Acquisitions (Details) - USD ($) $ in Thousands				1 Months Ended	12 Months Ended
	Aug. 31, 2017	Apr. 01, 2017	Feb. 01, 2017	Jul. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Purchase price allocation:
Goodwill					$ 171,563	$ 176,124	$ 144,835
Acquired finite-lived intangible assets, weighted average useful life					5 years 8 months
Contingent Consideration Liability, Payments					$ 0
Contingent Consideration Payments					0	$ 0	$ 4,657
YouTrain [Member]
Business Acquisition [Line Items]
Cash purchase price	$ 4,898
Fair value of contingent consideration	0
Working capital adjustment	180
Total purchase price	5,078
Purchase price allocation:
Cash	673
Accounts receivable and other assets	234
Fixed assets	215
Goodwill	3,268
Total assets	5,703
Accrued expenses	348
Deferred revenue	28
Deferred tax liability	249
Total liabilities	625
Net assets acquired	5,078
YouTrain [Member] | Marketing-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets	0
YouTrain [Member] | Technology-Based Intangible Assets [Member]
Purchase price allocation:
Intangible assets	0
YouTrain [Member] | Customer-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets	$ 1,313
Acquired finite-lived intangible assets, weighted average useful life	5 years
CLS [Member] [Member]
Business Acquisition [Line Items]
Cash purchase price	$ 436
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	2,200
Fair value of contingent consideration	888
Working capital adjustment	0
Total purchase price	1,324
Purchase price allocation:
Cash	0
Accounts receivable and other assets	0
Fixed assets	0
Goodwill	1,090
Total assets	1,343
Accrued expenses	19
Deferred revenue	0
Deferred tax liability	0
Total liabilities	19
Net assets acquired	1,324
CLS [Member] [Member] | Marketing-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets	0
CLS [Member] [Member] | Technology-Based Intangible Assets [Member]
Purchase price allocation:
Intangible assets	0
CLS [Member] [Member] | Customer-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets	$ 253
Acquired finite-lived intangible assets, weighted average useful life	3 years
Emantras [Member]
Business Acquisition [Line Items]
Cash purchase price		$ 3,191
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High		300
Fair value of contingent consideration		220
Working capital adjustment		0
Total purchase price		3,411
Purchase price allocation:
Cash		0
Accounts receivable and other assets		0
Fixed assets		50
Goodwill		3,156
Total assets		4,024
Accrued expenses		558
Deferred revenue		55
Deferred tax liability		0
Total liabilities		613
Net assets acquired		3,411
Emantras [Member] | Marketing-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets		0
Emantras [Member] | Technology-Based Intangible Assets [Member]
Purchase price allocation:
Intangible assets		0
Emantras [Member] | Customer-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets		$ 818
Acquired finite-lived intangible assets, weighted average useful life		4 years
McKinney Rogers [Member]
Business Acquisition [Line Items]
Cash purchase price			$ 3,259
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High			$ 18,000
Number of Twelve-Month Earnings Target Measurement Periods			3 years
Business Combination, Contingent Consideration, Term of Earnings Targets			5 months
Fair value of contingent consideration			$ 4,505
Working capital adjustment			0
Total purchase price			7,764
Purchase price allocation:
Cash			0
Accounts receivable and other assets			0
Fixed assets			0
Goodwill			5,196
Total assets			8,674
Accrued expenses			44
Deferred revenue			866
Deferred tax liability			0
Total liabilities			910
Net assets acquired			7,764
Contingent Consideration Liability, Payments					$ 0
McKinney Rogers [Member] | Marketing-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets			$ 121
Acquired finite-lived intangible assets, weighted average useful life			3 years
McKinney Rogers [Member] | Technology-Based Intangible Assets [Member]
Purchase price allocation:
Intangible assets			$ 2,704
McKinney Rogers [Member] | Customer-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets			$ 653
Acquired finite-lived intangible assets, weighted average useful life			5 years
Target Earnings Measurement Period One [Member] | McKinney Rogers [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Amount Contingent Upon Achievement of Certain Earnings Targets			$ 6,000
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				$ 1,000
Target Earnings Measurement Period Two [Member] | McKinney Rogers [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Amount Contingent Upon Achievement of Certain Earnings Targets			$ 12,000