Loans Receivable and Allowance for Loan Losses (Details 7) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	$ 248,436	$ 384,522
Collectively evaluated for impairment	11,661,286	12,001,856
Total	11,909,722	12,386,378
Individually evaluated for impairment	19,732	21,531
Collectively evaluated for impairment	91,868	117,469
Total allowance for loan losses	111,600	139,000	145,501	157,185
Consumer and other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	5,153
Collectively evaluated for impairment	244,215	239,681
Total	249,368	239,681
Individually evaluated for impairment	3,810
Collectively evaluated for impairment	5,015	8,824
Total allowance for loan losses	8,825	8,824	6,316	3,800
Mortgage loans (gross)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	11,660,354	12,146,697
Mortgage loans (gross) | Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	181,402	311,930
Collectively evaluated for impairment	6,692,134	7,725,346
Total	6,873,536	8,037,276
Individually evaluated for impairment	10,304	18,352
Collectively evaluated for impairment	35,979	61,985
Total allowance for loan losses	46,283	80,337	89,267	105,991
Mortgage loans (gross) | Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	42,611	52,538
Collectively evaluated for impairment	3,870,442	3,243,917
Total	3,913,053	3,296,455
Individually evaluated for impairment	3,172	2,877
Collectively evaluated for impairment	36,078	33,826
Total allowance for loan losses	39,250	36,703	35,514	35,422
Mortgage loans (gross) | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	19,270	20,054
Collectively evaluated for impairment	854,495	792,912
Total	873,765	812,966
Individually evaluated for impairment	2,446	302
Collectively evaluated for impairment	14,796	12,834
Total allowance for loan losses	$ 17,242	$ 13,136	$ 14,404	$ 11,972