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Acquisitions - Narrative (Details) - USD ($) $ in Thousands			6 Months Ended
Acquisitions - Narrative (Details) - USD ($) $ in Thousands	Jul. 01, 2019	Jan. 02, 2019	Jun. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill			$ 29,458	$ 47,396
Benefit Consultants Group Inc.
Business Acquisition [Line Items]
Transaction value		$ 25,000
Finite-lived intangible assets acquired		16,200
Goodwill		$ 10,100
Minimum \| Benefit Consultants Group Inc.
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, useful lives			10 years
Maximum \| Benefit Consultants Group Inc.
Business Acquisition [Line Items]
Acquired finite-lived intangible assets, useful lives			16 years
Subsequent Event [Member] \| NTA
Business Acquisition [Line Items]
Transaction value	$ 425,000
Transaction value, share of adjusted earnings	$ 20,000