Fair Value Disclosures - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) loan property	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent Consideration from New Acquisition		$ 0	$ 0	$ 1,525,000
Adjustment of Contingent Consideration		(247,000)	2,974,000
Valuation adjustments for loans held for sale		0	0
Carrying value of impaired loans held for investment		28,482,000
Valuation allowance of impaired loans held for investment		131,000	235,000
Mortgage Servicing Rights Carrying Amount Before Valuation Allowance		6,600,000	6,500,000
Mortgage Servicing Rights Valuation Allowance		0	0
Goodwill impairment		0	0	$ 0
Impairment of intangible assets		$ 0
Number of properties written-down | property		2
OREO write-downs		$ 199,000
Number of properties sold | property		7
Net gains on sales of other real estate owned		$ 383,000
Reversal of other noninterest expense	$ 301,000
Sterner Insurance Associates Inc [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent Consideration from New Acquisition		0	0
Adjustment of Contingent Consideration		(301,000)	512,000
Girard Partners [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent Consideration from New Acquisition		0	0
Adjustment of Contingent Consideration		54,000	2,394,000
John T Fretz Insurance Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent Consideration from New Acquisition			0
Adjustment of Contingent Consideration			68,000
Held for Investment [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of impaired loans held for investment		28,500,000	43,915,000
Valuation allowance of impaired loans held for investment		131,000	235,000
Lease Financings [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of impaired loans held for investment		1,300,000	$ 0
Valuation allowance of impaired loans held for investment		$ 0
Derivative Financial Instruments, Liabilities [Member] | Interest Rate Swap [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of Loans with Unrealized Gain | loan		2
Unrealized Gain On Loans		$ 51,000
Commercial Loan [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of loans | loan		2