Nature of Operations (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended		12 Months Ended
	Aug. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2018
Liquidity
Net loss attributable to common shareholders				$ 130,200	$ 57,600	$ 55,800
Accumulated deficit		$ 1,224,365		1,178,636
Net cash used in operating activities		45,179	$ 58,335
Net outflows from fluctuations in working capital and other assets and liabilities		10,700
Noncash gains		11,200
Cash and cash equivalents		15,035		24,828
Net working capital		8,200		$ 3,900
Net cash used in investing activities		(16,360)	(20,545)
Net cash provided by financing activities		48,942	32,208
Proceeds from Issuance of Debt		95,856
Proceeds from borrowing of long-term debt			621
Repayments of Long-term Debt		5,721	$ 1,278
Purchase of capped call and common stock forward		43,500
Sale or leaseback agreements
Liquidity
Remaining lease payments		28,200
Amended sale or leaseback agreements
Liquidity
Remaining lease payments		24,800
Amended sale or leaseback agreements | Subsequent event
Liquidity
Additional amount borrowed	$ 16,000
Convertible Senior Notes
Liquidity
Proceeds from Issuance of Debt		52,356
Principal amount		100,000
Interest rate (as a percent)							5.50%
Purchase of capped call and common stock forward		$ 43,500