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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at beginning of period	$ 540,014	$ 548,720	$ 540,651	$ 537,111
Provision for loan losses	160,759	43,344	253,936	128,651
Balance at end of period	646,913	555,855	646,913	555,855
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	65,674	66,995	68,877	63,563
Provision for loan losses	2,995	6,710	8,214	2,640
Net recoveries (charge-offs)	(1,569)	(4,134)	(9,991)	3,368
Balance at end of period	$ 67,100	$ 69,571	$ 67,100	$ 69,571