Regulatory Matters - Additional Information (Detail) - $ / shares		12 Months Ended
	Mar. 17, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Percentage of capital securities qualified as Tier I				25.00%	100.00%
Capital conservation buffer, phase-in period		5 years
Capital conservation buffer, percentage at the beginning stage		0.625%
Capital conservation buffer, percentage fully phased in 2019		2.50%
Exceeding percentage of Risk-based capital ratio above the minimum requirement for capital adequacy purposes		6.32%
Exceeding percentage of Risk-based capital ratio above the fully-phased in capital conservation buffer		3.82%
Minimum leverage capital ratio to be categorized as well capitalized		5.00%
Minimum Tier 1 risk based capital ratio to be categorized as well capitalized		8.00%
Minimum total risk based capital ratio to be categorized as well capitalized		10.00%
Minimum Common equity Tier 1 risk-based capital ratio		6.50%
Preferred stock par value		$ 0.01	$ 0.01
Depositary Shares [Member] | Series A Noncumulative Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Depositary shares issued	20,600,000
Per share ownership interest, percentage	2.50%
Preferred stock par value	$ 0.01
Preferred stock, liquidation preference per share	1,000
Depository shares, liquidation preference per share	$ 25
Fixed dividend rate per annum	6.375%
Floating dividend rate per annum	Three-month LIBOR plus 382.1 basis points
Dividends payable description	Dividends will be payable in arrears on March 17, June 17, September 17 and December 17 of each year, which commenced on June 17, 2017.