Fair Value Measurements - Schedule of reconciliation of opening and closing balances for fair value measurements categorized within Level 3 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Contingent Purchase Price Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 5,603	$ 3,686
Additions		1,300
Payments/Settlements	(280)	(152)
Accretion expense	967	887
Valuation gain for the period	(922)	(118)
Ending balance	5,368	5,603
Convertible Notes Derivative Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	27,532	33,337
Additions		0
Payments/Settlements	(25,951)	0
Accretion expense	0	0
Valuation gain for the period	(1,581)	(5,805)
Ending balance	$ 0	$ 27,532