Share Capital - Stock Option Activity (Details) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2018 $ / shares	Dec. 31, 2016 USD ($)
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options Outstanding, Beginning balance		2,339,905		1,910,823
Number of Options, Granted		706,600		620,950
Number of Options, Exercised	[1]	(251,163)		(71,006)
Number of Options, Forfeited, cancelled or expired		(123,436)		(120,862)
Number of Options Outstanding, Ending balance		2,671,906		2,339,905
Number of Options Exercisable		1,566,435	1,566,435
Weighted Average Exercise Price Outstanding, Beginning balance | (per share)		$ 7.41	$ 9.32	$ 7.32	$ 9.84
Weighted Average Exercise Price, Granted | (per share)		5.19	6.73	6.69	8.69
Weighted Average Exercise Price, Exercised | (per share)	[1]	3.53	4.57	2.86	3.72
Weighted Average Exercise Price, Forfeited, cancelled and expired | (per share)		10.50	13.61	6.98	9.06
Weighted Average Exercise Price Outstanding, Ending balance | (per share)		6.96	$ 9.49	$ 7.41	$ 9.32
Weighted Average Exercise Price, Exercisable Ending balance | (per share)		$ 7.84	$ 7.84			$ 10.70
Aggregate Intrinsic Value, Outstanding | $		$ 3,483	$ 3,483	$ 159	$ 159		$ 4,464
Aggregate Intrinsic Value, Exercised | $	[1]	1,028		$ 108
Aggregate Intrinsic Value, Exercisable, Ending balance | $		$ 2,198	$ 2,198

[1] During the year ended December 31, 2018, 49,502 (2017 – 63,425) stock options were exercised for the same number of common shares in exchange for cash. In the same period, the Company issued 106,474 (2017 – 4,405) common shares for the cashless exercise of 201,661 (2017 – 7,581) stock options.