Significant Accounting Policies - Components of Revenue (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)
Product Information [Line Items]
Concentration risk, Percent of net revenues	100.00%
Revenue	$ 3,350,224
Tuition and educational services
Product Information [Line Items]
Concentration risk, Percent of net revenues	116.00%
Revenue	$ 3,895,773
Gross revenue
Product Information [Line Items]
Concentration risk, Percent of net revenues	124.00%
Revenue	$ 4,149,104
Less: Discounts / waivers / scholarships
Product Information [Line Items]
Concentration risk, Percent of net revenues	(24.00%)
Revenue	$ 798,880

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration