CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Available-for-sale debt securities, amortized cost	$ 218,596,000	$ 335,206,000
Available-for-sale debt securities, allowance for credit losses	$ 0	$ 0
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock shares authorized (in shares)	100,000,000	100,000,000
Common stock shares issued (in shares)	50,902,874	43,088,921
Common stock shares outstanding (in shares)	50,902,874	43,088,921