Acquisitions - Narrative (Details) $ / shares in Units, $ in Thousands				2 Months Ended	3 Months Ended	9 Months Ended	23 Months Ended
	Nov. 01, 2017 USD ($) $ / shares shares	Apr. 01, 2017 USD ($) shares	Jan. 31, 2016 USD ($) bank shares	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2017 $ / shares	Dec. 31, 2016 USD ($)	Jan. 29, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Goodwill				$ 493,329		$ 493,329	$ 493,329		$ 102,490		$ 50,832
Plaza Bancorp
Business Acquisition [Line Items]
Total assets acquired	$ 1,245,740			1,256,313		1,256,313	1,256,313
Gross loans acquired	1,100,000
Deposits	$ 1,081,727			1,082,951		1,082,951	1,082,951
Equity issued (shares)	0.2
Consideration paid	$ 251,000			250,939
Paid by PLZZ prior to close	$ 6,500			6,544		6,544	6,544
Number of shares of common stock issued as consideration | shares	6,049,373
Closing stock price of common stock (in dollars per share) | $ / shares	$ 40.4
Goodwill	$ 122,000			121,885		121,885	121,885
Deferred tax assets				(6,876)
Heritage Oaks Bank
Business Acquisition [Line Items]
Total assets acquired		$ 2,005,637		2,015,822		2,015,822	2,015,822
Gross loans acquired		1,400,000
Deposits		$ 1,668,079		1,669,550		1,669,550	1,669,550
Equity issued (shares)		0.3471
Consideration paid		$ 465,000				465,482
Paid by PLZZ prior to close		3,900
Closing stock price of common stock (in dollars per share) | $ / shares								$ 38.55
Goodwill		$ 269,000		268,954		268,954	268,954
Deferred tax assets					$ 1,100	(6,567)
Security California Bancorp
Business Acquisition [Line Items]
Total assets acquired			$ 716,633	713,950		713,950	713,950
Gross loans acquired			456,000
Deposits			$ 636,450	636,591		636,591	636,591
Equity issued (shares)			0.9629
Consideration paid			$ 120,000				120,174
Paid by PLZZ prior to close			$ 788
Closing stock price of common stock (in dollars per share) | $ / shares										$ 20.53
Number of branches | bank			6
Goodwill			$ 51,700	$ 51,658		$ 51,658	51,658
Deferred tax assets							$ 1,130
Common Stock | Heritage Oaks Bank
Business Acquisition [Line Items]
Number of shares of common stock issued as consideration | shares		11,959,022
Common Stock | Security California Bancorp
Business Acquisition [Line Items]
Number of shares of common stock issued as consideration | shares			5,815,051
Value of shares of common stock to be issued										$ 119,400