Fair Value of Financial Instruments - Summary of Carrying Amount and Estimated Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financial assets:
Loans, net	$ 1,966,592	$ 1,877,320
Financial liabilities:
Deposits	2,624,883	2,593,113
Other borrowings		20,936
Carrying Amount [Member]
Financial assets:
Loans, net	1,934,754	1,868,419
Financial liabilities:
Deposits	2,624,663	2,591,566
Other borrowings		20,000
Level 1 [Member]
Financial assets:
Loans, net
Financial liabilities:
Deposits
Other borrowings
Level 2 [Member]
Financial assets:
Loans, net	1,966,592	1,877,320
Financial liabilities:
Deposits	2,624,883	2,593,113
Other borrowings		20,936
Level 3 [Member]
Financial assets:
Loans, net
Financial liabilities:
Deposits
Other borrowings