Acquisitions - Advantage (Details) - USD ($) $ in Thousands				3 Months Ended		6 Months Ended	12 Months Ended			30 Months Ended
	Apr. 03, 2019	Jul. 28, 2017	Jul. 01, 2017	Mar. 31, 2019	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Feb. 28, 2019
Business Acquisition [Line Items]
Cash consideration							$ 0	$ 1,930	$ 85,977
Proceeds from issuance of debt							0	0	62,000
Acquisition related costs							$ 311	$ 491	1,975
Advantage
Business Acquisition [Line Items]
Cash consideration			$ 86,600
Cash acquired			2,800
Purchase price			88,000
Net working capital adjustment			600
Reimbursement from working capital adjustment settled					$ 800
Contingent liability											$ 100
Release of remaining contingent liability										$ 500
Escrow payment related to tax liabilities			14,500
Escrow payment related to post-close liabilities			7,500
Release of escrow to seller	$ 2,900	$ 7,300		$ 7,000
Escrow deposit related to tax liabilities		$ 7,200
Escrow disbursed to pay taxes	$ 4,300
Escrow deposit related to post close liabilities				$ 500
Consideration transferred, available cash			19,900
Revenue since acquisition						$ 47,000
Net income since acquisition						$ 3,800
Assets acquired			$ 29,900
Weighted average useful life of assets acquired			10 years
Goodwill expected to be deductible			$ 43,600
Acquisition related costs									$ 2,000
Deferred Consideration Transferred | Advantage
Business Acquisition [Line Items]
Contingent liability			$ 600
Period of deferred consideration			20 months
Credit Agreement
Business Acquisition [Line Items]
Proceeds from issuance of debt			$ 66,900
Term Loan, net | Incremental Term Loan
Business Acquisition [Line Items]
Proceeds from issuance of debt			40,000
Trade names | Advantage
Business Acquisition [Line Items]
Assets acquired			$ 4,500
Weighted average useful life of assets acquired			10 years
Customer relationships | Advantage
Business Acquisition [Line Items]
Assets acquired			$ 13,800
Weighted average useful life of assets acquired			10 years
Databases | Advantage
Business Acquisition [Line Items]
Assets acquired			$ 11,300
Weighted average useful life of assets acquired			10 years
Non-compete agreements | Advantage
Business Acquisition [Line Items]
Assets acquired			$ 300
Weighted average useful life of assets acquired			5 years