Loans, net and allowance for loan losses - Summarize Information in Concerning to Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	$ 14,834	$ 2,008	$ 18,568
Average Recorded Investment, With an allowance recorded, Total	3,886	3,398	4,263
Unpaid Principal Balance, With no related allowance, Total	20,780	2,008	26,353
Interest Income Recognized, With an allowance recorded, Total	44	26	184
Average Recorded Investment, With no related allowance, Total	16,701	1,708	18,628
Interest Income Recognized, With no related allowance, Total
Recorded Investment, With an allowance recorded, Total	3,393	2,932	4,378
Unpaid Principal Balance, With an allowance recorded, Total	3,393	2,932	4,378
Related Allowance, With an allowance recorded, Total	1,832	861	2,024
Recorded Investment, Total	18,227	4,940	22,946
Average Recorded Investment, Total	20,587	5,106	22,891
Unpaid Principal Balance, Total	24,173	4,940	30,731
Interest Income Recognized, Total	44	26	184
Related Allowance, With an allowance recorded, Total	1,832	861	2,024
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	2,008	338	4,978
Average Recorded Investment, With an allowance recorded, Total	1,964	350	2,182
Unpaid Principal Balance, With no related allowance, Total	4,762	338	9,474
Interest Income Recognized, With an allowance recorded, Total	26	4	95
Average Recorded Investment, With no related allowance, Total	3,493	321	5,824
Interest Income Recognized, With no related allowance, Total
Recorded Investment, With an allowance recorded, Total	1,728	349	2,200
Unpaid Principal Balance, With an allowance recorded, Total	1,728	349	2,200
Related Allowance, With an allowance recorded, Total	1,128	349	1,500
Recorded Investment, Total	3,736	687	7,178
Average Recorded Investment, Total	5,457	671	8,006
Unpaid Principal Balance, Total	6,490	687	11,674
Interest Income Recognized, Total	26	4	95
Related Allowance, With an allowance recorded, Total	1,128	349	1,500
Real Estate Commercial [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	9,958	262	10,496
Average Recorded Investment, With an allowance recorded, Total	1,399	1,731	1,409
Unpaid Principal Balance, With no related allowance, Total	12,746	262	13,352
Interest Income Recognized, With an allowance recorded, Total	18	19	76
Average Recorded Investment, With no related allowance, Total	10,227	204	10,095
Interest Income Recognized, With no related allowance, Total
Recorded Investment, With an allowance recorded, Total	1,404	1,446	1,394
Unpaid Principal Balance, With an allowance recorded, Total	1,404	1,446	1,394
Related Allowance, With an allowance recorded, Total	542	300	300
Recorded Investment, Total	11,362	1,708	11,890
Average Recorded Investment, Total	11,626	1,935	11,504
Unpaid Principal Balance, Total	14,150	1,708	14,746
Interest Income Recognized, Total	18	19	76
Related Allowance, With an allowance recorded, Total	542	300	300
Real Estate Residential [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	2,740	1,321	3,004
Average Recorded Investment, With an allowance recorded, Total	523	1,317	672
Unpaid Principal Balance, With no related allowance, Total	3,144	1,321	3,437
Interest Income Recognized, With an allowance recorded, Total		3	13
Average Recorded Investment, With no related allowance, Total	2,872	1,125	2,614
Interest Income Recognized, With no related allowance, Total
Recorded Investment, With an allowance recorded, Total	261	1,137	784
Unpaid Principal Balance, With an allowance recorded, Total	261	1,137	784
Related Allowance, With an allowance recorded, Total	162	212	224
Recorded Investment, Total	3,001	2,458	3,788
Average Recorded Investment, Total	3,395	2,442	3,286
Unpaid Principal Balance, Total	3,405	2,458	4,221
Interest Income Recognized, Total		3	13
Related Allowance, With an allowance recorded, Total	162	212	224
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance, Total	128	87	90
Average Recorded Investment, With an allowance recorded, Total
Unpaid Principal Balance, With no related allowance, Total	128	87	90
Interest Income Recognized, With an allowance recorded, Total
Average Recorded Investment, With no related allowance, Total	109	58	95
Interest Income Recognized, With no related allowance, Total
Recorded Investment, With an allowance recorded, Total
Unpaid Principal Balance, With an allowance recorded, Total
Related Allowance, With an allowance recorded, Total
Recorded Investment, Total	128	87	90
Average Recorded Investment, Total	109	58	95
Unpaid Principal Balance, Total	128	87	90
Interest Income Recognized, Total
Related Allowance, With an allowance recorded, Total

Name:	us-gaap_FinancingReceivableImpairedLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953550-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRelatedAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant