XML 90 R77.htm IDEA: XBRL DOCUMENT v3.19.1
Short-Term Debt - Additional Information (Detail) - USD ($)
Dec. 31, 2018
Dec. 31, 2017
Short-term Debt [Line Items]    
Debt classified as short-term $ 0 $ 0
Unsecured lines of credit    
Short-term Debt [Line Items]    
Lines of credit, established amount 38,600,000  
Unsecured lines of credit | Federal Home Loan Bank [Member]    
Short-term Debt [Line Items]    
Lines of credit, maximum borrowing ability $ 169,800,000