Loans and Other Repossessed Assets Acquired (Detail) - Accretable yields of acquired loans (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Balance at beginning of period	$ 26,407	$ 16,965
Balance at end of period	19,512	15,782
Reclass of nonaccretable difference due to reduction of expected cash flows	(1,111)	0
Accretion	(5,784)	(1,183)
Non-Impaired Loans [Member]
Balance at beginning of period	5,474	2,811
Balance at end of period	5,081	2,638
Reclass of nonaccretable difference due to reduction of expected cash flows	0	0
Accretion	(393)	(173)
Impaired Loans [Member]
Balance at beginning of period	20,933	14,154
Balance at end of period	14,431	13,144
Reclass of nonaccretable difference due to reduction of expected cash flows	(1,111)	0
Accretion	$ (5,391)	$ (1,010)