INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current Income Tax Expense (Benefit) [Abstract]
Federal									$ 12,226	$ 20,818	$ 42,834
State and City									4,008	5,523	17,026
Current Income Tax Expense (Benefit), Total									16,234	26,341	59,860
Deferred Income Tax Expense (Benefit) [Abstract]
Federal									(554)	8,334	702
State and City									(253)	2,181	395
Deferred Income Tax Expense (Benefit), Total									(807)	10,515	1,097
Federal, Total									11,672	29,152	43,536
State and City, Total									3,755	7,704	17,421
Income Tax Expense (Benefit), Total	$ 3,183	$ 3,547	$ 4,110	$ 4,587	$ 15,442	$ 7,230	$ 7,295	$ 6,889	15,427	36,856	60,957
Income Tax Reconciliation [Abstract]
Tax at Federal statutory rate									14,010	31,058	46,715
State and local taxes, net of federal income tax benefit									2,967	5,008	11,323
ESOP acceleration expense									0	0	3,962
Benefit plan differences									(312)	(535)	(54)
Adjustments for prior period returns and tax items									(693)	84	(13)
Investment in BOLI									(605)	(776)	(957)
Enactment of federal tax reform									0	3,135	0
Equity based compensation									(128)	(1,283)	0
Other, net									188	165	(19)
Income Tax Expense (Benefit), Total	3,183	$ 3,547	$ 4,110	$ 4,587	15,442	$ 7,230	$ 7,295	$ 6,889	$ 15,427	$ 36,856	$ 60,957
Effective tax rate									23.12%	41.53%	45.67%
Deferred tax assets [Abstract]
Allowance for loan losses	7,071				6,836				$ 7,071	$ 6,836
Employee benefit plans	6,809				7,148				6,809	7,148
Tax effect of purchase accounting fair value adjustments	291				307				291	307
Tax effect of other components of income on investment securities and MBS	948				0				948	0
Other	2,112				2,135				2,112	2,135
Total deferred tax assets	17,231				16,426				17,231	16,426
Deferred tax liabilities [Abstract]
Tax effect of other components of income on investment securities, MBS, and interest rate derivatives	827				1,474				827	1,474
Difference in book and tax carrying value of fixed assets	1,497				20				1,497	20
Difference in book and tax basis of unearned loan fees	2,986				2,837				2,986	2,837
Difference in book and tax basis of deferred income from REIT subsidiary	0				2,262				0	2,262
Other	527				605				527	605
Total deferred tax liabilities	5,837				7,198				5,837	7,198
Net deferred tax asset (recorded in other assets)	11,394				9,228				$ 11,394	$ 9,228
Corporate income tax rate									21.00%	35.00%
Recorded tax expense										$ 3,135
Valuation allowance of deferred tax assets	0				0				$ 0	0
Bad debt reserve subject to recapture [Abstract]
Accumulated bad debt reserves for which no provision for income tax was required to be recorded	15,158				15,158				15,158	15,158
Additional income tax expense due to bad debt recapture									5,042
Unrecognized tax benefits	$ 0				$ 0				$ 0	$ 0