Condensed Parent Company Financial Statements - Schedule of Condensed Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
ASSETS
Cash and due from banks	$ 905,447	$ 234,796
Other assets	240,970	215,762
Total Assets	16,425,610	15,720,112
LIABILITIES
Junior subordinated debt owed to unconsolidated subsidiary trusts	132,190
Total Liabilities	13,668,873	13,126,191
SHAREHOLDERS’ EQUITY	2,756,737	2,593,921	$ 1,978,827	$ 1,395,321
Total Liabilities and Shareholders’ Equity	16,425,610	15,720,112
Parent Company [Member]
ASSETS
Cash and due from banks	223,224	170,854
Investment in subsidiaries—Bank	2,675,923	2,572,915
Investment in subsidiaries—Nonbank	9,731	9,170
Securities available-for-sale, at fair value		225
Other assets	38,194	38,393
Total Assets	2,947,072	2,791,557
LIABILITIES
Junior subordinated debt owed to unconsolidated subsidiary trusts	167,290	174,660
Dividends payable and other liabilities	23,045	22,976
Total Liabilities	190,335	197,636
SHAREHOLDERS’ EQUITY	2,756,737	2,593,921
Total Liabilities and Shareholders’ Equity	$ 2,947,072	$ 2,791,557