INCOME TAXES (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) ongoing_tax_audit	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Net loss before tax	$ (70,430,000)	$ (83,118,000)	$ (64,544,000)
Statutory combined US federal and state tax rate (2012 - statutory combined Canadian federal and provincial tax rate)	34.00%	34.00%	34.00%
Statutory federal and provincial taxes	$ (23,946,000)	$ (28,260,000)	$ (21,945,000)
Effect of change in valuation allowance	(4,154,000)	28,446,000	22,350,000
Non-deductible share-based compensation	695,000	1,247,000	923,000
Tax credits	(2,563,000)	(2,906,000)	(2,430,000)
Share issue costs - temporary difference	0	(78,000)	(184,000)
Write off of Methylgene US NOL	307,000	0	0
Differential in income tax rates of foreign subsidiary	(169,000)	261,000	31,000
Change in tax rate	303,000	0	0
Tax Cuts and Jobs Act		0	0
Uncertain tax positions	646,000	3,921,000	1,961,000
Return to provision and other true-ups	368,000	(2,619,000)	(899,000)
Other differences	(56,000)	(12,000)	193,000
Income tax expense (benefit)	0	0	0
Deferred tax asset
Tangible and intangible depreciable assets	17,927,000	990,000
Stock compensation	4,976,000	6,635,000
Provisions	611,000	853,000
Net operating loss carry forwards	44,598,000	66,489,000
Capital loss carryforward	83,000	51,000
Scientific research and experimental development expenditures	5,467,000	5,531,000
Research and development tax credits	7,016,000	4,266,000
Total gross deferred tax assets	80,678,000	84,815,000
Less valuation allowance	(80,678,000)	(84,815,000)
Net deferred tax assets	0	0
Additional disclosures
Amount of increase in valuation allowance	4,100,000
Reconciliation of the beginning and ending gross amounts of unrecognized tax positions
Accrual for interest or penalties on tax matters	$ 0
Number of ongoing tax audits | ongoing_tax_audit	0
Tax Cuts And Jobs Act Of 2017, change in tax rate, deferred tax asset, expense	$ 28,569,000
Domestic Tax Authority
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax expense (benefit)	0	0	0
Canadian Federal
Additional disclosures
Scientific research and experimental development expenses deductible for income tax purposes	19,900,000	19,900,000
Net operating loss carry forwards (NOLs)	80,567,000
Reconciliation of the beginning and ending gross amounts of unrecognized tax positions
Unrecognized tax positions, beginning of year	1,095,000	509,000	42,000
Gross increase — current period tax positions	588,000	598,000	445,000
Gross decrease — prior period tax positions	0	(9,000)	(4,000)
Gross increase — prior period tax positions	11,000	0	26,000
Expiration of statute of limitations	(1,000)	(3,000)	0
Unrecognized tax positions, end of year	1,693,000	1,095,000	509,000
Canadian Federal | 2030
Additional disclosures
Net operating loss carry forwards (NOLs)	5,907,000
Canadian Federal | 2031
Additional disclosures
Net operating loss carry forwards (NOLs)	7,059,000
Canadian Federal | 2032
Additional disclosures
Net operating loss carry forwards (NOLs)	13,308,000
Canadian Federal | 2033
Additional disclosures
Net operating loss carry forwards (NOLs)	18,623,000
Canadian Federal | 2034
Additional disclosures
Net operating loss carry forwards (NOLs)	32,401,000
Canadian Federal | 2035
Additional disclosures
Net operating loss carry forwards (NOLs)	1,084,000
Canadian Federal | 2036
Additional disclosures
Net operating loss carry forwards (NOLs)	777,000
Canadian Federal | 2037
Additional disclosures
Net operating loss carry forwards (NOLs)	1,408,000
Canadian Provincial
Additional disclosures
Scientific research and experimental development expenses deductible for income tax purposes	21,600,000	21,600,000
Net operating loss carry forwards (NOLs)	79,947,000
Reconciliation of the beginning and ending gross amounts of unrecognized tax positions
Unrecognized tax positions, beginning of year	7,333,000	2,274,000	18,000
Gross increase — current period tax positions	227,000	195,000	259,000
Gross decrease — prior period tax positions	(3,000)	0	(3,000)
Gross increase — prior period tax positions	0	4,866,000	2,000,000
Expiration of statute of limitations	(1,000)	(2,000)	0
Unrecognized tax positions, end of year	7,556,000	$ 7,333,000	$ 2,274,000
Canadian Provincial | 2030
Additional disclosures
Net operating loss carry forwards (NOLs)	5,985,000
Canadian Provincial | 2031
Additional disclosures
Net operating loss carry forwards (NOLs)	7,066,000
Canadian Provincial | 2032
Additional disclosures
Net operating loss carry forwards (NOLs)	12,433,000
Canadian Provincial | 2033
Additional disclosures
Net operating loss carry forwards (NOLs)	19,385,000
Canadian Provincial | 2034
Additional disclosures
Net operating loss carry forwards (NOLs)	31,809,000
Canadian Provincial | 2035
Additional disclosures
Net operating loss carry forwards (NOLs)	1,084,000
Canadian Provincial | 2036
Additional disclosures
Net operating loss carry forwards (NOLs)	777,000
Canadian Provincial | 2037
Additional disclosures
Net operating loss carry forwards (NOLs)	1,408,000
US Federal
Additional disclosures
Net operating loss carry forwards (NOLs)	110,283,000
US Federal | 2030
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US Federal | 2031
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US Federal | 2032
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US Federal | 2033
Additional disclosures
Net operating loss carry forwards (NOLs)	2,225,000
US Federal | 2034
Additional disclosures
Net operating loss carry forwards (NOLs)	7,276,000
US Federal | 2035
Additional disclosures
Net operating loss carry forwards (NOLs)	53,359,000
US Federal | 2036
Additional disclosures
Net operating loss carry forwards (NOLs)	23,379,000
US Federal | 2037
Additional disclosures
Net operating loss carry forwards (NOLs)	24,044,000
US Federal | Research Tax Credit Carryforward
Additional disclosures
Tax credit carryforward	7,200,000
US State
Additional disclosures
Net operating loss carry forwards (NOLs)	77,344,000
US State | 2030
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | 2031
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | 2032
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | 2033
Additional disclosures
Net operating loss carry forwards (NOLs)	2,232,000
US State | 2034
Additional disclosures
Net operating loss carry forwards (NOLs)	22,162,000
US State | 2035
Additional disclosures
Net operating loss carry forwards (NOLs)	52,950,000
US State | 2036
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | 2037
Additional disclosures
Net operating loss carry forwards (NOLs)	0
US State | Research Tax Credit Carryforward
Additional disclosures
Tax credit carryforward	$ 2,900,000