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Regulatory Matters - Additional Information (Detail)	12 Months Ended
Regulatory Matters - Additional Information (Detail)	Dec. 31, 2018	Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2017	Jan. 01, 2017	Jan. 01, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer period	4 years
Capital conservation buffer percentage	1.875%		0.625%	1.25%	0.625%	0.625%
Capital conservation buffer percentage maintained at bank	5.62%			5.12%
Scenario, Forecast
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer percentage		0.625%