INVESTMENT AND MORTGAGE-BACKED SECURITIES, Major Categories of Securities Owned (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 Security
Debt securities available-for-sale [Abstract]
Amortized Cost		$ 424,058		$ 424,058
Gross Unrealized Gains		660		660
Gross Unrealized Losses		(4,702)		(4,702)
Fair Value		420,016		420,016
Investment securities available-for-sale [Abstract]
Amortized Cost						$ 354,968
Gross Unrealized Gains						996
Gross Unrealized Losses						(574)
Fair Value						355,390
Securities pledged as collateral		28,151		28,151		28,738
Sale of TRUP CDO securities [Abstract]
Amortization of unrealized loss on securities transferred from available-for-sale to held-to-maturity				0	$ 47
Net decrease in non-credit component of OCI				0	(17)
Proceeds from sales of mortgage backed securities available-for-sale				158,484	0
Proceeds [Abstract]
Marketable equity securities		136	$ 0	529	0
Investment securities available-for-sale		0	68	0	101
Trading securities		0	4,544	0	4,544
Gross gain recognized on sale of mortgage backed securities available for sale				1,370	0
Net gains on securities	[1]	19	59	1,385	134
Marketable Equity Securities [Member]
Proceeds [Abstract]
Net gains on securities		19		15
Trading Securities [Member]
Proceeds [Abstract]
Net gains on securities			59		134
Agency Notes [Member]
Debt securities available-for-sale [Abstract]
Amortized Cost		5,082		5,082
Gross Unrealized Gains		0		0
Gross Unrealized Losses		(4)		(4)
Fair Value		5,078		$ 5,078
Investment and Mortgage-Backed Securities [Abstract]
Securities weighted average term to maturity				1 year 1 month 6 days
Pooled Bank Trust Preferred Securities ("TRUP CDOs") [Member]
Sale of TRUP CDO securities [Abstract]
Amortization of unrealized loss on securities transferred from available-for-sale to held-to-maturity			26		52
Net decrease in non-credit component of OCI			9		17
Number of TRUP CDO securities | Security							6
Number of TRUP CDO securities deemed OTTI | Security							5
Registered Mutual Funds [Member]
Investment securities available-for-sale [Abstract]
Amortized Cost						3,779
Gross Unrealized Gains						311
Gross Unrealized Losses						(84)
Fair Value						4,006
Pass-through MBS Issued by Government Sponsored Entities ("GSEs") [Member]
Debt securities available-for-sale [Abstract]
Amortized Cost		302,348		$ 302,348
Gross Unrealized Gains		39		39
Gross Unrealized Losses		(3,438)		(3,438)
Fair Value		298,949		$ 298,949
Investment securities available-for-sale [Abstract]
Amortized Cost						72,938
Gross Unrealized Gains						16
Gross Unrealized Losses						(325)
Fair Value						72,629
Investment and Mortgage-Backed Securities [Abstract]
Securities weighted average term to maturity				14 years
Sale of TRUP CDO securities [Abstract]
Proceeds from sales of mortgage backed securities available-for-sale		0	0	$ 0	0
Agency Collateralized Mortgage Obligation ("CMO") [Member]
Debt securities available-for-sale [Abstract]
Amortized Cost		116,628		116,628
Gross Unrealized Gains		621		621
Gross Unrealized Losses		(1,260)		(1,260)
Fair Value		115,989		$ 115,989
Investment securities available-for-sale [Abstract]
Amortized Cost						278,251
Gross Unrealized Gains						669
Gross Unrealized Losses						(165)
Fair Value						278,755
Investment and Mortgage-Backed Securities [Abstract]
Securities weighted average term to maturity				10 years 7 months 6 days
Sale of TRUP CDO securities [Abstract]
Proceeds from sales of mortgage backed securities available-for-sale		$ 0	$ 0	$ 158,484	$ 0
Proceeds [Abstract]
Gross gain recognized on sale of mortgage backed securities available for sale				1,370
Amount of tax expense related to the gain on sales of available for sale				$ 440
ASU 2016-01 [Member]
Unrealized Gains, Net of Taxes [Abstract]
Reclassification of unrealized gains and losses on marketable equity securities						0
Retained Earnings [Member] | ASU 2016-01 [Member]
Unrealized Gains, Net of Taxes [Abstract]
Reclassification of unrealized gains and losses on marketable equity securities						153
Accumulated Other Comprehensive Loss [Member] | ASU 2016-01 [Member]
Unrealized Gains, Net of Taxes [Abstract]
Reclassification of unrealized gains and losses on marketable equity securities	[2]					$ (153)

[1] Amount includes periodic valuation gains or losses on marketable equity and trading securities

[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.