Commitments and Credit Risk - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018
Minimum [Member]
Commitments And Contingencies [Line Items]
Fixed interest rate loan commitments	3.75%
Fixed interest rate loan commitments maturity period	1 month
Maximum [Member]
Commitments And Contingencies [Line Items]
Fixed interest rate loan commitments	8.50%
Fixed interest rate loan commitments maturity period	110 months