Debt - Schedule of Principal Repayment under the Financing Agreement (Detail) - Term Loan [Member] $ in Thousands	3 Months Ended
Mar. 31, 2016 USD ($)
Debt Instrument [Line Items]
Scheduled Payments	$ 50,505
Excess Cash Flow Payment	0
Total	50,505
Second Quarter [Member]
Debt Instrument [Line Items]
Scheduled Payments	15,500
Excess Cash Flow Payment	0
Total	15,500
Third Quarter [Member]
Debt Instrument [Line Items]
Scheduled Payments	15,500
Excess Cash Flow Payment	0
Total	15,500
Fourth Quarter [Member]
Debt Instrument [Line Items]
Scheduled Payments	19,505
Excess Cash Flow Payment	0
Total	$ 19,505

Excess Cash Flow Payments Amount

No definition available.

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

- Definition

Amount of the total principal payments made during the annual reporting period.

+ References

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

+ Details

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

- 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

Amount of the required periodic payments applied to principal.

+ References

Reference 1: 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)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentPeriodicPaymentPrincipal
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_StatementScenarioAxis=esi_SecondQuarterMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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