Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Mar. 23, 2018	Dec. 31, 2017	Jul. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Net deferred loan origination fees	$ 37,700		$ 37,700				$ 29,300
Net discount	159,000		159,000				159,300
Deposit liabilities reclassified as loans receivable	10,000		10,000				7,400
Loans with carrying value pledged to secure public deposits and other borrowings	7,600,000		7,600,000				6,600,000
Loans acquired with no evidence of deteriorated credit quality	18,274		18,274				14,953
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Net discount	83,300		83,300				94,700
Sabadell United
Accounts, Notes, Loans and Financing Receivable
Loans acquired								$ 4,030,777
Covered loans acquired	143,800		143,800				158,600
Sabadell United | Non-US [Member]
Accounts, Notes, Loans and Financing Receivable
Covered loans acquired	356,400		356,400				$ 325,500
Gibraltar Private Bank & Trust Company [Member]
Accounts, Notes, Loans and Financing Receivable
Loans acquired					$ 1,500,000	$ 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
Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable
TDRs during period	$ 20,108	$ 17,892	46,691	$ 28,398
TDRs during period on accrual status			20,600	22,800
TDRs during period on non-accrual status			$ 26,100	$ 5,600