Debt (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		25 Months Ended
	Aug. 08, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017	Dec. 31, 2017	Aug. 14, 2017	Sep. 30, 2015
Debt Instrument [Line Items]
Common stock, shares issued		54,251,000			54,040,000
Interest expense		$ 2,389	$ 183
Interest expense		2,000
Amortization of debt discount		98
Debt discount		600
Unamortized debt discount		1,900
Net carrying amount		73,138			$ 73,065
Line Of Credit-UBS
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 50,000
Outstanding balance		50,100
Accrued interest		$ 300		$ 1,100
Line Of Credit-UBS | 30-day LIBOR
Debt Instrument [Line Items]
Spread on interest rate (as a percent)		1.10%
2017 Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 100,000
Available borrowing capacity	75,000
Remaining borrowing capacity	$ 25,000
Additional interest in the event of default (as a percent)	3.00%
Debt instrument, term	84 months
Common stock, shares issued						300,000
Debt instrument, fee amount	$ 2,400
Stock price	$ 8.16
Payments of debt issuance costs	$ 300
Debt discount	$ 2,700
2017 Term Loan | Minimum
Debt Instrument [Line Items]
Prepayment premium (as a percent)	2.50%
2017 Term Loan | Maximum
Debt Instrument [Line Items]
Prepayment premium (as a percent)	12.50%
2017 Term Loan | Base Rate
Debt Instrument [Line Items]
Spread on interest rate (as a percent)	8.75%
Base interest rate (as a percent)	1.00%
2017 Term Loan | Direct reduction from outstanding debt balance
Debt Instrument [Line Items]
Debt instrument, fee amount	$ 2,000	$ 1,900