Note 5 - Loans - Loans Evaluated for Impairment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing receivables, ending balance	$ 5,573,324	$ 5,536,296
Financing receivables, individually evaluated for impairment	22,833	25,519
Financing receivables, collectively evaluated for impairment	5,550,491	5,510,777
Ending balance: individually evaluated for impairment	380	1,160
Ending balance: collectively evaluated for impairment	20,635	19,785
Multi-family Residential Portfolio Segment [Member]
Financing receivables, ending balance	2,256,447	2,269,048
Financing receivables, individually evaluated for impairment	4,104	4,500
Financing receivables, collectively evaluated for impairment	2,252,343	2,264,548
Ending balance: individually evaluated for impairment	98	100
Ending balance: collectively evaluated for impairment	5,395	5,576
Commercial Real Estate Portfolio Segment [Member]
Financing receivables, ending balance	1,529,001	1,542,547
Financing receivables, individually evaluated for impairment	1,097	1,435
Financing receivables, collectively evaluated for impairment	1,527,904	1,541,112
Ending balance: individually evaluated for impairment		0
Ending balance: collectively evaluated for impairment	4,278	4,315
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member]
Financing receivables, ending balance	582,049	577,741
Financing receivables, individually evaluated for impairment	2,987	3,098
Financing receivables, collectively evaluated for impairment	579,062	574,643
Ending balance: individually evaluated for impairment	54	143
Ending balance: collectively evaluated for impairment	1,737	1,724
One-To-Four Family - Residential Portfolio Segment [Member]
Financing receivables, ending balance	188,615	190,350
Financing receivables, individually evaluated for impairment	6,463	6,889
Financing receivables, collectively evaluated for impairment	182,152	183,461
Ending balance: individually evaluated for impairment	50	51
Ending balance: collectively evaluated for impairment	681	698
Co-Operative Apartments Portfolio Segment [Member]
Financing receivables, ending balance	7,903	8,498
Financing receivables, individually evaluated for impairment	0	0
Financing receivables, collectively evaluated for impairment	7,903	8,498
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	0	0
Construction Portfolio Segment [Member]
Financing receivables, ending balance	54,933	50,600
Financing receivables, individually evaluated for impairment	950	0
Financing receivables, collectively evaluated for impairment	53,983	50,600
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	351	329
Small Business Administration Portfolio Segment [Member]
Financing receivables, ending balance	15,188	15,210
Financing receivables, individually evaluated for impairment	1,227	1,267
Financing receivables, collectively evaluated for impairment	13,961	13,943
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	409	418
Taxi Medallion Portfolio Segment [Member]
Financing receivables, ending balance	3,891	4,539
Financing receivables, individually evaluated for impairment	3,891	4,539
Financing receivables, collectively evaluated for impairment	0	0
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	0	0
Commercial Business and Other Portfolio Segment [Member]
Financing receivables, ending balance	935,297	877,763
Financing receivables, individually evaluated for impairment	2,114	3,791
Financing receivables, collectively evaluated for impairment	933,183	873,972
Ending balance: individually evaluated for impairment	178	866
Ending balance: collectively evaluated for impairment	$ 7,784	$ 6,725