Investment Securities (Gains and losses by category) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - less than 12 month	$ 572,178	$ 148,896
Available for sale - Amortized cost - more than 12 month	270,131	220,334
Total Available for Sale Amortization cost	842,309	369,230
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	12,193	942
Available for sale - Unrealized Loss - more than 12 month	12,477	5,001
Total Available for Sale Unrealized Loss	24,670	5,943
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	559,985	147,954
Available-for-sale, Fair Value - more than 12 month	257,654	215,333
Total Available for Sale Fair Value	817,639	363,287
Continuous Unrealized Loss Position Amortized Cost [Abstract]
Held to Maturity - Amortized cost - less than 12 month	62,738	153,665
Held to Maturity - Amortized cost - more than 12 month	381,941	352,399
Held to Maturity - Amortized Cost	444,679	506,064
Held To Maturity Securities, Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Held to Maturity- Unrealized Loss - less than 12 month	1,994	1,119
Held to Maturity- Unrealized Loss - more than 12 month	17,619	7,264
Held to Maturity- Unrealized Loss	19,613	8,383
Held To Maturity Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Held-to-Maturity - Fair Value - less than 12 Month	60,744	152,546
Held-to-Maturity - Fair Value - more than 12 Month	364,322	345,135
Held to Maturity - Fair Value	425,066	497,681
Investment Securities Continuous Unrealized Loss Position [Abstract]
Investment Securities - Amortized Cost	1,286,988	875,294
Investment Securities - Fair Value	1,242,705	860,968
CMO's issued by us government sponsored agencies at loss
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - less than 12 month	1,000	9,464
Available for sale - Amortized cost - more than 12 month	68,960	72,562
Total Available for Sale Amortization cost	69,960	82,026
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	20	98
Available for sale - Unrealized Loss - more than 12 month	3,174	1,857
Total Available for Sale Unrealized Loss	3,194	1,955
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	980	9,366
Available-for-sale, Fair Value - more than 12 month	65,786	70,705
Total Available for Sale Fair Value	66,766	80,071
Obligation of Puerto Rico Government and public instrumentalities at loss
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - more than 12 month	0	2,455
Total Available for Sale Amortization cost	0	2,455
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - more than 12 month		362
Total Available for Sale Unrealized Loss		362
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available-for-sale, Fair Value - more than 12 month	0	2,093
Total Available for Sale Fair Value	0	2,093
FNMA and FHLMC [Member]
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - less than 12 month	425,094	125,107
Available for sale - Amortized cost - more than 12 month	160,420	111,635
Total Available for Sale Amortization cost	585,514	236,742
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	8,348	759
Available for sale - Unrealized Loss - more than 12 month	7,451	2,122
Total Available for Sale Unrealized Loss	15,799	2,881
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	416,746	124,348
Available-for-sale, Fair Value - more than 12 month	152,969	109,513
Total Available for Sale Fair Value	569,715	233,861
Continuous Unrealized Loss Position Amortized Cost [Abstract]
Held to Maturity - Amortized cost - less than 12 month	62,738	153,665
Held to Maturity - Amortized cost - more than 12 month	381,941	352,399
Held to Maturity - Amortized Cost	444,679	506,064
Held To Maturity Securities, Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Held to Maturity- Unrealized Loss - less than 12 month	1,994	1,119
Held to Maturity- Unrealized Loss - more than 12 month	17,619	7,264
Held to Maturity- Unrealized Loss	19,613	8,383
Held To Maturity Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Held-to-Maturity - Fair Value - less than 12 Month	60,744	152,546
Held-to-Maturity - Fair Value - more than 12 Month	364,322	345,135
Held to Maturity - Fair Value	425,066	497,681
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - less than 12 month	145,438	14,001
Available for sale - Amortized cost - more than 12 month	28,296	20,803
Total Available for Sale Amortization cost	173,734	34,804
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	3,825	85
Available for sale - Unrealized Loss - more than 12 month	1,606	499
Total Available for Sale Unrealized Loss	5,431	584
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	141,613	13,916
Available-for-sale, Fair Value - more than 12 month	26,690	20,304
Total Available for Sale Fair Value	168,303	34,220
Obligation of US Government sponsored agencies at loss [Member]
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - more than 12 month	2,484	2,927
Total Available for Sale Amortization cost	2,484	2,927
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - more than 12 month	89	48
Total Available for Sale Unrealized Loss	89	48
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available-for-sale, Fair Value - more than 12 month	2,395	2,879
Total Available for Sale Fair Value	2,395	2,879
US Treasury Securities at loss
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - less than 12 month	646	324
Available for sale - Amortized cost - more than 12 month	9,971	9,952
Total Available for Sale Amortization cost	10,617	10,276
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	0	0
Available for sale - Unrealized Loss - more than 12 month	157	113
Total Available for Sale Unrealized Loss	157	113
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	646	324
Available-for-sale, Fair Value - more than 12 month	9,814	9,839
Total Available for Sale Fair Value	$ 10,460	$ 10,163

Amortized cost of investments in available-for-sale securities that have been in a loss position.

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