Debt Securities Held-to-maturity - Weighted average yield and contractual maturities of debt securities HTM (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Amortized cost
Amortized cost	$ 9,004,729		$ 9,356,739
Book Value
Book Value	8,302,082		8,525,366
Allowance for credit losses
Allowance for credit losses	6,057		6,911
Net of Allowance
Net of Allowance	8,296,025		8,518,455
Gross unrecognized gains
Gross Unrealized Gains	2,370		4,918
Gross unrealized losses
Gross Unrealized Losses	233,328		83,177
Fair Value
Fair value	$ 8,065,067		$ 8,440,196
Weighted Average Yield
Weighted Average Yield	1.50%		1.55%
US Treasury Securities
Amortized cost
Amortized cost - Within 1 year	$ 597,876		$ 499,034
Amortized cost - After 1 to 5 year	7,516,523		6,147,568
Amortized cost - After 5 to 10 years	817,006		2,638,238
Amortized cost	8,931,405		9,284,840
Book Value
Book Value - within 1 year	597,876		499,034
Book Value - Within 1 to 5 years	6,900,125		5,640,767
Book Balue - After 5 to 10 years	730,757		2,313,666
Book Value	8,228,758		8,453,467
Allowance for credit losses
Allowance for credit losses - Within 1 Year	0		0
Allowance for credit losses - After 1 to 5 years	0		0
Allowance for credit losses - After 5 to 10 years	0		0
Allowance for credit losses	0		0
Net of Allowance
Net of Allowance - Within 1 Year	597,876		499,034
Net of Allowance - After 1 to 5 Years	6,900,125		5,640,767
Net of Allowance - After 5 to 10 Years	730,757		2,313,666
Net of Allowance	8,228,758		8,453,467
Gross unrecognized gains
Gross unrealized gains - Within 1 year	0		0
Gross unrealized gains - After 1 to 5 years	0		0
Gross unrealized gains - After 5 to 10 years	0		0
Gross Unrealized Gains	0		0
Gross unrealized losses
Gross unrealized losses - Within 1 year	9,036		6,203
Gross unrealized losses - After 1 to 5 years	193,838		59,806
Gross unrealized losses - After 5 to 10 years	26,819		14,857
Gross Unrealized Losses	229,693		80,866
Fair Value
Fair Value - within 1 year	588,840		492,831
Fair Value - After 1 to 5 years	6,706,287		5,580,961
Fair Value - After 5 to 10 years	703,938		2,298,809
Fair value	$ 7,999,065		$ 8,372,601
Weighted Average Yield
Weighted average yield - Within 1 Year	2.55%		2.83%
Weighted average yield - After 1 to 5 years	1.39%		1.49%
Weighted average yield - After 5 to 10 years	1.60%		1.41%
Weighted Average Yield	1.49%		1.54%
Obligations of Puerto Rico, States and political subdivisions
Amortized cost
Amortized cost - Within 1 year	$ 4,820		$ 4,530
Amortized cost - After 1 to 5 year	20,191		19,105
Amortized cost - After 5 to 10 years	845		1,025
Amortized cost - After 10 years	39,946		41,261
Amortized cost	65,802		65,921
Book Value
Book Value - within 1 year	4,820		4,530
Book Value - Within 1 to 5 years	20,191		19,105
Book Balue - After 5 to 10 years	845		1,025
Book Value - After 10 years	39,946		41,261
Book Value	65,802		65,921
Allowance for credit losses
Allowance for credit losses - Within 1 Year	13		8
Allowance for credit losses - After 1 to 5 years	154		234
Allowance for credit losses - After 5 to 10 years	28		34
Allowance for credit losses - After 10 years	5,862		6,635
Allowance for credit losses	6,057	$ 6,145	6,911	$ 7,210	$ 7,495	$ 8,096
Net of Allowance
Net of Allowance - Within 1 Year	4,807		4,522
Net of Allowance - After 1 to 5 Years	20,037		18,871
Net of Allowance - After 5 to 10 Years	817		991
