Acquisitions - Narrative (Details) $ / shares in Units, $ in Thousands					6 Months Ended	12 Months Ended
	Jul. 01, 2018 USD ($) $ / shares shares	Nov. 01, 2017 USD ($) $ / shares shares	Apr. 02, 2017 USD ($) shares	Jan. 31, 2016 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Nov. 01, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Apr. 01, 2018 USD ($)	Apr. 01, 2017 USD ($)	Mar. 31, 2017 $ / shares	Jan. 29, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Goodwill acquired during the year						$ 313,043			$ 390,839		$ 51,658
Goodwill					$ 808,726	808,726			$ 493,329		$ 102,490					$ 50,832
Grandpoint Capital, Inc.
Business Acquisition [Line Items]
Total assets acquired	$ 3,051,567				3,075,820	3,075,820
Gross loans acquired	2,400,000
Deposits	$ 2,506,663				2,506,929	2,506,929
Equity issued (shares)	0.4750
Consideration paid	$ 601,200				602,152
Aggregate cash paid for shares and consideration payable	$ 28,100
Closing stock price of common stock (in dollars per share) | $ / shares	$ 38.15
Goodwill acquired during the year						313,000
Goodwill					313,043	313,043
Plaza Bancorp
Business Acquisition [Line Items]
Total assets acquired		$ 1,245,740					$ 1,254,730
Gross loans acquired		1,060,000
Deposits		$ 1,081,727					1,082,951
Equity issued (shares)		0.2
Consideration paid		$ 245,800					245,761
Aggregate cash paid for shares and consideration payable		$ 6,500
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 acquired during the year						1,800
Goodwill		$ 124,000					$ 123,640
Heritage Oaks Bank
Business Acquisition [Line Items]
Total assets acquired												$ 2,014,822	$ 2,003,635
Gross loans acquired													1,360,000
Deposits												1,669,550	$ 1,668,085
Equity issued (shares)													0.3471
Consideration paid			$ 467,400					$ 467,439
Aggregate cash paid for shares and consideration payable													$ 3,900
Closing stock price of common stock (in dollars per share) | $ / shares														$ 38.55
Goodwill acquired during the year						600
Goodwill												$ 269,553	$ 270,000
Security California Bancorp
Business Acquisition [Line Items]
Total assets acquired				$ 716,633						$ 713,950
Gross loans acquired				456,200
Deposits				$ 636,450	$ 636,600	$ 636,600				636,591
Equity issued (shares)				0.9629
Consideration paid				$ 120,200						120,174
Aggregate cash paid for shares and consideration payable				788
Closing stock price of common stock (in dollars per share) | $ / shares															$ 20.53
Goodwill				$ 51,700						$ 51,658
Common Stock | Grandpoint Capital, Inc.
Business Acquisition [Line Items]
Number of shares of common stock issued as consideration | shares	15,758,089
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