Loans (Tier Risk Rating System) - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Repayment period of loan with a reasonable reduction of principal balance	2 years
Good [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Leverage position	1.50%
Satisfactory [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Leverage position	2.00%