Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Dec. 31, 2016	Mar. 31, 2016	Mar. 31, 2018	Sep. 30, 2016	Mar. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Litigation accrual					$ 0	$ 0
Indenix [Member]
Loss Contingencies [Line Items]
Damages awarded	$ 2,540
Motion invalidated past damages, amount			$ 2,540
Merck '499 and '712 patents
Loss Contingencies [Line Items]
Damages awarded		$ 200
Damages awarded but dismissed, amount				$ 200