Loans Receivable and Allowance for Loan Losses - Non-Covered Loans and Covered Loans by Class and Performance Status (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Due days for loan payments	30 days
Delinquent period	90 days
Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	$ 4,946	$ 7,916
90 Days Or More Past Due	3,036	4,388
Total Past Due	7,982	12,304
Non-Accrual	16,595	7,487
Current	4,686,053	4,204,373
Purchased Credit-Impaired Loans	44,100	45,316
Total Loans	4,754,730	4,269,480
Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	80	665
90 Days Or More Past Due	0	0
Total Past Due	80	665
Non-Accrual	1,187	4,246
Current	11,956	25,969
Purchased Credit-Impaired Loans	626	11,301
Total Loans	13,849	42,181
Multi-family | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Days Or More Past Due	0	0
Total Past Due	0	0
Non-Accrual	0	0
Current	2,401,727	2,203,686
Purchased Credit-Impaired Loans	3,673	2,717
Total Loans	2,405,400	2,206,403
Multi-family | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due		0
90 Days Or More Past Due		0
Total Past Due		0
Non-Accrual		0
Current		373
Purchased Credit-Impaired Loans		1,629
Total Loans		2,002
Commercial and industrial (including owner occupied commercial real estate) | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	366
90 Days Or More Past Due	0	0
Total Past Due	0	366
Non-Accrual	6,381	2,257
Current	675,939	542,667
Purchased Credit-Impaired Loans	1,620	2,102
Total Loans	683,940	547,392
Commercial and industrial (including owner occupied commercial real estate) | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due		518
90 Days Or More Past Due		0
Total Past Due		518
Non-Accrual		256
Current		578
Purchased Credit-Impaired Loans		1,191
Total Loans		2,543
Commercial real estate owner occupied | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	191	0
90 Days Or More Past Due	0	0
Total Past Due	191	0
Non-Accrual	1,851	2,342
Current	268,206	211,453
Purchased Credit-Impaired Loans	13,770	16,033
Total Loans	284,018	229,828
Commercial real estate owner occupied | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due		0
90 Days Or More Past Due		0
Total Past Due		0
Non-Accrual		172
Current		5,734
Purchased Credit-Impaired Loans		0
Total Loans		5,906
Commercial real estate non-owner occupied | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	1,047	0
90 Days Or More Past Due	0	0
Total Past Due	1,047	0
Non-Accrual	4,478	1,108
Current	894,449	816,114
Purchased Credit-Impaired Loans	12,997	10,718
Total Loans	912,971	827,940
Commercial real estate non-owner occupied | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due		0
90 Days Or More Past Due		0
Total Past Due		0
Non-Accrual		352
Current		5,932
Purchased Credit-Impaired Loans		5,086
Total Loans		11,370
Construction | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Days Or More Past Due	0	0
Total Past Due	0	0
Non-Accrual	0	0
Current	89,382	44,483
Purchased Credit-Impaired Loans	234	159
Total Loans	89,616	44,642
Construction | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due		0
90 Days Or More Past Due		0
Total Past Due		0
Non-Accrual		2,325
Current		0
Purchased Credit-Impaired Loans		2,751
Total Loans		5,076
Residential real estate | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	512	1,226
90 Days Or More Past Due	0	0
Total Past Due	512	1,226
Non-Accrual	1,232	849
Current	251,090	273,565
Purchased Credit-Impaired Loans	8,133	9,363
Total Loans	260,967	285,003
Residential real estate | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Days Or More Past Due	0	0
Total Past Due	0	0
Non-Accrual	1,046	1,006
Current	9,533	10,782
Purchased Credit-Impaired Loans	602	604
Total Loans	11,181	12,392
Manufactured housing | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	3,196	6,324
90 Days Or More Past Due	3,036	4,388
Total Past Due	6,232	10,712
Non-Accrual	2,653	931
Current	104,399	111,072
Purchased Credit-Impaired Loans	3,458	4,016
Total Loans	116,742	126,731
Other | Non-covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	0	0
90 Days Or More Past Due	0	0
Total Past Due	0	0
Non-Accrual	0	0
Current	861	1,333
Purchased Credit-Impaired Loans	215	208
Total Loans	1,076	1,541
Other | Covered Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-89 Days Past Due	80	147
90 Days Or More Past Due	0	0
Total Past Due	80	147
Non-Accrual	141	135
Current	2,423	2,570
Purchased Credit-Impaired Loans	24	40
Total Loans	$ 2,668	$ 2,892