Investment Securities (Gains and losses by category) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - less than 12 month	$ 507,777	$ 148,896
Available for sale - Amortized cost - more than 12 month	211,981	220,334
Total Available for Sale Amortization cost	719,758	369,230
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	7,428	942
Available for sale - Unrealized Loss - more than 12 month	7,575	5,001
Total Available for Sale Unrealized Loss	15,003	5,943
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	500,349	147,954
Available-for-sale, Fair Value - more than 12 month	204,406	215,333
Total Available for Sale Fair Value	704,755	363,287
Continuous Unrealized Loss Position Amortized Cost [Abstract]
Held to Maturity - Amortized cost - less than 12 month	146,883	153,665
Held to Maturity - Amortized cost - more than 12 month	338,260	352,399
Held to Maturity - Amortized Cost	485,143	506,064
Held To Maturity Securities, Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Held to Maturity- Unrealized Loss - less than 12 month	3,852	1,119
Held to Maturity- Unrealized Loss - more than 12 month	13,311	7,264
Held to Maturity- Unrealized Loss	17,163	8,383
Held To Maturity Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Held-to-Maturity - Fair Value - less than 12 Month	143,031	152,546
Held-to-Maturity - Fair Value - more than 12 Month	324,949	345,135
Held to Maturity - Fair Value	467,980	497,681
Investment Securities Continuous Unrealized Loss Position [Abstract]
Investment Securities - Amortized Cost	1,204,901	875,294
Investment Securities - Unrealized Loss	32,166	14,326
Investment Securities - Fair Value	1,172,735	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	8,183	9,464
Available for sale - Amortized cost - more than 12 month	69,921	72,562
Total Available for Sale Amortization cost	78,104	82,026
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	135	98
Available for sale - Unrealized Loss - more than 12 month	2,594	1,857
Total Available for Sale Unrealized Loss	2,729	1,955
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	8,048	9,366
Available-for-sale, Fair Value - more than 12 month	67,327	70,705
Total Available for Sale Fair Value	75,375	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	2,455	2,455
Total Available for Sale Amortization cost	2,455	2,455
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - more than 12 month	43	362
Total Available for Sale Unrealized Loss	43	362
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available-for-sale, Fair Value - more than 12 month	2,412	2,093
Total Available for Sale Fair Value	2,412	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	367,587	125,107
Available for sale - Amortized cost - more than 12 month	106,196	111,635
Total Available for Sale Amortization cost	473,783	236,742
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	5,329	759
Available for sale - Unrealized Loss - more than 12 month	3,804	2,122
Total Available for Sale Unrealized Loss	9,133	2,881
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	362,258	124,348
Available-for-sale, Fair Value - more than 12 month	102,392	109,513
Total Available for Sale Fair Value	464,650	233,861
Continuous Unrealized Loss Position Amortized Cost [Abstract]
Held to Maturity - Amortized cost - less than 12 month	146,883	153,665
Held to Maturity - Amortized cost - more than 12 month	338,260	352,399
Held to Maturity - Amortized Cost	485,143	506,064
Held To Maturity Securities, Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Held to Maturity- Unrealized Loss - less than 12 month	3,852	1,119
Held to Maturity- Unrealized Loss - more than 12 month	13,311	7,264
Held to Maturity- Unrealized Loss	17,163	8,383
Held To Maturity Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Held-to-Maturity - Fair Value - less than 12 Month	143,031	152,546
Held-to-Maturity - Fair Value - more than 12 Month	324,949	345,135
Held to Maturity - Fair Value	467,980	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	131,685	14,001
Available for sale - Amortized cost - more than 12 month	20,678	20,803
Total Available for Sale Amortization cost	152,363	34,804
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	1,964	85
Available for sale - Unrealized Loss - more than 12 month	906	499
Total Available for Sale Unrealized Loss	2,870	584
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	129,721	13,916
Available-for-sale, Fair Value - more than 12 month	19,772	20,304
Total Available for Sale Fair Value	149,493	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 - less than 12 month		2,927
Available for sale - Amortized cost - more than 12 month	2,773
Total Available for Sale Amortization cost	2,773	2,927
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - more than 12 month	72	48
Total Available for Sale Unrealized Loss	72	48
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available-for-sale, Fair Value - more than 12 month	2,701	2,879
Total Available for Sale Fair Value	2,701	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	322	324
Available for sale - Amortized cost - more than 12 month	9,958	9,952
Total Available for Sale Amortization cost	10,280	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	156	113
Total Available for Sale Unrealized Loss	156	113
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	322	324
Available-for-sale, Fair Value - more than 12 month	9,802	9,839
Total Available for Sale Fair Value	$ 10,124	$ 10,163

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