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Acquisitions - 2018 Acquisitions summary of Fair Value of the Consideration (Details) - USD ($) $ in Thousands		2 Months Ended	12 Months Ended
	Jul. 02, 2018	Jul. 02, 2018	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	May 15, 2018
Business Acquisition [Line Items]
Goodwill			$ 149,524	$ 285,214	$ 214,513
StudyBlue, Inc.
Business Acquisition [Line Items]
Cash	$ 152	$ 152
Accounts receivable	288	288
Other acquired assets	151	151
Acquired intangible assets	7,100	7,100
Total identifiable assets acquired	7,691	7,691
Liabilities assumed	(1,309)	(1,309)
Net identifiable assets acquired	6,382	6,382
Goodwill	13,996	13,996
Total fair value of purchase consideration	$ 20,378	$ 20,378
Weighted average amortization period	57 months
WriteLab, Inc.
Business Acquisition [Line Items]
Cash						$ 82
Accounts receivable						194
Other acquired assets						0
Acquired intangible assets						4,450
Total identifiable assets acquired						4,726
Liabilities assumed						(897)
Net identifiable assets acquired						3,829
Goodwill						10,677
Total fair value of purchase consideration						14,506
Acquisition related expenses			1,000
Weighted average amortization period		96 months
WriteLab, Inc. And StudyBlue, Inc.
Business Acquisition [Line Items]
Cash			234
Accounts receivable			482
Other acquired assets			151
Acquired intangible assets			11,550
Total identifiable assets acquired			12,417
Liabilities assumed			(2,206)
Net identifiable assets acquired			10,211
Goodwill			24,673
Total fair value of purchase consideration			$ 34,884
Weighted average amortization period			72 months
Trade name \| StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets	$ 140	$ 140
Weighted average amortization period	12 months
Trade name \| WriteLab, Inc.
Business Acquisition [Line Items]
Acquired intangible assets						0
Weighted average amortization period		0 years
Trade name \| WriteLab, Inc. And StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets			$ 140
Weighted average amortization period			12 months
Domain names \| StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets	$ 180	$ 180
Weighted average amortization period	12 months
Domain names \| WriteLab, Inc.
Business Acquisition [Line Items]
Acquired intangible assets						0
Weighted average amortization period		0 years
Domain names \| WriteLab, Inc. And StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets			$ 180
Weighted average amortization period			12 months
Non-compete agreements \| StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets	$ 220	$ 220
Weighted average amortization period	36 months
Non-compete agreements \| WriteLab, Inc.
Business Acquisition [Line Items]
Acquired intangible assets						0
Weighted average amortization period		0 years
Non-compete agreements \| WriteLab, Inc. And StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets			$ 220
Weighted average amortization period			36 months
Developed technology \| StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets	$ 1,340	$ 1,340
Weighted average amortization period	60 months
Developed technology \| WriteLab, Inc.
Business Acquisition [Line Items]
Acquired intangible assets						4,450
Weighted average amortization period		96 months
Developed technology \| WriteLab, Inc. And StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets			$ 5,790
Weighted average amortization period			88 months
Content library \| StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets	$ 5,220	$ 5,220
Weighted average amortization period	60 months
Content library \| WriteLab, Inc.
Business Acquisition [Line Items]
Acquired intangible assets						$ 0
Weighted average amortization period		0 years
Content library \| WriteLab, Inc. And StudyBlue, Inc.
Business Acquisition [Line Items]
Acquired intangible assets			$ 5,220
Weighted average amortization period			60 months