Fair Value of Financial Instrument - Carrying Amount and Estimated Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Financial assets:
Cash and due from banks	$ 69,421	$ 62,955	$ 53,516	$ 80,256
Federal funds sold and interest-bearing accounts	40,165	204,984	73,899
FDIC loss-share receivable	38,233	65,441	81,763	159,724
Financial liabilities:
Other borrowings	147,409	194,572	5,000
Subordinated deferrable interest debentures	65,084	55,466	42,269
Carrying Value [Member]
Financial assets:
Cash and due from banks	69,421	62,955	53,516
Federal funds sold and interest-bearing accounts	40,165	204,984	73,899
Loans, net	2,778,026	2,392,521	1,939,498
FDIC loss-share receivable	38,233	65,441	81,763
Accrued interest receivable	17,171	15,071	13,030
Accrued interest receivable	17,171	15,071	13,030
Financial liabilities:
Deposits	3,373,119	2,999,231	2,443,421
Securities sold under agreements to repurchase	32,351	83,516	20,255
Other borrowings	147,409	194,572
Accrued interest payable	1,444	1,431	831
Subordinated deferrable interest debentures	65,084	55,466	42,269
Fair Value [Member]
Financial assets:
Cash and due from banks	69,421	62,995	53,516
Federal funds sold and interest-bearing accounts	40,165	204,984	73,899
Loans, net	2,773,291	2,404,909	1,912,634
FDIC loss-share receivable	21,397	61,317	76,346
Accrued interest receivable	17,171	15,071	13,030
Accrued interest receivable	17,171	15,071	13,030
Financial liabilities:
Deposits	3,374,055	3,000,061	2,444,244
Securities sold under agreements to repurchase	32,351	83,516	20,255
Other borrowings	147,409	194,572
Accrued interest payable	1,444	1,431	831
Subordinated deferrable interest debentures	46,214	36,277	23,331
Fair Value [Member] | Level 1 [Member]
Financial assets:
Cash and due from banks	69,421	62,955	53,516
Federal funds sold and interest-bearing accounts	40,165	204,984	73,899
Accrued interest receivable	17,171	15,071	13,030
Accrued interest receivable	17,171	15,071	13,030
Financial liabilities:
Securities sold under agreements to repurchase	32,351	83,516	20,255
Accrued interest payable	1,444	1,431	831
Fair Value [Member] | Level 2 [Member]
Financial liabilities:
Deposits	3,374,055	3,000,061	2,444,244
Other borrowings	147,409	194,572
Subordinated deferrable interest debentures	46,214	36,277	23,331
Fair Value [Member] | Level 3 [Member]
Financial assets:
Loans, net	2,773,291	2,404,909	1,912,634
FDIC loss-share receivable	$ 21,397	$ 61,317	$ 76,346