Note Investment Securities Held-to-maturity (HTM securities in a continuous unrealized loss position) (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 7,473	$ 31,785
Less than 12 months Gross Unrealized Losses	85	1,711
12 months or more Fair Value	26,790	32,164
12 months or more Gross Unrealized Losses	22,505	22,186
Total Fair Value	34,263	63,949
Total Gross Unrealized Losses	22,590	23,897
Obligations of Puerto Rico, States and political subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	6,981	31,294
Less than 12 months Gross Unrealized Losses	77	1,702
12 months or more Fair Value	26,553	30,947
12 months or more Gross Unrealized Losses	22,492	22,153
Total Fair Value	33,534	62,241
Total Gross Unrealized Losses	22,569	23,855
Other
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	492	491
Less than 12 months Gross Unrealized Losses	8	9
12 months or more Fair Value	237	1,217
12 months or more Gross Unrealized Losses	13	33
Total Fair Value	729	1,708
Total Gross Unrealized Losses	$ 21	$ 42