Debt, Net - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Convertible Notes
Debt Instrument [Line Items]
Interest expense—stated coupon rate	$ 5,571	$ 3,651	$ 10,908	$ 7,293
Interest expense—amortization of debt discount	3,244	2,464	6,365	4,892
Total interest expense	8,815	6,115	17,273	12,185
Cabot senior secured notes | Senior Notes
Debt Instrument [Line Items]
Total interest expense	23,759	21,358	47,533	42,842
Interest expense | Cabot senior secured notes | Senior Notes
Debt Instrument [Line Items]
Interest expense—stated coupon rate	23,678	21,239	47,333	42,839
Interest expense—amortization of debt discount	$ 81	$ 119	$ 200	$ 3