Deposits Deposits and interest rates (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Deposits, by Type [Abstract]
Noninterest-bearing demand	$ 53,232	$ 58,239
Interest-bearing checking	24,271	25,927
Savings	98,051	98,066
Money market	127,655	113,259
Certificates of deposit	203,907	198,089
Mortgagors deposits	2,250	2,136
Deposits	$ 509,366	$ 495,716
Percentage of Total Deposits [Abstract]
Percentage of Noninterest bearing demand deposits to deposits	10.45%	11.75%
Percentage of Interest-bearing Domestic Deposits to Deposits	4.77%	5.23%
Percentage of Interest-bearing Domestic Deposits to Deposits, Savings	19.25%	19.78%
Percentage of Interest-bearing Domestic Deposits to Deposits, Money Market	25.06%	22.85%
Percentage of Interest-bearing Domestic Deposits to Deposits, Certificates of Deposit	40.03%	39.96%
Percentage of other deposits to deposits	0.44%	0.43%
Percent Total Deposits	100.00%	100.00%
Weighted Average Rate Domestic Deposit Liabilities [Abstract]
Weighted Average Rate Domestic Deposit, Demand	0.00%	0.00%
Weighted Average Rate Domestic Deposit, Checking	0.16%	0.16%
Weighted Average Rate Domestic Deposit, Savings	0.27%	0.26%
Weighted Average Rate Domestic Deposit, Money Market	0.46%	0.67%
Weighted Average Rate Domestic Deposit, Certificates of Deposit	1.01%	1.16%
Weighted Average Rate-Other Deposit	1.73%	1.80%
Weighted Average Rate Domestic Deposit	0.59%	0.68%

Other Deposits

No definition available.

Name:	carv_OtherDeposits
Namespace Prefix:	carv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage of Noninterest bearing demand deposits to deposits

+ References

No definition available.

+ Details

Name:	carv_PercentageOfNoninterestBearingDemandDepositsToDeposits
Namespace Prefix:	carv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of other deposits to deposits

+ References

No definition available.

+ Details

Name:	carv_PercentageOfOtherDepositsToDeposits
Namespace Prefix:	carv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	carv_PercentageofTotalDepositsAbstract
Namespace Prefix:	carv_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percent Total Deposits

+ References

No definition available.

+ Details

Name:	carv_PercentTotalDeposits
Namespace Prefix:	carv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted Average Rate-Other Deposit

+ References

No definition available.

+ Details

Name:	carv_WeightedAverageRateOtherDeposit
Namespace Prefix:	carv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.12)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 12

-Article 9

+ Details

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

- Details

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

- Definition

Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts.

+ References

+ Details

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

- Definition

Amount of interest bearing deposits with no stated maturity, which may include passbook and statement savings accounts and money-market deposit accounts (MMDAs).

+ References

+ Details

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

- Definition

Amount of interest-bearing domestic checking deposit liabilities.

+ References

+ Details

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

- Definition

The aggregate amount of all domestic and foreign noninterest-bearing deposits liabilities held by the entity.

+ References

+ Details

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

- Definition

Percentage of interest-bearing domestic deposit liabilities to total deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_PercentageOfInterestBearingDomesticDepositsToDeposits
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of interest-bearing domestic certificates of deposit liabilities to total deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsCertificatesOfDeposit
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of interest-bearing domestic money market demand account deposit liabilities to total deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsMoneyMarket
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of interest-bearing domestic savings deposit liabilities to total deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_PercentageOfInterestBearingDomesticDepositsToDepositsSavings
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of deposits that cannot be withdrawn before a set date without penalty or for which notice of withdrawal is required. Time deposits include, but are not limited to, certificates of deposits, individual retirement accounts and open accounts.

+ References

+ Details

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

- Definition

The weighted average interest rate for all domestic deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_WeightedAverageRateDomesticDeposit
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average interest rate for domestic certificates of deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_WeightedAverageRateDomesticDepositCertificatesOfDeposit
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average interest rate for domestic checking deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_WeightedAverageRateDomesticDepositChecking
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average interest rate for domestic demand deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_WeightedAverageRateDomesticDepositDemand
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Definition

The weighted average interest rate for domestic money market demand account deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_WeightedAverageRateDomesticDepositMoneyMarket
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average interest rate for domestic savings deposit liabilities.

+ References

No definition available.

+ Details

Name:	us-gaap_WeightedAverageRateDomesticDepositSavings
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant