Stockholders' equity - Schedule of convertible preferred and common stock (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Convertible preferred stock:
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding, beginning of period	125	125	125	3,459
Shares converted	0	0	0	(3,334)
Shares outstanding, end of period	125	125	125	125
Common stock:
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding, beginning of period	131,289	93,763	98,796	75,481
Shares converted	0	0	0	(3,334)
Common stock issued in connection with public offering (in shares)	0	786	23,058	11,136
Common stock issued on exercise of stock options, net (in shares)	245	71	553	411
Common stock issued pursuant to vesting of RSUs (in shares)	1,322	476	4,803	1,721
Common stock issued pursuant to exercises of warrants (in shares)	54	10	202	29
Common stock issued pursuant to employee stock purchase plan (in shares)	0	0	342	235
Common stock issued pursuant to business combinations (in shares)	358	1,409	5,514	4,168
Shares outstanding, end of period	133,268	96,515	133,268	96,515