Convertible Preferred Stock (Details) $ / shares in Units, $ in Thousands			6 Months Ended
	Jan. 30, 2018 USD ($) $ / shares shares	Jan. 23, 2018	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($)	Jan. 31, 2018 shares
Class of Stock [Line Items]
Preferred stock authorized (in shares) | shares			1,000,000.0		1,000,000
Transaction fees on issuance of stock			$ 70	$ 92
Gross proceeds from issuance of preferred stock, net of transaction fees			9,723	$ 0
Liquidation value			$ 200
Liquidation value (in dollars per share) | $ / shares			$ 20.83
Series A Preferred Stock
Class of Stock [Line Items]
Conversion ratio for convertible preferred stock			100.90817
Securities Purchase Agreement | Series A Preferred Stock
Class of Stock [Line Items]
Number of shares issued (in shares) | shares	9,926
Price per share (in dollars per share) | $ / shares	$ 1,000
Consideration received on transaction	$ 9,900
Transaction fees on issuance of stock	$ 200
Gross proceeds from issuance of preferred stock, net of transaction fees			$ 9,900
Dividend rate (as percent)	5.00%	5.00%