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	Jun. 30, 2016	Dec. 31, 2015
Available-for-sale securities:
Assets measured at fair value on a recurring basis	$ 2,841,721	$ 2,327,355
Assets
Assets measured at fair value on a nonrecurring basis	6,073	4,704
Specific reserves related to impaired loans	3,666	2,273
Derivative assets
Available-for-sale securities:
Assets measured at fair value on a recurring basis	19,492	9,295
Loans held for sale – fair value option
Available-for-sale securities:
Assets measured at fair value on a recurring basis	2,274,294	1,757,807
Derivative liabilities
Liabilities
Derivatives	27,624	13,932
Impaired loans, net of specific reserves
Assets
Assets measured at fair value on a nonrecurring basis	5,385	4,346
Specific reserves related to impaired loans	3,666	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	271,976	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	213,554	202,870
Available-for-sale Securities | Corporate notes
Available-for-sale securities:
Assets measured at fair value on a recurring basis	45,712	40,067
Available-for-sale Securities | Equity securities
Available-for-sale securities:
Assets measured at fair value on a recurring basis	16,693	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	16,693	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, net of specific reserves
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	16,693	19,212
Significant Other Observable Inputs (Level 2)
Available-for-sale securities:
Assets measured at fair value on a recurring basis	2,824,871	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	19,335	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	2,274,294	1,757,807
Significant Other Observable Inputs (Level 2) | Derivative liabilities
Liabilities
Derivatives	27,624	13,932
Significant Other Observable Inputs (Level 2) | Impaired loans, net of specific reserves
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	271,976	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	213,554	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	45,712	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	157	45
Assets
Assets measured at fair value on a nonrecurring basis	6,073	4,704
Significant Unobservable Inputs (Level 3) | Derivative assets
Available-for-sale securities:
Assets measured at fair value on a recurring basis	157	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, net of specific reserves
Assets
Assets measured at fair value on a nonrecurring basis	5,385	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