Disclosures about Fair Value of Financial Instruments - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring and Non-recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related Allowance	$ 1,342	$ 2,342
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	1,759,905	1,248,929
Loans held for sale, Fair Value	1,436,460	747,593
Derivative Asset	7,552	3,763
Investment securities available for sale, at fair value	416,685	497,573
Assets
Assets, Fair Value Disclosure, Nonrecurring	11,529	4,171
Not Designated as Hedging Instrument
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	7,552	3,763
Liabilities
Liabilities, Fair Value Disclosure, Recurring	9,716	3,537
Loans held for sale – fair value option
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	1,335,668	747,593
Impaired loans, net of reserves
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related Allowance	1,342	2,432
Assets
Assets, Fair Value Disclosure, Nonrecurring	2,380	3,836
Other real estate owned
Assets
Assets, Fair Value Disclosure, Nonrecurring	9,149	335
Mortgage-backed securities
Available-for-sale securities:
Investment securities available for sale, at fair value	377,311	451,536
Corporate notes (2)
Available-for-sale securities:
Investment securities available for sale, at fair value	15,104	25,323
Equity securities
Available-for-sale securities:
Investment securities available for sale, at fair value	24,270	20,714
Available-for-sale Securities | Mortgage-backed securities
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	377,311	451,536
Available-for-sale Securities | Corporate notes (2)
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	15,104	25,323
Available-for-sale Securities | Equity securities
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	24,270	20,714
Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	24,270	20,714
Loans held for sale, Fair Value	0	0
Derivative Asset	0	0
Investment securities available for sale, at fair value	24,270	20,714
Assets
Assets, Fair Value Disclosure, Nonrecurring	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Not Designated as Hedging Instrument
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	0	0
Liabilities
Liabilities, Fair Value Disclosure, Recurring	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Loans held for sale – fair value option
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Impaired loans, net of reserves
Assets
Assets, Fair Value Disclosure, Nonrecurring	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other real estate owned
Assets
Assets, Fair Value Disclosure, Nonrecurring	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Mortgage-backed securities
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Corporate notes (2)
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Equity securities
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	24,270	20,714
Significant Other Observable Inputs (Level 2)
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	1,735,592	1,227,975
Loans held for sale, Fair Value	1,335,668	747,593
Derivative Asset	7,509	3,523
Investment securities available for sale, at fair value	392,415	476,859
Assets
Assets, Fair Value Disclosure, Nonrecurring	0	0
Significant Other Observable Inputs (Level 2) | Not Designated as Hedging Instrument
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	7,509	3,523
Liabilities
Liabilities, Fair Value Disclosure, Recurring	9,716	3,537
Significant Other Observable Inputs (Level 2) | Loans held for sale – fair value option
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	1,335,668	747,593
Significant Other Observable Inputs (Level 2) | Impaired loans, net of reserves
Assets
Assets, Fair Value Disclosure, Nonrecurring	0	0
Significant Other Observable Inputs (Level 2) | Other real estate owned
Assets
Assets, Fair Value Disclosure, Nonrecurring	0	0
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Mortgage-backed securities
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	377,311	451,536
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Corporate notes (2)
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	15,104	25,323
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Equity securities
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	0	0
Significant Unobservable Inputs (Level 3)
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	43	240
Loans held for sale, Fair Value	100,792	0
Derivative Asset	43	240
Investment securities available for sale, at fair value	0	0
Assets
Assets, Fair Value Disclosure, Nonrecurring	11,529	4,171
Significant Unobservable Inputs (Level 3) | Not Designated as Hedging Instrument
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	43	240
Liabilities
Liabilities, Fair Value Disclosure, Recurring	0	0
Significant Unobservable Inputs (Level 3) | Loans held for sale – fair value option
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	0	0
Significant Unobservable Inputs (Level 3) | Impaired loans, net of reserves
Assets
Assets, Fair Value Disclosure, Nonrecurring	2,380	3,836
Significant Unobservable Inputs (Level 3) | Other real estate owned
Assets
Assets, Fair Value Disclosure, Nonrecurring	9,149	335
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Mortgage-backed securities
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	0	0
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Corporate notes (2)
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	0	0
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Equity securities
Available-for-sale securities:
Assets, Fair Value Disclosure, Recurring	$ 0	$ 0