Nature of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended			3 Months Ended			6 Months Ended		12 Months Ended
	Mar. 08, 2018	Jul. 21, 2017	Apr. 30, 2019	Mar. 31, 2019	Nov. 30, 2018	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018
Liquidity
Net loss attributable to common shareholders						$ 18,587		$ 25,881	$ 52,525	$ 45,729	$ 78,200	$ 130,200	$ 57,600
Accumulated deficit						1,312,815			1,312,815		1,260,290
Net cash used in operating activities									48,488	45,179
Net loss attributable to the Company						(18,561)		$ (25,868)	(52,499)	(45,703)
Net outflows from fluctuations in working capital and other assets and liabilities									18,500
Non-cash charges									22,500
Cash and cash equivalents						19,845			19,845		38,602
Net working capital						50,200			50,200		9,200
Net cash used in investing activities									(6,316)	(16,360)
Net cash provided by financing activities									80,026	48,942
Sale of common stock				$ 23,500					28,265
Proceeds from borrowing of long-term debt									99,546
Increase in cash flows from new finance obligations									25,609
Proceeds from issuance of debt										95,856
Purchase of capped call and common stock forward										43,500
Remaining lease payments						121,300			121,300
Security on lease						122,800			122,800
Letter of credit						82,900			82,900
Repayments of finance obligations									56,070	$ 17,760
Number of common stock sold				10,000,000
Share price (in dollars per share)				$ 2.35			$ 2.35
Additional Master Lease Agreements
Liquidity
Remaining lease payments						26,300			26,300
Wells Fargo
Liquidity
Remaining lease payments						84,700			84,700
Letter of credit						28,500			28,500		$ 28,500
Convertible Senior Notes
Liquidity
Principal amount	$ 100,000					$ 100,000			$ 100,000					$ 100,000
Interest rate (as a percent)														5.50%
Proceeds from issuance of debt	52,356
Purchase of capped call and common stock forward	$ 43,500
Share price (in dollars per share)						$ 2.25			$ 2.25
Series E Redeemable Convertible Preferred Stock
Liquidity
Shares issued (in shares)					35,000
Redeemable stock issued, stated value (in dollars per share)					$ 0.01	$ 0.01			$ 0.01		$ 0.01
Aggregate proceeds from issuance of preferred stock					$ 30,900
Loan and security agreement | Generate Lending, LLC
Liquidity
Repayments of finance obligations		$ 17,600					$ 17,600
Termination of certain equipment leases		$ 50,300					50,300
Loan and security agreement | Generate Lending, LLC | Secured term loan facility
Liquidity
Proceeds from borrowing of long-term debt			$ 15,000	$ 85,000			85,000
Principal amount				$ 100,000			$ 100,000
At Market Issuance Sales Agreement
Liquidity
Sale of common stock						$ 5,500
Number of common stock sold						2,100,000