Note Stockholders' equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Stockholders Equity Note [Line Items]
Puerto Rico Laws Restrictions On Banks Net Income	a minimum of 10% of BPPR’s net income
Equity Restrictions	$ 540,000			$ 540,000
Transfers To Statutory Reserve	0	$ 0
Dividends, Common Stock, Cash	$ 25,547	$ 25,615
Common Stock Dividends Per Share Declared	$ 0.25	$ 0.25	$ 0.15
Dividends Payable	$ 25,500
Stock Repurchase Program Authorized Amount		$ 75,000
Treasury Stock Value Acquired Cost Method	$ 1,328	$ 76,324
Total Common Shares Repurchased Accelerated Share Repurchase Agreements		1,847,372
Accelerate Share Repurchase Transaction
Stockholders Equity Note [Line Items]
Accelerated Share Repurchase Program Adjustment		$ 4,500
Treasury Stock Value Acquired Cost Method		$ 79,500