Acquisition - Consideration (Details) - USD ($) $ in Thousands		12 Months Ended
	Oct. 06, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Deferred consideration for acquisition of BNP Business			$ 0	$ 0
Net consideration		$ 14,451	$ 5,061	$ 0
Triage Business
Business Acquisition [Line Items]
Cash consideration	$ 399,798
Deferred consideration for acquisition of BNP Business		$ 220,550
Contingent consideration—BNP Business	19,700
Net consideration	$ 640,253