v3.10.0.1

Stock-Based Compensation - Expense (Details)		3 Months Ended		9 Months Ended
	Jun. 05, 2017 USD ($)	Sep. 30, 2018 USD ($) plan	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) plan	Sep. 30, 2017 USD ($)
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Number of share-based employee compensation plans | plan		2		2
Percentage of purchase price to fair market value	90.00%
Maximum payroll deduction amount per calendar year	$ 25,000
Stock-based compensation expense		$ 7,933,000	$ 6,147,000	$ 24,064,000	$ 15,537,000
Curriculum and teaching
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Stock-based compensation expense		3,000	2,000	10,000	2,000
Servicing and support
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Stock-based compensation expense		1,346,000	1,100,000	3,538,000	2,956,000
Technology and content development
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Stock-based compensation expense		1,089,000	904,000	2,875,000	2,447,000
Marketing and sales
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Stock-based compensation expense		839,000	463,000	2,046,000	1,235,000
General and administrative
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Stock-based compensation expense		$ 4,656,000	$ 3,678,000	$ 15,595,000	$ 8,897,000
Minimum
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Percentage of payroll deduction	1.00%
Maximum
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Percentage of payroll deduction	15.00%

X

- Definition

The percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

No definition available.

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X

- Definition

Represents the least amount of percentage difference from purchase price to fair value.

+ References

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X

- Definition

Represents the number of employee compensation plans under the share-based arrangements.

+ References

No definition available.

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X

- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Maximum amount the employee may contribute to a defined contribution plan.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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