Stockholders' Equity - Common Stock, Resale Registration Statement, and Follow-on Public Offering (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 31, 2019
Class of Stock [Line Items]
Stock issued during period (in shares)	441,410
Stock issued during period	$ 2,500
Reclassified out of accumulated other comprehensive loss for realized gains or losses on available for sale securities	0	$ 0	$ 0
Retained earnings subject to restriction	$ 9,200	$ 9,000
Minimum
Class of Stock [Line Items]
Accumulated profits	10.00%
Vendor
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)				103,734
Common stock, capital shares reserved for future issuance				$ 4,500
Employee stock options
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	7,720,441
Employee stock purchase plan
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)	1,717,211