Loans and Leases Receivable and Allowance for Loan and Lease Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 22,332	$ 15,551
Non-Accrual	22,769	27,494
Current	7,202,023	7,073,879
Loans and lease receivable, gross	7,267,246	7,138,498
Loans and leases receivable, at amortized cost or lower of cost or market	$ 7,267,246	7,138,498
Delinquent period	30 days
Due days for loan payments	90 days
Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	$ 20,122	21,574
30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	20,396	13,363
90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,936	2,188
Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,794	0
Non-Accrual	1,997	1,155
Current	3,204,879	3,282,452
Loans and lease receivable, gross	3,212,312	3,285,297
Multi-family \| Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	1,642	1,690
Multi-family \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,794	0
Multi-family \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,271	1,914
Non-Accrual	12,225	17,764
Current	1,441,679	1,353,586
Loans and lease receivable, gross	1,455,592	1,373,800
Commercial and industrial \| Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	417	536
Commercial and industrial \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,271	1,914
Commercial and industrial \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial real estate owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,566	193
Non-Accrual	839	1,037
Current	570,380	567,809
Loans and lease receivable, gross	582,637	577,477
Commercial real estate owner occupied \| Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	7,852	8,438
Commercial real estate owner occupied \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,566	193
Commercial real estate owner occupied \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Commercial real estate non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,976	1,190
Non-Accrual	102	129
Current	1,101,129	1,119,443
Loans and lease receivable, gross	1,107,336	1,125,106
Commercial real estate non-owner occupied \| Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	4,129	4,344
Commercial real estate non-owner occupied \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,976	1,190
Commercial real estate non-owner occupied \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Non-Accrual	0	0
Current	53,372	56,491
Loans and lease receivable, gross	53,372	56,491
Construction \| Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	0	0
Construction \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Construction \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,612	5,940
Non-Accrual	5,574	5,605
Current	609,874	550,679
Loans and lease receivable, gross	625,066	566,561
Residential real estate \| Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	4,006	4,337
Residential real estate \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,612	5,940
Residential real estate \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Manufactured housing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,622	6,114
Non-Accrual	1,924	1,693
Current	68,362	69,916
Loans and lease receivable, gross	77,778	79,731
Manufactured housing \| Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	1,870	2,008
Manufactured housing \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,686	3,926
Manufactured housing \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,936	2,188
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	491	200
Non-Accrual	108	111
Current	152,348	73,503
Loans and lease receivable, gross	153,153	74,035
Other \| Purchased Credit Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and lease receivable, gross	206	221
Other \| 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	491	200
Other \| 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0	$ 0

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