Stock-based Compensation - Stock Option Activity (Details)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
OnCore Option Plan
Number of optioned common shares
Balance - Number of optioned common shares (in shares)	139,290
Options exercised (in shares)	(40,000)
Options forfeited, canceled or expired (in shares)	0
Balance - Number of optioned common shares (in shares)	99,290
Weighted average exercise price
Balance - Weighted average exercise price (in CAD and USD per share) | $ / shares	$ 0.56
Options exercised - Weighted average exercise price (in CAD and USD per share) | $ / shares	0.58
Options forfeited, canceled or expired - Weighted average exercise price (in CAD and USD per share) | $ / shares	0.00
Balance - Weighted average exercise price (in CAD and USD per share) | $ / shares	$ 0.56
Arbutus Plans
Number of optioned common shares
Options forfeited, canceled or expired (in shares)	(1,016,995)
Weighted average exercise price
Options forfeited, canceled or expired - Weighted average exercise price (in CAD and USD per share) | $ / shares	$ 6.98
Stock Option
Number of optioned common shares
Balance - Number of optioned common shares (in shares)	8,576,584
Stock Option | Arbutus Plans
Number of optioned common shares
Balance - Number of optioned common shares (in shares)	6,331,088
Options granted (in shares)	3,018,000
Options exercised (in shares)	(83,000)
Options vested (in shares)	0
Balance - Number of optioned common shares (in shares)	8,249,093
Weighted average exercise price
Balance - Weighted average exercise price (in CAD and USD per share) | $ / shares	$ 6.05
Options granted - Weighted average exercise price (in CAD and USD per share) | $ / shares	3.41
Options exercised - Weighted average exercise price (in CAD and USD per share) | $ / shares	3.25
Options vested (USD per share) | $ / shares	0.00
Balance - Weighted average exercise price (in CAD and USD per share) | $ / shares	$ 5.00
Vested Stock Options | Arbutus Plans
Number of optioned common shares
Balance - Number of optioned common shares (in shares)	2,620,542
Options granted (in shares)	0
Options exercised (in shares)	(83,000)
Options forfeited, canceled or expired (in shares)	(477,848)
Options vested (in shares)	(2,234,955)
Balance - Number of optioned common shares (in shares)	4,294,649
Non-Vested Stock Options | Arbutus Plans
Number of optioned common shares
Balance - Number of optioned common shares (in shares)	3,710,546
Options granted (in shares)	3,018,000
Options exercised (in shares)	0
Options forfeited, canceled or expired (in shares)	(539,147)
Options vested (in shares)	(2,234,955)
Balance - Number of optioned common shares (in shares)	3,954,444
Weighted average exercise price
Balance - Weighted average exercise price (in CAD and USD per share) | $ / shares	$ 3.39
Options granted - Weighted average exercise price (in CAD and USD per share) | $ / shares	2.43
Options exercised - Weighted average exercise price (in CAD and USD per share) | $ / shares	0.00
Options forfeited, canceled or expired - Weighted average exercise price (in CAD and USD per share) | $ / shares	3.24
Options vested (USD per share) | $ / shares	3.10
Balance - Weighted average exercise price (in CAD and USD per share) | $ / shares	$ 2.86
Equivalent number of Company common shares | OnCore Option Plan
Number of optioned common shares
Balance - Number of optioned common shares (in shares)	140,273
Options exercised (in shares)	(40,282)
Options forfeited, canceled or expired (in shares)	0
Balance - Number of optioned common shares (in shares)	99,991