Capital Stock - Textual (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Stock options exercised (shares)	78,859	40,582
Weighted average exercise price of stock options exercised (usd per share)	$ 6.49	$ 2.45
Proceeds from exercises of stock options	$ 434	$ 99