Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Examination [Line Items]
Unrecognized tax benefits	$ 0		$ 0
Amortization method qualified affordable housing project investments, amortization	400,000	$ 400,000	1,200,000	$ 800,000
Tax benefits recorded as income tax expense			300,000
Carrying value of investment in affordable housing credits	14,200,000		14,200,000		$ 15,400,000
Tax Credit
Income Tax Examination [Line Items]
Affordable housing tax credits	$ 1,200,000		$ 1,200,000