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Share Based Payments - Summary of Stock Option Activity (Detail)
$ / shares in Units, $ in Thousands, $ in Millions
3 Months Ended
Mar. 31, 2018
USD ($)
shares
Mar. 31, 2018
CAD ($)
$ / shares
shares
Mar. 31, 2017
USD ($)
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Number of Options, Beginning balance outstanding | shares 2,448,646 2,448,646  
Number of Options, Exercised | shares (80,000) (80,000)  
Number of Options, Ending balance outstanding | shares 2,368,646 2,368,646  
Number of Options, Exercisable | shares   1,371,739  
Weighted Average Exercise Price, Beginning balance outstanding | $ / shares   $ 7.35  
Weighted Average Exercise Price, Exercised | $ / shares   3.00  
Weighted Average Exercise Price, Ending balance outstanding | $ / shares   7.50  
Weighted Average Exercise Price, Exercisable | $ / shares   $ 5.85  
Aggregate Intrinsic Value, Beginning balance outstanding | $   $ 21,089  
Aggregate Intrinsic Value, Exercised $ 0.6 560 $ 0.1
Aggregate Intrinsic Value, Ending balance outstanding | $   13,119  
Aggregate Intrinsic Value, Exercisable | $   $ 9,934