Related-Party Transactions (Details)	12 Months Ended
Dec. 31, 2017 USD ($) board_member	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Adobe Systems \| Chief Executive Officer
Related Party Transaction [Line Items]
Purchases from related party	$ 3,200,000	$ 3,100,000	$ 2,900,000
Revenue from related parties	100,000.0	0	100,000
Due to related parties	300,000
Due from related parties	0	0
Cengage \| Board of Directors Member
Related Party Transaction [Line Items]
Purchases from related party	11,500,000	10,200,000	11,500,000
Revenue from related parties	1,900,000	600,000	100,000
Due to related parties	100,000
Due from related parties	$ 300,000	100,000
Number of board members appointed to Board of Directors of related party \| board_member	1
Synack Inc. \| Board of Directors Member
Related Party Transaction [Line Items]
Purchases from related party	$ 100,000	200,000	100,000
Number of board members appointed to chief executive officer of related party \| board_member	1
Payment Processing Fees \| PayPal Holdings, Inc. \| Immediate Family Member of Management or Principal Owner
Related Party Transaction [Line Items]
Number of board members appointed to Board of Directors of related party \| board_member	1
Expenses from transactions with related party	$ 1,000,000	$ 900,000	$ 700,000

Related Party Transactions, Number of Board Members Appointed to Board of Directors of Related Party

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- Definition

Related Party Transactions, Number of Board Members Appointed to Chief Executive Officer of Related Party

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Amounts due to recorded owners or owners with a beneficial interest of more than 10 percent of the voting interests or officers of the company. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04(12))
-URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
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-Section 50
-Paragraph 1
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-Name Accounting Standards Codification
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-Section S99
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-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(17))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Receivables to be collected from (obligations owed to) related parties, net as of the balance sheet date where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
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-Name Accounting Standards Codification
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-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ 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.

+ References

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Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

No definition available.

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- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
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