Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 23, 2018	Dec. 31, 2017	Jul. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Net deferred loan origination fees	$ 31,400			$ 29,300
Net discount	158,100			159,300
Deposit liabilities reclassified as loans receivable	7,300			7,400
Loans with carrying value pledged to secure public deposits and other borrowings	6,800,000			6,600,000
Loans acquired with no evidence of deteriorated credit quality	17,000			15,000
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Net discount	100,800			94,700
Sabadell United
Accounts, Notes, Loans and Financing Receivable
Loans acquired					$ 4,025,946
Covered loans acquired	150,000			158,600
Sabadell United | Non-US [Member]
Accounts, Notes, Loans and Financing Receivable
Covered loans acquired	336,100			$ 325,500
Gibraltar Private Bank & Trust Company [Member]
Accounts, Notes, Loans and Financing Receivable
Loans acquired	1,500,000		$ 1,465,319
Loans acquired with no evidence of deteriorated credit quality	1,455,085
Loans acquired with deteriorated credit quality	10,234
Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable
TDRs during period	27,200	$ 13,165
TDRs during period on accrual status	12,900	11,800
TDRs during period on non-accrual status	$ 14,300	$ 1,400