Business Combinations - Additional Information (Details) $ in Thousands			12 Months Ended
	Dec. 31, 2019 USD ($) BranchLocation shares	Jul. 01, 2019 USD ($)	Dec. 31, 2019 USD ($) shares	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)
Business Acquisition [Line Items]
Goodwill	$ 485,336		$ 485,336	$ 43,061
Unfunded commitments	44,900		44,900	$ 39,700
Banking Segment
Business Acquisition [Line Items]
Goodwill	442,579		442,579
State Bank Financial Corporation
Business Acquisition [Line Items]
Loans added in acquisition	3,317,897		3,317,897
Deposits added in acquisition	$ 4,096,665		4,096,665
Shares issued for business acquisition | shares	49,232,008
Purchase price consideration	$ 826,400
Value of common stock in purchase price	826,113
Fair value of unexercised warrants	267
Goodwill	175,657		175,657
Unfunded commitments	26,800		26,800
Purchase consideration paid	826,380
Recognized provisional identifiable intangible assets with an estimated fair value	$ 117,038		117,038
State Bank Financial Corporation | Certificates of Deposit
Business Acquisition [Line Items]
Estimated useful life	12 months
Discount on transaction of certificates of deposit	$ 3,400
State Bank Financial Corporation | Banking Segment
Business Acquisition [Line Items]
Goodwill	175,700		175,700
State Bank Financial Corporation | Core Deposit
Business Acquisition [Line Items]
Intangible assets recognized	$ 111,900		111,900
Estimated useful life	10 years
State Bank Financial Corporation | Customer Relationship
Business Acquisition [Line Items]
Intangible assets recognized	$ 3,700		3,700
Estimated useful life	10 years
State Bank Financial Corporation | Trademark
Business Acquisition [Line Items]
Intangible assets recognized	$ 1,400		$ 1,400
Estimated useful life	20 years
State Bank Financial Corporation | Common Class A
Business Acquisition [Line Items]
Common stock in exchange for outstanding common shares | shares	1.271		1.271
Shares issued for business acquisition | shares	49,200,000
State Bank Financial Corporation | Georgia
Business Acquisition [Line Items]
Number of branch locations | BranchLocation	32
Wealth & Pension Services Group, Inc. | Linscomb & Williams, Inc.
Business Acquisition [Line Items]
Goodwill		$ 2,600
Purchase consideration paid		8,000
Cash payments		5,200
Future cash payments to acquire certain assets and assume liabilities		$ 2,100
Term of future cash payments		5 years
Recognized provisional identifiable intangible assets with an estimated fair value					$ 5,100
Merger-related expenses			$ 500
Wealth & Pension Services Group, Inc. | Linscomb & Williams, Inc. | Maximum
Business Acquisition [Line Items]
Estimated fair value finalization period		1 year