Fair Value Measurements - Derivative Warrant Liability (Details) $ / shares in Units, $ in Thousands		3 Months Ended		12 Months Ended
	Aug. 07, 2017 warrant $ / shares shares	Mar. 31, 2019 USD ($) $ / shares	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) $ / shares
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Plan of reorganization, number of warrants Issued | warrant	118,137
Exercise price of warrants (in USD per warrant) | $ / shares	$ 39.82	$ 39.82		$ 39.82
Expiration term (in years)	7 years
Par value of successor common stock (USD per share) | $ / shares	$ 0.01
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period		$ 34	$ 477	$ 477
Issuance of warrants		0		0
Adjustments to estimated fair value		41	$ 192	(443)
Balance at end of period		$ 75		$ 34
Common Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Warrant exercisable for common stock | shares	1
2018 Notes
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest Rate	9.875%