Loans - Schedule of Troubled Debt Restructurings Occurred During Period by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Contract	Dec. 31, 2013 Contract
Troubled Debt Restructurings [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	12	8
Pre-Modification Outstanding Recorded Investment	$ 6,486	$ 3,740
Post-Modification Outstanding Recorded Investment	5,573	3,371
Troubled Debt Restructurings [Member] | Commercial Non-Real Estate [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	1	1
Pre-Modification Outstanding Recorded Investment	29	926
Post-Modification Outstanding Recorded Investment	29	909
Troubled Debt Restructurings [Member] | Commercial Real Estate [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	3	5
Pre-Modification Outstanding Recorded Investment	4,488	1,844
Post-Modification Outstanding Recorded Investment	4,446	1,629
Troubled Debt Restructurings [Member] | Residential Mortgages [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	7	2
Pre-Modification Outstanding Recorded Investment	1,961	970
Post-Modification Outstanding Recorded Investment	1,090	833
Troubled Debt Restructurings [Member] | Consumer [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	1
Pre-Modification Outstanding Recorded Investment	8
Post-Modification Outstanding Recorded Investment	8
Troubled Debt Restructurings [Member] | Originated Loans [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	12	6
Pre-Modification Outstanding Recorded Investment	6,486	2,714
Post-Modification Outstanding Recorded Investment	5,573	2,396
Troubled Debt Restructurings [Member] | Originated Loans [Member] | Commercial Non-Real Estate [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	1	1
Pre-Modification Outstanding Recorded Investment	29	926
Post-Modification Outstanding Recorded Investment	29	909
Troubled Debt Restructurings [Member] | Originated Loans [Member] | Commercial Real Estate [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	3	4
Pre-Modification Outstanding Recorded Investment	4,488	1,332
Post-Modification Outstanding Recorded Investment	4,446	1,157
Troubled Debt Restructurings [Member] | Originated Loans [Member] | Residential Mortgages [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	7	1
Pre-Modification Outstanding Recorded Investment	1,961	456
Post-Modification Outstanding Recorded Investment	1,090	330
Troubled Debt Restructurings [Member] | Originated Loans [Member] | Consumer [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	1
Pre-Modification Outstanding Recorded Investment	8
Post-Modification Outstanding Recorded Investment	8
Troubled Debt Restructurings [Member] | Acquired Loans [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts		2
Pre-Modification Outstanding Recorded Investment		1,026
Post-Modification Outstanding Recorded Investment		975
Troubled Debt Restructurings [Member] | Acquired Loans [Member] | Commercial Real Estate [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts		1
Pre-Modification Outstanding Recorded Investment		512
Post-Modification Outstanding Recorded Investment		472
Troubled Debt Restructurings [Member] | Acquired Loans [Member] | Residential Mortgages [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts		1
Pre-Modification Outstanding Recorded Investment		514
Post-Modification Outstanding Recorded Investment		503
Troubled Debt Restructurings That Subsequently Defaulted [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	2	7
Recorded Investment	1,172	2,741
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Commercial Non-Real Estate [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	1
Recorded Investment	909
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Commercial Real Estate [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts		6
Recorded Investment		2,487
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Residential Mortgages [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	1	1
Recorded Investment	263	254
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Originated Loans [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	2	7
Recorded Investment	1,172	2,741
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Originated Loans [Member] | Commercial Non-Real Estate [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	1
Recorded Investment	909
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Originated Loans [Member] | Commercial Real Estate [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts		6
Recorded Investment		2,487
Troubled Debt Restructurings That Subsequently Defaulted [Member] | Originated Loans [Member] | Residential Mortgages [Member]
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Number of Contracts	1	1
Recorded Investment	$ 263	$ 254