Property and Equipment, Net - Schedule of Depreciation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
General and administrative expense	$ 15,060	$ 11,290	$ 32,255	$ 18,863
Research and development expense	4,764	2,915	10,116	8,488
Total depreciation and amortization expense			1,446	672
Depreciation [Member]
General and administrative expense	407	9	764	9
Research and development expense	363	345	682	663
Total depreciation and amortization expense	$ 770	$ 354	$ 1,446	$ 672