Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Useful Lives for Principal Classes of Assets (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Useful Lives for Principal Classes of Assets (Detail)
 12 Months Ended
Dec. 31, 2017
Leasehold improvements [Member]  
Property, Plant and Equipment [Line Items]  
Premises and equipment useful life Term of lease or useful life, whichever is shorter
Software [Member]  
Property, Plant and Equipment [Line Items]  
Premises and equipment useful life 3 years
Minimum [Member] | Buildings and improvements [Member]  
Property, Plant and Equipment [Line Items]  
Premises and equipment useful life 10 years
Minimum [Member] | Furniture and equipment [Member]  
Property, Plant and Equipment [Line Items]  
Premises and equipment useful life 3 years
Maximum [Member] | Buildings and improvements [Member]  
Property, Plant and Equipment [Line Items]  
Premises and equipment useful life 30 years
Maximum [Member] | Furniture and equipment [Member]  
Property, Plant and Equipment [Line Items]  
Premises and equipment useful life 10 years