Note Debt Securities Held-to-maturity (HTM debt securities in a continuous unrealized loss position) (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Debt Securities, Held-to-maturity [Line Items]
Less than 12 months Fair Value	$ 10,230	$ 0
Less than 12 months Gross Unrealized Losses	101	0
12 months or more Fair Value	38,013	36,439
12 months or more Gross Unrealized Losses	9,292	13,356
Total Fair Value	48,243	36,439
Total Gross Unrealized Losses	9,393	13,356
Obligations of Puerto Rico, States and political subdivisions
Debt Securities, Held-to-maturity [Line Items]
Less than 12 months Fair Value	9,980	0
Less than 12 months Gross Unrealized Losses	101	0
12 months or more Fair Value	37,517	35,696
12 months or more Gross Unrealized Losses	9,288	13,349
Total Fair Value	47,497	35,696
Total Gross Unrealized Losses	9,389	13,349
Other
Debt Securities, Held-to-maturity [Line Items]
Less than 12 months Fair Value	250	0
Less than 12 months Gross Unrealized Losses	0	0
12 months or more Fair Value	496	743
12 months or more Gross Unrealized Losses	4	7
Total Fair Value	746	743
Total Gross Unrealized Losses	$ 4	$ 7