Acquisition - Textual (Details)			3 Months Ended	6 Months Ended
	Jul. 30, 2019 shares	Apr. 12, 2019 USD ($) shares	Jun. 30, 2019 USD ($) financial_center	Jun. 30, 2019 USD ($) financial_center	Apr. 11, 2019 financial_center	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Stock issued for Reliance acquisition		$ 42,000,000.0	$ 144,830,000	$ 144,830,000
Number of financial centers | financial_center			212	212
Assets			$ 17,937,435,000	$ 17,937,435,000		$ 16,543,337,000	$ 15,000,000,000
Net loans			13,063,946,000	13,063,946,000		11,666,572,000
Deposits			13,516,213,000	13,516,213,000		12,398,752,000
Goodwill			926,450,000	926,450,000		$ 845,687,000
Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Shares issued (in shares) | shares		3,999,623
Payments to acquire businesses, gross		$ 62,700,000
Number of financial centers | financial_center					22
Assets		1,500,000,000
Net loans		1,100,000,000
Deposits		1,200,000,000
Goodwill		$ 80,763,000	$ 80,800,000	$ 80,800,000
Landrum Company
Business Acquisition [Line Items]
Number of financial centers | financial_center			39	39
Assets			$ 3,300,000,000	$ 3,300,000,000
Net loans			2,100,000,000	2,100,000,000
Deposits			$ 3,000,000,000.0	$ 3,000,000,000.0
Series A or B Preferred Stock | Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Shares issued, conversion ratio (in shares)		1
Series C Preferred Stock | Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Shares issued, conversion ratio (in shares)		1
Subsequent Event | Landrum Company
Business Acquisition [Line Items]
Shares issued (in shares) | shares	17,350,000