Loans Receivable and Allowance for Loan Losses (Summary of Aging Loans Receivable by Portfolio Segment and Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	$ 45,938	$ 34,929
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	67,151	52,458
Current	7,227,054	7,276,505
Total gross loans	7,294,205	7,328,963
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	12,673	12,311
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	8,540	5,218
Mortgage Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	12,608	15,195
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	26,929	28,815
Current	5,080,755	5,081,053
Total gross loans	5,107,684	5,109,868
Mortgage Portfolio Segment [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	8,343	8,105
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	20,748	20,239
Current	1,106,996	1,122,108
Total gross loans	1,127,744	1,142,347
Mortgage Portfolio Segment [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	4,265	7,090
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	6,181	8,576
Current	2,178,926	2,162,480
Total gross loans	2,185,107	2,171,056
Mortgage Portfolio Segment [Member] | Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	0	0
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	0	0
Current	1,423,834	1,403,885
Total gross loans	1,423,834	1,403,885
Mortgage Portfolio Segment [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	0	0
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	0	0
Current	370,999	392,580
Total gross loans	370,999	392,580
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	6,678	9,295
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	5,711	7,809
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	967	1,486
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	0	0
Mortgage Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	0	0
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	7,643	4,325
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	6,694	4,325
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	949	0
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	0	0
Mortgage Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	0	0
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	31,359	17,243
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	35,396	18,200
Current	1,690,384	1,726,938
Total gross loans	1,725,780	1,745,138
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	3,787	551
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	250	406
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual	1,971	2,491
Recorded Investment greater than 90 days accruing	0	0
Total Past Due	4,826	5,443
Current	455,915	468,514
Total gross loans	460,741	473,957
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	2,208	2,465
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment past due	$ 647	$ 487