INVESTMENT AND MORTGAGE-BACKED SECURITIES, Major Categories of Securities Owned (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 Security
Investment Securities Available-for-sale [Abstract]
Amortized Cost		$ 356,773		$ 354,968
Gross Unrealized Gains		492		996
Gross Unrealized Losses		(2,855)		(574)
Fair Value		354,410		355,390
Securities pledged as collateral		27,084		28,738
Sale of TRUP CDO securities [Abstract]
Amortization of unrealized loss on securities transferred from available-for-sale to held-to-maturity		0	$ 25
Net decrease in non-credit component of OCI		0	(8)
Proceeds from sales of mortgage backed securities available-for-sale		158,484	0
Proceeds [Abstract]
Marketable equity securities		393	0
Investment securities available-for-sale		0	35
Trading securities		0	0
Gross gain recognized on sale of mortgage backed securities available for sale		1,370	0
Loss on marketable equity securities		(4,000)
Gain on trading securities	[1]	1,366	75
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			25
Net decrease in non-credit component of OCI			8
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]
Investment Securities Available-for-sale [Abstract]
Amortized Cost		239,232		72,938
Gross Unrealized Gains		22		16
Gross Unrealized Losses		(1,889)		(325)
Fair Value		$ 237,365		72,629
Investment and Mortgage-Backed Securities [Abstract]
Securities weighted average term to maturity		14 years 7 months 6 days
Weighted average estimated duration		4 years 2 months 12 days
Sale of TRUP CDO securities [Abstract]
Proceeds from sales of mortgage backed securities available-for-sale		$ 0	0
Agency Collateralized Mortgage Obligation ("CMO") [Member]
Investment Securities Available-for-sale [Abstract]
Amortized Cost		117,541		278,251
Gross Unrealized Gains		470		669
Gross Unrealized Losses		(966)		(165)
Fair Value		$ 117,045		278,755
Investment and Mortgage-Backed Securities [Abstract]
Securities weighted average term to maturity		10 years 8 months 12 days
Sale of TRUP CDO securities [Abstract]
Proceeds from sales of mortgage backed securities available-for-sale		$ 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]
Schedule of Available-for-sale Securities [Line Items]
Reclassification of unrealized gains and losses on available-for-sale equity securities				0
Retained Earnings [Member] | ASU 2016-01 [Member]
Schedule of Available-for-sale Securities [Line Items]
Reclassification of unrealized gains and losses on available-for-sale equity securities				153
Accumulated Other Comprehensive Loss [Member] | ASU 2016-01 [Member]
Schedule of Available-for-sale Securities [Line Items]
Reclassification of unrealized gains and losses on available-for-sale 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.