Fair Value of Financial Instruments (Detail) - Assets measured at fair value on a nonrecurring basis categorized by the level of inputs (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011
Loans held for sale	$ 55,201	$ 48,303	$ 94,872
Impaired loans, net of specific allowance	24,632	24,668	24,139
Other repossessed assets acquired	18,338	20,487	26,212
Total nonrecurring basis measured assets	98,171	93,458	145,223
Fair Value, Inputs, Level 1 [Member]
Loans held for sale	0	0	0
Impaired loans, net of specific allowance	0	0	0
Other repossessed assets acquired	0	0	0
Total nonrecurring basis measured assets	0	0	0
Fair Value, Inputs, Level 2 [Member]
Loans held for sale	55,201	48,303	40,785
Impaired loans, net of specific allowance	0	0	0
Other repossessed assets acquired	0	0	0
Total nonrecurring basis measured assets	55,201	48,303	40,785
Fair Value, Inputs, Level 3 [Member]
Loans held for sale	0	0	54,087
Impaired loans, net of specific allowance	24,632	24,668	24,139
Other repossessed assets acquired	18,338	20,487	26,212
Total nonrecurring basis measured assets	42,970	45,155	104,438
Year to Date Losses [Member]
Loans held for sale	0	0	0
Impaired loans, net of specific allowance	3,511	(669)	(2,875)
Other repossessed assets acquired	1,138	(845)	(3,058)
Total nonrecurring basis measured assets	$ 4,649	$ (1,514)	$ (5,933)