Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) Segment	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of reportable operating segment | Segment	1
Unsettled investment security purchase transactions	$ 1,200,000		$ 0
Other than temporary impairment losses investments	$ 0	$ 0
Commercial loans and commercial real estate loans placed on non-accrual status	90 days
Goodwill impairment			0
Carrying amount of goodwill	$ 38,188,000		38,188,000
Investments in general account	28,700,000
Investments in separate account	54,900,000
Bank owned life insurance (BOLI)	$ 83,593,000		$ 83,109,000
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Delinquent loans charge-off	180 days
Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Delinquent loans charge-off	180 days
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Delinquent loans charge-off	180 days
Other consumer loans placed on non-accrual status	90 days
Residential Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Delinquent loans charge-off	180 days
Residential real estate loans placed on non-accrual status	90 days
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans delayed before impairment period	90 days