Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 85,114	$ 80,747	$ 16,155	$ 80,747	$ 20,952
Other comprehensive income, net	355	10	0	365	0
Ending balance	81,752	85,114	11,391	81,752	11,391
Gross realized gains, available for sale securities	23
Gross realized losses, available for sale securities	6
Proceeds from sale of debt securities, available-for-sale	9,404
Unrealized gains (losses) on short-term investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(17)	(27)		(27)
Other comprehensive income (loss) before reclassifications	352	10
Net losses (gains) reclassified from accumulated other comprehensive loss	3
Other comprehensive income, net	355	10
Ending balance	338	(17)		338
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(17)	(27)	0	(27)	0
Other comprehensive income (loss) before reclassifications	352	10
Net losses (gains) reclassified from accumulated other comprehensive loss	3
Other comprehensive income, net	355	10
Ending balance	$ 338	$ (17)	$ 0	$ 338	$ 0