Capital Stock - Textual (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Equity [Abstract]
Stock options exercised (shares)	218,572	78,859
Weighted average exercise price of stock options exercised (usd per share)	$ 3.55	$ 6.49
Proceeds from exercises of stock options	$ 776	$ 434

Number of share options (or share units) exercised during the current period.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration