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Significant Accounting Policies - Additional Information (Detail)
12 Months Ended
Dec. 31, 2017
Segment
Significant Accounting Policies [Line Items]  
Number of segment 1
Contractual delinquent period of loans 180 days
Bankruptcy delinquency threshold 60 days
Financing receivable suspended period 90 days
Delinquent period of accrual income 90 days
Tax benefit 50.00%
Minimum [Member] | Office Building [Member]  
Significant Accounting Policies [Line Items]  
Non cancellable lease period 3 years
Minimum [Member] | Furniture, Fixtures and Equipment [Member]  
Significant Accounting Policies [Line Items]  
Estimated useful lives 5 years
Maximum [Member] | Office Building [Member]  
Significant Accounting Policies [Line Items]  
Non cancellable lease period 7 years
Maximum [Member] | Furniture, Fixtures and Equipment [Member]  
Significant Accounting Policies [Line Items]  
Estimated useful lives 10 years