Business Combinations, Goodwill and Intangible Assets Business Combinations, Goodwill and Intangible Assets - Purchase Price Allocation (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 22, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 204,481		$ 186,770	$ 171,535
Health Integrated, Inc.
Business Acquisition [Line Items]
Tangible Assets		$ 5,945
Liabilities		(7,193)
Goodwill		15,957
Total purchase price		23,549
Health Integrated, Inc. | Customer relationships
Business Acquisition [Line Items]
Identifiable Intangible Assets		6,760
Health Integrated, Inc. | Developed technology
Business Acquisition [Line Items]
Identifiable Intangible Assets		1,510
Health Integrated, Inc. | Trade names and trademarks
Business Acquisition [Line Items]
Identifiable Intangible Assets		$ 570