Investment Securities - Schedule of Gross Unrealized Losses (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	$ 122,217	$ 444,968
Unrealized Loss, Less than 12 months	1,174	9,409
Fair Value, 12 months or more	314,406	22,199
Unrealized Loss, 12 months or more	6,799	810
Fair Value, Total	436,623	467,167
Unrealized Losses, Total	7,973	10,219
Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	122,217	444,968
Unrealized Loss, Less than 12 months	1,174	9,409
Fair Value, 12 months or more	311,356	19,073
Unrealized Loss, 12 months or more	6,650	675
Fair Value, Total	433,573	464,041
Unrealized Losses, Total	7,824	10,084
Debt Securities \| U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months		985
Unrealized Loss, Less than 12 months		13
Fair Value, 12 months or more	986
Unrealized Loss, 12 months or more	13
Fair Value, Total	986	985
Unrealized Losses, Total	13	13
Debt Securities \| Mortgage-backed Securities - Residential
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	107,611	390,595
Unrealized Loss, Less than 12 months	980	7,230
Fair Value, 12 months or more	290,258	19,073
Unrealized Loss, 12 months or more	6,170	675
Fair Value, Total	397,869	409,668
Unrealized Losses, Total	7,150	7,905
Debt Securities \| Municipals, Tax Exempt
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	7,354	43,132
Unrealized Loss, Less than 12 months	101	2,114
Fair Value, 12 months or more	20,112
Unrealized Loss, 12 months or more	467
Fair Value, Total	27,466	43,132
Unrealized Losses, Total	568	2,114
Debt Securities \| Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 months	7,252	10,256
Unrealized Loss, Less than 12 months	93	52
Fair Value, Total	7,252	10,256
Unrealized Losses, Total	93	52
Equity Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value, 12 months or more	3,050	3,126
Unrealized Loss, 12 months or more	149	135
Fair Value, Total	3,050	3,126
Unrealized Losses, Total	$ 149	$ 135

Amount of unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer.

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Amount of unrealized loss on securities classified as available-for-sale.

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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.

+ References

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

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-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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