Variable Interests - Guarantee Obligations Under 2009 RSA (Detail) (2009 RSA [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
2009 RSA [Member]
Variable Interest Entity [Line Items]
Guarantee obligation payment	$ 458	$ 560	$ 738	$ 1,141

Payments made under the risk-sharing agreement to third parties, net of recoveries.

No definition available.

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