Investment Securities (Gains and losses by category) (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - less than 12 month	$ 213,503,000	$ 335,079,000
Available for sale - Amortized cost - more than 12 month	72,100,000	38,563,000
Total Available for Sale Amortization cost	285,603,000	373,642,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	1,930,000	5,723,000
Available for sale - Unrealized Loss - more than 12 month	1,322,000	1,400,000
Total Available for Sale Unrealized Loss	3,252,000	7,123,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	211,573,000	329,356,000
Available-for-sale, Fair Value - more than 12 month	70,778,000	37,163,000
Total Available for Sale Fair Value	282,351,000	366,519,000
Continuous Unrealized Loss Position Amortized Cost [Abstract]
Held to Maturity - Amortized cost - less than 12 month	386,995,000	525,258,000
Held to Maturity - Amortized cost - more than 12 month	44,759,000
Held to Maturity - Amortized Cost	431,754,000	525,258,000
Held To Maturity Securities, Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Held to Maturity- Unrealized Loss - less than 12 month	3,831,000	7,266,000
Held to Maturity- Unrealized Loss - more than 12 month	884,000
Held to Maturity- Unrealized Loss	4,715,000	7,266,000
Held To Maturity Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Held-to-Maturity - Fair Value - less than 12 Month	383,164,000	517,992,000
Held-to-Maturity - Fair Value - more than 12 Month	43,875,000
Held to Maturity - Fair Value	427,039,000	517,992,000
Investment Securities Continuous Unrealized Loss Position [Abstract]
Investment Securities - Amortized Cost	717,357,000	898,900,000
Investment Securities - Unrealized Loss	7,967,000	14,389,000
Investment Securities - Fair Value	709,390,000	884,511,000
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	27,413,000	67,777,000
Available for sale - Amortized cost - more than 12 month	58,328,000	33,883,000
Total Available for Sale Amortization cost	85,741,000	101,660,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	169,000	1,430,000
Available for sale - Unrealized Loss - more than 12 month	869,000	793,000
Total Available for Sale Unrealized Loss	1,038,000	2,223,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	27,244,000	66,347,000
Available-for-sale, Fair Value - more than 12 month	57,459,000	33,090,000
Total Available for Sale Fair Value	84,703,000	99,437,000
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	2,455,000	4,680,000
Total Available for Sale Amortization cost	2,455,000	4,680,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - more than 12 month	249,000	607,000
Total Available for Sale Unrealized Loss	249,000	607,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available-for-sale, Fair Value - more than 12 month	2,206,000	4,073,000
Total Available for Sale Fair Value	2,206,000	4,073,000
FNMA and FHLMC [Member]
Available For Sale Securities Continuous Unrealized Loss Position Amortized Cost [Abstract]
Available for sale - Amortized cost - less than 12 month	146,578,000	184,782,000
Available for sale - Amortized cost - more than 12 month	8,196,000
Total Available for Sale Amortization cost	154,774,000	184,782,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	1,287,000	3,036,000
Available for sale - Unrealized Loss - more than 12 month	175,000
Total Available for Sale Unrealized Loss	1,462,000	3,036,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	145,291,000	181,746,000
Available-for-sale, Fair Value - more than 12 month	8,021,000
Total Available for Sale Fair Value	153,312,000	181,746,000
Continuous Unrealized Loss Position Amortized Cost [Abstract]
Held to Maturity - Amortized cost - less than 12 month	386,995,000	525,258,000
Held to Maturity - Amortized cost - more than 12 month	44,759,000
Held to Maturity - Amortized Cost	431,754,000	525,258,000
Held To Maturity Securities, Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Held to Maturity- Unrealized Loss - less than 12 month	3,831,000	7,266,000
Held to Maturity- Unrealized Loss - more than 12 month	884,000
Held to Maturity- Unrealized Loss	4,715,000	7,266,000
Held To Maturity Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Held-to-Maturity - Fair Value - less than 12 Month	383,164,000	517,992,000
Held-to-Maturity - Fair Value - more than 12 Month	43,875,000
Held to Maturity - Fair Value	427,039,000	517,992,000
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	29,243,000	29,445,000
Total Available for Sale Amortization cost	29,243,000	29,445,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	423,000	620,000
Total Available for Sale Unrealized Loss	423,000	620,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	28,820,000	28,825,000
Total Available for Sale Fair Value	28,820,000	28,825,000
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		3,903,000
Available for sale - Amortized cost - more than 12 month	3,121,000
Total Available for Sale Amortization cost	3,121,000	3,903,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month		19,000
Available for sale - Unrealized Loss - more than 12 month	29,000
Total Available for Sale Unrealized Loss	29,000	19,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month		3,884,000
Available-for-sale, Fair Value - more than 12 month	3,092,000
Total Available for Sale Fair Value	3,092,000	3,884,000
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	10,269,000	49,172,000
Total Available for Sale Amortization cost	10,269,000	49,172,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses [Abstract]
Available for sale - Unrealized Loss - less than 12 month	51,000	618,000
Total Available for Sale Unrealized Loss	51,000	618,000
Available For Sale Securities Continuous Unrealized Loss Position Fair Value [Abstract]
Available for sale - Fair Value - less than 12 month	10,218,000	48,554,000
Total Available for Sale Fair Value	$ 10,218,000	$ 48,554,000

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