Basis of Presentation and Accounting Policies - Carrying Amount and Estimated Fair Value of Company's Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Financial assets:
Loans, net	$ 2,000,952	$ 1,966,592	$ 1,975,541
Financial liabilities:
Deposits	2,444,263	2,624,883	2,546,740
Other borrowings			3,835
Carrying Amount [Member]
Financial assets:
Loans, net	1,975,127	1,934,754	1,941,028
Financial liabilities:
Deposits	2,443,103	2,624,663	2,544,672
Other borrowings			3,810
Level 1 [Member]
Financial liabilities:
Other borrowings			3,835
Level 2 [Member]
Financial assets:
Loans, net	1,512,681	1,406,366	1,313,527
Financial liabilities:
Deposits	2,444,263	2,624,883	2,546,740
Level 3 [Member]
Financial assets:
Loans, net	$ 488,271	$ 560,226	$ 662,014