Disclosures About Fair Value of Financial Instruments - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Available-for-sale securities:
Assets measured at fair value on a recurring basis	$ 2,513,091	$ 2,327,355
Assets
Assets measured at fair value on a nonrecurring basis	7,042	4,704
Specific reserves related to impaired loans	3,670	2,273
Derivative Assets
Available-for-sale securities:
Assets measured at fair value on a recurring basis	15,324	9,295
Loans held for sale – fair value option
Available-for-sale securities:
Assets measured at fair value on a recurring basis	1,941,602	1,757,807
Derivative Liabilities
Liabilities
Derivatives	22,957	13,932
Impaired loans
Assets
Assets measured at fair value on a nonrecurring basis	6,354	4,346
Specific reserves related to impaired loans	3,670	2,273
Other real estate owned
Assets
Assets measured at fair value on a nonrecurring basis	688	358
Available-for-sale Securities | Agency-guaranteed residential mortgage-backed securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	286,289	298,104
Available-for-sale Securities | Agency-guaranteed commercial real estate mortgage-backed securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	207,397	202,870
Available-for-sale Securities | Corporate notes
Available-for-sale securities:
Assets measured at fair value on a recurring basis	45,021	40,067
Available-for-sale Securities | Equity securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	17,458	19,212
Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale securities:
Assets measured at fair value on a recurring basis	17,458	19,212
Assets
Assets measured at fair value on a nonrecurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative Assets
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Loans held for sale – fair value option
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative Liabilities
Liabilities
Derivatives	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Impaired loans
Assets
Assets measured at fair value on a nonrecurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other real estate owned
Assets
Assets measured at fair value on a nonrecurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Agency-guaranteed residential mortgage-backed securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Agency-guaranteed commercial real estate mortgage-backed securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Corporate notes
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Equity securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	17,458	19,212
Significant Other Observable Inputs (Level 2)
Available-for-sale securities:
Assets measured at fair value on a recurring basis	2,495,560	2,308,098
Assets
Assets measured at fair value on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2) | Derivative Assets
Available-for-sale securities:
Assets measured at fair value on a recurring basis	15,251	9,250
Significant Other Observable Inputs (Level 2) | Loans held for sale – fair value option
Available-for-sale securities:
Assets measured at fair value on a recurring basis	1,941,602	1,757,807
Significant Other Observable Inputs (Level 2) | Derivative Liabilities
Liabilities
Derivatives	22,957	13,932
Significant Other Observable Inputs (Level 2) | Impaired loans
Assets
Assets measured at fair value on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2) | Other real estate owned
Assets
Assets measured at fair value on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Agency-guaranteed residential mortgage-backed securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	286,289	298,104
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Agency-guaranteed commercial real estate mortgage-backed securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	207,397	202,870
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Corporate notes
Available-for-sale securities:
Assets measured at fair value on a recurring basis	45,021	40,067
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Equity securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Significant Unobservable Inputs (Level 3)
Available-for-sale securities:
Assets measured at fair value on a recurring basis	73	45
Assets
Assets measured at fair value on a nonrecurring basis	7,042	4,704
Significant Unobservable Inputs (Level 3) | Derivative Assets
Available-for-sale securities:
Assets measured at fair value on a recurring basis	73	45
Significant Unobservable Inputs (Level 3) | Loans held for sale – fair value option
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Significant Unobservable Inputs (Level 3) | Derivative Liabilities
Liabilities
Derivatives	0	0
Significant Unobservable Inputs (Level 3) | Impaired loans
Assets
Assets measured at fair value on a nonrecurring basis	6,354	4,346
Significant Unobservable Inputs (Level 3) | Other real estate owned
Assets
Assets measured at fair value on a nonrecurring basis	688	358
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Agency-guaranteed residential mortgage-backed securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Agency-guaranteed commercial real estate mortgage-backed securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Corporate notes
Available-for-sale securities:
Assets measured at fair value on a recurring basis	0	0
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Equity securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	$ 0	$ 0