Business Combinations (Detail) $ in Thousands, shares in Millions		12 Months Ended
	Jan. 01, 2018 USD ($) office shares	Dec. 31, 2018 USD ($) office	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Loans		$ 24,883,610	$ 18,210,724
Goodwill from business combinations		$ 394,028
Core deposits
Business Acquisition [Line Items]
Estimated useful life		8 years
USAmeriBancorp, Inc.
Business Acquisition [Line Items]
Assets	$ 5,079,432
Loans	3,736,984
Deposits	$ 3,564,843
Number of branches acquired | office		29
Conversion ratio for shares issued	6.1
Total consideration	$ 737,230
Shares issued in connection with acquisition | shares	64.9
Merger expenses		$ 17,400
Goodwill from business combinations		$ 5,800
USAmeriBancorp, Inc. | Alabama
Business Acquisition [Line Items]
Number of branches acquired | office	15
USAmeriBancorp, Inc. | Core deposits
Business Acquisition [Line Items]
Estimated useful life		10 years