Goodwill and Intangible Assets - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Accumulated impairment loss	$ 8,300,000
Aggregate amortization expense	26,800,000	$ 19,300,000	$ 14,800,000
Intangible asset impairment charges	809,000	$ 0	$ 0
Distal Access, LLC
Finite-Lived Intangible Assets [Line Items]
Intangible asset impairment charges	$ 809,000