Acquisitions - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands				2 Months Ended	3 Months Ended	9 Months Ended	23 Months Ended
	Nov. 01, 2017	Apr. 01, 2017	Jan. 31, 2016	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
LIABILITIES ASSUMED
Goodwill recognized				$ 493,329		$ 493,329	$ 493,329	$ 102,490	$ 50,832
Plaza Bancorp
ASSETS ACQUIRED
Cash and cash equivalents	$ 150,459			150,459		150,459	150,459
Loans, gross	1,069,359			1,062,941		1,062,941	1,062,941
Allowance for loan losses	(13,009)			0		0	0
Fixed assets	7,389			7,195		7,195	7,195
Core deposit intangible	198			11,580		11,580	11,580
Deferred tax assets	11,849			4,973		4,973	4,973
Other assets	19,495			19,165		19,165	19,165
Total assets acquired	1,245,740			1,256,313		1,256,313	1,256,313
LIABILITIES ASSUMED
Deposits	1,081,727			1,082,951		1,082,951	1,082,951
Borrowings	40,755			41,152		41,152	41,152
Other Liabilities	8,956			8,334		8,334	8,334
Total liabilities assumed	1,131,438			1,132,437		1,132,437	1,132,437
Excess of assets acquired over liabilities assumed	114,302			123,876		123,876	123,876
Consideration paid	251,000			250,939
Paid by PLZZ prior to close	6,500			6,544		6,544	6,544
Capitalized merger-related expense				1,366		1,366	1,366
Goodwill recognized	$ 122,000			121,885		121,885	121,885
Fair Value Adjustment
Cash and cash equivalents				0
Loans, gross				(6,418)
Allowance for loan losses				13,009
Fixed assets				(194)
Core deposit intangible				11,382
Deferred tax assets				(6,876)
Other assets				(330)
Total assets acquired				10,573
Deposits				1,224
Borrowings				397
Other Liabilities				(622)
Total liabilities assumed				999
Excess of assets acquired over liabilities assumed				9,574
Heritage Oaks Bank
ASSETS ACQUIRED
Cash and cash equivalents		$ 78,728		78,728		78,728	78,728
Investment securities		447,520		442,923		442,923	442,923
Loans, gross		1,387,949		1,364,649		1,364,649	1,364,649
Allowance for loan losses		(17,200)		0		0	0
Fixed assets		35,567		34,902		34,902	34,902
Core deposit intangible		0		28,123		28,123	28,123
Deferred tax assets		17,850		11,283		11,283	11,283
Other assets		55,223		55,214		55,214	55,214
Total assets acquired		2,005,637		2,015,822		2,015,822	2,015,822
LIABILITIES ASSUMED
Deposits		1,668,079		1,669,550		1,669,550	1,669,550
Borrowings		141,996		139,034		139,034	139,034
Other Liabilities		7,290		8,061		8,061	8,061
Total liabilities assumed		1,817,365		1,816,645		1,816,645	1,816,645
Excess of assets acquired over liabilities assumed		188,272		199,177		199,177	199,177
Consideration paid		465,000				465,482
Paid by PLZZ prior to close		3,900
Capitalized merger-related expense				2,649		2,649	2,649
Goodwill recognized		$ 269,000		268,954		268,954	268,954
Fair Value Adjustment
Cash and cash equivalents						0
Investment securities						(4,597)
Loans, gross						(23,300)
Allowance for loan losses						17,200
Fixed assets						(665)
Core deposit intangible						28,123
Deferred tax assets					$ 1,100	(6,567)
Other assets						(9)
Total assets acquired						10,185
Deposits						1,471
Borrowings						(2,962)
Other Liabilities						771
Total liabilities assumed						(720)
Excess of assets acquired over liabilities assumed						10,905
Security California Bancorp
ASSETS ACQUIRED
Cash and cash equivalents			$ 40,947	40,947		40,947	40,947
Investment securities			191,881	190,254		190,254	190,254
Loans, gross			467,197	456,158		456,158	456,158
Allowance for loan losses			(7,399)	0		0	0
Fixed assets			5,335	4,190		4,190	4,190
Core deposit intangible			493	4,319		4,319	4,319
Deferred tax assets			5,618	6,748		6,748	6,748
Other assets			10,589	9,362		9,362	9,362
Total assets acquired			716,633	713,950		713,950	713,950
LIABILITIES ASSUMED
Deposits			636,450	636,591		636,591	636,591
Borrowings			0	0		0	0
Deferred tax liability			0	0		0	0
Other Liabilities			9,063	8,843		8,843	8,843
Total liabilities assumed			645,513	645,434		645,434	645,434
Excess of assets acquired over liabilities assumed			71,120	68,516		68,516	68,516
Consideration paid			120,000				120,174
Paid by PLZZ prior to close			788
Goodwill recognized			51,700	51,658		51,658	51,658
Fair Value Adjustment
Cash and cash equivalents							0
Investment securities							(1,627)
Loans, gross							(11,039)
Allowance for loan losses							7,399
Fixed assets							(1,145)
Core deposit intangible							3,826
Deferred tax assets							1,130
Other assets							(1,227)
Total assets acquired							(2,683)
Deposits							141
Borrowings							0
Deferred tax liability							0
Other Liabilities							(220)
Total liabilities assumed							(79)
Excess of assets acquired over liabilities assumed							(2,604)
Security California Bancorp | Bank Time Deposits
ASSETS ACQUIRED
Cash and cash equivalents			$ 1,972	$ 1,972		$ 1,972	1,972
Fair Value Adjustment
Cash and cash equivalents							$ 0