Net of Allowance - After 10 Years	34,084		34,626
Net of Allowance	59,745		59,010
Gross unrecognized gains
Gross unrealized gains - Within 1 year	2		5
Gross unrealized gains - After 1 to 5 years	67		150
Gross unrealized gains - After 5 to 10 years	0		34
Gross unrealized gains - After 10 years	2,301		4,729
Gross Unrealized Gains	2,370		4,918
Gross unrealized losses
Gross unrealized losses - Within 1 year	17		0
Gross unrealized losses - After 1 to 5 years	266		82
Gross unrealized losses - After 5 to 10 years	9		0
Gross unrealized losses - After 10 years	3,092		2,229
Gross Unrealized Losses	3,384		2,311
Fair Value
Fair Value - within 1 year	4,792		4,527
Fair Value - After 1 to 5 years	19,838		18,939
Fair Value - After 5 to 10 years	808		1,025
Fair Value - After 10 years	33,293		37,126
Fair value	$ 58,731		$ 61,617
Weighted Average Yield
Weighted average yield - Within 1 Year	6.17%		6.08%
Weighted average yield - After 1 to 5 years	3.80%		4.24%
Weighted average yield - After 5 to 10 years	5.80%		5.80%
Weighted average yield - After 10 years	1.41%		1.40%
Weighted Average Yield	2.55%		2.61%
Collateralized Mortgage Obligations - Federal agencies
Amortized cost
Amortized cost - Within 1 year	$ 15
Amortized cost - After 1 to 5 year			$ 19
Amortized cost - After 10 years	1,547
Amortized cost	1,562		19
Book Value
Book Value - within 1 year	15
Book Value - Within 1 to 5 years			19
Book Value - After 10 years	1,547
Book Value	1,562		19
Allowance for credit losses
Allowance for credit losses - Within 1 Year	0
Allowance for credit losses - After 1 to 5 years			0
Allowance for credit losses - After 10 years	0
Allowance for credit losses	0		0
Net of Allowance
Net of Allowance - Within 1 Year	15
Net of Allowance - After 1 to 5 Years			19
Net of Allowance - After 10 Years	1,547
Net of Allowance	1,562		19
Gross unrecognized gains
Gross unrealized gains - Within 1 year	0
Gross unrealized gains - After 1 to 5 years			0
Gross unrealized gains - After 10 years	0
Gross Unrealized Gains	0		0
Gross unrealized losses
Gross unrealized losses - Within 1 year	0
Gross unrealized losses - After 1 to 5 years			0
Gross unrealized losses - After 10 years	251
Gross Unrealized Losses	251		0
Fair Value
Fair Value - within 1 year	15
Fair Value - After 1 to 5 years			19
Fair Value - After 10 years	1,296
Fair value	$ 1,311		$ 19
Weighted Average Yield
Weighted average yield - Within 1 Year	6.44%
Weighted average yield - After 1 to 5 years			6.44%
Weighted average yield - After 10 years	2.87%
Weighted Average Yield	2.90%		6.44%
Securities in wholly owned statutory business trusts
Amortized cost
Amortized cost - After 10 years	$ 5,960		$ 5,959
Amortized cost	5,960		5,959
Book Value
Book Value - After 10 years	5,960		5,959
Book Value	5,960		5,959
Allowance for credit losses
Allowance for credit losses - After 10 years	0		0
Allowance for credit losses	0		0
Net of Allowance
Net of Allowance - After 10 Years	5,960		5,959
Net of Allowance	5,960		5,959
Gross unrecognized gains
Gross unrealized gains - After 10 years	0		0
Gross Unrealized Gains	0		0
Gross unrealized losses
Gross unrealized losses - After 10 years	0		0
Gross Unrealized Losses	0		0
Fair Value
Fair Value - After 10 years	5,960		5,959
Fair value	$ 5,960		$ 5,959
Weighted Average Yield
Weighted average yield - After 10 years	6.33%		6.33%
Weighted Average Yield	6.33%		6.33%