Fair Value Measurement - Estimates Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Financial Assets
Cash and due from banks	$ 92,974	$ 94,002	$ 175,196	$ 95,551
Securities available-for-sale	1,654,264us-gaap_AvailableForSaleSecurities	917,424us-gaap_AvailableForSaleSecurities
Securities held-to-maturity	743,925us-gaap_HeldToMaturitySecurities	593,670us-gaap_HeldToMaturitySecurities
Net loans	4,829,548	4,042,112
Loans held for sale	6,064	5,865
Accrued interest receivable	25,232us-gaap_InterestReceivable	18,481us-gaap_InterestReceivable
Bank-owned life insurance	153,991us-gaap_BankOwnedLifeInsurance	123,298us-gaap_BankOwnedLifeInsurance
Financial Liabilities
Deposits	6,416,202us-gaap_Deposits	5,048,983us-gaap_Deposits
Federal Home Loan Bank borrowings	432,456	223,126
Other borrowings	76,630us-gaap_OtherShortTermBorrowings	80,690us-gaap_OtherShortTermBorrowings
Junior subordinated debt	142,269	106,176
Accrued interest payable	2,297	1,620
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial Assets
Cash and due from banks	92,974	94,002
Securities available-for-sale	8,538	8,440
Accrued interest receivable	25,232	18,481
Bank-owned life insurance	153,991	123,298
Financial Liabilities
Deposits	4,532,314	3,743,887
Other borrowings	73,589	77,534
Accrued interest payable	2,297	1,620
Significant Other Observable Inputs (Level 2) [Member]
Financial Assets
Securities available-for-sale	1,645,726	908,984
Securities held-to-maturity	772,088	618,895
Loans held for sale	6,064	5,865
Financial Liabilities
Deposits	1,891,185	1,312,941
Federal Home Loan Bank borrowings	435,089	225,456
Other borrowings	3,032	3,162
Junior subordinated debt	116,070	79,212
Significant Unobservable Inputs (Level 3) [Member]
Financial Assets
Securities held-to-maturity	755	722
Net loans	4,820,779	4,047,648
Carrying Amount [Member]
Financial Assets
Cash and due from banks	92,974	94,002
Securities available-for-sale	1,654,264	917,424
Securities held-to-maturity	743,925	593,670
Net loans	4,829,548	4,042,112
Loans held for sale	6,064	5,865
Accrued interest receivable	25,232	18,481
Bank-owned life insurance	153,991	123,298
Financial Liabilities
Deposits	6,416,202	5,048,983
Federal Home Loan Bank borrowings	432,456	223,126
Other borrowings	76,630	80,690
Junior subordinated debt	142,269	106,176
Accrued interest payable	2,297	1,620
Fair Value Estimate [Member]
Financial Assets
Cash and due from banks	92,974	94,002
Securities available-for-sale	1,654,264	917,424
Securities held-to-maturity	772,843	619,617
Net loans	4,820,779	4,047,648
Loans held for sale	6,064	5,865
Accrued interest receivable	25,232	18,481
Bank-owned life insurance	153,991	123,298
Financial Liabilities
Deposits	6,423,499	5,056,828
Federal Home Loan Bank borrowings	435,089	225,456
Other borrowings	76,621	80,696
Junior subordinated debt	116,070	79,212
Accrued interest payable	$ 2,297	$ 1,620

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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The carrying amount of a life insurance policy on an officer, executive or employee for which the reporting entity (a bank) is entitled to proceeds from the policy upon death of the insured or surrender of the insurance policy.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

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Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Amount of interest payable on debt, including, but not limited to, trade payables.

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Including the current and noncurrent portions, the carrying value of junior subordinated long-term debt owed to unconsolidated subsidiary trusts as of the balance sheet date. Such debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets and was initially scheduled to be repaid after one year or beyond the normal operating cycle if longer.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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No definition available.

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Sum of the carrying amounts at the balance sheet date of short-term borrowings not otherwise specified in the taxonomy having initial terms less than one year or the normal operating cycle, if longer.

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