Loans and Leases Receivable and Allowance for Credit Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
Mar. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 111,379	$ 111,379	$ 35,123
Non-accrual	49,034	49,034	20,021
Loans and leases not past due	7,241,883	7,241,883	7,244,271
Loans and lease receivable, gross	7,353,262	$ 7,353,262	7,318,988
Purchased-credit-impaired loans	16,600		17,488
Financing receivable, at amortized cost or lower of cost or market			7,316,903
Delinquent period		30 days
30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	52,717	$ 52,717
60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,385	6,385
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	52,277	52,277	1,794
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,399	6,399	2,133
Non-accrual	4,020	4,020	4,117
Loans and leases not past due	1,615,234	1,615,234	1,901,336
Loans and lease receivable, gross	1,621,633	1,621,633	1,909,274
Purchased-credit-impaired loans			1,688
Multi-family \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,378	2,378
Multi-family \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
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	4,021	4,021	0
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	12,173	12,173	2,395
Non-accrual	9,993	9,993	4,531
Loans and leases not past due	2,060,779	2,060,779	1,882,700
Loans and lease receivable, gross	2,072,952	2,072,952	1,889,980
Purchased-credit-impaired loans			354
Commercial and industrial \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,332	1,332
Commercial and industrial \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	659	659
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	10,182	10,182	0
Commercial real estate owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,102	8,102	5,388
Non-accrual	2,411	2,411	1,963
Loans and leases not past due	535,843	535,843	537,992
Loans and lease receivable, gross	543,945	543,945	552,007
Purchased-credit-impaired loans			6,664
Commercial real estate owner occupied \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,391	4,391
Commercial real estate owner occupied \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	971	971
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	2,740	2,740	0
Commercial real estate non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	52,193	52,193	8,034
Non-accrual	21,479	21,479	76
Loans and leases not past due	1,200,633	1,200,633	1,211,892
Loans and lease receivable, gross	1,252,826	1,252,826	1,223,529
Purchased-credit-impaired loans			3,527
Commercial real estate non-owner occupied \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	30,723	30,723
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	21,470	21,470	0
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0	0
Non-accrual	0	0	0
Loans and leases not past due	115,448	115,448	118,418
Loans and lease receivable, gross	115,448	115,448	118,418
Purchased-credit-impaired loans			0
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	11,569	11,569	5,924
Non-accrual	6,054	6,054	6,128
Loans and leases not past due	350,478	350,478	359,491
Loans and lease receivable, gross	362,047	362,047	375,014
Purchased-credit-impaired loans			3,471
Residential real estate \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,253	5,253
Residential real estate \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	68	68
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	6,248	6,248	0
Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,189	8,189	5,493
Non-accrual	2,558	2,558	1,655
Loans and leases not past due	61,051	61,051	61,649
Loans and lease receivable, gross	69,240	69,240	70,398
Purchased-credit-impaired loans			1,601
Manufactured housing \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,138	2,138
Manufactured housing \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	962	962
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	5,089	5,089	1,794
Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	12,754	12,754	5,756
Non-accrual	2,519	2,519	1,551
Loans and leases not past due	1,302,417	1,302,417	1,170,793
Loans and lease receivable, gross	1,315,171	1,315,171	1,178,283
Purchased-credit-impaired loans			183
Other consumer \| 30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,502	6,502
Other consumer \| 60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,725	3,725
Other consumer \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due			5,756
Other consumer \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 2,527	$ 2,527	$ 0

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