Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.

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Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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Amount due from customers or clients, more than one year from the balance sheet date, for goods or services that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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Significant Accounting Policies - Tuition Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Schedule of tuition receivable and allowance for doubtful accounts
Tuition receivable	$ 77,922		$ 35,809
Allowance for doubtful accounts	(25,395)	$ (15,048)	(12,687)	$ (12,557)	$ (11,760)	$ (10,201)
Tuition receivable, net	52,527		23,122
Other assets
Schedule of tuition receivable and allowance for doubtful accounts
Tuition receivable, noncurrent	$ 3,900		$ 2,900