Summary of Significant Accounting Policies - Summary of Useful Lives of Principal Classes of Assets (Detail)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Estimated economic lives of leasehold improvements	Shorter of estimated economic lives of 15 years or term of the lease.
Minimum [Member] | Bank premises [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	15 years
Minimum [Member] | Computer equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	3 years
Minimum [Member] | Furniture, fixtures and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	5 years
Maximum [Member] | Bank premises [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	40 years
Maximum [Member] | Computer equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	5 years
Maximum [Member] | Furniture, fixtures and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	7 years