Loans and Allowance for Loan and Lease Losses - Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Recorded Balance	$ 9,024	$ 7,889	$ 9,023
All Impaired Loans, Recorded Balance	10,848	15,544	10,839
Loans without a specific valuation allowance, Unpaid Principal Balance	9,783	8,577	9,768
All Impaired Loans, Unpaid Principal Balance	11,728	17,119	11,692
Loans without a specific valuation allowance, Average Investment In Impaired Loans	8,957	7,907	8,332
Loans without a specific valuation allowance, Interest Income Recognized	73	61	306
Loans with a specific valuation allowance, Recorded Balance	1,824	7,655	1,816
Loans with a specific valuation allowance, Unpaid Principal Balance	1,945	8,542	1,924
All Impaired Loans, Specific Allowance	547	999	497
Loans with a specific valuation allowance, Average Investment In Impaired Loans	1,854	7,871	5,958
All Impaired Loans, Average Investment in Impaired Loans	10,811	15,778	14,290
Loans with a specific valuation allowance, Interest Income Recognized	5	59	155
All Impaired Loans, Interest Income Recognized	78	120	461
Commercial Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Recorded Balance	4,263	3,553	4,263
Loans without a specific valuation allowance, Unpaid Principal Balance	4,742	4,011	4,742
Loans without a specific valuation allowance, Average Investment In Impaired Loans	4,263	3,538	4,025
Loans without a specific valuation allowance, Interest Income Recognized	43	44	176
Loans with a specific valuation allowance, Recorded Balance		1,277
Loans with a specific valuation allowance, Unpaid Principal Balance		1,277
All Impaired Loans, Specific Allowance		86
Loans with a specific valuation allowance, Average Investment In Impaired Loans		1,285	481
Loans with a specific valuation allowance, Interest Income Recognized		15	22
Residential Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Recorded Balance	2,715	2,638	2,686
Loans without a specific valuation allowance, Unpaid Principal Balance	2,967	2,712	2,923
Loans without a specific valuation allowance, Average Investment In Impaired Loans	2,634	2,637	2,342
Loans without a specific valuation allowance, Interest Income Recognized	13	14	58
Loans with a specific valuation allowance, Recorded Balance	1,344	2,836	1,281
Loans with a specific valuation allowance, Unpaid Principal Balance	1,404	2,840	1,340
All Impaired Loans, Specific Allowance	365	474	319
Loans with a specific valuation allowance, Average Investment In Impaired Loans	1,346	3,236	2,806
Loans with a specific valuation allowance, Interest Income Recognized	5	19	78
Construction Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Recorded Balance	1,975	1,247	2,004
Loans without a specific valuation allowance, Unpaid Principal Balance	1,975	1,247	2,004
Loans without a specific valuation allowance, Average Investment In Impaired Loans	1,989	1,260	1,744
Loans without a specific valuation allowance, Interest Income Recognized	17	3	72
Loans with a specific valuation allowance, Recorded Balance		3,219
Loans with a specific valuation allowance, Unpaid Principal Balance		4,061
All Impaired Loans, Specific Allowance		251
Loans with a specific valuation allowance, Average Investment In Impaired Loans		3,029	2,368
Loans with a specific valuation allowance, Interest Income Recognized		25	55
Commercial Loans and Leases [Member]
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Recorded Balance	71	471	70
Loans without a specific valuation allowance, Unpaid Principal Balance	99	607	99
Loans without a specific valuation allowance, Average Investment In Impaired Loans	71	472	221
Loans with a specific valuation allowance, Recorded Balance	424	250	446
Loans with a specific valuation allowance, Unpaid Principal Balance	485	291	495
All Impaired Loans, Specific Allowance	154	180	166
Loans with a specific valuation allowance, Average Investment In Impaired Loans	435	255	222
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans with a specific valuation allowance, Recorded Balance	56	73	89
Loans with a specific valuation allowance, Unpaid Principal Balance	56	73	89
All Impaired Loans, Specific Allowance	28	8	12
Loans with a specific valuation allowance, Average Investment In Impaired Loans	$ 73	$ 66	$ 81