Note Allowance for loan losses (Activity in Allowance for Loan Losses Related to ASC 310-30 Acquired Loans) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	$ 623,426	$ 540,651
Provision for loan losses	71,063	40,698
Charge-offs	(67,816)	(59,068)
Recoveries	13,905	22,215
Balance at end of period	640,578	544,496
Westernbank Puerto Rico | Acquired loans in an FDIC assisted transaction | Credit Impaired Loans | ASC Subtopic 310-30
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	70,129	68,877
Provision for loan losses	21,570	(322)
Net recoveries (charge-offs)	(1,936)	(2,011)
Balance at end of period	$ 89,763	$ 66,544