Basis of Presentation and Accounting Policies - Carrying Amount and Estimated Fair Value of Company's Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financial assets:
Loans, net	$ 1,960,478	$ 1,966,592	$ 1,981,385
Financial liabilities:
Deposits	2,491,282	2,624,883	2,667,731
Other borrowings			3,854
Carrying Amount [Member]
Financial assets:
Loans, net	1,930,095	1,934,754	1,948,532
Financial liabilities:
Deposits	2,489,973	2,624,663	2,665,360
Other borrowings			3,810
Level 1 [Member]
Financial assets:
Loans, net
Financial liabilities:
Deposits
Other borrowings
Level 2 [Member]
Financial assets:
Loans, net	1,458,604	1,406,366	1,258,402
Financial liabilities:
Deposits	2,491,282	2,624,883	2,667,731
Other borrowings			3,854
Level 3 [Member]
Financial assets:
Loans, net	501,874	560,226	722,983
Financial liabilities:
Deposits
Other borrowings