Nature of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended		12 Months Ended
	Nov. 30, 2018	Sep. 30, 2018	Sep. 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		$ 1,243,430		1,178,636
Net cash used in operating activities		41,642	$ 81,294
Net outflows from fluctuations in working capital and other assets and liabilities		1,900
Non-cash gains		17,700
Cash and cash equivalents		13,825		24,828
Net working capital		6,700		$ 3,900
Net cash used in investing activities		(17,528)	(28,291)
Net cash provided by financing activities		53,216	65,190
Proceeds from Issuance of Debt		95,856
Proceeds from borrowing of long-term debt			20,147
Repayments of Long-term Debt		11,944	$ 4,261
Purchase of capped call and common stock forward		43,500
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
Subsequent event | Series E Redeemable Convertible Preferred Stock
Liquidity
Shares issued (in shares)	35,000
Redeemable stock issued, stated value (in dollars per share)	$ 0.01
Aggregate proceeds from issuance of preferred stock	$ 31,000
Sale or leaseback agreements
Liquidity
Remaining lease payments		53,500
Amended sale or leaseback agreements
Liquidity
Remaining lease payments		$ 51,900