Acquisitions - Narrative (Details) shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
	Jul. 01, 2020 USD ($) bank_branch shares	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Assets		$ 15,004,887		$ 15,004,887		$ 12,916,016
Total loans		10,132,510		10,132,510		8,812,553
Deposits		12,702,085		12,702,085		$ 10,897,244
Merger-related costs excluded from pro forma		397	$ 3,894	1,205	$ 4,440
Three Shores Bancorporation, Inc.
Business Acquisition [Line Items]
Assets		2,160,000		2,160,000
Total loans		1,470,000		1,470,000
Deposits		$ 1,790,000		$ 1,790,000
Three Shores Bancorporation | Subsequent Event
Business Acquisition [Line Items]
Number of banking offices | bank_branch	14
Total consideration	$ 188,000
Equity consideration	164,000
Cash consideration	$ 24,100
Shares issued in acquisition (in shares) | shares	8,130
FMBT | Merger-related costs
Business Acquisition [Line Items]
Merger-related costs excluded from pro forma			$ 924		$ 1,020