Goodwill and Core Deposit Intangibles - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 01, 2019	Nov. 01, 2018	Apr. 01, 2018	Nov. 01, 2017	Apr. 01, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill	$ 808,322,000	$ 808,322,000	$ 808,726,000	$ 493,329,000						$ 102,490,000
Goodwill adjustments		(404,000)	2,354,000	0
Goodwill acquired during the year		0	313,043,000	390,839,000
Impairment losses	0	0	0	0
Net CDI	83,312,000	83,312,000	100,556,000	$ 43,014,000
Estimated aggregate amortization expense
2020	15,400,000	15,400,000
2021	13,400,000	13,400,000
2022	11,700,000	11,700,000
2023	10,200,000	10,200,000
2024	$ 9,200,000	$ 9,200,000
Core Deposits | Minimum
Goodwill [Line Items]
Weighted average useful life (in years)		6 years
Core Deposits | Maximum
Goodwill [Line Items]
Weighted average useful life (in years)		11 years
Grandpoint Capital, Inc.
Goodwill [Line Items]
Goodwill					$ 312,639,000
Goodwill adjustments		$ 580,000
Goodwill acquired during the year		$ 312,600,000	313,000,000.0
Plaza Bancorp
Goodwill [Line Items]
Goodwill						$ 123,640,000		$ 124,000,000.0
Goodwill acquired during the year			1,800,000
Heritage Oaks Bank
Goodwill [Line Items]
Goodwill							$ 269,553,000		$ 270,000,000.0
Goodwill acquired during the year			$ 600,000