Note Commitments and contingencies (FDIC dealings section) - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2017 USD ($) D		Jun. 30, 2015 USD ($)	Dec. 31, 2016 USD ($)		Nov. 12, 2015 USD ($)	Sep. 30, 2015 USD ($)
FDIC Dealings [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount, Covered	$ 551,980			$ 572,878
True Up Payment Term | D	45
FDIC
FDIC Dealings [Line Items]
Business Combination Contingent Consideration Liability	$ 160,543			153,158
Pending Dispute With FDIC
FDIC Dealings [Line Items]
Loss Contingency Aggregate Claims Damages Sought	4,300		$ 4,900
Banco Popular de Puerto Rico
FDIC Dealings [Line Items]
F D I C Seeks To Clawback Reimbursement				12,600
Banco Popular de Puerto Rico | Pending Dispute With FDIC
FDIC Dealings [Line Items]
Unreimbursed Claims Submitted to the FDIC							$ 6,900
Payments Withheld By The FDIC						$ 5,500
Loss Contingency Damages Paid Value	5,500
Litigation Settlement Amount	5,500
Covered loans
FDIC Dealings [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount, Covered	$ 551,980	[1]		$ 572,878	[2]

[1] Includes $325 million pledged to secure credit facilities at the FHLB which are not permitted to sell or repledge the collateral.

[2] Includes $337 million pledged to secure credit facilities at the FHLB which are not permitted to sell or repledge the collateral.