Acquisitions - Assets Acquired and Liabilities Assumed - Schedule (Details) - USD ($) $ in Thousands			5 Months Ended	12 Months Ended
	Nov. 01, 2017	Apr. 01, 2017	Mar. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
LIABILITIES ASSUMED
Goodwill recognized			$ 493,785	$ 493,785	$ 493,329
Plaza Bancorp
ASSETS ACQUIRED
Cash and cash equivalents	$ 150,459		150,459	150,459
Loans, gross	1,069,359		1,062,901	1,062,901
Allowance for loan losses	(13,009)		0	0
Fixed assets	7,389		7,195	7,195
Core deposit intangible	198		11,580	11,580
Deferred tax assets	11,849		4,990	4,990
Other assets	19,495		19,165	19,165
Total assets acquired	1,245,740		1,256,290	1,256,290
LIABILITIES ASSUMED
Deposits	1,081,727		1,082,951	1,082,951
Borrowings	40,755		41,152	41,152
Other Liabilities	8,956		8,334	8,334
Total liabilities assumed	1,131,438		1,132,437	1,132,437
Excess of assets acquired over liabilities assumed	114,302		123,853	123,853
Consideration paid	246,000		245,761
Goodwill recognized	$ 122,000		121,908	121,908
Fair Value Adjustments
Cash and cash equivalents			0
Loans, gross			(6,458)
Allowance for loan losses			13,009
Fixed assets			(194)
Core deposit intangible			11,382
Deferred tax assets			(6,859)
Other assets			(330)
Total assets acquired			10,550
Deposits			1,224
Borrowings			397
Other Liabilities			(622)
Total liabilities assumed			999
Excess of assets acquired over liabilities assumed			9,551
Heritage Oaks Bancorp
ASSETS ACQUIRED
Cash and cash equivalents		$ 78,728	78,728	78,728
Investment securities		447,520	442,923	442,923
Loans, gross		1,387,949	1,364,649	1,364,649
Allowance for loan losses		(17,200)	0	0
Fixed assets		35,567	34,902	34,902
Core deposit intangible		0	28,123	28,123
Deferred tax assets		17,850	11,283	11,283
Other assets		55,223	55,214	55,214
Total assets acquired		2,005,637	2,015,822	2,015,822
LIABILITIES ASSUMED
Deposits		1,668,079	1,669,550	1,669,550
Borrowings		141,996	139,034	139,034
Other Liabilities		7,290	8,061	8,061
Total liabilities assumed		1,817,365	1,816,645	1,816,645
Excess of assets acquired over liabilities assumed		188,272	199,177	199,177
Consideration paid		468,000		468,131
Goodwill recognized		$ 269,000	$ 268,954	268,954
Fair Value Adjustments
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				(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