 14,745		$ 15,423		$ 13,313		$ 11,989		$ 11,157		51,288	51,882	$ 72,514
Less: Dividends paid on earnings allocated to participating securities																		(160)	(131)	(109)
Income attributable to Common Stock																		$ 51,128	$ 51,751	$ 72,405
Weighted average common shares outstanding, including participating securities (in shares) | shares																		37,163,023	37,593,715	36,898,951
Less: weighted average participating securities (in shares) | shares																		(155,553)	(163,056)	(186,058)
Weighted average common shares outstanding (in shares) | shares																		37,007,470	37,430,659	36,712,893
Basic EPS (in dollars per share) | $ / shares		$ 0.34	[1]	$ 0.32	[1]	$ 0.33	[1]	$ 0.39	[1]	$ 0.41	[1]	$ 0.36	[1]	$ 0.32	[1]	$ 0.30	[1]	$ 1.38	$ 1.38	$ 1.97
Income attributable to Common Stock																		$ 51,128	$ 51,751	$ 72,405
Weighted average common shares outstanding (in shares) | shares																		37,007,470	37,430,659	36,712,893
Weighted average common equivalent shares outstanding (in shares) | shares																		80,292	79,790	51,193
Weighted average common and equivalent shares outstanding (in shares) | shares																		37,087,762	37,510,449	36,764,086
Diluted EPS (in dollars per share) | $ / shares		$ 0.34	[1]	$ 0.32	[1]	$ 0.33	[1]	$ 0.39	[1]	$ 0.41	[1]	$ 0.35	[1]	$ 0.32	[1]	$ 0.30	[1]	$ 1.38	$ 1.38	$ 1.97
Disclosure about Segments of an Enterprise and Related Information [Abstract]
Number of reportable segments | Segment																		1
Number of operating segments | Segment																		1
Number of customers that account for more than 10% of consolidated revenue | Customer																		0	0	0
ASU 2016-01 [Member]
Securities [Abstract]
Reclassification of unrealized gains and losses on marketable equity securities										$ 0									$ 0
Buildings [Member] | Minimum [Member]
Premises and Fixed Assets, Net [Abstract]
Percentage of Depreciation																		2.22%
Buildings [Member] | Maximum [Member]
Premises and Fixed Assets, Net [Abstract]
Percentage of Depreciation																		2.50%
Furniture, Fixtures and Equipment [Member]
Premises and Fixed Assets, Net [Abstract]
Percentage of Depreciation																		10.00%
Retained Earnings [Member]
Numerator [Abstract]
Net Income per the Consolidated Statements of Operations																		$ 51,288	51,882	$ 72,514
Retained Earnings [Member] | ASU 2016-01 [Member]
Securities [Abstract]
Reclassification of unrealized gains and losses on marketable equity securities										153									153
Accumulated Other Comprehensive Income (Loss) [Member]
Numerator [Abstract]
Net Income per the Consolidated Statements of Operations																		$ 0	0	$ 0
Accumulated Other Comprehensive Income (Loss) [Member] | ASU 2016-01 [Member]
Securities [Abstract]
Reclassification of unrealized gains and losses on marketable equity securities	[2]									$ (153)									$ (153)
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Abstract]
Weighted average shares excluded from earnings per share calculation (in shares) | shares																		0	0	77,432

[1] The quarterly EPS amounts, when added, may not coincide with the full fiscal year EPS reported on the Consolidated Statements of Operations due to differences in the computed weighted average shares outstanding as well as rounding differences.

[2] Represents the impact of adopting ASU 2016-01 allowing the reclassification of unrealized gains and losses on available-for-sale equity securities from accumulated other comprehensive income to Retained Earnings.