Loans Receivable and Allowance for Loan Losses - Balances of Loan Portfolio Segments by Credit Quality Indicator(Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment
Total loans	$ 10,165,236	$ 10,380,358
Not criticized
Financing Receivable, Recorded Investment
Total loans	9,896,692	10,100,670
Special mention
Financing Receivable, Recorded Investment
Total loans	45,844	50,158
Substandard
Financing Receivable, Recorded Investment
Total loans	222,700	229,530
Doubtful
Financing Receivable, Recorded Investment
Total loans	0	0
Consumer and Other Loans
Financing Receivable, Recorded Investment
Total loans	225,827	239,114
Home Equity and Other Consumer | Consumer and Other Loans
Financing Receivable, Recorded Investment
Total loans	134,853	139,338
Home Equity and Other Consumer | Consumer and Other Loans | Not criticized
Financing Receivable, Recorded Investment
Total loans	130,219	134,305
Home Equity and Other Consumer | Consumer and Other Loans | Special mention
Financing Receivable, Recorded Investment
Total loans	495	550
Home Equity and Other Consumer | Consumer and Other Loans | Substandard
Financing Receivable, Recorded Investment
Total loans	4,139	4,483
Home Equity and Other Consumer | Consumer and Other Loans | Doubtful
Financing Receivable, Recorded Investment
Total loans	0	0
Commercial and Industrial | Consumer and Other Loans
Financing Receivable, Recorded Investment
Total loans	90,974	99,776
Commercial and Industrial | Consumer and Other Loans | Not criticized
Financing Receivable, Recorded Investment
Total loans	89,075	99,087
Commercial and Industrial | Consumer and Other Loans | Special mention
Financing Receivable, Recorded Investment
Total loans	1,867	647
Commercial and Industrial | Consumer and Other Loans | Substandard
Financing Receivable, Recorded Investment
Total loans	32	42
Commercial and Industrial | Consumer and Other Loans | Doubtful
Financing Receivable, Recorded Investment
Total loans	0	0
Mortgage Loans
Financing Receivable, Recorded Investment
Total loans	9,939,409	10,141,244
Mortgage Loans | Residential
Financing Receivable, Recorded Investment
Total loans	5,214,770	5,365,363
Mortgage Loans | Residential | Not criticized
Financing Receivable, Recorded Investment
Total loans	5,019,425	5,158,878
Mortgage Loans | Residential | Special mention
Financing Receivable, Recorded Investment
Total loans	12,849	14,922
Mortgage Loans | Residential | Substandard
Financing Receivable, Recorded Investment
Total loans	182,496	191,563
Mortgage Loans | Residential | Doubtful
Financing Receivable, Recorded Investment
Total loans	0	0
Mortgage Loans | Multi-Family
Financing Receivable, Recorded Investment
Total loans	4,023,764	4,046,622
Mortgage Loans | Multi-Family | Not criticized
Financing Receivable, Recorded Investment
Total loans	3,984,135	4,005,703
Mortgage Loans | Multi-Family | Special mention
Financing Receivable, Recorded Investment
Total loans	23,777	24,804
Mortgage Loans | Multi-Family | Substandard
Financing Receivable, Recorded Investment
Total loans	15,852	16,115
Mortgage Loans | Multi-Family | Doubtful
Financing Receivable, Recorded Investment
Total loans	0	0
Mortgage Loans | Commercial Real Estate
Financing Receivable, Recorded Investment
Total loans	700,875	729,259
Mortgage Loans | Commercial Real Estate | Not criticized
Financing Receivable, Recorded Investment
Total loans	673,838	702,697
Mortgage Loans | Commercial Real Estate | Special mention
Financing Receivable, Recorded Investment
Total loans	6,856	9,235
Mortgage Loans | Commercial Real Estate | Substandard
Financing Receivable, Recorded Investment
Total loans	20,181	17,327
Mortgage Loans | Commercial Real Estate | Doubtful
Financing Receivable, Recorded Investment
Total loans	$ 0	$ 0