Investment Securities - Summary of Amortized Cost of Securities and Fair Values (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized cost		$ 548,898
Gross unrealized gains		3,067
Gross unrealized losses		(7,973)
Available-for-sale securities, at fair value		543,992
Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 608,754	541,028
Gross unrealized gains	1,819	3,066
Gross unrealized losses	(16,325)	(7,824)
Available-for-sale securities, at fair value	594,248	536,270
Debt Securities \| U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	999	999
Gross unrealized losses	(17)	(13)
Available-for-sale securities, at fair value	982	986
Debt Securities \| Mortgage-backed Securities - Residential
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	486,907	425,557
Gross unrealized gains	237	374
Gross unrealized losses	(14,214)	(7,150)
Available-for-sale securities, at fair value	472,930	418,781
Debt Securities \| Municipals, Tax Exempt
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	113,492	107,127
Gross unrealized gains	1,582	2,692
Gross unrealized losses	(1,916)	(568)
Available-for-sale securities, at fair value	113,158	109,251
Debt Securities \| Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	7,356	7,345
Gross unrealized losses	(178)	(93)
Available-for-sale securities, at fair value	$ 7,178	7,252
Equity and Other Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized cost		7,870
Gross unrealized gains		1
Gross unrealized losses		(149)
Available-for-sale securities, at fair value		$ 7,722

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
-Topic 320
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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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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-SubTopic 10
-Section S99
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