Business Combinations - Summary of Fair Value of Assets Purchased, Including Goodwill and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Apr. 01, 2019
Assets:
Purchased credit impaired loans			$ 18,616
Goodwill	$ 1,204,417	$ 1,204,417
National Commerce Corporation [Member]
Assets:
Cash and cash equivalents			268,524
Loans, held for investment			3,309,234
Purchased credit impaired loans			18,616
Loans held for sale			14,588
Investments			178,488
Accrued interest receivable			11,006
Branch real estate			61,295
Furniture and fixtures			7,204
Bank property held for sale			12,436
FHLB, FRB and other stock			17,076
Bank owned life insurance			55,474
Other real estate owned			875
Servicing asset			1,581
Core deposit intangible			39,900
Goodwill			401,537
Deferred tax asset			16,285
Other assets			23,663
Total assets acquired			4,437,782
Liabilities:
Deposits			3,486,732
Securities sold under agreement to repurchase			18,833
Subordinated debt			38,802
Accrued interest payable			2,095
Other liabilities			47,622
Noncontrolling interest			12,002
Total liabilities assumed and noncontrolling interest			$ 3,606,086