Loans Receivable and Allowance for Loan Losses - Summary of Loans Receivable by Credit Quality Risk Rating Indicator (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 7,337,564	$ 7,253,902
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	128,694	87,801
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	88,526	74,242
Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	836	923
Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Total Classified And Criticized
Financing Receivable, Recorded Investment [Line Items]
Total loans	218,056	162,966
Acceptable/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,119,508	7,090,936
Mortgage Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	5,311,445	5,127,453
Total loans	5,311,445	5,127,453
Mortgage Portfolio Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	49,160	19,795
Mortgage Portfolio Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	29,843	27,351
Mortgage Portfolio Segment | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Mortgage Portfolio Segment | Loss
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Mortgage Portfolio Segment | Total Classified And Criticized
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	79,003	47,146
Mortgage Portfolio Segment | Acceptable/Watch
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	5,232,442	5,080,307
Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,634,759	1,695,021
Commercial Portfolio Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	79,248	67,396
Commercial Portfolio Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	57,015	45,180
Commercial Portfolio Segment | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	836	923
Commercial Portfolio Segment | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial Portfolio Segment | Total Classified And Criticized
Financing Receivable, Recorded Investment [Line Items]
Total loans	137,099	113,499
Commercial Portfolio Segment | Acceptable/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,497,660	1,581,522
Consumer Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total loans	391,360	431,428
Consumer Portfolio Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans	286	610
Consumer Portfolio Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,668	1,711
Consumer Portfolio Segment | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment | Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment | Total Classified And Criticized
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,954	2,321
Consumer Portfolio Segment | Acceptable/Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	389,406	429,107
Residential Real Estate | Mortgage Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	1,077,689	1,099,464
Total loans	1,077,689	1,099,464
Residential Real Estate | Mortgage Portfolio Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	2,402	5,071
Residential Real Estate | Mortgage Portfolio Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	10,204	7,878
Residential Real Estate | Mortgage Portfolio Segment | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Residential Real Estate | Mortgage Portfolio Segment | Loss
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Residential Real Estate | Mortgage Portfolio Segment | Total Classified And Criticized
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	12,606	12,949
Residential Real Estate | Mortgage Portfolio Segment | Acceptable/Watch
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	1,065,083	1,086,515
Commercial Real Estate | Mortgage Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	2,578,393	2,299,313
Total loans	2,578,393	2,299,313
Commercial Real Estate | Mortgage Portfolio Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	46,758	14,496
Commercial Real Estate | Mortgage Portfolio Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	13,458	13,292
Commercial Real Estate | Mortgage Portfolio Segment | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Commercial Real Estate | Mortgage Portfolio Segment | Loss
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Commercial Real Estate | Mortgage Portfolio Segment | Total Classified And Criticized
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	60,216	27,788
Commercial Real Estate | Mortgage Portfolio Segment | Acceptable/Watch
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	2,518,177	2,271,525
Multifamily | Mortgage Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	1,225,551	1,339,677
Total loans	1,225,551	1,339,677
Multifamily | Mortgage Portfolio Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	228
Multifamily | Mortgage Portfolio Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Multifamily | Mortgage Portfolio Segment | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Multifamily | Mortgage Portfolio Segment | Loss
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Multifamily | Mortgage Portfolio Segment | Total Classified And Criticized
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	228
Multifamily | Mortgage Portfolio Segment | Acceptable/Watch
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	1,225,551	1,339,449
Construction Loans | Mortgage Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	429,812	388,999
Total loans	429,812	388,999
Construction Loans | Mortgage Portfolio Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Construction Loans | Mortgage Portfolio Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	6,181	6,181
Construction Loans | Mortgage Portfolio Segment | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Construction Loans | Mortgage Portfolio Segment | Loss
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	0	0
Construction Loans | Mortgage Portfolio Segment | Total Classified And Criticized
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	6,181	6,181
Construction Loans | Mortgage Portfolio Segment | Acceptable/Watch
Financing Receivable, Recorded Investment [Line Items]
Total mortgage loans	$ 423,631	$ 382,818