Acquisitions (Details) - USD ($) $ in Thousands					12 Months Ended
	Nov. 30, 2018	Aug. 07, 2018	May 01, 2018	Jan. 02, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Purchase price allocation:
Goodwill					$ 120,589	$ 171,563	$ 176,124
Acquired finite-lived intangible assets, weighted average useful life					5 years 2 months 12 days
TTi Global [Member] [Member]
Business Acquisition [Line Items]
Cash purchase price	$ 14,195
Fair value of contingent consideration	0
Working capital adjustment	(850)
Total purchase price	13,345
Purchase price allocation:
Cash	1,780
Accounts receivable and other assets	14,218
Fixed assets	300
Goodwill	4,655
Total assets	25,835
Accrued expenses	10,066
Deferred revenue	219
Deferred tax liability	2,205
Total liabilities	12,490
Net assets acquired	13,345
TTi Global [Member] [Member] | Marketing-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets	$ 454
Acquired finite-lived intangible assets, weighted average useful life	1 year
TTi Global [Member] [Member] | Customer-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets	$ 4,428
Acquired finite-lived intangible assets, weighted average useful life	9 years
TTi (Europe) Limited [Member] [Member]
Business Acquisition [Line Items]
Cash purchase price		$ 3,000
Fair value of contingent consideration		0
Working capital adjustment		0
Total purchase price		3,000
Purchase price allocation:
Cash		125
Accounts receivable and other assets		1,684
Fixed assets		9
Goodwill		2,179
Total assets		4,804
Accrued expenses		1,609
Deferred revenue		126
Deferred tax liability		69
Total liabilities		1,804
Net assets acquired		3,000
TTi (Europe) Limited [Member] [Member] | Marketing-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets		45
TTi (Europe) Limited [Member] [Member] | Customer-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets		$ 762
Acquired finite-lived intangible assets, weighted average useful life		9 years
IC Axon [Member]
Business Acquisition [Line Items]
Cash purchase price			$ 30,535
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High			3,500
Fair value of contingent consideration			905
Working capital adjustment			0
Total purchase price			31,440
Purchase price allocation:
Cash			538
Accounts receivable and other assets			3,110
Fixed assets			368
Goodwill			21,613
Total assets			36,233
Accrued expenses			983
Deferred revenue			979
Deferred tax liability			2,831
Total liabilities			4,793
Net assets acquired			31,440
IC Axon [Member] | Marketing-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets			$ 239
Acquired finite-lived intangible assets, weighted average useful life			3 years
IC Axon [Member] | Customer-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets			$ 10,365
Acquired finite-lived intangible assets, weighted average useful life			8 years
Hula Partners [Member] [Member]
Business Acquisition [Line Items]
Cash purchase price				$ 10,000
Fair value of contingent consideration				0
Working capital adjustment				0
Total purchase price				10,000
Purchase price allocation:
Cash				0
Accounts receivable and other assets				0
Fixed assets				0
Goodwill				8,527
Total assets				10,000
Accrued expenses				0
Deferred revenue				0
Deferred tax liability				0
Total liabilities				0
Net assets acquired				10,000
Hula Partners [Member] [Member] | Marketing-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets				$ 106
Acquired finite-lived intangible assets, weighted average useful life				2 years
Hula Partners [Member] [Member] | Customer-Related Intangible Assets [Member]
Purchase price allocation:
Intangible assets				$ 1,367
Acquired finite-lived intangible assets, weighted average useful life				4 years