Loans and Leases Receivable and Allowance for Credit Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) - USD ($)
$ in Thousands

Loans and Leases Receivable and Allowance for Credit Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) - USD ($) $ in Thousands		6 Months Ended	9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 64,700		$ 64,700	$ 35,123
Non-accrual	43,880		43,880	20,021
Loans and leases not past due	7,636,192		7,636,192	7,244,271
Purchased-credit-impaired loans	14,400	$ 17,488
Loans and lease receivable, gross	7,700,892		$ 7,700,892	7,318,988
Financing receivable, at amortized cost or lower of cost or market				7,316,903
Delinquent period			30 days
Loans receivable, PPP	4,964,105		$ 4,964,105	0
30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,688		6,688
60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	26,847		26,847
30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due				33,329
90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	31,165		31,165	1,794
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	20,236		20,236	2,133
Non-accrual	11,710		11,710	4,117
Loans and leases not past due	1,930,064		1,930,064	1,901,336
Purchased-credit-impaired loans		1,688
Loans and lease receivable, gross	1,950,300		1,950,300	1,909,274
Multi-family \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0		0
Multi-family \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	15,446		15,446
Multi-family \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due				2,133
Multi-family \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,790		4,790	0
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	9,767		9,767	2,395
Non-accrual	9,633		9,633	4,531
Loans and leases not past due	2,210,948		2,210,948	1,882,700
Purchased-credit-impaired loans		354
Loans and lease receivable, gross	2,220,715		2,220,715	1,889,980
Commercial and industrial \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0		0
Commercial and industrial \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,072		2,072
Commercial and industrial \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due				2,395
Commercial and industrial \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,695		7,695	0
Commercial real estate owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,388		3,388	5,388
Non-accrual	3,599		3,599	1,963
Loans and leases not past due	554,207		554,207	537,992
Purchased-credit-impaired loans		6,664
Loans and lease receivable, gross	557,595		557,595	552,007
Commercial real estate owner occupied \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0		0
Commercial real estate owner occupied \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	952		952
Commercial real estate owner occupied \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due				5,388
Commercial real estate owner occupied \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,436		2,436	0
Commercial real estate non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,356		2,356	8,034
Non-accrual	2,408		2,408	76
Loans and leases not past due	1,213,160		1,213,160	1,211,892
Purchased-credit-impaired loans		3,527
Loans and lease receivable, gross	1,215,516		1,215,516	1,223,529
Commercial real estate non-owner occupied \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0		0
Commercial real estate non-owner occupied \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0		0
Commercial real estate non-owner occupied \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due				8,034
Commercial real estate non-owner occupied \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,356		2,356	0
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0		0	0
Non-accrual				0
Loans and leases not past due	122,963		122,963	118,418
Purchased-credit-impaired loans		0
Loans and lease receivable, gross	122,963		122,963	118,418
Construction \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0		0
Construction \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0		0
Construction \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due				0
Construction \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0		0	0
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	9,923		9,923	5,924
Non-accrual	10,634		10,634	6,128
Loans and leases not past due	325,529		325,529	359,491
Purchased-credit-impaired loans		3,471
Loans and lease receivable, gross	335,452		335,452	375,014
Residential real estate \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	436		436
Residential real estate \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,160		3,160
Residential real estate \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due				5,924
Residential real estate \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,327		6,327	0
Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,855		5,855	5,493
Non-accrual	2,778		2,778	1,655
Loans and leases not past due	58,783		58,783	61,649
Purchased-credit-impaired loans		1,601
Loans and lease receivable, gross	64,638		64,638	70,398
Manufactured housing \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	784		784
Manufactured housing \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	608		608
Manufactured housing \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due				3,699
Manufactured housing \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,463		4,463	1,794
Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,175		13,175	5,756
Non-accrual	3,118		3,118	1,551
Loans and leases not past due	1,220,538		1,220,538	1,170,793
Purchased-credit-impaired loans		$ 183
Loans and lease receivable, gross	1,233,713		1,233,713	1,178,283
Installment \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,468		5,468
Installment \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,609		4,609
Installment \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due				5,756
Installment \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 3,098		$ 3,098	$ 0