Fair Value Measurements and Disclosures - Changes in Fair Value of Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Balance, end of period	$ 26,791	$ 16,030
Level 3 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Balance, beginning of period	16,030	14,770
Additions to impaired loans and troubled debt restructurings	15,904	2,960
Principal payments, charge-offs and transfers to other real estate	(1,614)	(1,654)
Change in allowance for loan losses on impaired loans	(3,529)	(46)
Balance, end of period	$ 26,791	$ 16,030