Investment Securities - Summary of Amortized Cost of Securities and Fair Values (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 548,898	$ 588,459
Gross unrealized gains	3,067	3,943
Gross unrealized losses	(7,973)	(10,219)
Available-for-sale securities, at fair value	543,992	582,183
Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	541,028	579,715
Gross unrealized gains	3,066	3,942
Gross unrealized losses	(7,824)	(10,084)
Available-for-sale securities, at fair value	536,270	573,573
Debt Securities \| U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	999	998
Gross unrealized losses	(13)	(13)
Available-for-sale securities, at fair value	986	985
Debt Securities \| Mortgage-backed Securities - Residential
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	425,557	450,874
Gross unrealized gains	374	939
Gross unrealized losses	(7,150)	(7,905)
Available-for-sale securities, at fair value	418,781	443,908
Debt Securities \| Municipals, Tax Exempt
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	107,127	116,034
Gross unrealized gains	2,692	3,003
Gross unrealized losses	(568)	(2,114)
Available-for-sale securities, at fair value	109,251	116,923
Debt Securities \| Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	7,345	11,809
Gross unrealized losses	(93)	(52)
Available-for-sale securities, at fair value	7,252	11,757
Equity Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	7,870	8,744
Gross unrealized gains	1	1
Gross unrealized losses	(149)	(135)
Available-for-sale securities, at fair value	$ 7,722	$ 8,610

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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