Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 23, 2018	Dec. 31, 2017	Jul. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Net deferred loan origination fees	$ 29,600		$ 29,600			$ 29,300
Net discount	143,200		143,200			159,300
Deposit liabilities reclassified as loans receivable	6,300		6,300			7,400
Loans with carrying value pledged to secure public deposits and other borrowings	7,500,000		7,500,000			6,600,000
Loans acquired with no evidence of deteriorated credit quality	7,249		7,249			14,953
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Net discount	75,600		75,600			94,700
Sabadell United
Accounts, Notes, Loans and Financing Receivable
Loans acquired							$ 4,030,777
Covered loans acquired						158,600
Sabadell United | Non-US
Accounts, Notes, Loans and Financing Receivable
Covered loans acquired	228,200		228,200			$ 325,500
Gibraltar Private Bank & Trust Company
Accounts, Notes, Loans and Financing Receivable
Loans acquired					$ 1,465,278
Loans acquired with no evidence of deteriorated credit quality	1,455,044		1,455,044
Loans acquired with deteriorated credit quality	10,234		10,234
TDRs Occurring during the Period | TDRs
Accounts, Notes, Loans and Financing Receivable
TDRs during period	$ 6,537	$ 24,586	45,954	$ 51,517
TDRs during period on accrual status			20,200	40,500
TDRs during period on non-accrual status			$ 25,800	$ 11,000