Acquisitions - Narrative (Details) $ / shares in Units, $ in Thousands				12 Months Ended
	Jul. 01, 2018 USD ($) $ / shares shares	Nov. 01, 2017 USD ($) $ / shares shares	Apr. 02, 2017 USD ($) shares	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Nov. 01, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jul. 01, 2019 USD ($)	Apr. 01, 2018 USD ($)	Apr. 01, 2017 USD ($)	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Goodwill acquired during the year				$ 0		$ 313,043			$ 390,839
Purchase accounting adjustments				(404)		2,354			0
Goodwill				808,322		808,726			$ 493,329					$ 102,490
Grandpoint Capital, Inc.
Business Acquisition [Line Items]
Total assets acquired	$ 3,051,567									$ 3,076,224
Gross loans acquired	2,400,000
Deposits	$ 2,506,663									2,506,929
Equity issued shares	0.4750
Consideration paid	$ 602,200				$ 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				312,600		313,000
Purchase accounting adjustments				$ 580
Goodwill										$ 312,639
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		0.2000
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 (in shares) | shares		6,049,373
Closing stock price of common stock (in dollars per share) | $ / shares		$ 40.40
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	$ 2,010,000
Gross loans acquired													1,360,000
Deposits											1,669,550	$ 1,668,085	$ 1,670,000
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
Common Stock | Grandpoint Capital, Inc.
Business Acquisition [Line Items]
Number of shares of common stock issued as consideration (in shares) | shares	15,758,089
Common Stock | Heritage Oaks Bank
Business Acquisition [Line Items]
Number of shares of common stock issued as consideration (in shares) | shares			11,959,022