Property and Equipment - Depreciation and Amortization Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 25,603esi_AssetDepreciationAndAmortization	$ 27,007esi_AssetDepreciationAndAmortization	$ 29,320esi_AssetDepreciationAndAmortization

The aggregate expense recognized in the current period that allocates the cost of tangible assets, leasehold improvements and software to periods that benefit from the use of the assets.

No definition available.

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