Regulatory Capital Requirements - Actual Capital Amounts and Ratios and FDIC Minimum Capital Adequacy Requirements (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital to Average Assets to be Well Capitalized	6.50%
FRB [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Leverage (Tier 1), Actual Amount	$ 779,139,000	$ 740,958,000
Leverage (Tier 1), Actual Ratio	9.25%	9.21%
Leverage (Tier 1), minimum capital adequacy requirements, Amount	$ 337,070,000	$ 321,809,000
Leverage (Tier 1), minimum capital adequacy requirements, Ratio	4.00%	4.00%
Leverage (Tier 1), To be well-capitalized under prompt corrective action provisions, Amount	$ 421,337,000	$ 402,262,000
Leverage (Tier 1), To be well-capitalized under prompt corrective action provisions, Ratio	5.00%	5.00%
Common Equity Tier One Risk Based Capital	$ 779,139,000
Common Equity Tier One Capital to Average Assets	11.65%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy	$ 301,041,000
Common Equity Tier One Capital to Average Assets for Capital Adequacy	4.50%
Common Equity Tier One Leverage Capital Required to be Well Capitalized	$ 434,837,000
Common Equity Tier One Capital to Average Assets to be Well Capitalized	6.50%
Risk-based capital: Tier 1, Actual Amount	$ 779,139,000	$ 740,958,000
Risk-based capital: Tier 1, Actual, Ratio	11.65%	12.06%
Risk-based capital: Tier 1, minimum capital adequacy requirements, Amount	$ 401,388,000	$ 245,859,000
Risk-based capital: Tier 1, minimum capital adequacy requirements, Ratio	6.00%	4.00%
Risk-based capital: Tier 1, To be well-capitalized under prompt corrective action provisions, Amount	$ 535,184,000	$ 368,788,000
Risk-based capital: Tier 1, To be well-capitalized under prompt corrective action provisions, Ratio	8.00%	6.00%
Risk-based capital: Total, Actual Amount	$ 840,563,000	$ 802,692,000
Risk-based capital: Total, Actual, Ratio	12.56%	13.06%
Risk-based capital: Total, minimum capital adequacy requirements, Amount	$ 535,184,000	$ 491,717,000
Risk-based capital: Total, minimum capital adequacy requirements, Ratio	8.00%	8.00%
Risk-based capital: Total, to be well-capitalized under prompt corrective action provisions, Amount	$ 668,981,000	$ 614,646,000
Risk-based capital: Total, To be well-capitalized under prompt corrective action provisions, Ratio	10.00%	10.00%
FDIC [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Leverage (Tier 1), Actual Amount	$ 709,690,000	$ 674,483,000
Leverage (Tier 1), Actual Ratio	8.42%	8.38%
Leverage (Tier 1), minimum capital adequacy requirements, Amount	$ 337,060,000	$ 321,805,000
Leverage (Tier 1), minimum capital adequacy requirements, Ratio	4.00%	4.00%
Leverage (Tier 1), To be well-capitalized under prompt corrective action provisions, Amount	$ 421,325,000	$ 402,257,000
Leverage (Tier 1), To be well-capitalized under prompt corrective action provisions, Ratio	5.00%	5.00%
Common Equity Tier One Risk Based Capital	$ 709,690,000
Common Equity Tier One Capital to Average Assets	10.61%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy	$ 301,030,380
Common Equity Tier One Capital to Average Assets for Capital Adequacy	4.50%
Common Equity Tier One Leverage Capital Required to be Well Capitalized	$ 434,821,660
Common Equity Tier One Capital to Average Assets to be Well Capitalized	6.50%
Risk-based capital: Tier 1, Actual Amount	$ 709,690,000	$ 674,483,000
Risk-based capital: Tier 1, Actual, Ratio	10.61%	10.97%
Risk-based capital: Tier 1, minimum capital adequacy requirements, Amount	$ 401,374,000	$ 245,853,000
Risk-based capital: Tier 1, minimum capital adequacy requirements, Ratio	6.00%	4.00%
Risk-based capital: Tier 1, To be well-capitalized under prompt corrective action provisions, Amount	$ 535,165,000	$ 368,779,000
Risk-based capital: Tier 1, To be well-capitalized under prompt corrective action provisions, Ratio	8.00%	6.00%
Risk-based capital: Total, Actual Amount	$ 771,268,000	$ 736,217,000
Risk-based capital: Total, Actual, Ratio	11.53%	11.98%
Risk-based capital: Total, minimum capital adequacy requirements, Amount	$ 535,165,000	$ 491,705,000
Risk-based capital: Total, minimum capital adequacy requirements, Ratio	8.00%	8.00%
Risk-based capital: Total, to be well-capitalized under prompt corrective action provisions, Amount	$ 668,956,000	$ 614,631,000
Risk-based capital: Total, To be well-capitalized under prompt corrective action provisions, Ratio	10.00%	10.00%