Subsequent Events (Details)		12 Months Ended
	Jan. 01, 2019 USD ($) branch	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 07, 2019 USD ($)
Subsequent Event [Line Items]
Loans, net		$ 25,696,018,000	$ 24,538,196,000
Deposits		26,720,322,000	26,147,900,000
Merger-related expense		$ 10,065,000	$ 110,000	$ 1,636,000
Interest rate during the year		0.96%	0.37%	0.18%
FCB Financial Holdings, Inc.
Subsequent Event [Line Items]
Merger-related expense		$ 10,100,000
Pro forma total revenue, net of interest expense		1,900,000,000
Pro forma net income available to common shareholders		$ 613,000,000
Subsequent Event | 5.9% Subordinated Notes
Subsequent Event [Line Items]
Debt, face amount					$ 300,000,000.0
Subsequent Event | FCB Financial Holdings, Inc.
Subsequent Event [Line Items]
Consideration transferred	$ 1,600,000,000
Loans, net	9,420,000,000
Deposits	$ 10,890,000,000
Number of branches | branch	51
Maximum | Subsequent Event | 5.9% Subordinated Notes
Subsequent Event [Line Items]
Stated percentage					5.90%
Minimum | Subsequent Event | 5.9% Subordinated Notes
Subsequent Event [Line Items]
Stated percentage					3.379%