Note FDIC loss share asset (FDIC loss share - Additional Information) (Detail) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($) D	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) D	Sep. 30, 2016 USD ($)	Dec. 31, 2016
Business Acquisition, Contingent Consideration [Line Items]
True Up Payment Term | D	45		45
Calculation Percent Asset Discount Per Bid	$ 1,100,000		$ 1,100,000
Intrinsic Loss Estimate	4,600,000		$ 4,600,000
Servicing Amount Period Trueup Payment			twelve-month period
Fair Value Inputs Discount Rate			4.72%		5.97%
Arbitration decision charge	0	$ 54,924	$ 0	$ 54,924
Payment Percentage True-up Payment
Business Acquisition, Contingent Consideration [Line Items]
Fixed Percentage True Up Payment			50.00%
Intrinsic Loss Estimate True-up Payment
Business Acquisition, Contingent Consideration [Line Items]
Percent Calculation Intrinsic Loss Estimate	$ 925,000		$ 925,000
Fixed Percentage True Up Payment			20.00%
Asset Discount True-up Payment
Business Acquisition, Contingent Consideration [Line Items]
Fixed Percentage True Up Payment			25.00%
Cumulative Shared Loss Payments True-up Payment
Business Acquisition, Contingent Consideration [Line Items]
Fixed Percentage True Up Payment			25.00%
Servicing Percentage True-up Payment
Business Acquisition, Contingent Consideration [Line Items]
Fixed Percentage True Up Payment			1.00%
Single Family Loan
Business Acquisition, Contingent Consideration [Line Items]
Weighted Average Life Of Loan Subject To F D I C Agreement			7 years 1 month
Banco Popular de Puerto Rico
Business Acquisition, Contingent Consideration [Line Items]
Loss Sharing Agreement Allocation Percentage			80.00%
FDIC
Business Acquisition, Contingent Consideration [Line Items]
Loss Sharing Agreement Allocation Percentage			80.00%
FDIC | Residential Mortgage
Business Acquisition, Contingent Consideration [Line Items]
Loss Sharing Term	10		10