Debt instrument base rate percentage.

No definition available.

Name:	esi_DebtInstrumentBaseRatePercentage
Namespace Prefix:	esi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument prepayment premium percentage.

+ References

No definition available.

+ Details

Name:	esi_DebtInstrumentPrepaymentPremiumPercentage
Namespace Prefix:	esi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of outstanding principal owed under a debt agreement.

+ References

No definition available.

+ Details

Name:	esi_DebtOutstandingPrincipalBalance
Namespace Prefix:	esi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The period of time after entering into an agreement that excess cash flow must be paid to a lender.

+ References

No definition available.

+ Details

Name:	esi_ExcessCashFlowTerm
Namespace Prefix:	esi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount paid during the period under the Excess Cash Flow provision of the Financing Agreement.

+ References

No definition available.

+ Details

Name:	esi_ExcessCashFlowTermLoanPrepayment
Namespace Prefix:	esi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Mandatory Prepayment of Outstanding Principal Amount

+ References

No definition available.

+ Details

Name:	esi_MandatoryPrepaymentOfOutstandingPrincipalAmount
Namespace Prefix:	esi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The percentage of excess cash flow, as defined in an agreement, that is required to be paid to a lender.

+ References

No definition available.

+ Details

Name:	esi_PercentageOfExcessCashFlows
Namespace Prefix:	esi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

- Definition

The average effective interest rate during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Represents the charge against earnings during the period for commitment fees and debt issuance expenses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=esi_TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=esi_OptionOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=esi_OptionTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=esi_FederalFundRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=esi_FinancingAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Term Loans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2016	Dec. 31, 2015
Term Loan [Member]
Debt Instrument [Line Items]
Aggregate principal amount	$ 100,000			$ 100,000
Commitment fee			$ 3,000
Excess cash flow for prepayment of debt				$ 9,000
Percentage of outstanding principal amount in excess of cash flow				50.00%
Percentage of premium on prepayment of principal				1.00%
Period of prepayment of outstanding principal on Financing Agreement that requires premium payment				2 years
Term Loan [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Mandatory prepayment of outstanding principal amount, minimum				$ 9,000
Term Loan [Member] \| Scenario, Forecast [Member]
Debt Instrument [Line Items]
Outstanding loan balance						$ 0
Option One [Member]
Debt Instrument [Line Items]
Variable rate basis				LIBOR
Base rate percentage				1.00%
Option One [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Variable rate, margin percentage				8.50%
Option Two [Member]
Debt Instrument [Line Items]
Base rate percentage				2.00%
Option Two [Member] \| Federal Fund Rate [Member]
Debt Instrument [Line Items]
Variable rate, margin percentage				0.50%
Option Two [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate, margin percentage				1.00%
Option Two [Member] \| Prime Rate [Member]
Debt Instrument [Line Items]
Variable rate, margin percentage				8.00%
Financing Agreement [Member]
Debt Instrument [Line Items]
Outstanding loan balance	$ 34,681	$ 95,000		$ 34,681	$ 95,000		$ 69,681
Effective interest rate on borrowings	14.50%	9.91%		14.30%	9.91%