Loans And Allowance For Loan Losses (Loans Outstanding By Classification) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Past Due [Line Items]
Total loans	$ 37,187,814		$ 25,970,716	$ 24,812,795
Deferred fees and costs, net	(25,364)		(24,143)	$ (25,300)
Total loans, net of deferred fees and costs	37,162,450		25,946,573
FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Total loans	7,464,040
Deferred fees and costs, net	0
Total loans, net of deferred fees and costs	7,464,040
Loans		$ 9,288,028
Parent Company
Financing Receivable, Past Due [Line Items]
Total loans	29,723,774
Deferred fees and costs, net	(25,364)
Total loans, net of deferred fees and costs	29,698,410
Total commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans outstanding	16,782,670		12,781,206
Total loans			12,781,206
Total commercial and industrial | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	2,584,991
Total loans	2,584,991
Total commercial and industrial | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	14,197,679
Total loans	14,197,679
Total commercial and industrial | Commercial, financial, and agricultural
Financing Receivable, Past Due [Line Items]
Loans outstanding	10,252,859		7,449,698
Total loans			7,449,698
Total commercial and industrial | Commercial, financial, and agricultural | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	1,665,772
Total loans	1,665,772
Total commercial and industrial | Commercial, financial, and agricultural | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	8,587,087
Total loans	8,587,087
Total commercial and industrial | Owner-occupied
Financing Receivable, Past Due [Line Items]
Loans outstanding	6,529,811		5,331,508
Total loans			5,331,508
Total commercial and industrial | Owner-occupied | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	919,219
Total loans	919,219
Total commercial and industrial | Owner-occupied | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	5,610,592
Total loans	5,610,592
Total commercial real estate
Financing Receivable, Past Due [Line Items]
Loans outstanding	10,480,484		6,564,491
Total loans			6,564,491
Total commercial real estate | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	2,895,708
Total loans	2,895,708
Total commercial real estate | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	7,584,776
Total loans	7,584,776
Total commercial real estate | Investment properties
Financing Receivable, Past Due [Line Items]
Loans outstanding	9,042,679		5,560,951
Total loans			5,560,951
Total commercial real estate | Investment properties | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	2,546,776
Total loans	2,546,776
Total commercial real estate | Investment properties | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	6,495,903
Total loans	6,495,903
Total commercial real estate | 1-4 family properties
Financing Receivable, Past Due [Line Items]
Loans outstanding	780,015		679,870
Total loans			679,870
Total commercial real estate | 1-4 family properties | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	152,833
Total loans	152,833
Total commercial real estate | 1-4 family properties | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	627,182
Total loans	627,182
Total commercial real estate | Land and development
Financing Receivable, Past Due [Line Items]
Loans outstanding	657,790		323,670
Total loans			323,670
Total commercial real estate | Land and development | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	196,099
Total loans	196,099
Total commercial real estate | Land and development | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	461,691
Total loans	461,691
Total consumer
Financing Receivable, Past Due [Line Items]
Loans outstanding	9,924,660		6,625,019
Total loans			6,625,019
Total consumer | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	1,983,341
Total loans	1,983,341
Total consumer | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	7,941,319
Total loans	7,941,319
Total consumer | Consumer mortgages
Financing Receivable, Past Due [Line Items]
Loans outstanding	5,546,368		2,934,235
Total loans			2,934,235
Total consumer | Consumer mortgages | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	1,916,735
Total loans	1,916,735
Total consumer | Consumer mortgages | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	3,629,633
Total loans	3,629,633
Total consumer | Home equity lines
Financing Receivable, Past Due [Line Items]
Loans outstanding	1,713,157		1,515,796
Total loans			1,515,796
Total consumer | Home equity lines | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	58,061
Total loans	58,061
Total consumer | Home equity lines | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	1,655,096
Total loans	1,655,096
Total consumer | Credit cards
Financing Receivable, Past Due [Line Items]
Loans outstanding	268,841		258,245
Total loans			258,245
Total consumer | Credit cards | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	0
Total consumer | Credit cards | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	268,841
Total loans	268,841
Total consumer | Other consumer loans
Financing Receivable, Past Due [Line Items]
Loans outstanding	2,396,294		1,916,743
Total loans			$ 1,916,743
Total consumer | Other consumer loans | FCB Financial Holdings, Inc.
Financing Receivable, Past Due [Line Items]
Loans outstanding	8,545
Total loans	8,545
Total consumer | Other consumer loans | Parent Company
Financing Receivable, Past Due [Line Items]
Loans outstanding	2,387,749
Total loans	$ 2,387,749