Investment Securities (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 20, 2017
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Pledged As Collateral Amortized Cost	$ 458,100
Proceeds from sales of securities available-for-sale	571,800	$ 759,300	$ 393,509
Available-for-sale Securities, Gross Realized Gains	9,200	3,300	11,100
Available-for-sale Securities, Gross Realized Losses	1,000	3,800	1,600
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Reclassification Adjustments, Net of Tax	(37,544)	24,709	(16,244)
Federal Home Loan Bank stock, at cost	$ 32,103	$ 20,790
Federal Home Loan Bank Minimum Stock Ownership As Percent Of Outstanding Advances	0.00%	2.70%
Purchases of FHLB Stock	$ 55,600
Redemptions of FHLB stock	(44,300)
Federal Home Loan Bank of San Francisco [Member]
Schedule of Available-for-sale Securities [Line Items]
Increase (Decrease) in Marketable Securities, Restricted	11,300
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales of securities available-for-sale	563,600	$ 355,400	$ 384,000
CU Bancorp [Member]
Schedule of Available-for-sale Securities [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities				$ 446,980
FHLB stock				$ 11,902
CU Bancorp [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains	$ 0
CU Bancorp [Member] | Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales of securities available-for-sale		$ 404,500