Loans and Leases Receivable and Allowance for Credit Losses - Credit Ratings of Covered and Non-Covered Loan Portfolio (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 1,240,838
2019	1,658,063
2018	807,657
2017	1,147,074
2016	657,408
2015	1,274,192
Revolving loans amortized cost basis	915,660
Revolving loans converted to term	0
Total loans and leases receivable	7,700,892	$ 7,318,988
Financing receivable, at amortized cost or lower of cost or market		7,316,903
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable	6,067,089	5,690,820
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable	1,633,803	1,628,168
Pass/Satisfactory
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		5,442,307
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		111,157
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		139,744
Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		1,597,188
Non-performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		26,507
Commercial loans and leases receivable \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	914,239
2019	849,986
2018	683,709
2017	1,129,197
2016	612,618
2015	1,126,535
Revolving loans amortized cost basis	750,805
Revolving loans converted to term	0
Total loans and leases receivable	6,067,089
Multi-family
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable	1,950,300	1,909,274
Multi-family \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	139,734
2019	23,396
2018	305,351
2017	666,691
2016	296,204
2015	518,924
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	1,950,300	1,907,331
Multi-family \| Pass/Satisfactory
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		1,816,200
Multi-family \| Pass/Satisfactory \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	139,734
2019	23,396
2018	305,351
2017	626,402
2016	271,981
2015	485,023
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	1,851,887
Multi-family \| Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		69,637
Multi-family \| Special mention \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	22,430
2016	10,424
2015	26,836
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	59,690
Multi-family \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		23,437
Multi-family \| Substandard \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	17,859
2016	13,799
2015	7,065
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	38,723
Multi-family \| Doubtful \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015	0
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	0
Multi-family \| Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Multi-family \| Non-performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable	2,220,715	1,889,980
Commercial and industrial \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	583,934
2019	429,191
2018	168,224
2017	134,898
2016	56,666
2015	99,452
Revolving loans amortized cost basis	748,350
Revolving loans converted to term	0
Total loans and leases receivable	2,220,715
Commercial and industrial \| Pass/Satisfactory
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		1,841,074
Commercial and industrial \| Pass/Satisfactory \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	564,313
2019	418,961
2018	153,659
2017	118,548
2016	48,470
2015	81,179
Revolving loans amortized cost basis	739,151
Revolving loans converted to term	0
Total loans and leases receivable	2,124,281
Commercial and industrial \| Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		26,285
Commercial and industrial \| Special mention \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	13,200
2019	1,193
2018	222
2017	14,739
2016	112
2015	15,348
Revolving loans amortized cost basis	1,315
Revolving loans converted to term	0
Total loans and leases receivable	46,129
Commercial and industrial \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		22,621
Commercial and industrial \| Substandard \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	6,421
2019	9,037
2018	14,343
2017	1,611
2016	8,084
2015	2,925
Revolving loans amortized cost basis	7,884
Revolving loans converted to term	0
Total loans and leases receivable	50,305
Commercial and industrial \| Doubtful \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015	0
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	0
Commercial and industrial \| Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Commercial and industrial \| Non-performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Commercial real estate owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable	557,595	552,007
Commercial real estate owner occupied \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	46,303
2019	185,921
2018	88,769
2017	81,045
2016	50,445
2015	104,371
Revolving loans amortized cost basis	741
Revolving loans converted to term	0
Total loans and leases receivable	557,595
Commercial real estate owner occupied \| Pass/Satisfactory
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		536,777
Commercial real estate owner occupied \| Pass/Satisfactory \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	46,303
2019	185,921
2018	88,291
2017	71,438
2016	48,202
2015	93,679
Revolving loans amortized cost basis	741
Revolving loans converted to term	0
Total loans and leases receivable	534,575
Commercial real estate owner occupied \| Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		8,286
Commercial real estate owner occupied \| Special mention \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	478
2017	9,260
2016	0
2015	245
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	9,983
Commercial real estate owner occupied \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		6,944
Commercial real estate owner occupied \| Substandard \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	347
2016	2,243
2015	10,447
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	13,037
