Capital and Regulatory Matters - Additional Information (Detail) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 28, 2007	Mar. 31, 2016 USD ($) quarter	Dec. 31, 2015 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock value issued include for regulatory tier one capital calculations		$ 144,500
Preferred stock dividend rate percentage		5.375%
Corporation's aggregate subordinated notes		$ 136,083	$ 136,069
Maximum dividends available without prior regulatory approval		$ 362,500
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures | quarter		20
Trust Preferred Securities Tier One Allowable Portion [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities			33,300
Trust Preferred Securities Tier One Excluded Portion [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities		$ 133,000	99,800
Floating Rate Subordinated Notes [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Permissible portion of subordinated note included in total capital			$ 20,000
Corporation's aggregate subordinated notes		$ 100,000
Per Year Percentage decrease in permissible portion of subordinate note included in Total Capital		20.00%
Final years of the term of the notes		5 years
Debt Instrument, Maturity Date	Feb. 15, 2017