Investment Securities - Reconciliation of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total securities, Available for Sale, Amortized Cost	$ 647,112	$ 607,112
Gross Unrealized Gains	5,023	6,760
Gross Unrealized Losses	(4,843)	(7,168)
Total securities, Available for Sale, Fair Value	647,292	606,704
US Treasury and Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities, Available for Sale, Amortized Cost	142,423	118,537
Gross Unrealized Gains	232	102
Gross Unrealized Losses	(824)	(1,280)
Total securities, Available for Sale, Fair Value	141,831	117,359
Mortgage-Backed Securities, Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities, Available for Sale, Amortized Cost	422,090	406,851
Gross Unrealized Gains	1,199	1,174
Gross Unrealized Losses	(3,320)	(4,487)
Total securities, Available for Sale, Fair Value	419,969	403,538
Mortgage-Backed Securities, Multifamily [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities, Available for Sale, Amortized Cost	10,148	10,192
Gross Unrealized Gains	54	30
Gross Unrealized Losses	(36)	(35)
Total securities, Available for Sale, Fair Value	10,166	10,187
Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities, Available for Sale, Amortized Cost	51,991	48,868
Gross Unrealized Gains	700	391
Gross Unrealized Losses	(277)	(933)
Total securities, Available for Sale, Fair Value	52,414	48,326
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities, Available for Sale, Amortized Cost	5,000	5,350
Gross Unrealized Gains	100	63
Gross Unrealized Losses		(1)
Total securities, Available for Sale, Fair Value	5,100	5,412
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total securities, Available for Sale, Amortized Cost	15,460	17,314
Gross Unrealized Gains	2,738	5,000
Gross Unrealized Losses	(386)	(432)
Total securities, Available for Sale, Fair Value	$ 17,812	$ 21,882

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
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 2
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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