Business Combinations - Narrative (Details) - USD ($)							12 Months Ended
	Jan. 10, 2019	Nov. 15, 2018	Nov. 01, 2018	Oct. 02, 2018	May 01, 2018	Dec. 18, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 05, 2017	Jan. 13, 2017
Business Acquisition [Line Items]
Total assets							$ 35,408,629,000	$ 34,527,512,000
Loans and Leases							25,523,276,000	23,596,825,000
Deposits							30,672,460,000	29,266,275,000
PCI loans							30,190,000	199,682,000	$ 80,690,000
Goodwill recorded for Palmetto Heritage							236,347,000	150,601,000	150,601,000
Merger-related expenses							6,462,000	9,015,000	5,341,000
Gain on acquisitions							0	134,745,000	$ 5,831,000
First South Bancorp
Business Acquisition [Line Items]
Total assets							238,500,000
Loans and Leases							180,900,000
Deposits							204,100,000
First South Bancorp | Subsequent Event
Business Acquisition [Line Items]
Share price (usd per share)	$ 1.15
Purchase Price	$ 37,500,000
Biscayne Bancshares
Business Acquisition [Line Items]
Share price (usd per share)		$ 25.05
Purchase Price		$ 118,700,000
Total assets							1,010,000,000
Loans and Leases							850,300,000
Deposits							746,400,000
Palmetto Heritage Bancshares
Business Acquisition [Line Items]
Share price (usd per share)			$ 135.00
Purchase Price			$ 30,426,000
Total assets acquired			162,248,000
Total non-PCI loans and leases							131,283,000			$ 131,300,000
PCI loans			3,863,000							3,863,000
Total liabilities assumed			149,272,000
Deposits			124,892,000
Goodwill recorded for Palmetto Heritage			17,450,000
Merger-related expenses							546,000
Revenue of acquired business							1,200,000
Intangible assets			1,706,000
Palmetto Heritage Bancshares | Core deposits
Business Acquisition [Line Items]
Core deposit intangibles			$ 1,700,000
Capital Commerce Bancorp
Business Acquisition [Line Items]
Share price (usd per share)				$ 4.75
Purchase Price				$ 28,063,000
Total assets acquired				221,887,000
Total non-PCI loans and leases							173,354,000			173,400,000
PCI loans				10,772,000						10,772,000
Total liabilities assumed				204,504,000
Deposits				172,387,000
Goodwill recorded for Palmetto Heritage				10,680,000
Merger-related expenses							1,200,000
Revenue of acquired business							3,200,000
Intangible assets				2,680,000
Capital Commerce Bancorp | Core deposits
Business Acquisition [Line Items]
Core deposit intangibles				$ 2,700,000
HomeBancorp Inc.
Business Acquisition [Line Items]
Share price (usd per share)						$ 15.03
Purchase Price					$ 112,657,000	$ 112,700,000
Total assets acquired					842,693,000
Total non-PCI loans and leases							550,618,000			550,600,000
PCI loans					15,555,000					15,555,000
Total liabilities assumed					787,652,000
Deposits					619,589,000
Goodwill recorded for Palmetto Heritage					57,616,000
Merger-related expenses							2,300,000
Revenue of acquired business							17,400,000
Intangible assets					13,206,000
HomeBancorp Inc. | Core deposits
Business Acquisition [Line Items]
Core deposit intangibles					$ 9,900,000
Guaranty Bank
Business Acquisition [Line Items]
Total assets acquired										875,100,000
Total non-PCI loans and leases							574,553,000			574,600,000
PCI loans										114,533,000
Total liabilities assumed										982,700,000
Deposits										982,300,000
Merger-related expenses							2,300,000	7,400,000
Gain on acquisitions							122,700,000
Revenue of acquired business							17,300,000	20,500,000
Guaranty Bank | Core deposits
Business Acquisition [Line Items]
Core deposit intangibles										$ 9,900,000
Harvest Community Bank
Business Acquisition [Line Items]
Total assets acquired											$ 111,600,000
PCI loans											85,149,000
Total liabilities assumed											121,800,000
Merger-related expenses							0	1,200,000
Gain on acquisitions							12,000,000
Revenue of acquired business							$ 3,700,000	$ 3,800,000
Intangible assets											$ 850,000