Covered Loans - Composition of Covered Loans by Lending Classification (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Covered Loans [Line Items]
Covered loans	$ 136,840	$ 147,708	$ 194,161
Allowance for loan losses	(2,203)	(3,552)	(6,014)
Covered loans, net	134,637
Commercial Loans [Member]
Covered Loans [Line Items]
Covered loans	13,829
Commercial Real Estate Loan [Member]
Covered Loans [Line Items]
Covered loans	36,499
Residential [Member]
Covered Loans [Line Items]
Covered loans	20,248
Consumer [Member]
Covered Loans [Line Items]
Covered loans	66,264
Loans Accounted for Under ASC 310-30 (Purchased Credit Impaired) [Member]
Covered Loans [Line Items]
Covered loans	70,567
Allowance for loan losses	(802)
Covered loans, net	69,765
Loans Accounted for Under ASC 310-30 (Purchased Credit Impaired) [Member] | Commercial Loans [Member]
Covered Loans [Line Items]
Covered loans	5,255
Loans Accounted for Under ASC 310-30 (Purchased Credit Impaired) [Member] | Commercial Real Estate Loan [Member]
Covered Loans [Line Items]
Covered loans	33,540
Loans Accounted for Under ASC 310-30 (Purchased Credit Impaired) [Member] | Residential [Member]
Covered Loans [Line Items]
Covered loans	20,101
Loans Accounted for Under ASC 310-30 (Purchased Credit Impaired) [Member] | Consumer [Member]
Covered Loans [Line Items]
Covered loans	11,671
Loans Excluded from ASC 310-30 (1) (Not Purchased Credit Impaired) [Member]
Covered Loans [Line Items]
Covered loans	66,273
Allowance for loan losses	(1,401)
Covered loans, net	64,872
Loans Excluded from ASC 310-30 (1) (Not Purchased Credit Impaired) [Member] | Commercial Loans [Member]
Covered Loans [Line Items]
Covered loans	8,574
Loans Excluded from ASC 310-30 (1) (Not Purchased Credit Impaired) [Member] | Commercial Real Estate Loan [Member]
Covered Loans [Line Items]
Covered loans	2,959
Loans Excluded from ASC 310-30 (1) (Not Purchased Credit Impaired) [Member] | Residential [Member]
Covered Loans [Line Items]
Covered loans	147
Loans Excluded from ASC 310-30 (1) (Not Purchased Credit Impaired) [Member] | Consumer [Member]
Covered Loans [Line Items]
Covered loans	$ 54,593