Property and Equipment, Net - Schedule of Depreciation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
General and administrative expense	$ 17,195	$ 7,573
Research and development expense	5,352	5,572
Total depreciation and amortization expense	676	318
Depreciation [Member]
General and administrative expense	357
Research and development expense	319	318
Total depreciation and amortization expense	$ 676	$ 318