Investment Securities (Gains and losses by category) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 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	$ 563,785	$ 148,896
Available for sale - Amortized cost - more than 12 month	200,843	220,334
Total Available for Sale Amortization cost	764,628	369,230
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	10,292	942
Available for sale - Unrealized Loss - more than 12 month	8,415	5,001
Total Available for Sale Unrealized Loss	18,707	5,943
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	553,493	147,954
Available-for-sale, Fair Value - more than 12 month	192,428	215,333
Total Available for Sale Fair Value	745,921	363,287
Continuous Unrealized Loss Position Amortized Cost [Abstract]
Held to Maturity - Amortized cost - less than 12 month	140,464	153,665
Held to Maturity - Amortized cost - more than 12 month	324,963	352,399
Held to Maturity - Amortized Cost	465,427	506,064
Held To Maturity Securities, Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Held to Maturity- Unrealized Loss - less than 12 month	3,886	1,119
Held to Maturity- Unrealized Loss - more than 12 month	13,594	7,264
Held to Maturity- Unrealized Loss	17,480	8,383
Held To Maturity Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Held-to-Maturity - Fair Value - less than 12 Month	136,578	152,546
Held-to-Maturity - Fair Value - more than 12 Month	311,369	345,135
Held to Maturity - Fair Value	447,947	497,681
Investment Securities Continuous Unrealized Loss Position [Abstract]
Investment Securities - Amortized Cost	1,230,055	875,294
Investment Securities - Unrealized Loss	36,187	14,326
Investment Securities - Fair Value	1,193,868	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	7,849	9,464
Available for sale - Amortized cost - more than 12 month	66,298	72,562
Total Available for Sale Amortization cost	74,147	82,026
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	170	98
Available for sale - Unrealized Loss - more than 12 month	2,822	1,857
Total Available for Sale Unrealized Loss	2,992	1,955
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	7,679	9,366
Available-for-sale, Fair Value - more than 12 month	63,476	70,705
Total Available for Sale Fair Value	71,155	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	0	362
Total Available for Sale Unrealized Loss	0	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	413,181	125,107
Available for sale - Amortized cost - more than 12 month	101,571	111,635
Total Available for Sale Amortization cost	514,752	236,742
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	7,275	759
Available for sale - Unrealized Loss - more than 12 month	4,296	2,122
Total Available for Sale Unrealized Loss	11,571	2,881
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	405,906	124,348
Available-for-sale, Fair Value - more than 12 month	97,275	109,513
Total Available for Sale Fair Value	503,181	233,861
Continuous Unrealized Loss Position Amortized Cost [Abstract]
Held to Maturity - Amortized cost - less than 12 month	140,464	153,665
Held to Maturity - Amortized cost - more than 12 month	324,963	352,399
Held to Maturity - Amortized Cost	465,427	506,064
Held To Maturity Securities, Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Held to Maturity- Unrealized Loss - less than 12 month	3,886	1,119
Held to Maturity- Unrealized Loss - more than 12 month	13,594	7,264
Held to Maturity- Unrealized Loss	17,480	8,383
Held To Maturity Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Held-to-Maturity - Fair Value - less than 12 Month	136,578	152,546
Held-to-Maturity - Fair Value - more than 12 Month	311,369	345,135
Held to Maturity - Fair Value	447,947	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	142,431	14,001
Available for sale - Amortized cost - more than 12 month	20,388	20,803
Total Available for Sale Amortization cost	162,819	34,804
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	2,847	85
Available for sale - Unrealized Loss - more than 12 month	1,055	499
Total Available for Sale Unrealized Loss	3,902	584
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	139,584	13,916
Available-for-sale, Fair Value - more than 12 month	19,333	20,304
Total Available for Sale Fair Value	158,917	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	2,622	2,927
Total Available for Sale Amortization cost	2,622	2,927
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - more than 12 month	81	48
Total Available for Sale Unrealized Loss	81	48
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available-for-sale, Fair Value - more than 12 month	2,541	2,879
Total Available for Sale Fair Value	2,541	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	324	324
Available for sale - Amortized cost - more than 12 month	9,964	9,952
Total Available for Sale Amortization cost	10,288	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	161	113
Total Available for Sale Unrealized Loss	161	113
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	324	324
Available-for-sale, Fair Value - more than 12 month	9,803	9,839
Total Available for Sale Fair Value	$ 10,127	$ 10,163

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Amount of unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months.

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