Fair Value Disclosures - Assets measured at fair value on a non-recurring basis (Detail) (Fair Value, Measurements, Nonrecurring [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets measured at fair value on a non-recurring basis [Line Items]
Impaired loans held for investment	$ 38,324	$ 44,976
Mortgage servicing rights		4,152
Loans held for sale	3,609
Other real estate owned		1,607
Total assets	41,933	50,735
Level 1 [Member]
Assets measured at fair value on a non-recurring basis [Line Items]
Impaired loans held for investment
Mortgage servicing rights
Loans held for sale
Other real estate owned
Total assets
Level 2 [Member]
Assets measured at fair value on a non-recurring basis [Line Items]
Impaired loans held for investment
Mortgage servicing rights		4,152
Loans held for sale	3,609
Other real estate owned		1,607
Total assets	3,609	5,759
Level 3 [Member]
Assets measured at fair value on a non-recurring basis [Line Items]
Impaired loans held for investment	38,324	44,976
Mortgage servicing rights
Loans held for sale
Other real estate owned
Total assets	$ 38,324	$ 44,976