Income Taxes - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
State income tax benefit	$ 5,687esi_StateIncomeTaxExpenseBenefit
Unrecognized tax benefits that, if recognized, would affected effective tax rate	11,109
Interest and penalties accrued related to unrecognized tax benefits	6,135	6,371
Minimum [Member]
Income Taxes [Line Items]
Unrecognized tax benefits that could decrease in the 12 months immediately following the date of this filing	0
Maximum [Member]
Income Taxes [Line Items]
Unrecognized tax benefits that could decrease in the 12 months immediately following the date of this filing	$ 6,932

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State Income Tax Expense Benefit

+ References

No definition available.

+ Details

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- Definition

The amount of the unrecognized tax benefit of a position taken for which it is reasonably possible that the total amount thereof will significantly increase or decrease within twelve months of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319

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- Definition

Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319

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- Definition

The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

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