Loans Receivable and Allowance for Loan Losses (Loans Receivable and Related Allowance by Impairment Methodology) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Loans:
Individually evaluated for impairment	$ 229,803	$ 237,518
Collectively evaluated for impairment	10,735,500	10,874,209
Total	10,965,303	11,111,727
Allowance for loan losses:
Individually evaluated for impairment	13,976	14,813
Collectively evaluated for impairment	80,224	83,187
Total allowance for loan losses	94,200	98,000	$ 110,500	$ 111,600
Consumer and Other Loans
Loans:
Individually evaluated for impairment	4,537	4,968
Collectively evaluated for impairment	250,919	247,725
Total	255,456	252,693
Allowance for loan losses:
Individually evaluated for impairment	381	421
Collectively evaluated for impairment	6,053	5,867
Total allowance for loan losses	6,434	6,288	9,819	8,825
Mortgage Loans
Loans:
Total	10,709,847	10,859,034
Mortgage Loans | Residential
Loans:
Individually evaluated for impairment	196,365	192,914
Collectively evaluated for impairment	5,624,140	5,822,501
Total	5,820,505	6,015,415
Allowance for loan losses:
Individually evaluated for impairment	13,337	13,148
Collectively evaluated for impairment	31,041	31,803
Total allowance for loan losses	44,378	44,951	43,481	46,283
Mortgage Loans | Multi-Family
Loans:
Individually evaluated for impairment	15,733	24,643
Collectively evaluated for impairment	4,062,700	3,999,462
Total	4,078,433	4,024,105
Allowance for loan losses:
Individually evaluated for impairment	173	456
Collectively evaluated for impairment	32,847	35,088
Total allowance for loan losses	33,020	35,544	40,082	39,250
Mortgage Loans | Commercial Real Estate
Loans:
Individually evaluated for impairment	13,168	14,993
Collectively evaluated for impairment	797,741	804,521
Total	810,909	819,514
Allowance for loan losses:
Individually evaluated for impairment	85	788
Collectively evaluated for impairment	10,283	10,429
Total allowance for loan losses	$ 10,368	$ 11,217	$ 17,118	$ 17,242