Investment Securities - Securities with gross unrealized losses - (Details) $ in Thousands	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Investment Securities
Number of securities with gross unrealized loss \| item	223
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	$ 5,020	$ 8,184
Twelve Months or More	7,797	424
Securities Available for Sale, Fair Value
Less Than Twelve Months	654,893	688,376
Twelve Months or More	374,582	3,453
Government-sponsored entities debt
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	403	846
Twelve Months or More	674
Securities Available for Sale, Fair Value
Less Than Twelve Months	27,442	84,642
Twelve Months or More	52,324
State and municipal obligations
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	124	190
Securities Available for Sale, Fair Value
Less Than Twelve Months	17,400	11,506
Mortgage-backed securities. issued by Government sponsored entities
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	4,493	7,148
Twelve Months or More	7,123	77
Securities Available for Sale, Fair Value
Less Than Twelve Months	610,051	592,228
Twelve Months or More	$ 322,258	2,058
Common Stock
Securities Available for Sale, Gross Unrealized Losses
Twelve Months or More		347
Securities Available for Sale, Fair Value
Twelve Months or More		$ 1,395

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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