Fair Values of off-Balance Sheet Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Assets:
Cash and cash equivalents	$ 51,764	$ 30,877	$ 36,712	$ 23,181
Securities available-for-sale	251,813	214,393
Securities held-to-maturity	8,446	8,470
Other securities	4,624	3,438
Loans, net	566,841	408,971
Liabilities:
Noninterest-bearing deposits	169,001	109,625
Interest-bearing deposits	644,964	487,002
Subordinated debentures	10,310	10,310
FHLB and other borrowings	30,000	36,771
Estimated Fair Value
Assets:
Cash and cash equivalents	51,764	30,877
Securities available-for-sale	251,813	214,393
Securities held-to-maturity	9,441	7,055
Other securities	4,624	3,438
Loans, net	580,204	422,029
Liabilities:
Noninterest-bearing deposits	169,001	109,625
Interest-bearing deposits	644,511	487,599
Subordinated debentures	10,310	10,310
FHLB and other borrowings	$ 30,000	$ 36,771