Commercial real estate owner occupied \| Doubtful \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015	0
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	0
Commercial real estate owner occupied \| Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Commercial real estate owner occupied \| Non-performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Commercial real estate non-owner occupied
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable	1,215,516	1,223,529
Commercial real estate non-owner occupied \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	135,589
2019	113,247
2018	116,794
2017	246,563
2016	199,535
2015	403,788
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	1,215,516
Commercial real estate non-owner occupied \| Pass/Satisfactory
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		1,129,838
Commercial real estate non-owner occupied \| Pass/Satisfactory \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	135,589
2019	113,247
2018	116,794
2017	225,952
2016	197,116
2015	346,107
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	1,134,805
Commercial real estate non-owner occupied \| Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		6,949
Commercial real estate non-owner occupied \| Special mention \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015	10,559
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	10,559
Commercial real estate non-owner occupied \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		86,742
Commercial real estate non-owner occupied \| Substandard \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	20,611
2016	2,419
2015	47,122
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	70,152
Commercial real estate non-owner occupied \| Doubtful \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015	0
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	0
Commercial real estate non-owner occupied \| Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Commercial real estate non-owner occupied \| Non-performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable	122,963	118,418
Construction \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,679
2019	98,231
2018	4,571
2017	0
2016	9,768
2015	0
Revolving loans amortized cost basis	1,714
Revolving loans converted to term	0
Total loans and leases receivable	122,963	117,617
Construction \| Pass/Satisfactory
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		118,418
Construction \| Pass/Satisfactory \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,679
2019	98,231
2018	4,571
2017	0
2016	9,768
2015	0
Revolving loans amortized cost basis	1,714
Revolving loans converted to term	0
Total loans and leases receivable	122,963
Construction \| Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Construction \| Special mention \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015	0
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	0
Construction \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Construction \| Substandard \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015	0
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	0
Construction \| Doubtful \| Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
2015	0
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	0
Construction \| Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Construction \| Non-performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Consumer loans \| Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	326,599
2019	808,077
2018	123,948
2017	17,877
2016	44,790
2015	147,657
Revolving loans amortized cost basis	164,855
Revolving loans converted to term	0
Total loans and leases receivable	1,633,803
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable	335,452	375,014
Residential real estate \| Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	7,514
2019	15,252
2018	7,807
2017	13,031
2016	44,233
2015	82,760
Revolving loans amortized cost basis	164,855
Revolving loans converted to term	0
Total loans and leases receivable	335,452	382,634
Residential real estate \| Pass/Satisfactory
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Residential real estate \| Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Residential real estate \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Residential real estate \| Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		362,962
Residential real estate \| Performing \| Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	7,514
2019	15,252
2018	7,647
2017	12,246
2016	42,883
2015	78,365
Revolving loans amortized cost basis	161,575
Revolving loans converted to term	0
Total loans and leases receivable	325,482
Residential real estate \| Non-performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		12,052
Residential real estate \| Non-performing \| Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	160
2017	785
2016	1,350
2015	4,395
Revolving loans amortized cost basis	3,280
Revolving loans converted to term	0
Total loans and leases receivable	9,970
Manufactured housing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable	64,638	70,398
Manufactured housing \| Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	307
2018	632
2017	79
2016	42
2015	63,578
Revolving loans amortized cost basis	0
Revolving loans converted to term	0
Total loans and leases receivable	64,638	71,359
Manufactured housing \| Pass/Satisfactory
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Manufactured housing \| Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Manufactured housing \| Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		0
Manufactured housing \| Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases receivable		63,250
Manufactured housing \| Performing \| Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	307

Loans and Leases Receivable and Allowance for Credit Losses - Credit Ratings of Covered and Non-Covered Loan Portfolio (Detail) - USD ($)
$ in Thousands