Shareholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Thousands					3 Months Ended			120 Months Ended
	Jan. 27, 2020 USD ($) $ / shares shares	Jun. 24, 2019 USD ($) $ / shares shares	Jun. 07, 2018	Jul. 14, 2006	Mar. 31, 2020 USD ($) $ / shares shares	Mar. 31, 2020 CAD ($) shares	Mar. 31, 2019 USD ($)	Dec. 31, 2028	Dec. 31, 2019 USD ($) shares
Subsidiary or Equity Method Investee [Line Items]
Shares issue price (in dollars per share) | $ / shares	$ 46.50	$ 18.00
Underwriting discounts, commissions and offering expenses | $	$ 19,900,000
Preferred stock, shares issued (in shares)					0				0
Preferred stock, shares outstanding (in shares)					0				0
Shares granted with respect to maximum fixed amount equal, percentage				20.00%
Options granted under original plan exercisable period					10 years	10 years
Shares available for issuance under the Original Plan vesting period				4 years
Proceeds from stock options exercised					$ 1,447,000	$ 1,946
Unamortized compensation expense related to unvested options					$ 35,650,000	$ 50,598
Remaining unamortized compensation expense, weighted-average period					1 year 11 months 1 day	1 year 11 months 1 day
Total amount contributed by ESPP participants | $					$ 357,000				$ 435,000
Offering
Subsidiary or Equity Method Investee [Line Items]
Number of shares issued (in shares)	5,824,729	7,013,892
Pre funded warrants issued in lieu of common shares to underwriters (in shares)	1,075,271	4,166,690
Warrants issued price (in dollars per share) | $ / shares	$ 46.4999	$ 17.9999
Net proceeds from issuance | $	$ 300,900,000	$ 188,000,000.0
Underwriting discounts, commissions and offering expenses | $		$ 13,300,000
Warrant exercise price (in dollars per share) | $ / shares	$ 0.0001	$ 0.0001
Over-Allotment Option
Subsidiary or Equity Method Investee [Line Items]
Number of shares issued to underwriters (in shares)	900,000	1,458,336
Restricted Share Units (RSUs)
Subsidiary or Equity Method Investee [Line Items]
Shares available for issuance under the Original Plan vesting period					3 years	3 years
Grants in period (in shares)					71,879,000	71,879,000
Grant date fair value (in dollars per share) | $ / shares					$ 2,530,000
Compensation charge | $					$ 91,000		$ 0
U.S Dollar Under the New Option Stock Plan
Subsidiary or Equity Method Investee [Line Items]
Shares granted with respect to maximum fixed amount equal, percentage			20.00%
Shares available for issuance under the Original Plan vesting period					10 years	10 years
Maximum number of common shares reserved for issuance (in shares)					8,654,682
Shares issuable upon exercise of stock options (in shares)					6,106,531
Employees Stock Purchase Plan
Subsidiary or Equity Method Investee [Line Items]
Share-based compensation arrangement by share-based payment award, plan modification, description and terms					On June 7, 2018, certain amendments to the ESPP were approved by shareholders. Prior to these amendments, the ESPP allowed eligible employees to acquire common shares at a discounted purchase price of 85% of the market value of the Company's common shares on the purchase date. The ESPP, as amended, allows eligible employees to acquire common shares at a discounted purchase price of the lesser of (i) 85% of the market price of a common share on the first day of the applicable purchase period and (ii) 85% of the market price of a common share on the purchase date.	On June 7, 2018, certain amendments to the ESPP were approved by shareholders. Prior to these amendments, the ESPP allowed eligible employees to acquire common shares at a discounted purchase price of 85% of the market value of the Company's common shares on the purchase date. The ESPP, as amended, allows eligible employees to acquire common shares at a discounted purchase price of the lesser of (i) 85% of the market price of a common share on the first day of the applicable purchase period and (ii) 85% of the market price of a common share on the purchase date.
Maximum eligible employees contribution under ESPP					15.00%
Purchase of shares under ESPP, maximum limit for each employee | $					$ 25,000
Compensation charge | $					$ 155,000		$ 83,000
Employees Stock Purchase Plan | Prior to Amendment
Subsidiary or Equity Method Investee [Line Items]
Percentage of discounted purchase price of average market price			85.00%
Employees Stock Purchase Plan | After Amendment
Subsidiary or Equity Method Investee [Line Items]
Percentage of discounted purchase price of average market price			85.00%
Director
Subsidiary or Equity Method Investee [Line Items]
Shares available for issuance under the Original Plan vesting period				3 years
Forecast | U.S Dollar Under the New Option Stock Plan
Subsidiary or Equity Method Investee [Line Items]
Maximum number of common shares reserved for issuance increase in percentage								4.00%